isiolo airport executive summary

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Airport Pavement Design

Report

Engineering Report No:

ISAT-ES 0211 02

EXECUTIVE SUMMARY

Kensetsu Kaihatsu LtdFebruary 2011

Government of the Republic of Kenya

Kenya Airports Authority [KAA]


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EXECUTIVE SUMMARY

Isiolo Airport Pavement Design Engineering Report No: ISAT 0211/01 Page 3

2011KENSETSU

KAIHATSU

EXECUTIVE SUMMARY

ES1 Introduction

The Kenya Airport Authority (KAA)

commissioned Kensetsu Kaihatsu Consultants

in the Rehabilitation and Restoration of Isiolo

Airport Pavement Project in Isiolo County to

carry out a design of the airport pavement

facility using the Boeing 737-800 as the design

aircraft with provision for future expansion.

The existing airstrip was constructed during

the colonial era and what is remaining is a

dilapidated runway. The airport is part of the

LAPSSET Corridor initiative where it will play

a big role in connecting the Lamu Port in Lamu,Coastal Kenya to Ethiopia and South Sudan.

The airport will be constructed in phases;

phase one will involve the terminal buildings

with 1.2km runway and other facilities like

apron, taxiway. The runway will be expanded

later under subsequent phase[s] to cater for

lager planes.

Actual implementation of the project started in

July 2004 with the engagement of a local

contractor to construct an arrival building,control tower, fire and rescue building, a

3.3km runway, access road, car park and apron

up to sub-base level. The government then

requested its development partners to provide

funding for further development.

The Contract for the first phase of the project

was signed in January 2011 between the

Kenya Airport Authority and Kundan Singh

Construction Company. The pavement worksare anticipated to take about 6 months.

A detailed description of the Scope of Worksunder this phase of construction is given in the

Contract Documents of the Construction ofBuildings and Pavements of Isiolo Airport.

Plate ES1.2 Site photo showing the condition

of the pavement

ES.2 Background of Design Review of IsioloAirport Pavement Structure

ES2.1 Necessity for Design Review

Upon signing of the Contract, the Contractor, in

accordance with Clause 8 of The FourthEdition 1987 FIDIC Conditions of Contract (ref.

to Table 1.2.1 of the Main Report), undertook

monitoring, technical evaluation and

geotechnical engineering investigations in

order to confirm, more precisely, the

engineering properties of the existing soils as

well as the behavior of the existing ground andpavement structure.

The preliminary results indicate that theexisting ground and pavement structure

exhibited much higher bearing capacity and

strength responses in comparison to the

values that may have been considered in the

Original Design.

As a consequence, the Contractor made a

decision to embark on further and more

detailed laboratory and in-situ experimental

testing, technical evaluation, geotechnical

engineering investigations and analyses.This was also in consideration of the fact that it

is most likely the Original Design did not take


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into account the pozzolanic cementetious

nature of the existing Geomaterial and its

immediate response to compaction and the

effects of time related consolidation,

thixotropy and creep (secondary

consolidation).

This would certainly therefore have influencedthe Original Design Concept, selection of

materials and design of the pavement layerconfiguration.

In view of the foregoing facts, and in

consideration of the recent International trend

whereby emphasis is placed on fostering and

enhancing Value Engineering (VE) based

approach in the design and construction of

civil engineering structures (ref. to Sub-Clause

13.2 quoted hereafter), the Contractor made

the engineering judgment to undertake a

Detail Design Review (DDR) of the IsioloAirport Pavement Structure.

Relevant VE Sub-Clause 13.2 of The Bank

Harmonized Edition of the Conditions of

Contract IFCE, FIDIC

Clause 13.2 Value Engineering

The Contractor may, at any time, submit to the

Engineer a written proposal which (in the

Contractors opinion will, if adopted, (i)

accelerate completion, (ii) reduce the cost to

the Employer of executing, maintaining or

operating the Works, (iii) improve theefficiency or value to the Employer of the

completed Works, or (iv) otherwise be of

benefit to the Employer.

The proposal shall be prepared at the cost of the

Contractor and shall include the items listed in

Sub-Clause 13.3 [Variation Procedure].

If a proposal, which is approved by the Engineer,

includes a change in the design of part of the

Permanent Works, then unless otherwise agreed

by both Parties:

(a) The Contractor shall design this part,(b) Sub-paragraphs (a) to (d) of Sub-Clause 4.1

[Contractors General Obligations] shallapply, and

(c) If this change results in a reduction in thecontract value of this part, the Engineer shall

proceed in accordance with Sub-Clause 3.5

[Determinations] to agree or determine a fee,

which shall be included in the Contract Price.

This fee shall be half (50%) of the difference

between the following amounts:

(i) Such reduction in contract value, resultingfrom the change, excluding adjustments

under Sub-Clause 13.7 [Adjustments for

Changes in Legislation] and Sub-Clause

13.8 [Adjustments for Changes in Cost],and

(ii) The reduction (if any) in the value to theEmployer of the varied works, taking

account of any reductions in quality,

anticipated life or operational efficiencies.

However, if amount (i) is less than amount (ii),

there shall not be a fee.

Interpretation of Clause 13.2

Value Engineering is basically the development

and application of Advanced Technologies aimed

at realizing cost-effective, durable, sound

engineering and maintenance friendly structures.

The Contractor intends to achieve this goal by

adopting the State of the Art Technologies

developed and widely applied in this region and

introduced in the various sections of the Main

Report.

These Technologies have realized enormous time

savings, whilst further enhancing the

Engineering Properties by at least 150 300%.

Specifically, this mainly culminates in the

enhancement of the Structural Capacity,

Serviceability Level, Bearing Capacity, Strength

and Deformation Resistance of the Pavement

Structure.

ES2.2 Scope of Investigation and Main

Objective of Study

1.2.2 Scope of Works

The consultants, Kensetsu Kaihatsu Limited

were commissioned by the Client, Kenya

Airport Authority, to undertake acomprehensive geotechnical engineering

analysis and review of the Existing design by

employing a Value Engineering (VE) approach

and set up State-of-the-Art International

Standards fostering engineering and

scientific concepts that can be tailored and

applicable in Isiolo, Kenya.

The assignment included but was not limited

to the following tasks:-

i) Review the design using Boeing 737-800as the design aircraft.

ii) Review comprehensively, the ExistingDesign documents.

iii) Study the US Federal Aviation Administration (FAA) Advisory Circular

Airport Pavement Design and

Evaluation AC 150/5320-6D, ICAO

Aerodrome Design Manual, Materials and

Specifications, ICAO recommended

practices as detailed in Annex 14 Volume

1, and any other relevant documents.

iv) Undertake comprehensive Site Surveysand Investigations.

v) Carry out detailed analyses andassessment of the test data obtained fromboth in-situ and laboratory tests

performed in Kenya.


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vi) Assessment of the laboratory equipmentand capability of the same to carry out

material acceptance and pavement

control testing.

vii)Carry out material investigation,sampling and testing for the proposed

runway.viii) Perform tests on any other suitable

material sites for aggregate sources, later

to be utilized civil works.

ix) Carry out geo-material improvement,mechanical, & chemical stabilization and

testing for any non-compliance materials

and/or for purposes of enhancing the

engineering properties of the compliant

materials.

x) Build capacity in terms of trainingmanpower, and laboratory Technicians

on test methods and quality control.

ES2.2.2 Isiolo Airport Project and

Surrounding Areas

Fig. 1.1 shows the surrounding districts of

Isiolo district

Fig. ES1.1 Lay Out of Isiolo

Fig. 1.2 Satellite Image of Isiolo Airport

ES2.3 Geophysical Details of Isiolo Airport inIsiolo within Isiolo Region of Kenya

The site for the Isiolo Airport located in Isiolo,

Kenya, and its geographical coordinates are

020'17" North and 3735'28" East and its

original name (with diacritics) is Isiolo.

Airports in Isiolo and in the neighbourhood:

Garbatula Airport (distanced

approximately 105.7 km)

Garissa Airport (distanced approximately

247 km)

Hola Airport (distanced approximately

341 km)

Marsabit Airport (distanced

approximately 225 km)

Wajir Airport (distanced approximately

317 km)

Bura Airport (distanced approximately

308 km)ES2.4 Relevant Documents and Records

Reference is made mainly to the following

documents and records.

1. United States Federal AviationAdministration (US FAA) Advisory Circular

No. 150/5320-6D

2. International Civil Aviation Organization(ICAO) Annex 14 Volume I AerodromeDesign and Operations

3. Aerodrome Design Manual, Part 34. Boeing 747-100 Guide to Aerodrome

Design and Technical Data

5. The Civil Aviation (Aerodromes)Regulations, 2007

6. AASHTO Guide to Pavement Design7. Transport Research Laboratory (TRL)

Overseas Road Note 31, Berkshire, UnitedKingdom

8. Japan Road Association Pavement DesignManual

9. Kenya Roads Design Manuals10.Materials Report and Test Results11.Reconstruction of Airport Pavements at

Isiolo Airport

ES2.5 Brief Background of Project Area

The Study including GeotechnicalInvestigation was carried out for Isiolo Airport

and the site photos are depicted in Plate 1.3

ISIOLO

GARISA

MERU

MARSABIT


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Plate ES1.3 - Photos Superimposed on

Satellite Imagery showing the Airport

Figure ES1.4 Location map of Isiolo Airport

Kenya is located in Eastern Africa between

longitude 340 and 420 East, Latitude 50 North

and 50 South.

Kenya is the second largest of the East Africa

countries (i.e. Kenya, Uganda, Rwanda,Burundi and Kenya), has a spectacular

landscape of mainly three physiographic

regions namely the coastal plains to the east;the inland plateau; and the highlands. The

Great Rift Valley that runs from north east of

Africa through North western and southwestern Kenya down to Kenya is another

landmark that adds to the scenic view of the

country. The valley is dotted with unique lakes

which include Lakes Turkana, Baringo,

Bogoria, Naivasha, Nakuru, Elementaita, Logipi

and Magadi.

ES3 Determination of PavementStructural Design

Determination of Total Pavement Thickness

Required

Subsequent to determining the Mean-sectionDesign CBR values for the subgrade and the

sub-base (ref. to table 3.1), the weight on the

main landing gear was determined from Fig.

7.2.4 in Chapter 7 of the Main Report. Having

pre-determined the design aircraft and the

number of annual departures of the design

aircraft, the design curves in Fig. 7.2.5

presented in Chapter 7, based on the U.S. ArmyCorps of Engineers Design Method S-77-1 and

the U.S. FAA Design method, the totalpavement thickness required was derived.

ES3.2 Thickness of Sub-base

Refer to Section ES7.1.1 of this Executive

Summary.

ES3.3 Thickness of Surface Course


Summary.

ES3.4 Thickness of Base Course


Summary.

ES3.5 Thickness of Non-Critical Areas


Summary.

ES3.6 Typical Cross-section


Summary.

ES4.4 Construction Time Comparative

Analysis


Summary.

ES5 Materials Characterization and

Analysis of Test Results

ES5.1 Basic Physical and Mechanical

Parameters

Table ES5.1.1 shows the typical basic physical,mechanical and bearing capacity properties of

existing BCS soils within the Isiolo Airport

Project Area.

Table ES5.1.1 Typical Pre-treatment/Pre-

consolidation Material Test Results

1

2

3

4

5

6

7

8

9

# TESTED PARAMETERSTEST VALUE

REMARKS

Computed UCS (Mpa)

CBR@100%MDD - Soak

MDD - Kg per Cubic meter

OMC

Atterberg - LL

0.05

2.00

1,129.00

34.50

120.00

The subgrade soil has a lot of fines

CBR@100%MDD - Unsoaked 17.00

Atterberg - PI

Atterberg - LS

53.0067.00

23.00

Atterberg - PL


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ES5.2 Correlation between Physical,

Mechanical and Strength parameters

The typical pre-treatment (pre-

stabilization)/pre-consolidation basic physical,

mechanical and bearing capacity for material

tested from the sub-base material at BP3 Ruiri.

ES 5.3 Development of test regimes

To attain Optimum and a value engineered

design, several Test Regimes were developedto help us achieve the optimum designs. It

involves the comparison of various designs

options and modeling the different structuresin the Lab.

Table ES5.2.1 Summary of Stabilization

Test Results

A. Neat Material

B. OBRM SUBBASE MATERIAL

C. OPMC SUBBASE MATERIAL

D. SUMMARY OF THE TEST RESULTS-

COMPARATIVE ANALYSIS

E. SUMMARY AND COMPARISON OF

GRANULAR SUB-BASE MATERIAL FOUND IN

THE VICINITY

From the tables above the following can beinferred:

The gravel at BP3 is of good sub-base quality.

It has natural intrinsic cementetious

behaviour. This makes it posses high

engineering properties in comparison to

other materials within the location [see table

above].

The grading of BP3 is satisfactory but we will

be required to add 20% Quarry Dust to

improve on the densities.

Neat 1 1 1 1 1 1 1

1 1 1 1 1 1 2

1 1 1 1 1 1 21 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 2

1 1 1 1 1 1 4

Granular Material-

Gravel

Stabilization

RateM ode of c uring M DD O MC

1d c/s

PL LL PI GRADING

1d/c

UCS

3d/c7d/c

1d/c

1d c/s

3d c/s

3d/c

7d/c

3d c/s

1d/c

3d c/s

1d/c

3d/c

7d/c

1d c/s

3d c/s

BP3

3d/c

7d/c

1d c/s

3d c/s

1%

2%

3%

4%

6%

1d/c

3d/c

7d/c

1d c/s

REMARKS

BP3-NEAT SUBBASE BASE

1 1.23

2 52.00 Not


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The strength properties, densities and

particle of the neat BP3 material is

enhanced by the inclusion of the 20%

quarry dust and 2% cement.

The cement used is Bamburi PowerPlus. It

is reported that PowerPlus type of cementgains strength immediate/sporadically

after stabilization and after about 28 days

the strength normalizes; PowerMax gains

strength with time and its expected to

yield maximum strength after 28 days.

Laboratory tests and monitoring are

ongoing to confirm this.

The OPMC batched material evidently

shows improved properties. We have an

increase of more than 150% in strengthsafter 3 day cure. Further tests are still on-going to ascertain the behaviour with time

and at different conditions as described in

5.2

From the 1 day cure results we can

tentatively decide that our design will be

BP3+20% Quarry Dust + Tensar TX170Geogrids + 2% cement is the optimum

design

ES5.3 Dynamic Cone Penetration Test ResultsThe ground and Geomaterials characteristics

under dynamic loading as simulated by the

Dynamic Cone Penetration determined in this

Study, are summarized in the Tables below,

while their behavior is graphically

characterized in the corresponding Figures.

The fact that the existing pavement is very

sound can be derived from the very highbearing capacity and strength magnitudes that

it exhibits.

Series 5.4.1 Tables and Figures for DynamicCone Penetration Results for Isiolo Airport

The following derivations can further be made

from these tables and figures.

1. Most of the locations on thecarriageway of the existing

pavement structure exhibit high

bearing strengths under

conditions tested with averages of

CBR 62%.

2. The average CBR mean results isabout 62% for dry in situ

conditions while the soaked

conditions gives average CBR

mean of less than 5%. From the

two CBR figures, it is prudent that

the subgrade/foundation Design

considers options for moisture

control in its design. We are

proposing the GI-MC method for

the design and construction of the

improved subgrade. This because

when the foundation is dry i.e.

when moisture is controlled, the

in-situ strengths are very high

compared when it is partially orcompletely soaked.

3. The Subgrade BCS soil has PIvalues of 67%. This indicates a

very high value of fines and clay

minerals in its composition. The

design needs to cater on how to

prevent the contamination of the

Base/sub-base layers through

infiltration/ingress of fines into

the upper pavement layers

[base/sub-base]. The presence of

fines into these layers will be very


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Laboratory UCS Tests of Cement Stabilized

[Chemical stabilization]

Table ES5.7.1(b) Summary of Consolidation

Stress Parameters Derived from

Laboratory UCS test of Cement- Geogrid

Stabilized OPMC-[Chemical - Mechanical

stabilization]

ES5.8 Shearing Strength Test Results

The shearing strength parameters aresummarized in Tables ES5.2.1 Series present

the UCS laboratory test results for specimens

tested at 1%, 2% and 3% cement treatmentlevels, while the graphical characteristics of

the loading to failure are shown in the

corresponding figures. Table ES5.8.1 is asummary of these results in comparison with

values that are computed adopting empirical

equations defined in Chapter 4 of the Main

Report.

On the other hand, a summary of the shear

parameters derived from in-situ tests is given

in Table ES5.2.3.

This Table presents the results computed by

adopting Eqns. 4.18 in sub-section 4.3.1 and4.33 ~ 4.38 in sub-section 4.5.1 of Chapter 4 of

the Main Report.

The derivations from these results are briefly

presented after Table ES5.8.2.

Table ES5.8.2 Summary of Shear Stress

Parameters Derived from In-situ Tests

The following observations can be made from

the foregoing Tables ES5.8.1 ~ 5.8.2 and the

corresponding Figures.

The laboratory test results indicate enhanced

intrinsic shearing properties of the pozzolanic

material even at very low cement treatment

ratios (ref. to results of 1% additive tocomparative parameters presented in Chapter7 from various International Agencies).

1) The in-situ test results show that theshearing strength is immensely enhanced

as a result of the coupled effects of long

term consolidation and cementetious

agglomeration.

2) From Table ES5.8.1, it can be observed thatthere is a very good agreement between

the tested and computed values. Thisconfirms the precision of the test results

accordingly.

3) On the average, the in-situ values arehigher that the laboratory test results

{UCSlab = 7.75 MPa compared to UCSin-situ =

8.95 MPa(average)}.

However, as can be observed from the results

summarized in Tables ES5.5.1 in the preceding

section ES5.5, the results tend to be very

similar when corrected for the effects of Long

Term Consolidation by applying the following

equation.

STCn

STC

STCSTCLTC

CSRAttK

qKq

'/100

max0

max

Where,

Superscript LTC and STC denote long term and

short term consolidation respectively whereas t

: LTC time and to : STC time., for OC conditions

( a/ t)fcSTC=1.

MIX

Sample (MPa) (MPa) (MPa) (MPa) ( MP a) ( MP a)

1 P o zz o lan ic 0 .6 6 0. 33 1. 06 4 8. 06 0 1. 291 1 5. 787 0 .3 28 1 .01 0 0 .93 8 0. 42 3 0. 38 0 1 .31 0. 26 1. 06 1. 48

3 P ow er Ma x 0 .6 0. 30 0. 96 4 7. 95 2 1. 290 1 5. 770 0 .3 29 1 .01 1 0 .93 6 0. 42 4 0. 38 1 1 .19 0. 23 0. 96 1. 35

4 P o wer Pl u s 0 .9 6 0. 48 1. 54 4 8. 60 2 1. 295 1 5. 875 0 .3 27 1 .00 8 0 .94 9 0. 41 9 0. 37 9 1 .90 0. 37 1. 54 2. 15

Notethatthe cementcontectis 3% andthe curingmode3days soak

qC pC

SerialNo. UCSqu (MPa)Cu

CSR

maxq

CSR CSR/1

CSR OK

CK

1

ac

1

rc

MIX

Sample (MPa) (MPa) (MPa) (MPa) ( MP a) ( M

1 Pozzolanic 0 .792 0.40 1.27 48.2 99 1.2 92 15.8 26 0.3 28 1.0 10 0.94 3 0.42 1 0.3 80 1.5 7 0.3 1 1.2 7

0 P o we rM ax 0 . 9 62 0.48 1.54 48.6 06 1.2 95 15.8 76 0.3 27 1.0 08 0.94 9 0.41 9 0.3 79 1.9 1 0.3 7 1.5 4

4 P o we rP l us 1 .1 48 0.57 1.84 48.9 42 1.2 97 15.9 31 0.3 26 1.0 07 0.95 6 0.41 6 0.3 77 2.2 7 0.4 4 1.8 4

Notethatthe cementcontectis 3% andthe curingmode3days soak

pqCSerialNo. UCS qu (MPa)

CuCSR

CSR CSR/1

CSR OK

CK1

ac

1

rc


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ES5.9 Modulus of Deformation, Elastic

Modulus and Linear Elastic Range

A summary of the derived modulus of

deformation, elastic and shear modulus and

elastic limit strain, which is defined as the

range of linear elastic and recoverablebehavior, given in Tables ES5.9.1 and 5.9.2,

were computed by applying Equations 4.48 ~

4.52 of the Main Report.

The normalized relations are also presented in

the same Tables.

Table 5.9.1 Summary of Modulus ofDeformation Parameters from Lab Test

Results

Table ES5.9.2 Summary of Modulus of

Deformation Parameters - In-situ Test

Results

The results of deformation properties and the

linear elastic range are presented in Table

5.10.1 below.

The results basically indicate that as the

shearing strength increases with the

deformation resistance, the linear elastic rangeis immensely enhanced.

ES5.10 Deformation Properties and Linear

Elastic Range

The results of deformation properties and the

linear elastic range are presented in Table

5.10.1 below.

The results basically indicate that as the

shearing strength increases with the

deformation resistance, the linear elastic rangeis immensely enhanced.

Table ES5.10.1 Summary of Modulus of

Deformation Parameters - in-situ Test

Results

ES5.11 Summary of the effects of curing

period on soil particle agglomeration and

unconfined strength.

From the laboratory test results OPMC

Stabilized + Geogrid samples yields UCS values

of 3.32 after 3day cure with 2% cement

content [PowerPlus]. After extrapolation from

the relation that is explained in chapter 4, the

following table gives the expected calculated

properties after several days of curing.

Table ES5.11.1 Table: Effects of curing

period on OPMC Level 3

Table 5.11.2 Effects of curing period on

Resulting, ER Composite Pavement

7. PAVEMENT STRUCTURAL DESIGN

7.1 Scope

1 BCS subgrade 12 1 07 4 35 7. 85 5 .2 3 0 .3 8 0 .1 02 78 2 0. 16 98 85 1 37 13

2 BP1 LMD gravel 347 3 83 4 1 27 8. 04 4 1. 76 0 .6 3 0 .2 50 79 4 0 .3 98 41 0 1 71 8

3 BP2 78 Tank Batt 389 4 00 7 1 33 5. 55 4 4. 87 0 .6 7 0 .2 69 63 2 0 .4 26 03 3 1 59 9

5 BP5 Murero 173 2 94 6 98 2. 10 2 7. 17 0 .5 0 0 .1 74 09 7 0. 28 22 99 2 64 1

6 BP6 LMD Sandy 49 1 81 8 60 6. 02 1 2. 36 0 .4 1 0 .1 18 92 9 0. 19 55 80 5 80 6

Specimen

MIXE50

(MPa)

Emax

(MPa)

Gmax

(MPa)ELS

(a)max

(calculated)

(%)

(a)50

(calculated) (%)

(a)ELS

(10-3) (%)

Emax /

qmax

Effects of curing period on OPMC Level 3 & Geogrid, PowerPlus 2% for 3 days Cure/soa

1 24 2.28 4,621.72 95.00

3 72 3.31 5,327.08 138.06

7 168 5.51 6,463.93 229.68

14 336 11.09 8,431.71 462.23

28 672 26.11 11,673.06 1,087.98

56 1344 66.30 16,632.49 2,762.40

112 2688 173.09 23,951.49 7,212.12

Curing Periods,

CP[hours]UCS, qu

f[Mpa]Days Emax CBR [%]

Effects of curing period on Resulting Er (composite pavement)

UCS, QurFCB

1 24 2.11 0.80 1,414.00 1,317.00 87.92

3 72 3.76 1.64 5,589.87 4,073.88 156.71

7 168 5.77 1.89 6,576.69 4,305.93 240.38

14 336 8.23 2.10 7,527.62 4,481.61 342.95

28 672 11.44 2.31 8,530.34 4,646.73 476.60

56 1344 15.59 2.52 9,595.18 4,802.78 649.52

112 2688 20.93 2.73 10,731.70 4,950.97 872.02

224 5376 27.77 2.94 11,949.16 5,092.26 1,157.02

448 10752 36.50 3.15 13,256.83 5,227.42 1,520.65

896 21504 47.59 3.36 14,664.18 5,357.11 1,983.08

1792 43008 61.67 3.57 16,181.03 5,481.88 2,569.43

Days Curing Periods,

CP[hours]UCS, qur

FCA[Mpa] EmaxER

CACBR [%]EmaxER


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This chapter reviews the EXISTING pavement

design, determines the design based on the US

FAA/ ICAO method of Design, analyzes various

options and recommends the VE based design

for the Isiolo Airport aimed at serving aircraft

with gross weights of up to 79,016kgs for

B737-800 series.

The design review is limited to the Airport

Pavement and does not include geometric

design or design for any other of the airportfacilities.

7.2 Fundamental Design Philosophy

The design largely adopts the

recommendations made through the Advisory

Circular (AC) No. 150/5320-6D dated April

30th

, 2004, Airport Pavement Design andEvaluation.

Reference is also made to the 737 Airplane

Characteristics Airport Planning D6-58325-6published in May 1984 by Commercial

Airplane Company, which is a Division of the

Boeing Company.

The Design Philosophy is based on the United

States Federal Aviation Administration (FAA)

and the International Civil Aviation

Organization (ICAO) recommended practices.

Table 7.2.1 Summary of Major Design

Considerations

Table 7.2.2 Technical Specifications for

Boeing Aircraft detailing the B737-800

Fig. 7.4 Landing Gear Loading on Pavement

- Model 737-800 Aircraft


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Fig. 7.5: Pavement Thickness Design as per

the Conventional Design.

Fig. 7.6: Pavement Thickness Design using

the OPMC GI-MC Technique;

Table 7.7.1 Summary of Main Design

Parameters Adopted

Based on the data presented in Table 7.5, the

Total Pavement Thickness required

conventionally is 16 inches or 400mm

Based on the data presented in Table 7.6, the

Total Pavement Thickness required using

OPMC technique in this design is 200mm.

7.7.6 Typical Cross-section A

Table 7.8.1 Summary of the structural

capacity, deformation resistance of thecomposite pavement

The Table above shows the results of the

individual layers and the composite pavementsafter one day cure. The strength as explained

and inferred in Chapter 5 will increase with

time.

The summaries from table 7.8.1 above shows

that our proposed pavement structure is

adequate to perform as a runway that will

handle Boeing 737-800 aircraft with annual

departures of 3000 flights for 20 years.

Cross-

section A

Cross-

section B

TA TA qu,A[Mpa] qu,B[Mpa]

T 1 A sp ha lt co nc re te ACWearing/Binding

Course 1 7 7 4.50 4.50 4,419.00 4,419.00

T2 OPMC Level 3

Subbase

Geomaterial +

Geogrid 0.62 20 20 3.32 3.32 5,331.15 5,331.15

T3

BCS

Ground

Improvement

Subgrade 0.35 20 40 1.38 1.38 2,179.02 2,179.02

where:

ERCA

- resultant ER for cross section A

ERCB

- resultant ER for cross section B

492.32

1414

1317100

1.46

65.13

Composite

pavementERCB

T1+T2+T3+

T4

0.94

0.05

Composite

pavementER

CA100

0.83T4Existing Black

Cotton SoilSubgrade 0.05 53 33

S/No Description Pavement LayerOPMC/GG

CoefficientE

Bmax[Mpa]

qu[Mpa]E

Amax[Mpa]

Determin

ation of

Thickness

for This


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Conclusion:

The design used in this project realizes a

reduction of the overall thickness of about

125mm as compared to the conventional

designs.

CHAPTER 9

9. METHOD OF CONSTRUCTION

General Method of Construction:

9.1 Procedure for Construction of Ground

Improved Subgrade

9.2 Procedure for Construction of Sub-

Base/Base Course

9.3 Procedure for Construction of Asphalt

Concrete Wearing Course

10 Conclusions and Recommendations

10.1 Conclusions

Based on the derivations noted in this Report,

the following main conclusions can be made.

1. The subgrade CBR is high when thesubgrade condition is Unsoaked and

the CBR values drops tremendouslywhen the subgrade is wet. The


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subgrade soil, predominantly Black

Cotton Soil [BCS] have very high

amount of fines [PI of 62%]. The

intrusion of the fines into the well

graded base/sub-base material should

be stopped since the presence of fineswill result to the increase of the

capillary action of the layer making the

base vulnerable to moisture. The

presence of fines will therefore lead to

the drop in strength of the pavement

structure.

2. The subgrade is improved using theGround Improvement Moisture

Control Technique where sand

piles/columns are used to control

moisture.

3. The gravel materials from borrow pitswithin the vicinity of the Project Area

are suitable for the construction of the

Base Course pavement layer. The

existing gravel material is porous and

has relatively low densities. We have

batched the gravel with 0.6mm quarry

dust to improve on its compaction.

4. The gravel exhibit high values ofstrength when stabilized; chemicallyusing cement and mechanically using

Tensar TX 170 TriAx Geogrids. Tensar

TX 170G geogrids are used to

mechanically stabilize the base layer

thereby enhancing the durability,

longevity and versatility of the

pavement. Through the confinement of

the granular material, the geogrid will

maintain and improve the mechanical

stability of the pavement once the

pavement structure starts showing

signs of deterioration due to age and

increased passes of traffic.

5. The pavement structure is expected toexhibit increase in strength with time

as the curing process continues.

6. This pavement design reduces theoverall thickness of pavement from

400mm to 200mm in comparison to

the conventional approach and cuts on

the use of cement from 7-8%conventionally to less than 3%. This

design does not entail the excavation

and subsequent backfilling of the Black

Cotton Subgrade Soil with selected

granular Geomaterial.

7. Due mainly to the nature of thematerial and the existing naturalground, the magnitude of the bearing

capacity, strength and deformation

resistance of the existing sub-base and

subgrade supersedes to a large extent,

values specified as material

requirements for base course layers by

International Agencies and

Researchers.

8. The Cement-Geogrid stabilizedGeomaterials exhibits higher values in

terms of strength, bearing capacity and

deformation resistance as compared to

the Cement stabilized materials.

9. This Design satisfies all theengineering properties and VE aspects.

10.2 Recommendations:

From the foregoing analysis, discussions and

conclusions, the following recommendations

can be made accordingly.

1. The GI-MC technique is meant to controlmoisture levels in the subgrade. It also

incorporates Geotextile/Geofabrics which

will enhance the mobilization of the

stresses within the Black Cotton Soil

subgrade thereby improving further the

strength of the subgrade. The geofabrics

will also act as a filtration/separation

membrane and will act to stop the ingressof fines into the well graded base/sub-base

granular material.

2. The inclusion of the Geogrid is ofimportance as can be inferred from the

material analysis and conclusion.

3. From the effects of curing on the strengthcharacteristics of the cement-geogrid

stabilized Geomaterials, the proposed

pavement structure will depict increase of

strength with time.


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4. A comprehensive hydrological survey needto be done so as to analyze the effects of

drainage and runoff to the general

operation of the airport and also design

structures that will be able to control therunoff since the proposed airport is

located on a flood plain.

5. From the subgrade analysis, the accessroads in and out of the airport need to be

adequately designed to enable delivery of

material during construction.

6. It is envisaged that the above design[OPMC GI-MC Technique] will realize and

overall saving on material and

construction time of more than 40%. This

savings will come from:

a. Reduction in cement quantitiesfrom 7-8% conventionally to less

than 3%

b. No excavation and subsequentbackfilling of the subgrade Black

Cotton Soil.

c. Reduction in construction time.