final report executive

EXECUTIVE SUMMARY

On

B.Tech. Project

Entitled

“Geo-sedimentation investigation of Vishnugad-Pipalkoti hydro-power project”

Under the guidance ofProf. U.C. Kothyari

Dr. Z. AhmadProf. Mahendra Singh

Submitted by:Akshay Wahal

Ankit Khandelwal Mohit Saxena Prashant Patel

Batch of 2009Department of Civil Engineering

Indian Institute of Technology Roorkee

DECLARATION OF THE CANDIDATES

We hereby certify that the work being presented here entitle “Geo-sedimentation investigation of the

hydro-power project” is an authentic record of our own work from the period August,08 till May, 2009

under the guidance of our supervisors Prof. U.C. Kothyari, Dr. Z. Ahmad and Prof. Mahendra Singh,

Department of Civil Engineering, IIT Roorkee. The matter embodied in this report, to the best of our

knowledge, has not been produced elsewhere by anybody else for the purpose of any award or degree.

May 20, 2009

Ankit KhandelwalEnroll No: 050109

Akshay Wahal Enroll No: 050104

Prashant PatelEnroll No: 050150

Mohit Saxena Enroll No:050143

ACKNOWLEDGEMENT

We would like to express our sincere thanks and gratitude to Prof. U.C. Kothyari, Dr. Z. Ahmad and Prof.

Mahendra Singh for the encouragement, whole hearted support and guidance they extended to us

which has been instrumental in the successful completion of the project in the allotted time. We are

deeply indebted to them for their valuable insights and directions.

The comments and suggestions of the evaluation committee have been a constructive feedback to

our work. For the active participation and positive inputs, we extend special thanks to Dr. Rajat Rastogi,

Dr. Satyendra Mittal and Dr. MPS Chauhan.

Ankit KhandelwalEnroll No: 050109

Akshay Wahal Enroll No: 050104

Prashant PatelEnroll No: 050150

Mohit Saxena Enroll No:050143

TABLE OF CONTENTS

S.No TOPIC PAGE NO:

1) Introduction to Problem 1

2) Objective and scope of work

I. Sedimentation Analysis

II. Geotechnical Analysis

3) Methodology

I. Sedimentation Analysis

II. Geotechnical Analysis

4) Data Used

I. Time series for inflow discharge and sediment data

II. Cross section data of River Alaknanda

III.

5) Salient features of the Project

6) Appendix 1

7) Appendix 2

INTRODUCTION TO THE PROBLEM

Vishnugad- hydro electric project located in chamoli district in Uttarakhand is a “run of the river scheme” on the river Alaknanda envisaging a power generation of 444 Mwatt. Intake of the project is located near Helang about 10 km downstream of Joshimath. Concrete gravity dam of 65m height would create a live storage of 2.473 Million cubic meter with FRL at EL. 1267m and MDDL at 1252.5m for utilizing a gross head of 237.0m.

Fig 1: Layout of “Vishnugad Pipalkoti Hydropower Project”

For power generation design discharge of 274.63 m3/s (including 20% flushing discharge) will be taken through three modified horse shoe intake each of 6m dia located on the right bank of the river

Head Race Tunnel

upstream of dam. The invert level of the intake is EL. 1242.5m. Three nos of silt slushing conduits below the power intake have also been provided to flush the sediments that are likely to accumulate near the trash rack and intake gates.

Fig 1(a): Plan of Intake

Water from the intake is taken to three nos of underground sedimentation chamber (through penstock) for removing sediment particles of size 0.2mm and above to protect the turbine parts against erosion. Each sedimentation chamber is of size 350m (L) X 16m (W) X 20.6m (D). the sediment form this chamber is flushed through a silt flushing tunnel of size 3.6m (W) X 4.0m (D-shaped) using a flushing discharge of 47.6 m3/s.

Spilling arrangement has been provided by providing four under-sluices and an Ogee spillway in the dam section and a diversion cum spillway tunnel upstream of the dam on the left bank of the river. The salient features of this spilling arrangement are given below

Fig 1(b). Cross Section of Diversion Structure

In such hydro electric power projects, we generally face the problem of sediment management in the reservoir. As the sediments deposit over time in the reservoir effective volume of water stored in the reservoir decreases, thereby decreasing the capacity of the reservoir. Fig 1a, demonstrate the sediment deposition in reservoir. These sediments also cause heavy damage (wear) to under-water turbine equipments as shown in fig 1b. The solution to this problem lies in flushing, which is allowing the water in the reservoir to pass through the dam in very short duration of time with high velocities (30-35 m/s), thereby, the sediments deposited on the bed get carried away by water.

The problem faced in analyzing a dam-foundation system is that the foundation is composed of hard rock strata which has an all together different properties as compared to the intact rock properties. The rock mass strength can be estimated by creating a solid rock mass from the intact rock material which can be collected from the site. But this procedure of creating the same geology of the rock mass as that present at the site can be really expensive. So, an easy way out is to work out the intact rock properties and then by using a number of rock mass classification techniques, we can predict the rock mass properties to a fairly accurate value. One of the tasks in this project shall be predicting the rock mass properties based on the intact rock properties and the rock mass characteristics.

Fig 1c: Illustration of decrease in reservoir capacity due to sediment deposition

Fig 1d: Erosion after 1492 hours of operation.(silt load passed = 6.1 lac tones)

OBJECTIVE AND SCOPE OF WORK

1) Sedimentation Analysis:

To deal with problem of sediment deposition in “run of a river scheme”, flushing is used to remove the deposited sediment in reservoir. Flushing of sediment from reservoirs requires large volumes of water and also reservoirs have to be drawn down for substantial periods while flushing is carried out. Thus this project aims to assess the feasibility of flushing sediment from reservoir and also to determine the frequency and duration of flushing required for Vishnugad-Pipalkoti hydro-electric project by developing a numerical model using Mike 11.

2) Geotechnical Analysis:

A) To carry out the Stress-strain analysis of Dam-Foundation system: Once the rock mass properties are known, then the stability analysis of the dam-foundation system can be carried out by suitably dimensioning the dam and then carrying out the static analysis of the dam. The design of the dam is basically a trial and error procedure where we try to achieve the configuration which is safe as well as economical.

B) To identify the Weak-Plane in the rock mass: By carrying out the advanced analysis using UDEC by treating the rock mass as a discontinuous medium, we aim to identify the weak plane in the rock mass

METHODOLOGY

Sedimentation Analysis:

The mathematical model MIKE 11 developed by DHI (Danish Hydraulic Institute) is used in present study. It is a windows based mathematical model which simulates the flow of water and sediment transport in rivers using saint-venant equations and solves these equations using Abott six point scheme.

Stepwise procedure for simulation of River with dam structure and for tackling the problem of flushing:

1) Simulation of Alakananda river (without the dam structure in position) taking 5 km reach, where Chainage 0 is 4 km upstream and Ch. 5000 m is 1 km downstream of the dam site. This simulation is carried out to calibrate the Manning’s roughness coefficient to be used in future simulations.

2) Hydrodynamic model of the complete dam structure (i.e. Under sluice, spillway and intake structure) is developed to know the variation of water level

3) Sediment Model for the complete dam structure (i.e. under sluice, spillway and intake structure) is developed to know the variation of bed level (due to deposition of sediment) upstream of the dam. These results were then used to determine the time at which flushing is required and also the water level available at that time.

4) Simulation of sediment flushing procedure, to estimate the frequency an duration of flushing (for an increased efficiency).

Geotechnical Analysis:

1) Assessment of Geological Data, Sub-Surface Conditions and Rock Structure:

The drill-hole tests were conducted at various locations on the proposed dam-site for a chainage of up to 50m upstream and 70m downstream of the dam-axis and the various geological parameters recorded in a geological log.

From the available data Rock mass tunneling quality index was calculated to evaluate the rock mass strength. Mohr Coulomb Failure envelope was plotted to calculate the shear strength parameters (c & φ) for the rock mass. Elastic modulus of the rock mass, Emass was calculated using normalization of Q-values (Barton, 2002).

2) Gravity Dam Analysis:

The gravity dam profile was assumed and its stability analysis was carried out under two loading conditions.a) Normal loading condition: Earthquake forces were inoperative.b) Extreme loading condition: Earthquake forces were operative.

3) Advanced Analysis:

UDEC (Universal Distinct Element Code) is a numerical modeling code for advanced geotechnical analysis of soil, rock and structural support in two dimensions. Using the data acquired so far, the dam-foundation system was analyzed in the following stages under various iterations.

DATA USED :

1) Time series for inflow discharge and sediment data

10-daily discharge data at the project site for the period 1971-72 to 2003 -2004 derived from flows at Joshimath (catchment area 4508 km2) transferred to the project site (catchment area 4672 km2) in proportion to the catchment area were used to get the average yearly time series inflow data as shown in Fig.1e. Since model requires time series data for a specified period, therefore, to meet this requirement the derived average yearly time series was named as for the year June 2003 to May 2004 as shown in Fig. 1e and this has been used in present mathematical model simulation. Corresponding to average yearly time series inflow data, the time series sediment data for sediment load (coarse, medium, and fine sediments) are plotted in Figs. 2,3,4.

Fig 1(e). Average yearly time series inflow data

Fig 2: Time series of coarse sediment inflow data

Fig 3: Time series of medium sediment inflow data

Fig 4: Time series of fine sediment inflow data

2) Cross section data

Following cross sections were provided to the model over the 5 Km stretch of the river (i.e. 4 Km upstream of the dam site as chainage 0 m and 1 Km downstream of the dam site as chainage

Chainage: 1000Chainage: 0

Fig 5: Cross-section of Alaknanda River at its different chainages

Chainage: 2000

Chainage: 4200

Chainage: 3800

Chainage: 5000

Chainage: 3000

Chainage: 3995

3) On site data:

The on-site data consists of the drill hole test data and the point load test data.

A) Drill Hole Test Data: The drill-hole data was collected at various cross sections by performing the drill-hole test on the site. It is been used to evaluate the various parameters of the rock mass required to calculate the rock tunneling quality index. One of the sample drill hole data sheet is shown:

Fig: 5(a) Drill hole data

B) Point Load Test Data: The point load test data as shown in fig 5(b) was collected by performing the point load test on the rock specimen collected from the site and is been used to calculate the intact rock strength(σci).

4) Property of Concrete

The material property of concrete was taken assuming it to be of M-48 Grade for the dam construction (as per USACE recommendations).

Unconfined Compression Strength MPa (psi) Young's Modulus GPa (ksi)

Poisson's Ratio

Bulk Modulus GPa (ksi)

Shear Modulus GPa (ksi)

48 (6,962) 32.6 (4,728) 0.15 15.5 (2,248) 14.2 (2,060)

5) Available On site Literature :

From the available on-site literature following data have been considered for the analysis:(A) Rock mass properties:

Poisson’s Ratio, μ= 0.3Unit Weight, ρ= 2700 kg/m3

(B) Basic Friction Angle, фµ =30 degrees(C) Joint Roughness Coefficient, Jrc = 12

Fig 5(b) : Point Load test data

Salient features of the project

The salient features of the spilling arrangement and of other components of the Vishnugad-Pipalkoti hydroelectric power project are given below:

DIVERSION DAM

Top of Dam ( Concrete gravity) 1270 m

River bed level 1225 m

Foundation Level 1205 m

Length 89.3 m

RESERVOIR

Full Reservoir Level (FRL) 1267 m

Maximum water level 1269 m

Minimum draw down level (MDDL) 1252.5

Gross storage at FRL 3.63 Mm3

Storage at MDDL 1.16 Mm3

Live Storage 2.47 Mm3

Surface area at FRL 24.5 ha

Catchment area at dam site 4672 km2

POWER INTAKE

Number 3

Maximum discharge 274.63 m3/s

Invert Level 1242.5 m

Size 6 m modified Horse shoe type

SLUICES

Numbers 4

Design flood 8004 m3/s

Size of each sluice 6.6 m (W) x 15 m (H)

Type of gate Radial

Crest level of sluice 1233 m

OGEE SPILLWAY

Number 1

Type of gate Vertical

Size 4 m (W) x 3 m (H)

Design flow 80.0 m3/s

Crest level 1264 m

DIVERSION CUM SPILLWAY TUNNEL

Shape and size Circular 10 m diameter

Invert level at entry 1249 m

Length 490 m

Design discharge 1074 m3/s

SPILL TUNNEL

Shape and size Circular 12 m diameter

Invert level at entry 1245 m

Length 250 m

Design discharge 1618 m3/s

Sedimentation Analysis:

1) Determination of Manning’s roughness coefficient

A basic hydrodynamic and sediment model was developed to estimate the manning’s coefficient of the 5 Km stretch (4 Km upstream of dam site and 1Km downstream of dam site) of the Alaknanda River. Transverse distribution of resistance, i.e., Manning's coefficient is considered to be uniform as no flood plain exists for the reach of the Alaknanda River considered in the present study. Initial value of Manning's coefficient was estimated using Golbutsov (1969) empirical equation, which is generally used for the boulder streams:

n = 0.222 S0.33

In which S is the longitudinal slope of the river and the equation is valid for S varying from 0.4% to 20 %. The available data show a very steep bed slope of 1 in 29.1 in the upper portion of the river (Chainage 0 to 1000m) while in a reach (Ch. 1000 to 5000m) the average river bed slope is 1 in 96.99. For these two values of S, Manning's n as per the above equation is 0.073 for S=1 in 29.1 and 0.05 for S = 1 in 96.99. Model takes Manning's number M (inverse of conventional Manning's n). The value of M is thus 13.5 for n= 0.073 and M=20 for n= 0.05.

With these initial values of M, the model is first run for the hydrodynamic and sediment module. The computed water surface profile and bed levels are closely examined in the light of minimum changes of bed levels over a period of one year. Finally, the values of M were selected from the values, which gave minimum changes in the bed level over a long period of time. After different trials, i.e. (13.5, 20), (14, 20), (14.5, 21), (15, 21), (15.5, 21) the values of M adopted are 15 and 21 instead of initial values of 13.5 and 20.

Thus for the further computations Manning’s number M is taken as follows:

For Chainage 0 to 1000 m M = 15

For Chainage 1000 m to 5000 m M = 20

Software input files are given in Appendix I (a).

2) Simulation of River with Under sluice

A model of the river stretch, with an under sluice (at chainage 3995 m), is prepared in order to assess the potential of the software to simulate the control structure. The purpose of making this model is to understand the intricacies in the software and experiment with the various parameters associated with modeling and also to check whether the results provided by the software with under-sluice are practically viable or not.

This model considers 5 Km stretch of Alaknanda River with an under-sluice structure at chainage 3990 m. The value of manning’s number was taken from the hydrodynamic model as mentioned above.

The results thus obtained (in terms of bed level variation and water surface profile) are practically viable and this mathematical model can be used for modeling of river with dam structure (i.e. with under sluice, spillway and intake structure).

Software input files for this simulation are given in Appendix I (b).

3) Simulation of the river with complete dam structure in place

Hydrodynamic Model

The hydrodynamic model was run for the average yearly inflow data to simulate the flow conditions in the river reach with full capacity withdrawal from the intake and to release extra inflow through low level Sluices and the Ogee Spillway. The operation of Intake gates, Sluice gates, and the gate on the Ogee Spillway was so modeled as to draw the design discharge of 274.63 m3/s, through the intake and releasing extra inflow, first through the sluices and subsequently over the Ogee spillway. The operational schedule of the gate was specified as input to the model keeping boundary conditions with respect to full reservoir level and minimum drawdown level and geometry and discharge characteristics of the gates.

The model was run for the time period of 1/6/2003 to 1/6/2004 i.e. for one year as we had average yearly time series data for the same time period.

The observations from the simulation results are as follows:

1) Water surface profile as on July 1, 2003 i.e., at the end of one month from the starting time of June 1, 2003 clearly indicates that the reservoir level has been maintained at the FRL 1267m and this level extends up to about 3 km upstream of the dam.

2) Water level on the downstream side for the period June 1, 2003 to July 1, 2003, clearly indicates that the inflow discharge exceeded the design discharge of intake and the balance has passed through the sluices.

3) Times series discharges through Sluices and Intake indicates that the inflow was adequate for intake to draw its capacity discharge of 274.63 m3/s for a period of slightly more than three months starting from June 1, 2003. Thereafter, the intake discharge was gradually reduced and reached a minimum value of 35 m3/s on the first week of February 2004. After this the intake discharge again started increasing and reached to the design discharge by the end of may 2004.

4) Sluices and spillway were in operation for the period of slightly more than 3 months from the start of simulation period from June 1, 2003. Thereafter, the sluices were closed as inflow was less than the intake design discharge. This also confirms the adopted gate operation schedule specified for the Intake and Sluice gates.

Sediment Model

The sediment model has been run considering the transported suspended load as graded sediment. This gradation has been estimated using transported data for coarse, medium and fine sediment. Since no information is available regarding the specific sizes of coarse, medium and fine fractions. Therefore, it is assumed that the measured suspended load consist of coarse, medium, and fine sand fractions. Accordingly, the sediment sizes of these three fractions have been taken as 1 mm, 0.35 mm and 0.13 mm, respectively. Further their percentages available for the graded sediment have been taken as equal to the percentage transport in each of these fractions. This yields the percentages of three sediment fractions as 18.7, 48.2 and 33.1, respectively. For the graded sediment, model requires thicknesses for active and passive bed layers to be identified. The thicknesses of active and passive layers have been taken 0.1 m and 5 m, respectively. The active and passive layers have been assigned the same sediment gradation as indicated above. The bed has been considered as non-scouring in the model. Van-Rijn sediment equation has been used for bed load and suspended load transport. Other methods of sediment transport were also used for the computations but the ones producing realistic results for present set of data only are reported here.


1) It was observed that the disposition on the bed moved progressively towards downstream. After 6 days of running the model, the peak of the deposited sediment has moved up to Chainage 2500 m with peak at 1258m and sediment deposited in the reach from Chainage 1000 to 3000. At the end of 12 days, the peak was at Chainage 3000 with level as 1266 m. Deposition occurred from Chainage 0 to 3990. After 18 days, the peak moved to Chainage 3500 with peak at 1265 m, still the peak of the deposited profile at the end of 18 days was well upstream of the location of the Intake.

2) Even though after 18 days, the peak of deposited sediment has not moved up to the Intake, it will not be desirable to the run the power house continuously for 18 days as the storage capacity between the FRL and the silted bed will reduce significantly due to the sediment depositions occurring during these periods. At this stage, the results of the model suggest that recurrent flushing of sediment deposition from upstream of the dam shall have to be carried out after running the power house continuously for about 6-7 days.

3) The Intake level being 1242.5m, the deposited profile even after 18 days of running gives silted bed level 1240 m i.e., well below the Intake level. Therefore, with this Intake level, the deposited sediment is not likely to enter into the Intake. Nevertheless, the effect of Intake level on the deposited sediment profile has been examined through use of the mathematical model. For this, the model was run by using the intake level respectively of 2 m higher and 2 m lower than the proposed level of 1242.5 m. The results indicated that due to revised invert levels, there is practically no change in the pattern of deposited bed profiles. Thus, the proposed invert level is found to be OK.

Software input files for this simulation are given in Appendix I (C).

4) Simulation of Flushing procedure

As we have seen from the above results that the after running powerhouse continuously for 18 days results in large amount of sediment deposition and thereby decreasing the capacity of reservoir to a great extent, thus we need to carry out flushing of deposited sediment. It is suggested that recurrent flushing of sediment deposition from upstream of the dam has to be carried out after running the power house continuously for about 6-7 days.

In the model the sediment were allowed to deposit till 6/14/2003 06:00:00 AM, then the gates were scheduled to open within 7.5 hours to initiate the process of flushing.


1) The profile of deposited sediment after 16 hrs of flushing shows that as a result of flushing the peak of deposited profile(= 1262 m) at chainage 3000m was lowered to 1248.2 m (at chainage 3500 m). It is also observed that the silt level at intake, after flushing, was 1242m, which is very close to invert of intake which is at 1242.5m.

2) The profile of deposited sediment after 48 hrs of flushing i.e. at 6/16/2003 06:00:00 shows that between ch. 1500 to ch. 3000m , whole of the sediment is flushed out but sediment between ch. 3000 to ch. 3900 is still there, which shows the inadequacy of the sill level of under sluice.

3) This flushing pattern was re-examined after lowering the invert level of sluices to 1230 m. The deposited profile with invert level of sluice at 1230 m shows that as a result of flushing not only the peak was lowered to 1243 m at Chainage 3500 m, but deposited profile also got flushed to the bed near the intake and sluices. This level of 1230 m was fixed after various trials on the model varying the design invert level of sluice to 1232 and 1231 m.

4) The model results give the period for sediment flushing around 15 to 16 hrs, which is quite comparable with the flushing duration( 12 to 13 hrs) needed in such type of run-of-the-river schemes.

5) A minor drawback in the simulation results is due to the fact that the rate of gate closure is restricted because instabilities occur in the mathematical solution of saint – venant equations if the rate of gate closure is high(large amount of water passes in small amount of time).

Software input files for this simulation are given in Appendix I (d).

Geo-Technical Analysis and Inferences:

1) Assessment of Geological Data, Sub-Surface Conditions and Rock Structure:

The drill-hole tests were conducted at various locations on the proposed dam-site for a chainage of up to 50m upstream and 70m downstream of the dam-axis and the various geological parameters recorded in a geological log.

The objective was to evaluate the rock mass strength to a fairly accurate value by taking into account the various parameters influencing the rock mass properties and the intact rock strength by calculating the Rock Tunneling Quality Index (Q). The various parameters which were required in this approach were the RQD (Rock Quality Designation) value, Jn (Joint set Number), Jr (Joint Roughness Number), Ja (Joint Alteration Number), Jw (Joint Water Reduction Factor) and SRF (Stress Reduction Factor).

The Geological log corresponding to each drill-hole test conducted gave the value of RQD and the number of joint sets present (both as a function of depth). Since a large number of such tests were conducted throughout the dam site, all the data was compiled and frequency charts were drawn to estimate the most probable value of RQD as well as the number of prominent joint sets present. The other parameters used to calculate ‘Q’ (Appendix-4(a)) were evaluated based on the site conditions referring to the literature shown in Appendix-3.

Based on the Q-value and the intact rock strength computed from the point-load test, the uniaxial compressive strength of the rock mass (σcj) was calculated using Barton’s Modified Formulae (Appendix-4(c) ). Now, for various values of minor principle stress σ3f (Mpa) corresponding value of major principle stress σ1f (MPa) were calculated using Equation (Appendix-4(d)) and the Mohr circle was plotted to obtain the Mohr-Coulomb parameters (C & φ) for the rock mass. The failure envelop for the rock mass was also obtained. Thus, the rock mass strength parameters were obtained as; C=8.3 MPa, Ø= 30 degrees. The Elastic Modulus for the rock mass was computed by normalizing the Q-value using Equation (Appendix-4(e)). This normalized value of Q (Qc) was then used to calculate the Elastic modulus for the rock mass using Equation (Appendix-4(e)) which came out to be Emass =16.81 GPa

2) Gravity Dam Analysis:

The design of the dam profile is a trial and error procedure where we aim to obtain the most economical and safe design. The gravity dam profile was assumed as shown in Figure 6 and its stability analysis was then carried out.

The dam-stability analysis was carried out for both the cases of Normal Loading and Extreme Loading (Earthquake Operating) Conditions. The following results were obtained:

Loading Conditions FOS (Sliding)* FOS (Overturning)

Normal 8.01 1.63

Extreme 6.12 1.39

Fig 6: Assumed Gravity dam profile for preliminary analysis

3) Advanced Analysis:

Advanced analysis deals with the stress-strain analysis of the rock mass foundation considering it to be composed of infinite number of elementary blocks using the software UDEC. UDEC (Universal Distinct Element Code) is a numerical modeling code for advanced geotechnical analysis of soil, rock and structural support in two dimensions. UDEC simulates the response of discontinuous media (such as jointed rock) that is subjected to either static or dynamic loading. The following input parameters were required to simulate the block model:

1. Rock mass strength parameters: (C= 8.3 MPa & Ø= 30 degrees)

2. Other rock mass properties: Emass =16.81 GPa, μ (Poison’s ratio) = 0.3, ρ (Density of rock mass) = 2700 kg/m3

3. Contact Normal stiffness and Shear stiffness coefficients: These were calculated using Equation (Appendix-4(g,h)) as Kn= 4.21 e10 Pa/m & Ks= 0.421 e10 Pa/m. Also, the spacing between the joint sets was calculated as 1.2 m using Equation (Appendix(i)).

4. The material properties of concrete were taken assuming it to be of M-48 Grade (as suggested by the ACI Code Committee).

Unconfined Compression Strength MPa (psi)

Young's Modulus GPa

(ksi)

Poisson's Ratio

Bulk Modulus GPa (ksi)

Shear Modulus GPa (ksi)

48 (6,962) 32.6 (4,728) 0.15 15.5 (2,248) 14.2 (2,060)

Model Generation: MODEL 1

The basic model was prepared considering the following conditions:

The jointed-rock foundation was modeled as a block of 120m*100m. The modeling length was chosen as 120 m because the data for the rock mass properties was available for a chainage of 50m upstream and 70 m downstream of the dam-axis.

In soil mass, it is observed that the effect of the stress pressure bulb is pronounced up to a depth of 2*Base Width. Hence, to study the influence of stresses (imposed by the dam as well as the in-situ stresses) on the rock-mass, the depth was assumed to be 100 m (=2* base width of the dam).

The Dam was supposed to be built as a monolithic structure with no joint-sets present. Also the dam-foundation depth was assumed to be 2m.

The analysis of the drill-hole test data revealed that the rock mass has two prominent joint sets at an angle of 43 degrees and -62 degrees. The two joint sets were modeled in the block created with a spacing of 1.2m.

The joint properties were kept the same as the rock mass properties thus making the model to represent the case of glued joints.

The edge length was kept to be 5m for the zoning of the rock mass as well as the dam.

After the boundary conditions were fixed, the loads were applied under 2 stages and the model was simulated to achieve equilibrium after every stage.

Stage 1: Gravity Loads: The in-situ stresses were assumed to act along with the gravity loads thus representing the Empty Reservoir condition and the model was allowed to attain equilibrium.

Stage 2: Full Reservoir: During this stage, the water table is assumed to be at a height of 62 m, exerting hydrostatic pressure on the upstream side of the dam and the rock foundation. The Joint contacts along the bottom and sides of the model are assumed to have zero permeability. On the rock surface upstream of the dam, the head is fixed at 62m while on the downstream; the head is set to zero. The interface between the dam and rock foundation is assumed to have low permeability.

The algorithm for steady flow (SET flow steady) is used. The model was then simulated to attain equilibrium.

Selected results for Stage 2 are shown in the figures 7a to d. The history plots of the x- and y-displacements at the crest of the dam are shown in Figure 7a. The figure indicates that the model is in equilibrium with the reservoir full. Figure 7b shows that the maximum shear displacement occurs below heel of the dam. The plot of flow rates in Figure 7c shows that most of the flow is concentrated in the joint directly beneath the dam foundation. Fig 7d shows the Factor of Safety contour for the dam-foundation system. The FOS is greater than 2 throughout the body of the dam as well as the jointed rock foundation.

Fig 7a: x and y-components of displacement at crest of dam

Fig 7b: Shear displacement just below heal of the dam

Heel of the dam

Fig 7c: The plot of flow rates

.

Fig7d: Mohr Coulomb strength/stress ratio (FOS)

The software input data file for the generation of MODEL 1 are given in Appendix 2.

Heel of the dam

Limitations (MODEL 1):

Figure 8 shows the concentration of principal stresses at the boundary which are quite high. Therefore the effect of the stress pressure bulb is quite pronounced even at a depth of 100 m. Hence, in the next model the depth of the model block is increased to 250 m (= 5*base width of the dam) to take into account the effect of the stress pressure bulb. Also the length of the model block is increased to 200m.

Figure 8: Principal stresses at the boundary

The dam is assumed to be a monolithic structure with no joint sets present. Practically, both vertical and horizontal joint sets are present throughout the body of the dam. Therefore in the next model a pair of fictitious joint set is modeled at a spacing of approximately 2m.

The joints present in the rock mass are assumed to have the same normal and shear stiffness co-efficient as that of the rock mass; thus making the joints behave as glued. Whereas it has been observed that both the normal and shear co-efficient have a lesser value in case of the joints which will result in the relative displacement of joints. The next model takes into account the effect of displacement of joints.

The displacement of the crest is observed to be around 13 cm. Therefore, next simulation is performed with the model having a top width of 8 m and base width of 60 m.

MODEL 2

Concentration of stresses

The limitations of Model 1 were taken into account in the generation of the next model. Therefore, the following changes were made:

The dimensions of the model block have been taken to be 200m (length) * 250m (depth).

Fictitious horizontal and vertical joint sets were created in the body of the dam at a spacing of 2m.

The normal and shear stiffness co-efficient were computed using the equation (Appendix 4-j) and the effect of the same have been taken into account.

The top-width of the dam has been increased to 8m and the base width to 60m as the displacement of the crest in the basic model was coming to be around 14 cm which is quite large.

The loads were applied as before under two stages and the model simulated to achieve equilibrium. The following results were obtained:

1) The final horizontal displacement of the crest of the dam comes out to be 2.3 cm.

Figure: x-displacement (24,65)

This shows that MODEL 2 is more stable as compared to the basic model. Therefore, the dam base width should be kept as 60m and its top width as 8m.

2) The Stress-contour in the vertical direction shows that the vertical stress below the heel of the dam is about 1Mpa which is very close to 1.03 MPa as computed in static analysis of the dam.

Figure: y-Stress contours

3) The Mohr-coulomb Factor of safety is coming out to be greater than 2.

Figure: Mohr-Coulomb FOS

CONCLUSION

The results obtained after carrying out the advanced analysis proves that MODEL 2 is more stable and therefore the recommended dam profile is as shown:

Although a thorough analysis of the dam-foundation system has been carried out, it is recommended that a proper geo-technical analysis should be carried out on the dam site at the time of construction. This will result in estimating the rock mass properties up to a fairly accurate value as the properties considered throughout the analysis are on the conservative side.

Appendix-2

Input data file for MODEL 1:

65 m

20 m

60 m

8 m

10 m

.75

1

1

.15

1) File: damstage1.dat

;new

title

(Dam Cross-section)

;Insitu stresses; Gravity

;Rock blocks;

; material properties of block

; joints (no cohesion)

prop mat=1 d=2700 b=7.61e9 s=5.71e9 fric=30 coh=15e6

prop mat=1 jkn=4.21e10 jks=.421e10 jfric=30

; dam and foundation joint

prop mat=2 d=2400 b=15.5e9 s=14.2e9


; material properties; joints

prop mat=3 d=2700 b=7.61e9 s=5.71e9 fric=30 coh=15e6


; viscous boundaries (equivalent elastic properties) ; joints (cohesion)

prop mat=5 d=2700 b=7.61e9 s=5.71e9


;

round 1.0

;set minimum edge length

set edge 10.0

; set minimum contact length

set clemin= 5.0

;creation of model

bl (0,-102) (0,65) (120,65) (120,-102)

;structure: gravity dam

cr 0,0 24,0

cr 24,0 27,20

cr 27,20 27,65

cr 33,65 33,55

cr 33,55 76,0

cr 76,0 120,0

cr 24,0 24,-2

cr 24,-5 76,-5

cr 76,-5 76,0

delete region 0,0 0,65 27,65 27,20

delete region 33,65 120,65 120,0 76,0

;CREATE JOINT SETS

jregion id 1 0,0 120,0 120,-102 0,-102

jset 43,0 200,0 0,0 1.2,0 0,0 range jregion 1

jset -62,0 200,0 0,0 1.2,0 0,0 range jregion 1

jregion id=1 (24,0) (76,0) (76,-2) (24,-2) delete

change mat=1 range 0,120 -102,0.1

change mat=2 range 24,76 -2,65

;Discretizing

gen edge 5 range 0,120 -102,0

gen edge 5 range 24,76 -2,65

;all joints

change jmat=1 range -1,121 -103,0.1

; cohesion below y=-150

change jmat=3 range -1,121 -150,-1

; foundation joint

change jmat=2 range 24,76 -3,-1 ang=42,44

;boundary conditions lateral: x-fixed; bottom: y-fixed

bound xvel=0 range 0,120 -102.1,-101.9

bound yvel=0 range 0,120 -102.1,-101.9

bound xvel=0 range -.1,0.1 -102,0

bound xvel=0 range 119.9 120.1 -102,0

;set fluid density

fluid dens 1000 bulk 0.0

set flow off

;set gravity ; set in-situ stresses (total)

grav 0 -9.8

insitu 0,120 -102,0 ygrad= 1794, 0, 2600 & zgrad 0 17885 ywtab=0

;

hist type=2

hist unbal solve_ratio

hist xdis=24,65 ydis=24,65

hist xvel=24,65 yvel=24,65

hist xvel=24,-50 yvel=24,-50

;damp auto

solve

label hist 1

Unbalanced Forces

label hist 2

Solve ratio

label hist 3

x-displacement (24,65)

label hist 4

y-displacement (24,65)

label hist 5

X-velocity (24,65)

label hist 6

Y-velocity (24,65)

label hist 7

X-velocity (24,-50)

label hist 8

Y-velocity (24,-50)

;save file as: damstage1.dat

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

2) File damstage2.dat

title

(Dam Stage 2) Water Loads and Flow

;

reset dis jdis hist

;

;flow properties

;ares: residual aperture at high stress

;azero: aperture for zero normal stress

;jperm: Joint permeability (1/Pa.s)

;dynamic viscosity=0.85(N s/m2) x 10-3 (Temp=25C)

;rock mass

prop mat=1 jperm=98.04 azero=0.001 ares=0.0005


; foundation joint


;

; set max. aperture

set caprat=2.0

; set lateral and bottom boundary contacts to zero permeability

; fix head upstream of dam (full reservoir) ; downstream is zero

bound pp=62e4 range -1,25 -1,1

; apply vertical water load upstream of dam

bound stress= 0, 0, -62e4 range -1,25 -1,1

; fix lateral boundaries (horizontally)

bound xvel=0 range -1,1 -103,0.1

bound xvel=0 range 119.9,120.1 -103,0.1

bound yvel=0 range -1,1 -102,0.1

bound yvel=0 range 119.9,120.1 -102,0.1

; apply horizontal load to dam

bound stress= -62e4,0,0 range 23.9,27.1 0,62.1

bound ygrad 10000,0,0 range 23.9,24.1 0,62.1

; monitor contact variables at x=20 y=-30

hist type=10


hist xdis(24,65) ydis(24,65)

hist sdis(20,-30) ndis(20,-30)

; (flow rate thru contact)

hist flowrate(20,-30)

; fluid properties (nonzero bulk modulus)

fluid dens 1000 bulk 2.2e9

;switch on fast flow logic

set flow steady

;solve

label hist 1

Unbalanced Forces

label hist 2

Solve ratio

label hist 3


label hist 4


label hist 5

s-displacement (20,-30)

label hist 6

n-displacement (20,-30)

label hist 7

Flowrate (20,-30)

;save file as: damstage2.dat

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Input data file for MODEL 2:

1) Filename: dam1stage1.dat

;new

title

(Dam Cross-section)

;Insitu stresses; Gravity

;Rock blocks;

; material properties of block

; joints (no cohesion)

prop mat=1 d=2700 b=7.61e9 s=5.71e9 fric=30 coh=8.3e6


; dam and foundation joint

prop mat=2 d=2400 b=15.5e9 s=14.2e9


;joints

prop mat=3 d=2700 b=7.61e9 s=5.71e9 fric=32.088 coh=2.075e6

prop mat=3 jkn=4.21e10 jks=.421e10 jfric=32.088

;fictitious joints

prop mat=4 d=2400 b=15.5e9 s=14.2e9 fric=60 coh=8.3e6

prop mat=4 jkn=13.04e10 jks=6.52e10 jfric=60

;Ratio of normal stiffness coefficient to concrete elastic modulus kn/Ec=4.0

; viscous boundaries (equivalent elastic properties) ; joints (cohesion)

prop mat=5 d=2700 b=7.61e9 s=5.71e9

prop mat=5 jkn=4.21e10 jks=.421e10 jfric=32.088

round 0.3

;set minimum edge length

set edge 12.0

; set minimum contact length

set clemin= 5.0

;creation of model

bl (-50,-252) (-50,65) (200,65) (200,-252)

;structure: gravity dam

cr -50,0 24,0

cr 24,0 27,20

cr 27,20 27,65

cr 35,65 35,55

cr 35,55 84,0

cr 84,0 200,0

cr 24,0 24,-5

cr 24,-5 84,-5

cr 84,-5 84,0

delete region -50,0 -50,65 27,65 27,20

delete region 35,65 200,65 200,0 84,0

;CREATE JOINT SETS

jregion id 1 -50,0 200,0 200,-252 -50,-252

jset 43,0 600,0 0,0 1.2,0 -50,0 range jregion 1

jset -62,0 600,0 0,0 1.2,0 -50,0 range jregion 1

jregion id=2 (24,0) (84,0) (84,-5) (24,-5) delete

;Create Fictitious Joint sets

jregion id 2 24,0 27,20 63.64,20 84,0

jregion id 3 27,20 27,55 35,55 63.64,20

jregion id 4 27,55 27,65 35,65 35,55

jset 0,0 200,0 0,0 2,0 27,20 range jregion 2

;jset 90,0 400,0 0,0 2,0 27,20 range jregion 2





change mat=1 range -50,200 -252,0.1

change mat=2 range 24,84 -5,65

;Discretizing

gen edge 3 range 14,94 -56,0.1

gen edge 1.5 range 24,84 -10,65

gen edge 6 range 0,14 -56,0.1

gen edge 6 range 94,120, -56,0.1

gen edge 6 range 0,120 -102,-56

gen edge 10 range -50,200 -252,-102

gen edge 10 range -50,0 -102,0

gen edge 10 range 120,200 -102,0

;all joints

change jmat=1 range -51,201 -253,0.1

; foundation joint

change jmat=2 range 24,84 -6,-4 ang=42,44

;fictitious joint in dam

change jmat=4 range 24,84 0,65

;boundary conditions lateral: x-fixed; bottom: y-fixed

bound xvel=0 range -50,200 -252.1,-251.9

bound yvel=0 range -50,200 -252.1,-251.9

bound xvel=0 range -50.1,-49.9 -252,0

bound xvel=0 range 199.9 200.1 -252,0

;

;set fluid density

fluid dens 1000 bulk 0.0

set flow off

;set gravity ; set in-situ stresses (total)

grav 0 -9.8

insitu 0,120 -102,0 ygrad= 1794, 0, 2600 & zgrad 0 1794 ywtab=0

;

hist type=2


hist xdis=24,65 ydis=24,65

hist xvel=24,65 yvel=24,65

hist xvel=24,-50 yvel=24,-50

;

;damp auto

solve

label hist 1

Unbalanced Forces

label hist 2

Solve ratio

label hist 3


label hist 4


label hist 5

X-velocity (24,65)

label hist 6

Y-velocity (24,65)

label hist 7

X-velocity (24,-50)

label hist 8

Y-velocity (24,-50)

; save as: dam1stage1.dat

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

2) Filename: dam1stage2.dat

title

(Dam Stage 2) Water Loads and Flow

;

reset dis jdis hist

;

;flow properties

;ares: residual aperture at high stress

;azero: aperture for zero normal stress

;jperm: Joint permeability (1/Pa.s)

;dynamic viscosity=0.85(N s/m2) x 10-3 (Temp=25C)

; rock mass



; foundation joint


;

; set max. aperture

set caprat=2.0

; set lateral and bottom boundary contacts to zero permeability

; fix head upstream of dam (full reservoir) ; downstream is zero

bound pp=62e4 range -1,25 -1,1

; apply vertical water load upstream of dam

bound stress= 0, 0, -62e4 range -51,25 -1,1

;

; apply horizontal load to dam

bound stress= -62e4,0,0 range 23.9,27.1 0,62.1

bound ygrad 10000,0,0 range 23.9,24.1 0,62.1

; fix lateral boundaries (horizontally)

bound xvel=0 range -50,200 -252.1,-251.9

bound yvel=0 range -50,200 -252.1,-251.9

bound xvel=0 range -50.1,-49.9 -252,0

bound xvel=0 range 199.9 200.1 -252,0

; monitor contact variables at x=20 y=-30

hist type=3


hist xdis(24,65) ydis(24,65)

hist sdis(20,-30) ndis(20,-30)

;(flow rate thru contact)

hist flowrate(20,-30)

; fluid properties (nonzero bulk modulus)

fluid dens 1000 bulk 2.2e9

;

;switch on fast flow logic

set flow steady

;

solve

label hist 1

Unbalanced Forces

label hist 2

Solve ratio

label hist 3


label hist 4


label hist 5

s-displacement (20,-30)

label hist 6

n-displacement (20,-30)

label hist 7

Flowrate (20,-30)

; save as: dam1stage2.dat

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

APPENDIX-3

Tables used to calculate the various parameters used in calculating the Q-value.

APPENDIX-4

a) Rock Tunneling Quality Index ‘Q’ :

Q =(RQD/Jn)*(Jr/Ja)*(Jw/SRF)

where:

• RQD is the Rock Quality Designation

• Jn is the joint set number

• Jr is the joint roughness number

• Ja is the joint alteration number

• Jw is the joint water reduction factor

• SRF is the stress reduction factor

b) Singh’s Formula:

σcj= 7γQ1/3 MPa (Singh)

c) Barton’s Modified Formula:

σcj= 5γ(Q σci/100)1/3 MPa (Barton Modified)

d) Value of major principle stress σ1f (MPa) were calculated using:

σ1f= A(σ3f)2 + (1-2Aσci)σ3f + σcj

where A= -0.43(σci)-0.72

e) Elastic Modulus for the rock mass :

Emass = 10 Qc^(1/3) Gpa

Where, Qc =Q*(σci/100)

σci is intact rock strength.

f) Modulus Ratio (Ref: Stagg & Zienkiewicz)

Mr= Ei/σci = 357 (for Quartzite)

g) Contact Normal Stiffness Co-eff:

Kn= Ei/A = Ei/60(cm)

h) Shear Stiffness Co-eff:

Ks= Kn /10

i) Spacing of Joint sets ‘s’:

s = (Em* Ei)/(Kn(Ei-Em))

j) Normal and Shear Stiffness Co-efficient:

Here values of σn is assumed and the corresponding value of τ is found by using the relation :

τ = σn * tan (фµ+ Jrc log (Jcs/ σn))

where,

фµ = Basic Friction angle= 30 degrees

Jrc =Joint roughness coefficient =12

To obtain the c, ф values the graph is plotted and the best fit curve is drawn with equation y = 0.627x + 2.075.

Thus, the c, ф values obtained are 2.075, 0.627.

final report executive

Documents