design review report for bridges in northern uganda
TRANSCRIPT
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May 2011
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Ethiopia
Office
(Head Office)
P.O.Box 62668; Tel. 0114391065 /0114391499 /0114 391733 /0114393004; Fax 0114391230 /0114391617
E-mail: [email protected] Web-site: www.saba-engineering.com
Addis Ababa, Ethiopia
Uganda
Office
P. O. Box 21321, Plot No. 1376, Block No. 244, Muyenga Diplomat Zone
Tel. +25641267547; Fax. +25641268352; Mobile +256772712178, Email: saba-
Kampala, Uganda
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UUggaannddaa NNaattiioonnaall RRooaaddss AAuutthhoorriittyy
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TABLE OF CONTENTSPage
LIST OF FIGURES ....................................... ........................................ ................................. iv
LIST OF TABLES ......................................... ............................................ .............................. v
1 INTRODUCTION ........................................... ....................................... ................. 1-1
1.1 General .......................................... ........................................... .................... 1-1
1.2 Scope of the Design Review ......................................... ............................... 1-2
1.3 Purpose and Content of the Report ........................................... .................... 1-3
1.4 Approach of Design Review ......................................... ............................... 1-3
2 FIELD INVESTIGATION BY THE DESIGN REVIEW CONSULTANT ....... 2-1
2.1 Project Background ................................. ............................................ ......... 2-1
2.2 Field Visit ...................................... ........................................... .................... 2-1
2.3 Factual Findings ...................................... ........................................... .......... 2-1
2.4 Recommendation ..................................... ........................................ ............. 2-2
2.4.1 Supervision Team ............................................................................ 2-2
2.4.2 Surveying Work ............................................................................... 2-2
3 GEOTECHNICAL INVESTIGATION OF BRIDGE SITES AND
CONSTRUCTION MATERIAL SOURCES ............................................... ......... 3-1
3.1 General .......................................... ........................................... .................... 3-1
3.2 Determination of Allowable Bearing Pressure for Bridge Foundations ....... 3-1
3.3 Foundation Recommendation........................................ ............................... 3-2
3.4 Investigation of Construction Material Sources .................................. ......... 3-7
3.4.1 General ............................................................................................ 3-7
3.4.2 Potential Quarry Stone Sources ...................................................... 3-7
3.4.3 Potential Gravel (Muram) Sources ............................................... 3-17
3.4.4 Potential Sand Sources .................................................................. 3-22
4 HYDROLOGICAL and HYDRAULIC STUDY REVIEW ................................ 4-1
4.1 Background ...................................... ........................................... ................. 4-1
4.2 Objective ...................................... ............................................ .................... 4-1
4.3 Hydrology..................................................................................................... 4-2
4.4 Data Collection ........................................ ........................................... .......... 4-2
4.4.1 DEM and Aerial Photographs ......................................................... 4-2
4.5 Drainage Characteristics, Geology and Topography .................................. .. 4-2
4.6 Climate ...................................... ........................................... ........................ 4-5
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4.7 Peak Discharge Estimation ..................................... ...................................... 4-5
4.7.1 Rational Method .............................................................................. 4-5
4.7.2 SCS Method ..................................................................................... 4-6
4.7.3 Regression Equation........................................................................ 4-7
4.7.4 Historic data Analysis ..................................................................... 4-7
4.7.5 TRRL Flood Model ......................................................................... 4-7
4.8 Hydrology Review Summery ........................................ ............................. 4-49
4.9 Hydraulics ............................................ .............................................. ........ 4-49
4.10 HEC Ras 4.0 Bridge Hydraulic Analysis ........................................ ........... 4-50
4.11 HY-8.7 Culvert Hydraulic Analysis ......................................... .................. 4-62
4.12 Culvert Hydraulic Design Review Output ......................................... ........ 4-70
4.13 Hydraulic Design Review ...................................... .................................... 4-70
4.14 Existing Structures Physical Assessment .................................. ................. 4-71
4.15 Conclusion and Recommendations .......................................... .................. 4-76
5 STRUCTURAL DESIGN REVIEW .......................................... ............................ 5-1
5.1 General .......................................... ........................................... .................... 5-1
5.2 Scope ...................................... ............................................. ......................... 5-1
5.3 Structural System ............................................ ........................................... .. 5-1
5.4 Design Codes ........................................... ........................................... .......... 5-2
5.5 Materials Properties ..................................... ........................................... ...... 5-3
5.5.1 Concrete Grade: .............................................................................. 5-3
5.5.2 Reinforcement Steel ......................................................................... 5-35.5.3 Structural steel grade: ..................................................................... 5-3
5.6 Design Limit States ........................................ ............................................ .. 5-3
5.6.1 Strength Limit State ......................................................................... 5-3
5.6.2 Serviceability Limit State ................................................................ 5-4
5.7 Minimum Clear Cover to Reinforcement .................................... ................. 5-4
5.8 Detailed Design Review of Bridges ......................................... .................... 5-4
5.8.1 Superstructure ................................................................................. 5-4
5.8.2 Substructure .................................................................................... 5-4
5.8.3 Review Procedure ........................................................................... 5-5
5.9 Geometric Design Review of Approach Road ....................................... ...... 5-6
5.10 Conclusion and Recommendation .................................... ............................ 5-7
5.10.1 Structural Analysis .......................................................................... 5-7
5.10.2 Foundation ...................................................................................... 5-7
6 KIA-KIA BRIDGE REVIEW ...................................................................... .......... 6-1
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6.1 Background ...................................... ........................................... ................. 6-1
6.2 Field Investigation ....................................... ........................................ ......... 6-2
6.2.1 General ............................................................................................ 6-2
6.2.2 Field Visit........................................................................................ 6-2
6.2.3 Surveying Work.............................................................................. 6-3
6.2.4 Geotechnical Investigations ............................................................ 6-5
6.2.5 Investigation of Construction Material Sources .............................. 6-5
6.2.6 Physical Hydrological Investigation ............................................... 6-7
6.3 Preliminary Design .......................................... ........................................... .. 6-8
6.3.1 General ............................................................................................ 6-8
6.3.2 Hydrological and Hydraulic Analysis ............................................. 6-8
6.3.3 Geometric Design.......................................................................... 6-13
6.3.4 Structures....................................................................................... 6-13
6.4 Conclusions and Recommendations ............................................ ............... 6-14
7 NYAGAK-3 Culvert Hydraulic Design Adjustment .......................................... .. 7-1
8 TENDER DOCUMENT REVIEW ......................................... ............................... 8-1
8.1 Introduction ...................................... ........................................... ................. 8-1
8.2 Section I: Invitation to Bid ............................................ ............................... 8-2
8.3 Section II: Instructions to Bidders .................................... ............................ 8-2
8.3.1 Contents of Bid Documents ............................................................. 8-2
8.3.2 Documents Comprising the Bid ....................................................... 8-2
8.4 Section III: Bidding Data ....................................... ...................................... 8-3
8.5 Section IV: Part 1: General Conditions of Contract ..................................... 8-3
8.6 Section V: Part 2: Conditions of Particular Application .............................. 8-3
8.6.1 Contract Documents ........................................................................ 8-3
8.6.2 Settlement of Disputes ..................................................................... 8-4
8.6.3 Changes in Cost and Legislation..................................................... 8-4
8.7 Section VI: Technical Specifications .................................... ....................... 8-7
8.7.1 General Specifications .................................................................... 8-7
8.7.2 Special Provisions for the Standard Technical Specifications ........ 8-7
8.7.3 New Work Items .............................................................................. 8-7
8.8 Section VII: Forms of Bid, Appendix to Bid and Bid Security .................. 8-118.8.1 Appendix to Form of Tender ......................................................... 8-11
8.8.2 Tender Security ............................................................................. 8-25
8.9 Section VIII: Bill of Quantities ......................................... ......................... 8-26
8.9.1 BOQ Specific Remark .................................................................... 8-26
8.9.2 New Updated BOQ ........................................................................ 8-26
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8.10 Section IX: Form of Agreement, Forms of Performance Security, Bank
Guarantee for Advance Payment & Letter of Acceptance ......................... 8-26
8.10.1 Form of Agreement ........................................................................ 8-26
8.10.2 Letter of Acceptance ...................................................................... 8-27
8.11 Section X: Drawings ...................................... ............................................ 8-28
8.12 Section XI: Dispute Resolutions Procedure ....................................... ........ 8-28
9 CHANGES MADE ON THE TENDER DOCUMENT UNDER THE NEW
SCOPE OF WORK .............................................................. ................................... 9-1
LIST OF FIGURES
PageFigure 2-1: Location of 21 Bridges ............................................................................ 2-3
Figure 4-1: Areas for Calculation of 2 and 7 Day Antecedent Rainfall ................. 4-11
Figure 4-2: Soil zones .............................................................................................. 4-12
Figure 4-3: Rainfall Time (TP) Zones ...................................................................... 4-16
Figure 4-4: 2yr 24hrs point storm rainfall................................................................ 4-18
Figure 4-5: 10 year to 2 year ratio ........................................................................... 4-19
Figure 4-6: Flood Factor .......................................................................................... 4-20
Figure 4-7: Oluffe Bridge catchment area drainage description .............................. 4-22
Figure4-8: Oluffebridge catchment area floworinetation ........................................ 4-23
Figure 4-9: Ore culvert watershed area drainage pattern ......................................... 4-26
Figure 4-10: Ore culvert drainage orientation with elevation labeling .................... 4-27
Figure 4-11 Enve Bridge drainage pattern ............................................................... 4-31
Figure 4-12: Enve bridge drainage orientation with elevation labeling .................. 4-32
Figure 4-13: Goli bridge drainage pattern ............................................................... 4-35
Figure 4-14: Goli bridge drainage orientation with elevation labeling.................... 4-36
Figure4-15: Lebijo Culvert e drainage ..................................................................... 4-40
Figure 4-16: Lebijo Culvert drainage orientation with elevation labeling .............. 4-41
Figure 4-17: Enyau-3Bridge drainage pattern ......................................................... 4-46
Figure 4-18: Enyau-3 bridge drainage orientation with elevation labeling ............. 4-47
Figure 4-19: Oluffe proposed bridge U/S & D/S cross sectional view.................... 4-51
Figure 4-20: Oluffe proposed bridge with 25 years design flood ............................ 4-52
Figure 4-21: Enve proposed bridge U/S & D/S cross sectional view ...................... 4-54
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Figure 4-22: Enve proposed bridge with 25 years design flood .............................. 4-55
Figure 4-23: Goli proposed bridge U/S & D/S cross sectional view ....................... 4-57
Figure 4-24: Goli proposed bridge with 25 years design flood ............................... 4-58
Figure 4-25: Enyau-3 proposed bridge U/S & D/S cross sectional view ................ 4-60
Figure 4-26: Enyau-3 proposed bridge with 25 years design flood ......................... 4-61
Figure 4-27: Ore existing culvert cross sectional view ............................................ 4-64
Figure 4-28: Ore new culvert cross sectional view .................................................. 4-66
Figure 4-29: Lebijo existing culvert cross sectional view ....................................... 4-68
Figure 4-30: Lebijo culvert (with additional culvert) cross sectional view. ............ 4-70
Figure 6-1: Kia-Kia Stream catchment and cross section over view ......................... 6-8
Figure 6-2: kia kia flood plain cross section along with water surface and proposed
structures position ................................................................................. 6-13
LIST OF TABLES
Page
Table 2-1: List of GPS Data for Bridges ................................................................... 2-4
Table 3-1: Presumptive Allowable Pressures for Different Foundation Conditions . 3-2
Table 3-2: Review of Bridge Site Foundation Investigation and Presumptive
Allowable Pressures ............................................................................... 3-4
Table 3-3: Review of Bridge Site Foundation Investigation and Presumptive
Allowable Pressures as per the new scope of work
(Lot 1,Lot 2 &Lot 3) ............................................................................... 3-6
Table 3-4: Summary of Test Results on Rock Sources ............................................. 3-7
Table 3-5: Summary of Laboratory test results of the potential gravel sources ...... 3-22
Table 3-6: Summary of Laboratory test results of the potential Sand sources ........ 3-28
Table 4-1: Bridge catchment area physiographic description
(As per the new scope) ........................................................................... 4-4
Table 4-2: Antecedent Moisture Conditions for Storms of Greater than 50mm ..... 4-10
Table 4-3: Standard contributing area coefficients (Cs) .......................................... 4-13
Table 4-4: Catchment Wetness Factor (CW) ........................................................... 4-14
Table 4-5: Land Use Factor (CL) ............................................................................ 4-14
Table 4-6: Catchment lag Times ............................................................................. 4-15
Table 4-7: Rainfall time (Tp) for East African 10 year storms ............................... 4-17
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Table 4-8: Oluffe Bridge Catchment TRLL Model 25 Years Peak Discharge
Determination ....................................................................................... 4-24
Table 4-9: Ore Culvert Catchment TRLL Model 25 Years Peak Discharge
Determination ....................................................................................... 4-28
Table 4-10:Enve Bridge Catchment TRLL Model 25 Years Peak Discharge
Determination ....................................................................................... 4-33
Table 4-11:Goli Bridge Catchment TRLL Model 25 Years Peak Discharge
Determination ....................................................................................... 4-37
Table 4-12: Lebijo Culvert Catchment TRLL Model 25 Years Peak Discharge
Determination ....................................................................................... 4-42
Table 4-13:Enyau-3 bridge Catchment TRLL Model 25 Years Peak Discharge
Determination ....................................................................................... 4-48
Table 4-14: Ore existing culvert input data for HY-8.7 hydraulic analysis ............ 4-63
Table 4-15: Ore existing culvert hydraulic analysis summery (scenario one) ........ 4-63
Table 4-16: Ore existing culvert input data for HY-8.7 hydraulic analysis ............ 4-65
Table 4-17: Ore new culvert hydraulic analysis summery (scenario two) ............. 4-65
Table 4-18: Lebijo existing culvert input data for HY-8.7 hydraulic analysis ....... 4-67
Table 4-19: Lebijo Existing culvert hydraulic analysis summery (scenario one) ... 4-67
Table 4-20: Lebijo culvert (additional culvert) HY-8.7 input data .......................... 4-69
Table 4-21: Lebijo culvert (with additional culvert) hydraulic analysis summery
(scenario two) ....................................................................................... 4-69
Table 4-22: bridge physical survey summery for the 6 bridges under the new
scope of services. .................................................................................. 4-72
Table 4-23: Lot 1 bridge physical survey summery ............................................... 4-73
Table 4-24: Lot 2 bridge physical survey summery ............................................... 4-74
Table 4-25: Lot 3 bridge physical survey summery ............................................... 4-75
Table 5-1: List of Sample Bridges ............................................................................. 5-1
Table 5-2: Slope ratio table (Vertical to Horizontal ratio) ......................................... 5-6
Table 6-1:Kia-Kia Bridge Catchment TRLL Model 25 Years Peak DischargeDetermination ......................................................................................... 6-9
Table 8-1: Bill 1000 General .................................................................................. 8-8
Table 8-2: Bill 3000 Earth Works and Pavement Layers of Gravel or
Crushed Stone ......................................................................................... 8-9
Table 8-3: Bill 5000 Ancillary Road Works ........................................................... 8-9
Table 8-4: Bill 6000 Structures ............................................................................... 8-9
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Table 8-5: Bill No 8: Schedule of Day Works ......................................................... 8-10
Table 8-6: Summary of currencies of the Bid .......................................................... 8-12
Table 8-7: Interest Rates .......................................................................................... 8-12
Table 8-8: Weightings for use with Local Currency (UGSH) ................................. 8-13
Table 8-9: Weightings for use with Foreign Currency 1: ........................................ 8-13
Table 8-10: Weightings for use with Foreign Currency 2: ...................................... 8-14
Table 8-11: Weightings for use with Foreign Currency 3: ...................................... 8-15
Table 8-12: Summary of Payment Currencies ......................................................... 8-16
Table 8-13: Weightings Applicable for Bill No. 3: Earth Works &
Pavement layers .................................................................................... 8-17
Table 8-14: Weightings Applicable for Bill No. 2 & 6 Drainage & Structures ...... 8-17
Table 8-15: Weightings Applicable for Bill No. 5 Ancillary Works ....................... 8-18
Table 8-16: Local Currency ..................................................................................... 8-19
Table 8-17: Foreign Currency 1 (FC1)(a) ................................................................ 8-19
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1 INTRODUCTION
1.1 General
Recognizing the vital role the road network plays in enabling national objectives to be
achieved, the Government of Uganda, represented by the Ministry of Works andTransport (MoWT) recently Uganda National Roads Authority took the
responsibility, is undertaking improvements to the countrys road network to a
standard that can cope with the present and anticipated traffic growth.
With financial support of the Arab Bank and Economic Development in Africa
(BADEA), economic and technical studies for rehabilitation of 66 bridges in the
eastern and northern regions of the country were carried out in 2002. Following
outcomes of the study, the bridges were rank ordered and placed in priorities 1 and 2
according to traffic levels, existing structural condition and risk of flooding. Based on
these criteria, 21 bridges were placed in priority I and the rest in priority II.
Twenty one (21) priority I structures have been selected for inclusion in phase 1 of
the implementation scheme. The Detailed Engineering Design and Tender
Documents for the Project have been prepared by an International Consultant, ACE
Consulting Engineers in the year 2002/ 2003.
The consultancy contract agreement between the Ministry of Works and Transport
and SABA Engineering Plc was signed on May 30th, 2007.
Though the project has progressed through design review stage, recently Ugandan
National Road Authority has agreed with BADEA to scale down the project scope to
exclude all the bridges located along the Vurra-Arua-Koboko-Oraba road where the
road is scheduled for upgrading under World Bank Financed Transport Sectordevelopment Program (TSDP).The very recent revised scope now comprises only 6
bridges packaged to Enayao-3, Alla-1, Goli, Nyagak-3, Nyacara, Pakwala, bridges.
The bridges are subdivided into three lots as shown on the table below
LOT I LOT II LOT III
Arua Nebbi Nebbi
1 Alla Goli Nyacara
2 Enyau 3 Nyagak 3 Packwala
This Design Review report mainly emphasis 21 bridges in North West Ugandaincluding the recently agreed 10 bridges packaged but engineering estimates and
tender documents are revised based on the new scope for subsequent retendering
purpose. Kia-Kia bridge which took a special concern due to design insufficiency
problem as discussed with UNRA on 19 July 2010 also included and elaborated as
separate chapter though review report on Kia Kia bridge submitted to the client
before this report.
No
Lot and District
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The high cost of the civil work as compared to the available budget has forced the
client to seek alternative solution by abandoning Kia-Kia bridge which is considered
to be very expensive, Cido Bridge which is replaced in 2003 and still in a good
condition except its single lane configuration and Ora2 & Ora2.
Objectives of the Project
The project is divided into two distinct phases:
Stage I: Pre Construction Services
Stage II: Construction Supervision
The objectives of the services as described in the Terms of Reference are:
In Pre Construction phase, the Consultant familiarize himself with the
designs, reports and tender documents relating to the project; inspect the
respective bridge sites and propose any minor modifications deemed
necessary on the designs and packaging of the works. Subsequently the
consultant will assist the Client with procurement of Contractors.
During the Construction Supervision phase, supervise construction of the
Works (on behalf of the Employer) throughout the entire construction phase,
including the defects liability (maintenance) period.
1.2 Scope of the Design Review
In accordance with the Contract Agreement, the main objectives of the Design
Review are to carry out the following;
To Review all documents of previous studies, designs, reports etc after
acquainting himself with the location and structural condition of each bridgestructure included in the project, and compare these with the intervention measure
proposed for the structure.
To carry out field and laboratory tests where necessary to enable verification of
essential aspects in the detailed engineering design. This will also include
information on construction material sources.
Based on the above, recommend minor modifications deemed necessary to the
designs, bills of quantities, cost estimates and any other relevant aspects.
Accordingly prepare any necessary drawings at appropriate scales, incorporating
any modifications approved by the Client.
To prepare a detailed time schedule for the project and for each structureassuming a practical sequence of activities under given climatic conditions and
taking into account the time for procuring a contractor. The expected cash flow
shall also be indicated.
The consultant shall satisfy himself with suitability of the existing bidding
documents (or propose any amendments thereof) prepared for national
competitive bidding,
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1.3 Purpose and Content of the Report
Tue purpose of this report is to provide a full and detailed description of the work
undertaken by the consultant in carrying out the design review services of each
respective review task. The report is dealing with all technical aspects of the projects
review works, detailed information, investigations, results and recommendations.
The following aspects of the Engineering Design Review have been addressed within
the report:
Section 1: General Introduction
Section 2: Field Investigation by the Design Review Consultant
Section 3: Geotechnical Investigation of Bridge sites and Construction
Material Sources Geotechnical Investigation
Section 4: Hydrological and Hydraulic Study Review
Section 5: Structural Design Review
Section 6: Tender Document Review
1.4 Approach of Design Review
Basically, the design review was carried out as per our technical proposal. Both field
investigations and desktop studies were carried out in the respective disciplines.
Details are presented in subsequent sections of this report.
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2 FIELD INVESTIGATION BY THE DESIGN REVIEW
CONSULTANT
2.1 Project Background
The selected bridges are located along national and district roads in the north
western region of Uganda in the districts of Arua and Nebbi and are categorized inthree Lots.
The Detailed Engineering Design and Tender Documents for the Project have been
prepared by an International Consultant, ACE Consulting Engineers in the year 2002/
2003.
The consultancy contract agreement between the Ministry of Works and Transport
and SABA Engineering Plc was signed on May 30th, 2007.
2.2 Field Visit
The review consultant conducted the field investigation for the Project from
September 27/2007 to October 1/2007. Kia-Kia and Pakwala bridge sites were notvisited due to their inaccessibility. The team composition is shown below;
S.No Name Profession/ Assignment
1
2
3
4
5
Dereje Tilahun
Kassa Dessie
Michael Abebe
Yared Amdie
Samuel Girma
Resident Engineer/ Team leader
Material Engineer
Structural Engineer
Hydrologist
Surveyor
Two personnel that were assigned from the Ministry of Works have been with the
team all the time.
2.3 Factual Findings
Of the 21 bridges considered under the review found in this project, all are proposed
to be replaced by the design consultant. The following main reasons are given for
replacement,
The non-compliance of the design load of the existing structure with the
required specifications.
The existing bridge width is too narrow.
The level of the existing bridge is lower than the flood water level.
The present span length of the bridge increases the water velocity, which
leads to the erosion of the substructure.
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The review consultant has visited all the sites except Kia Kia and Pakwala Bridge
sites, which were inaccessible at the time of the visit. The location of the bridges/
bridge sites under the new work scope is shown in Figure 2-1.
2.4 Recommendation
Following the completion of the field visit, the review consultant would like to bring
the following general recommendations.
2.4.1 Supervision Team
The field investigation during the review period took five days to cover the nineteen
sites. The proposed one team is in no way sufficient to efficiently conduct the
supervision work, so the following personnel list is advisable;
Full Time Staff
Resident Engineer (1)
Assistant Resident Engineer (3)
Senior Surveyors (3)
Inspector of Works (3)
Intermittent Staff
Material Engineer (1)
Contract/ Claims Engineer (1)
Environment Specialist (1)
The Design Consultant has also included office, vehicle and housing for Assistant
Resident Engineer for each lot. In addition, the Engineers house drawing prepared by
the Design Consultant also shows a housing accommodation for the Assistant
Resident Engineer. This shows that the Design Consultant has considered the
necessity of Assistant Resident Engineer for each lot. But it will be advisable to
assign resident engineer to address the revised neighboring lots and assistant resident
engineer for the other lot according to the new consensus.
2.4.2 Surveying Work
The design consultant established bench marks using relative coordinates and did not
connect it to the national grid. This has created problem in locating the bench marks.
Even on the BMs found, the markings are no more there. If it was tied to the national
grid, it would have been easier to identify each BM.
During the construction stage, the consultant will tie the bench marks to the national
grid.
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Figure 2-1: Location of 21 Bridges
Figure 2-1: Location of 21 Bridges Legend: Location: selected 6 bridges
7
14
Bridge Lege
Lot II
Lot I
Lot III
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Table 2-1: List of GPS Data for Bridges
No Description East North Elevation
1 Alla 285641 321381 873
2 Enyo-3 267062 333770 1192
3 Enayu-1 267125 342069 1140
4 Enve 267147 348930 1152
5 Oluffe 270332 352993 1119
6 Ayi 271353 360296 1106
7 Yoyo 271976 368197 1128
8 Oru 272522 369028 1106
9 Apa-1 272909 375995 1184
10 Ore 272892 373464 1165
11 Kochi 273325 381108 1194
12 Debara 265890 390867 1137
13 Lebijo 279881 380785 1064
14 ORA 1 321246 300833 636
15 ORA 2 321235 300861 628
16 Nyagak 3 266974 270220 1514
17 Goli 280863 263203 1375
18 Cido 262039 284418 1297
19 Nyacara 274042 287827 1003
Note: The highlighted including Pakwala bridges in table 2.1 above are the one
considered under the newly revised scope of work.
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3 GEOTECHNICAL INVESTIGATION OF BRIDGE SITES
AND CONSTRUCTION MATERIAL SOURCES
3.1 General
Preliminary foundation investigations were conducted by the Design Consultant,Arab Consulting engineers (ACE), on the major river crossing sites to identify
possible bearing layers and make recommendations on bearing capacity and
determine the required depth of foundation for safely conveying the superstructure
loads to the supporting strata. The field investigation and laboratory testing were
conducted by the Central Materials Laboratory in 2003.
The drilling investigations involved Standard Penetration Tests (SPT) and recovery of
undisturbed and disturbed soil/silty sand samples for laboratory tests. However, depth
of drilling was limited to top of hard stratum; no drilling was made in hard
formations/rock strata. Thus, the strength and extent of hard formations were not
adequately investigated. It seems that due to these uncertainties, a very low bearing
capacity of 300KPa has been assumed for all hard formations including those where
rock outcrops are evident.
The design consultant recommended placing the foundation on replaced soil/selected
granular fill material over river beds were exposed rock are encountered on the
surface, for example Ayi, Yoyo, Apa and Lebijo crossing sites. This has a potential
risk of scouring of the foundation soil; hence the review consultant recommends
placing the footings on the rock strata where sound rock is encountered at shallow
depths.
3.2 Determination of Allowable Bearing Pressure for Bridge Foundations
Most of the river crossings are constituted of alluvium deposit which is mainly clayey
silty/sandy loam on top of weathered gneiss. Rocky outcrops are visible at some
rivers.
Allowable (presumptive) bearing pressure values are commonly assigned for the
foundation bearing layers for foundation design purposes, taking their geology,
compactness of alluvial deposits, and degree of weathering and consistency of rock
outcrops, if any, into consideration as classified during the site investigation.
The presumptive bearing pressure values recommended by different codes of
practice, design manuals and reference texts for different type of foundation materialsand consistency are presented in Table 3.1 below.
The presumptive bearing pressure values for various foundation materials have been
adopted from the following code of standards, design manuals and reference texts:
Foundation Analysis and Design, 5th Edition, McGraw-Hill Companies,
Inc., 1996, by J. E. Bowles;
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Naval Facilities Engineering Command Design Manual (NAVFAC DM -
7.02, sec.4, table1: on Foundations & Earth Structures, 1986);
Overseas Road Note No. 9, Transport Research Laboratory (TRL), Design
of Small Bridges; 2nd Edition, 2000.
Table 3-1: Presumptive Allowable Pressures for Different Foundation Conditions
*Depth of ground water is assumed to be not less than B below the
base of foundation.
The presumptive bearing pressures should be used with caution to allow for the
uncertainties as determination of the actual extent and jointing requires drilling and
coring.
3.3 Foundation Recommendation
The minimum depth below riverbed at which the bottom of abutment / pier will beplaced is governed by the maximum scour depth and the presence of a good bearing
layer. An average depth of 2 meters below the lowest level of the river bed, is
recommended for those crossing foundations composed of alluvial deposits, is
recommended. For riverbanks and riverbeds composed of rock outcrops, a minimum
depth of 0.5m in sound rock for keying (anchorage) purpose is recommended. The
presumptive bearing pressures are used with caution assuming soft rock to allow for
the uncertainties.
Type of Bearing MaterialConsistency in
place
Recommended Allowable
Bearing Pressure (KPa)
ORN 9 NAVFAC Bowles
Massive igneous and
metamorphic rock (basalt,
granite, gneiss)
Hard and sound 10,000 7,600 9,600
Foliated metamorphic rock
and sedimentary rocks (un-
weathered)
Medium hard and
sound4,000 3,300 -
Weathered or broken bed rock
of any kindSoft rock 1,500 1,000 1,400
Gravel, gravel-sand mixtures,
boulder gravel mixtures , and
Sand with little gravel
[Non-cohesive Soils]
-Dense/very
compact
-Medium dense
- Loose
600
500
150
600
480
280
400*
380*
200
Clay [Cohesive Soils]
Silt
-Hard
-Stiff
-Hard
-Stiff
200
150
200
150
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The bearing pressure values recommended by the Design Consultant are generally
conservative and need to be amended during construction. Investigation by core
drilling (ASTM D2113) is neither feasible nor scope of this assignment; it is foreseen
that verification/confirmatory investigations would be scheduled during construction,
by means of rotary core drilling to a depth of at least 10m in soft /loose formation and
at least 3 meters into solid rock. If the foundation conditions encountered during
excavation are different from what has been revealed or assumed at design stage, the
necessary modifications on the foundation design shall be made by the engineer.
Pile load test shall also be conducted for bridges to be founded on pile foundations.
Static Load Tests are performed to determine the ultimate failure load of a foundation
pile and to determine the piles capability of supporting a load without excessive or
continuous displacement. The purpose of such tests is to verify that the allowable
loads used for the design of a pile are appropriate and that the installation procedure
is satisfactory. The Pile Load Test shall be conducted in accordance with the
procedures given in ASTM D1143.
Hence pay items for the structures shall include the estimated costs for confirmatoryinvestigations by core drilling and for pile load testing in the BOQ.
Tables 3.2 and 3.4 present the summary of Geotechnical Investigations conducted by
the Design Consultant.
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Table 3-2: Review of Bridge Site Foundation Investigation and Presumptive Allowable
Sr.
No.
River
Name
Route & DistrictGPS
Coordinates
Foundation Material Description
1 Enayu-1Arua-Koboko-Orba
(Arua)
267125 E,
342069 N
Arua side: Sandy clay withfew gravels 0.7m 5.0m,
SPT values: 7,8,9 at 3.0m
-Hard pan/rock below 5.0m
(refusal to penetration)
Koboko side: Stiff Sandy c0.7m 5.0m,
-Hard pan/rock below 5.0m
2 Enve Arua-Koboko-Oraba(Arua)
267147 E,
348930 NDark brown silty clay on both abutments and the river bed
3 Oluffe
Arua-Koboko-Oraba(Arua)
270332 E,
352993 N
Arua side: Firm Sandy clay ,SPT values: 3,2,4 at 1.5m and
7,9,9 at 3.0m and Hard
pan/weathered rock below5.0m
Koboko side:Sandy clay 2.0 6.0m,
Hard pan/rock below 6.0m
4 AyiArua-Koboko-
Orba(Arua)
271353 E,
360296 NRocky outcrops at both abutments and the river bed
5 Kia-KiaArua-Wandi-Invep-Rhino-Camp
Odupi Side: Grayish brownfirm clay up to 3.0m below
which is a hard pan/rock
Rhino Camp side: LooseBrown sand up to 9.0
medium dense below 9.0m:
N-values at 6.0m and 9.0m
and 24, respectively.
6Yoyo
Arua-Koboko-Oraba
(Arua)
271976 E,
368197 N
Rock outcrops at both abutments, silty clay/sand
7 Oru
Arua-Koboko-Oraba
(Arua)
272522 E,
369028 N 0.0 -4.0m: Loose Clayey sand and hard formation below 4.0
8 Apa-1Arua-Koboko-Oraba
(Arua)
272909 E,
375995 N
0 4.0m Silty Sand on downstream
and exposed rock on up stream,
hard formation below 4.0m
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Sr.
No.
River
NameRoute & District
GPS
CoordinatesFoundation Material Description
9
Ore
Arua-Koboko-Oraba
(Arua)
272892 E,
373464 NSilty Sand at both abutments
10 KochiArua-Koboko-Oraba
(Arua)
273325 E,
301108 NSilty sand and sandy Clay, up to
11Debara
Arua-Koboko-Oraba
(Arua)
265890 E,
390867 NClayey silt alluvium, with some boulders exposed on down
12Lebijo
Arua Koboko-
Yumbe (Arua)
279881E,
380785NExposed rock at abutments and pier position
13 Ora-1(Lot 3)
Nebbi-Akaba-Kucwiny-Wadela
(Nebbi)
321246E,300833N
Arua side:Sandy clay : 0 3.0m,Below 3.0m hard pan
Pakwach side:Stiff, black clay 0-2.0mGranular fill material,
2.0 6.0m black sandy clay (N-v
6.0m -14m (N-value=15) Black to gray
14Cido(Lot 2)
Nebbi-Goli-
Japanziri-Erussi(Nebbi)
262039E,284418N
Goli side: Dense Sandyclay with gravel(0.0 3.0m),
Hard pan below 3.0m
Errusi side: Sandy clay with quartz(0.0 4.0m),Hard pan below 4.0m; i.e. refu
penetration,
N-value=45
15
Ora-2(Lot 3)
Nebbi-Akaba-Kucwiny-
Wadela(Nebbi)
321235E,
300861NDense Silty Sand at both abutments
Note:All the bridges on table 3-2 are excluded under the revised work scope.
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Table 3-3: Review of Bridge Site Foundation Investigation and Presumptive Allowable Pressures as per t
1,Lot 2 &Lot 3)
Sr.
No.
River
NameRoute & District
GPS
CoordinatesFoundation Material Description
1Alla-1
Arua-Inde-packwach
(Arua)
285641 E,
321381 N
Arua side:Brown to red silty
clay/alluvium, with gravel.
Hard pan at 2.0m
Inde side:Light brown silty clay/allu
2 Enayu-3 Arua-Ediofe (Arua)267062 E,
333770 NReddish brown clayey Sand at both abutments
3Nyagak-3
Jqang-Okoro-
Alyenda(Nebbi)
266974E,
270220NSilty Clay with few gravel at both abutments
4Goli
Nebbi-Goli
Custom-Mahagi
(Nebbi)
280863E,
263203N
Goli customs side:Stiff to very stiff sandy clay with
gravel,
SPT-values: 5,6,7 at 3.0m and 12,11,9 at 6.0m,
Hard pan (refusal to pen.) at 8.0m
Mahagi side:Sandy clay with gravel,
SPT-values: 3,4,5 at 3.0m
Hard pan below 5.0m
5Nyacara
Nebbi-Erussi(Nebbi)
274042E,287827N
Sandy gravel with boulders
6Pakwala
Nebbi-Erussi
(Nebbi)
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3.4 Investigation of Construction Material Sources
3.4.1 General
As part of the assignments in the Design Review Contract, the Consultant (SABA
Eng.) has conducted field investigations and laboratory tests on Potential
Construction Material sources; i.e. to enable verification of the findings during
detailed engineering design. These included assessment of the Geotechnical
Investigations report, and identification of construction material sources which were
conducted by the Design Consultant (ACE).
Based on the physical inspection of the potential construction material sources and
results of laboratory tests conducted on some representative samples, the Design
Review Consultant has evaluated the available design documents with regards to
adequacy of the investigations and compliance of the values obtained with relevant
standard specification requirements.
A total of twelve (12) locations; i.e. 7 were potential stone sources, 4 sand sources,
and 1 gravel source have been investigated by the Design Consultant. However, 5(five) of these sources are located near Lira and Soroti district HQs, which are very
far from the project sites. The gravel source is located on the Lira Aloi road, 6.4Km
from Lira town.
3.4.2 Potential Quarry Stone Sources
Coarse aggregate for concrete has to be strong, durable and must have a particle size
distribution and particle shape which provide high mechanical stability.
Potential sources of hard rock for production of crushed aggregate for concrete works
were identified by the Design Consultant. Based on the test results report, conducted
by the Central Materials Laboratory in June 2003, four (4) of the stone quarrysamples tested meet all the specification requirements for concrete aggregates. The
following table has been taken directly from the Materials Investigation Report
prepared by the Design Consultant:
Table 3-4: Summary of Test Results on Rock Sources
Sr.No.
Rock SourceSpecificgravity(g/cc)
WaterAbs.(%)
Acv(%)
Aiv(%)
Tfv(KN)
Laa(%)
SSS(%)
Bitumen Affinity
1 Oparra (Arua) 2.5 0.1 29 30 150 28 0.3 Good
2
Over Senia
River 2.6 0.8 19 23 180 16 0.5 Good3 Ngweny 2.6 0.2 16 11 200 18 0.3 Good
4 Akia 2.7 0.1 19 19 170 22 0.4 Fair
5 Ngetta 2.6 0.3 27 23 160 23 0.2 Good
Spec. Limits >2.5 -25
Max.
26
Max
160
Min.
28
Max
12
MaxGood
ACV Aggregate Crushing Value, AIV-Aggregate Impact Value, TFV-10% Fines
Value LAA Los Angeles Abrasion, SSS Sodium Sulfate Soundness
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From the test results, it can be concluded that with the exception of the rock source at
Oparra (Arua) which has marginally weaker values, all the investigated rock sources
fulfill the specification requirements.
The Design Review Consultant has inspected these sources and identified additional
potential sources. Photographs of the sites showing selected features of the source and
location of each quarry stone from the bridge sites is also given. Under the newlyrevised scope of work all construction material indicated under lot 2 below can be
considered for Lot 1 bridges. Similarly the material sites under lot 3 could be
shared by lot 2 and lot 3 bridges.
3.4.2.1 Stone Quarry Sites Proposed For Lot 1
Priority 1 Lot 1
Description
Quarry Name Orawa
Location 3.5 km from Arua TownRoad Name Arua Air field Road
GPS Coordinates Elevation 1198
Easting 36N 269053
Northing 337155
Estimated Quantity (Cum) >11,000 m3
Overburden Varies from 0 -1.5m
Access Existing and in good Condition
Rock type Gneiss
Degree of weathering Un weathered
Distance from: Enyau 3 bridge 5 kmEnyau 1 bridge 7 km
Enve bridge 14 km
Oluffe bridge 21 k m
Ayi bridge 31 km
Alai-1 bridge 30.5 km
Kia Kia bridge 70 km
photos Orawa-Photo 1 through 6
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Orawa Site- Photo 3Orawa
Orawa Site Photo 1 Orawa Site- Photo 2
Orawa Site Photo 3 Orawa Site Photo 4
Orawa Site Photo 5 Orawa Site Photo 6
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Description
Quarry Name Arivu
Location 14 km from Arua Town
Road Name Arua Nebbi Road
GPS Coordinates Elevation 1027
Easting 36N 274510Northing 319462
Estimated Quantity( Cum)
>100,000 m3
Overburden None
Access Existing and in good Condition
Rock type Gneiss
Degree of weathering Minor surface disintegrations
Distance from: Enyau 3 bridge 18.1km
Enyau 1 bridge 23.5 km
Enve bridge 31 kmOluffe bridge 37.2 k m
Ayi bridge 47.7 km
Alai-1 bridge 23 km
Kia Kia bridge 88 km
photos Arivu Site Photo 1 through 4
Priority 2 Lot 1
Arivu Site Photo 1 Arivu Site Photo 2
Arivu Site Photo 3 Arivu Site Photo 4
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Priority 3 Lot 1
DescriptionQuarry Name Ovisoni , adjacent to Ovisoni trading centre, LHSLocation 14 km from Arua TownRoad Name Arua Odiya -Vurra customs RoadGPS Coordinates Elevation 1337
Easting 36N 264731Northing 321521
Estimated Quantity(Cum)
>1,000 m3
Overburden 0.1-0.5mAccess Existing and in good ConditionRock type GneissDegree of weathering Un weathered
Distance from; Enyau-3 bridge 18.1kmEnyau-1 bridge 23.5 km
Enve bridge 31 km
Oluffe bridge 37.2 k m
Ayi bridge 47.7 km
Alai-1 bridge 27km
Kia Kia bridge 88 km
photos Ovisoni Site- Photo 1 through 4
Ovisoni Site- Photo 1 Ovisoni Site- Photo 2
Ovisoni Site- Photo 3 Ovisoni Site- Photo 4
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3.4.2.2 Stone Quarry Sites Proposed For Lot 2
Priority 1- Lot 2
DescriptionQuarry Name Liru New proposal
Location 14 km from koboko Town
Road Name Koboko- liru RoadGPS Coordinates Elevation 1198
Easting 36N 269053
Northing 337155
Estimated Quantity ( Cum) > 11,000 m3
Overburden Varies from 0 -1.5m
Access Existing and in good Condition
Rock type Gneiss
Degree of weathering Un weatheredDistance from: Yoyo bridge 26 km
Oru bridge 25 km
Ore bridge 20.3 km
Apa bridge 18 k mKochi bridge 16 km
Lebijo bridge 20.3 km
Debara bridge 30 km
photos Liru Site Photo 1 through 4
Liru Site Photo 1 Liru Site Photo 2
Liru Site Photo 3 Liru Site Photo 4
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3.4.2.3 Stone Quarry Sites Proposed For Lot 3
Priority 1 Lot 3
DescriptionQuarry Name Acwera Chinese QuarryLocation 12.3 km from NebbiTownRoad Name Nebbi- Pakwach Road
GPS Coordinates Elevation 985Easting 36N 295868
Northing 273361
Estimated Quantity ( Cum) >10,000 m3Overburden Varies from 0 -1.5 mAccess Existing and in good ConditionRock type Granite
Degree of weathering Un weathered
Distance from: Nyacara bridge 13.3 kmPakwala bridge 15.3 km
Goli bridge 26.3 km
Cido bridge 29.3 k m
Nyagak 3 bridge 51.3 kmOra-1 bridge 37 km
Ora-2 bridge 37 km
photos Acwera Chinese Qs Photo 1 through 4
Acwera Chinese Qs Photo 1 Acwera Chinese Qs Photo 2
Acwera Chinese Qs Photo 3 Acwera Chinese Qs Photo 4
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Priority 2 Lot 3
DescriptionQuarry Name Ngweny kumiLocation 3.6 km from NebbiTownRoad Name Nebbi- Goli Road ( New road in angir village)GPS Coordinates Elevation 1097
Easting 36N 285917Northing 271332
Estimated Quantity ( Cum) >15,000 m3Overburden Varies -1m approxAccess Existing and in good ConditionRock type Gneiss
Degree of weathering Un weathered bouldersDistance from; Nyacara bridge 2.6 km
Pakwala bridge 0.7 km
Goli bridge 12 km
Cido bridge 15 k m
Nyagak 3 bridge 42.6 km
Ora-1 bridge 49.6 km
Ora-2 bridge 49.6 km
photos Ngweny k- Photo 1 through 4
Ngweny kumi - Photo 1 Ngweny k - Photo 2
Ngweny k - Photo 3 Ngweny k - Photo 4
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Priority 3 Lot 3
Description
Quarry Name Cananyira rock New proposal
Location 1.2 km from NebbiTown
Road Name Nebbi- cananyira RoadGPS Coordinates Elevation 986
Easting 36N 288156
Northing 273405
Estimated Quantity ( Cum) >10,000 m3
Overburden None
Access Existing and in good Condition
Rock type Gneiss
Degree of weathering Un weathered
Distance from; Nyacara bridge 1.5 km
Pakwala bridge 4 kmGoli bridge 15 km
Cido bridge 18k m
Nyagak 3 bridge 40 km
Ora-1 bridge 47.5 km
Ora-2 bridge 47.5 km
photos Cananyira Photo 1 through 2
Cananyira Photo 1 Cananyira Photo 2
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Priority 4 Lot 3
Description
Quarry Name Angir rocks New proposal
Location 1.6 km from NebbiTown
Road Name Nebbi- Goli Road ( near Angir primary school)GPS Coordinates Elevation 1061
Easting 36N 286537
Northing 272491
Estimated Quantity ( Cum) >5,000 m3
Overburden None
Access Available and in good Condition
Rock type Gneiss
Degree of weathering Un weathered
Distance from: Nyacara bridge 0.6 km
Pakwala bridge 2.4 km
Goli bridge 12.4 km
Cido bridge 15.4 k m
Nyagak 3 bridge 40.6 km
Ora-1 bridge 47.6 km
Ora-2 bridge 47.6 km
photos Angir Photo 1 through 2
Angir Photo 1 Angir Photo 2
3.4.2.4 Conclusions and Recommendations on Potential Stone Sources:
Following the investigations conducted on the stone quarry sites proposed by the
design consultant, the following is recommendable:
For Lot 1: Stone aggregates from Orawa, Arivu or Ovisoni quarries are
recommended.
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For Lot 2: The virgin rock at Liru (new proposal) is recommended as source
of stone aggregates ( as per the revised scope of work this material site
should be considered for lot 1 if the need arise)
For Lot 3: Stone Quarries Acwera Chinese Quarry, Ngweny Kumi,
Cananyira rock (new proposal) and Angir rock (new proposal) are
recommended. ( as per the revised scope of work these material site shall beconsidered for both Lot 2 and Lot 3)
Ngetta Hill Quarry (5.3 Km from Lira town, on Lira kitgum road), Akia Hill Quarry
(5.9 km from Lira Town, on Lira Aloi road) and Ochuloi Quarry (19Km from
Soroti town, on Soroti Lira road), are all located at distances that are not
economically viable (more than 300Km far) relative to the project sites and are
therefore not recommendable for use as aggregate sources.
3.4.3 Potential Gravel (Muram) Sources
Gravel sources were not identified by the Design Consultant, for all the three lots.
Granular borrow materials are required for construction of embankments in approach
roads and for backfilling behind abutments. The Design Review Consultant has
identified a total of eleven (11) potential sources of gravel and collected
representative samples for laboratory tests.
It should, however, be noted that the construction material sources identified during
this phase are by no means exhaustive. Additional sources should be further located
and investigated by the contractors during construction.
I. Location of Gravel Sources for Lot 1:
Sample ID Location/nearest town Estimated Qty (m3)
G1/Lot (1)11 Km from Arua town,
Arua District, Kijomoro Subcounty,
Near Loliragoro town
85,000
(200mx340mX1.3m)
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Gravel G1/Lot 1 (1) Gravel G1/Lot 1 (2)
Sample ID Location/nearest town Estimated Qty (m3)
G2/Lot (1)
19 Km from Arua town,
Arua District, Oleba Subcounty, 2Kmfrom Oleba Trading Center (ExistingPit)
10,000
(165mx70mX1.0m)
G2/Lot 1 (1) Borrow area used by MoWT G2/Lot 1 (2) Borrow area used by MoWT
Sample ID Location/nearest town Estimated Qty (m3)
G3/Lot (1)29 Km from Arua town,
Arua District, Oluffe Subcounty,
near Ombere town ( Existing Pit)
17,000
(150mx100mX1.2m)
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G3/Lot 1 (1) G3/Lot 1 (2)
SampleID
Location/nearest town Estimated Qty (m3)
GravelAruaTC
8Km from Arua town, along Arua-AjonoRoad, Vura Subcounty, near Gil-gil
Existing Borrow pit, 200m away fromCongo/Uganda Boarder (at Ajono village)
100,000 (200mx500mx1m)
Sample ID Location/nearest town Estimated Qty (m3)
Gravel at Ala 1Bridge
5Km from Arua town, along Arua Pakwach Road, Ajiya Subcounty,near Ajiya
8,600
(120mx60mx1.2m)
II.Location of Gravel Sources for Lot 2:
Sample ID Location/nearest town Estimated Qty (m3)
G1/Lot 2
5.5Km from Koboko town, along
Arua Koboko Road, MidiaSubcounty, near Danya TC
28,800(120mx240mx1.0m)
Sample ID Location/nearest town Estimated Qty (m3)
G2/Lot 2 8.0Km from Koboko town, alongArua Koboko Road, MidiaSubcounty, near Koboko
74,880
(320mx180mx1.3m)
Note:The Bridges under lot 2 are discarded under the new scope of work. Thus
these material locations can be considered for lot 1 bridges if the need arise,
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G2/Lot 2
Sample ID Location/nearest town Estimated Qty (m3)
G3/Lot 28.0Km from Koboko town, along
Arua Koboko Road, MidiaSubcounty, near Koboko
74,880
(320mx180mx1.3m)
G3/Lot 2 (a) G3/Lot 2 (b)
G3/Lot 2 (a) G3/Lot 2 (b)
G3/Lot 2 (1) G3/Lot 2 (2)
Sample ID Location/nearest town Estimated Qty (m3)
G4/Lot 2 8.0Km from Koboko town, alongArua Koboko Road, MidiaSubcounty, near Koboko
74,880
(320mx180mx1.3m)
G4/Lot 2 (a) G4/Lot 2 (a)
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III. Location of Gravel Sources for Lot 3:
Sample ID Location/nearest town Estimated Qty (m3)
G1/Lot 35.0Km from Nebbi town, near Okeya Village,
Used by MoWT
> 10,000
(150mx50mx1.5m)
G1/Lot 3(a) G1/Lot 3(b)
Sample ID Location/nearest town Estimated Qty (m3)
G2/Lot 35.0Km from Nebbi town, near Okeya Village,
Used by MoWT
> 100,000
(210mx300mx1.5m)
G2/Lot 3 (a) G2/Lot 3 (b)
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Table 3-5: Summary of Laboratory test results of the potential gravel sources
Sr. ID Location
Grading, % passingSieves
Laboratory Test Results
2.0mm
0.425mm
0.075mm
LL(%)
PI(%)
OMC(%)
MDD(g/cc)
BS Light
CBR@ 95%MDD
G1-Lot1
11 Km from Arua town, Arua
District, Kijomoro Subcounty,
Near Loliragoro town
39 30 20 46 25 11 2.02 26
G2-Lot1
19 Km from Arua town, Arua
District, Oleba Subcounty,
2Km from Oleba T C
40 30 23 47 24 11 2.06 20
G3-Lot129 Km from Arua town, AruaDistrict, Oluffe Subcounty,
near Ombere town
52 39 25 46 24 14 1.82 10
ALA 1
Bridge
5Km from Arua town, along
Arua Pakwach Road 38 30 22 50 25 12 1.86 22
Arua TC
8Km from Arua town, along
Arua-Ajono Road, VuraSubcounty, near Gil-gil
42 32 25 45 21 11 1.84 27
G1-Lot25.5Km from Koboko town,
along Arua Koboko Road43 33 25 44 24 10 1.96 20
G2-Lot28.0Km from Koboko town,
along Arua Koboko Road32 25 13 36 17 10 12.10 45
G3-Lot28.0Km from Koboko town,along Arua Koboko Road
50 34 21 45 22 10 1.90 18
G4-Lot28.0Km from Koboko town,
along Arua Koboko Road36 27 16 37 23 11 1.98 27
G1-Lot35.0Km from Nebbi town, near
Okeya Village44 33 22 40 22 10 2.03 15
G2 - Lot3 5.0Km from Nebbi town 45 33 25 42 21 11 2.02 37
Spec. requirements for Subbase to be usedfor approach road & backfill
20%) strength but all have higher plasticity to be directly used as
subbase. Thus, it is recommended stabilized the materials with lime (usually 3% to
5% with the red clayey sandy lateritic gravels in Uganda), in order to improve both
on their plasticity and CBR values to within the specification limits.
Those sources with CBR values more than 10% and less than 20% can be used for
improved subgrade layers and embankments for approach roads.
3.4.4 Potential Sand Sources
The Design Consultants have identified and tested three sources of sand. The sources
were from Oreku on the Arua-Koboko Road, Ayi 1 on the Arua-Koboko Road, and
Akaba which is 6.6Km from Nebbi town. The test results showed that had high clay
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contents and only the sand from Akaba fulfilled the specification limits for gradation.
As a result, only the sand from Akaba was recommended to be used as a filter media
(drainage layer) under high embankments and crushed fine was recommended
instead.
Efforts have been made by the Design Review consultant to exhaustively search for
possible sources of sand in the project area. As a result, the following sand sourceshave been identified and laboratory tests conducted on them to assess their suitability
for concrete and mortar works.
I. Potential Sand Sources for Lot 1
Sample ID Location/nearest town Estimated Qty (m3)
S1/Lot 16.2Km from Arua town, from
Enyayu River bridge, on Arua
Koboko - Oraba Road
3,000
S1/Lot1 (1) S1/Lot1 (2)
S1/Lot1 (3) S1/Lot1 (4)
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Sample ID Location/nearest town Estimated Qty (m3)
S2/Lot 117Km from Arua town, near Kijomoro
town, from Enve river bridge, on Arua
Koboko - Oraba Road
2,000
S2/Lot 1(1) S2/Lot 1(2)
Sample ID Location/nearest town Estimated Qty (m3)
S3/Lot 133.7Km from Arua town, near
Nyoro town, from Ayi river
bridge, on Arua Koboko - Oraba
Road
2,000
S3/Lot 1 (1) S3/Lot 1 (2)
Sample ID Location/nearest town Estimated Qty (m3)
ALA River Sand17Km from Arua town, Arivu
Subcounty, from ALA river
bridge
2,000
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II.Potential Sand Sources for Lot 2
Sample ID Location/nearest town Estimated Qty (m3)
S1/Lot2Near Oleba town, from Oru 1
river bridge, on Arua Koboko
Oraba Road
1,000
S1/Lot2 (1) S1/Lot2 (2)
Sample ID Location/nearest town Estimated Qty (m3)
S2/Lot2
8.2Km from Koboko town, from
Lebijo river bridge, on Koboko
Yumbe Road, Appx. 2.1Km from
the Road
4,000
S2/Lot2 (1) S2/Lot2 (2)
Sample ID Location/nearest town Estimated Qty (m3)S3/Lot 2 Otumbari Subcounty, from Oru
river bridge,
3,000
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S3/Lot 2 (1) S3/Lot 2 (2)
III. Potential Sand Sources for Lot 3
Sample ID Location/nearest town Estimated Qty (m3)
S1/Lot 3
9.0Km from Nebbi town, from
Acwera river bridge, along NebbiWadi Lai district rural road,
2Km off the highway
2,500
S1/Lot 3 (1) S1/Lot 3 (2)
S1/Lot 3 (C)
S1/Lot 3 (3) S1/Lot 3 (4)
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Sample ID Location/nearest town Estimated Qty (m3)
S2/Lot 35.0Km from Nebbi town, from
Akaba river bridge, along Nebbi
Pakwach Road
2,500
S2/Lot 3 (1) S2/Lot 3 (2)
S2/Lot 3 (3) S2/Lot 3 (4)
Sample ID Location/nearest town Estimated Qty (m3)
S3/Lot 330Km from Nebbi town, from
Nam-Rwadho river bridge, along
Nebbi Pakwach Road
4,000
S3/Lot 3 (1) S3/Lot 3 (2)
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Table 3-6: Summary of Laboratory test results of the potential Sand sources
From the laboratory test results, it can be seen that most of the identified sources can be used with some treatm
grading requirements or by washing to remove clay lumps and minor organics contents.
Sr.No.
LocationOf Sand
Sieve Analysis, % passing, mmSilt and
ClayContent
(%)
Compress
Strength Cement Mo
(7 days, MP10.0 5.0 2.36 1.18 0.60 0.30 0.15
1 S1/Lot 1 100 99 94 83 51 8 2 1.8 30
2 S2/Lot 1 100 99 92 38 28 3.8 32
3 S3/Lot 1 97 94 89 73 34 6 4 3.4 28
4 Lot 1- C 99 98 97 90 69 10 4 3.2 30
5 S1/Lot 2 100 98 94 70 13 5 4.2 29
6 S2/Lot 2 100 98 90 65 13 3 2.0 35
7 S3/Lot 2 100 99 97 87 51 14 4 1.6 31
8 S1/Lot 3 100 99 95 79 38 8 3 2.0 30 9 S2/Lot 3 100 97 88 66 34 6 2 1.6 29
10 S3/Lot 3 98 95 84 65 39 16 11 9.6 35
11 ALA River Sand 96 94 91 81 56 14 3 2.4 32
Ugandan Grading
Spec. I100 90-100 60-95 30-70 15-34 5-20 0-10 6% Max. 28 Min
II 100 90-100 75-100 55-90 35-59 8-30 0-10
III 100 90-100 85-100 75-100 60-79 12-40 0-10
IV 100 95-100 95-100 90-100 80-100 15-50 0-15
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4 HYDROLOGICAL and HYDRAULIC STUDY REVIEW
4.1 Background
Highway drainage is an important consideration in the design of many projects. The
term drainage is defined in several different ways, including the process of removing
surplus groundwater or surface waters by artificial means, the manner in which the
waters of an area are removed, and the area from which waters are drained. A project
may alter the existing drainage. When this occurs, drainage features should be
provided which protect the highway, adjacent landowners, and the traveling public
from water, while maintaining water quality and protecting other environmental
resources.
Bridge is a structure which provides passage facilities over an obstacle without
closing the water way underneath. In a highway project the obstacle is usually of
valley water way that will be passed by the provision of a structure which can safely
pass both motorized and non motorized transport facilities without causing any
natural flow system disturbance on its underside zone.
The design of a bridge across a stream demands a special attention towards route
location, potential traffic flow and structural and foundation details, but also to the
characteristics of the stream beneath the structure. Collecting information and data
regarding to stream channel stability, anticipated flood, and sediment discharge and
scour potential is a basic and primary task prior to a detailed hydraulic design work of
a bridge.
A bridge must not only be hydraulically efficient, but also be consistent with the
importance of the road, safety, initial cost, aesthetics, environmental considerations,
maintenance and legal responsibilities. Highway bridge hydraulic design comprisestwo major components:
1. Hydrological study
2. Hydraulic Analysis
Hydrology/Hydraulics design review of 21 bridges where the recently selected 10
bridges contained on it is conducted by undertaking a detailed hydrological and
hydraulic investigation at sample bridges and/or culverts representing the overall
design approach together with physical hydrologic survey data of the existing
structures.
4.2 Objective
The review has the following objectives:
Undertaking a detailed hydrological and hydraulic investigation at selected
sample bridges and culverts to examine and to compare the overall bridge/culvert
hydrological and hydraulic design of the consultant.
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Estimating maximum probable flood through flood mark physical identification
and local people consultation and compare it with the design consultant remarks.
Examining the existing structure flood accommodation capacity or hydraulic
sufficiency or insufficiency in relation to the proposed once.
River bank condition assessment to visualize the extent of erosion in and around
the bridge sites and to identify the necessity of protection works
To check the design consultant remedial recommendations in relation to existing
and proposed structure.
4.3 Hydrology
Hydrology in a highway development deals with estimating flood magnitudes as the
result of precipitation (usually the peak discharge) .The necessity and extent of the
hydrologic analysis to be performed is based on the type of project, road design
standard and type of structure that will be laid in a highway.
An overview of the process of performing a hydrologic analysis, including criteria
(design flood frequency) and methodologies for determining the peak discharge. The
overall process which should be used to conduct the hydrologic analysis for a given
project is listed below:
Conduct preliminary assessment at the office level.
Take an initial field trip to the project site.
Select a methodology and design flood frequency, and calculate the design
discharge with some methods.
Take a final field trip to verify the analysis/design and to recheck flood damage
potential.
4.4 Data Collection
The hydrological analysis has been made using available digital elevation models
(DEM) and aerial photographs together with keen physical hydrologic survey made at
each bridge/culvert site. Additional hydrological and geological information have
been gathered by consulting local residents and from concerned bodies around the
project area.
4.4.1 DEM and Aerial Photographs
Available 90m resolution digital elevation model (DEM) showing all the drainage
pattern to the required level is used as an input to delineate bridge catchment area at
road. Widely used public domain GIS softwares (ARC View 3.3, WMS 8.1 and
ILWIS) are used for DEM hydro processing purpose at selected bridges watershedareas thereby determining catchment characteristics such as area, slope, stream length
etc.
4.5 Drainage Characteristics, Geology and Topography
The overall watershed areas draining towards each bridge outlet point comprises a
number of minor and major tributaries originating from most remote and/or nearby
hillsides or dividing lines depending upon the nature of the stream and topographic
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conditions. Dissected plateau with a number of narrow valleys and active flow nature
is the dominant surface drainage pattern on the area. Most streams are perennial in its
very nature but others are intermittent streams flowing only during rainy seasons of
the year. Dense vegetation cover (Dry combretum and grass) with some cultivation is
the major land use cover forms where most watershed areas are characterized. Sandy
loam, lithosols and sandy clay loam are the main soil types covering the catchment
area. The catchment area is also dominated by quartzo-feldspathic genesis,
magmatites of Aruan Complex, charnockites, enderbites, hypersthenes genesis and
basic granulites geological forms.
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Table 4-1: Bridge catchment area physiographic description (As per the new scope)
S/NBridge
Name
Route & District Flow directionStream
nature
Topography Catchm
1 Alla
Arua-Inde-
packwach(Arua)
R to L (from Arua
to Inde) perennial Relatively Rolling terrain
Originates fro
neighborhood
highlands
2 Enayu-3 Arua-Ediofe (Arua)
L to R (from Arua
to Ediofe) perennial Relatively steep terrain
Originates fro
neighborhood
highlands
3 Nyagak-3
Jqang-Okoro-
Alyenda(Nebbi)
L to R (from
Okoro to
Alyenda) perennial
Slightly steep
topographic condition
Originates fro
neighborhood
highlands
4 Goli
Nebbi-Goli
Custom(Nebbi)
R to L (from
Nebbi to Goli)
perennial Moderately rolling Originates fro
neighborhood
highlands
5 Nyacara
Nebbi-
Erussi(Nebbi)
L to R (from
Nebbi town to
Pakwala) perennial Rolling terrain
Originates fro
nearby highla
6 Pakwala
Nebbi-
Erussi(Nebbi) - perennial
Relatively rolling to hilly
terrain
Originates fro
nearby highla
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4.6 Climate
The distinction in climate characteristics mainly caused by altitude differences and its
location where rainfall on the area is highly influenced by Inter Tropical Convergence
Zone (ITCZ).
Watershed areas of twenty one bridges mainly falls under the same climatic
zonation with an expected mean annual rainfall ranging from 1000-1500mm and
mean annual temperature in between 25 and 30 0C .
4.7 Peak Discharge Estimation
There are several methods to compute peak discharge, among these methods the most
commonly used once are stated below:
1. Rational Method.
2. Modified Soil Cover Complex Method, SCS (plotting a hydrograph).
3. Regression Equations
4. Historical Data statistical analysis.
5. TRRL Model (East African Flood Model)
4.7.1 Rational Method
Rational method is recommended to determine the peak discharge, or runoff rate,
from drainage areas up to 80 ha and its application requires appropriate intensity data.
Assumptions under Rational Method are:
Peak discharge occurs when all of the drainage area is contributing,
A storm that has duration equal to the time of concentration (Tc) produces the highest
peak discharge for the selected frequency,
Intensity is uniform over a duration of time equal to or greater than the Tc, and
The frequency of the peak flow is equal to the frequency of the intensity.
The rational method formula is:
Q = kCiA, where:
Q = peak discharge or rate of runoff (m3/s)
k = 0.00278 (m 3/s) hr / (ha C mm)
C = runoff coefficient
i = intensity (mm/hr)
A = drainage area (ha)
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4.7.2 SCS Method
A relationship between accumulated rainfall and accumulated runoff was derived by
SCS from experimental plots for numerous hydrologic and vegetative cover
conditions. Data for land-treatment measures, such as contouring and terracing, from
experimental catchment areas were included. The equation was developed mainly for
small catchment areas for which daily rainfall and catchment area data are ordinarily
available. It was developed from recorded storm data that included total amount of
rainfall in a calendar day but not its distribution with respect to time. The SCS runoff
equation is therefore a method of estimating direct runoff from 24-hour or 1-day
storm rainfall. The equation is:
SPforSP
SPQ 2.0
8.0
)2.0( 2
-------------------------------eq. (4.1)
Where:Q Effective accumulated rainfall depth (mm)
P Gross accumulated rainfall depth (mm)
S Potential maximum retention (mm)
The potential maximum retention S has been expressed in terms of the Curve Number
CN in order to make the operations of interpolating, and weighting more nearly
linear. This relationship is:
25425400
CN
S ---------------------------------------eq. (4.2)
CN refers the runoff response characteristics of the watershed area.
Using the equation of the area of the triangle and expressing the volume in m3, the
peak discharge qp of the triangular unit hydrograph is given by the equation shown
below: