In book: Proceedings of the Indian Geotechnical Conference 2019, 2019
Particularly, for granular soils, several correlations are available in the literature for predic... more Particularly, for granular soils, several correlations are available in the literature for predicting the coefficient of permeability of soils as a function of particle size, properties of pore fluid, void ratio, shape of particles, etc. In this paper, a comparative study of some of the existing predictive models is presented to examine how far these are applicable to natural sands. With the above in view, coefficients of permeability of two different types of sands (sub-angular Ganga sand and rounded Ennore sand) were found out with varying void ratios by constant head laboratory test. The laboratory test data is compared with various predictive models available in the literature. This study highlights the fact that there exists no unique relationship that would be the panacea for predicting the coefficient of permeability values for all types of soils. The expressions as given by Kozeny–Carman, Taylor and Chapuis are rational and scientific. These may be used for quick predictions of the coefficient of permeability, but the coefficients and parameters appearing in these equations need to be properly determined specific to the concerned soil.
In book: Geotechnical Characterization and Modelling, Proceedings of IGC 2018, 2018
The paper is mainly focused on the strain rate effect on shear strength of sands in direct shear ... more The paper is mainly focused on the strain rate effect on shear strength of sands in direct shear test. Experimental investigations on two sands, one with rounded smooth grains (Ennore standard sand) and another with angular grains (Ganga sand), were carried out with a view to investigate the difference in shear strength of the sands at different shear strain rates. From the test results, it was found out that friction angle depends largely on gradation and particle angularity. Angular well-graded particles give the highest friction angle, and the rounded uniform particles give the least. Angle of shearing resistance increases with increasing the strain rate. For these two sands, relationships have also been established for prediction of peak friction angle as a function of relative density and rate of shearing strain.
SYNOPSIS Energy Storage Technologies are the need of the hour. With more and stricter carbon emis... more SYNOPSIS Energy Storage Technologies are the need of the hour. With more and stricter carbon emission norms combined with ambitious targets for the green power a niche is getting created for Energy Storage Technologies. Such technologies are absolutely essential keeping in mind the fact that output from all the current generation renewable energy sources such as solar or wind are fluctuating in nature. Today there are plenty of energy storage technologies available including battery storage, flywheel, molten salt, compressed air, pumped storage etc. But most of them (excluding pumped storage and battery bank) are in initial state of technological development. Battery Storage looks promising but only when used in electric vehicles, emergency situations or grid stability. But for large Grid size energy storage the pumped storage plants still proves to be the best bet in terms of economy, reliability & technical maturity. Sea Water Pumped Storage is a type of artificial pumped storage scheme which harness coastal mountainous topography and abundant seawater. A sea water pumped storage provides a simple solution for storing electrical energy minus the problems associated with the conventional hydro plants of obstructing natural freshwater flow, high cost of building dams, water availability etc. Such type of plants can be very useful in an island type condition and remote areas. India which has almost 3500 km coastline and islands dotted with mountainous topography such plants of the scale of MW to Few MWs can be readily built. In this paper, the merits and demerits of various types of energy storage technologies have been discussed. We have also done a study which demonstrate the importance of energy storage in an Island (isolated grid condition) where they become an absolute necessity if renewable energy is added substantially. Further, a preliminary techno economic study is presented for construction of a typical sea water pumped storage plant at any suitable site (inland or in an Island) in India.
This study undertook stability analysis of nailed soil slopes using the limit-equilibrium method ... more This study undertook stability analysis of nailed soil slopes using the limit-equilibrium method (LEM) and considering a three-dimensional (3D) rigid-body rotational failure mechanism with the assumed slip surface being a part of a sphere. The moment equilibrium of the 3D wedge formed by the slope surface and the slip surface along with the nails embedded in it were analyzed as a whole. A specific-purpose computer code was written for factor-of-safety (FS) computation; the developed computer code is capable of analyzing an unreinforced slope and a nailed slope. The critical slip surface and the corresponding minimum FS value of the unreinforced slope were initially determined, taking into account all possibilities of failure (base failure, slope failure, and toe failure). For the critical slip surface so obtained, nails were then introduced at desired positions, and the FS value for the nailed slope was then estimated with the developed procedure. The developed method and computer code were verified by comparing the FS values of some benchmark problems [two-dimensional (2D) and 3D] obtained by the proposed method with those reported in the literature. The critical slip surfaces obtained from the proposed method were also compared with some of the benchmark problems. A parametric study was conducted to determine the effects of the inclination and spacing of the nails on the FS values.
In storage type hydroelectric projects, proper diversion of river inflow is one of the major work... more In storage type hydroelectric projects, proper diversion of river inflow is one of the major works which require extensive planning not only for construction period but also during first reservoir filling. Owing to the inherent flexible nature of earth and rockfill dams, the process of first reservoir impounding gains critical importance in case of these type of dams. In order to avoid development of undue stresses within the dam body due to internal readjustment during first reservoir impounding, the first reservoir impounding is carried out slowly, in a controlled manner and under close surveillance. Koldam Hydro Electric Power Project is located on Satluj river in Bilaspur district of Himachal Pradesh in India. The project utilizes a drop in head of about 140m by constructing a 167m high (from the deepest foundation level) rockfill dam and a dam toe surface power house with an installed capacity of 800MW. The design of the Koldam project is such that it will also arrest the silt flow from upper reaches and thus increase the life of Bhakra Dam by almost 18 years and therefore the spillway was placed at higher level and cannot be used for controlling the reservoir filling till 144m height of dam. For achieving the controlled first reservoir impounding of 167m high Earth and Rockfill dam of Kol Dam HEPP, a low level outlet named Bottom Outlet had been envisaged. This structure has been constructed inside one of the two diversion tunnels constructed at Koldam HEPP. Owing to the factors like high operating head (approx. 135m), the limited working period and the tough conditions inside the tunnel, construction and operation of Bottom Outlet was always going to be a challenge, requiring dynamic planning and midcourse review of some design aspects. First reservoir impounding of Koldam HEPP has been completed in June 2015 with effective utilization of Bottom Outlet for controlling the reservoir impoundment rate. Present paper discusses the various aspects viz. design, planning, challenges faced and midcourse corrections necessitated thereof in the Bottom Outlet.
In present study, finite element simulation of footing on full-scale model double-faced wall has ... more In present study, finite element simulation of footing on full-scale model double-faced wall has been done using plane strain software Plaxis. The construction of the wall was done in stages, which is simulated in the model wall. After construction, footing is placed on top using plate element and load is applied. The finite element analysis predictions are compared with the experimental results. FEM based predictions of load-deformation behaviour of footing on large-scale model reinforced soil wall are in excellent agreement with experimental data. The predictions of deformation of facings are found to be conservative but the pattern of tilting of footing was in good agreement with the experimental observations.
There are three distinct phases of monitoring in the lifetime of an earth and rockfill dam. viz. ... more There are three distinct phases of monitoring in the lifetime of an earth and rockfill dam. viz. construction, first reservoir filling and operation stage. During construction stage, rate of construction of earth and rockfill dam may require modifications on the basis of the instrumentation results to achieve safe construction. During initial reservoir impounding, instrumentation results are of paramount importance and have a consequential impact on the decisions regarding future rate of filling, to enable safe impounding of dam. During normal period of operation these instruments are required to monitor the behaviour of dam due to fluctuation in reservoir levels or even in steady state conditions. Koldam Hydro Electric Power Project is located on Satluj River in Bilaspur district of Himachal Pradesh in India. The project has 800MW installed capacity and a 167m high (from the deepest foundation level) rockfill dam which creates a head of about 140 m. Earth and Rockfill dam of Kol Dam HEPP has an elaborate monitoring instruments network for monitoring the health of the various structures viz. earth and rock-fill dam, spillway and galleries. First phase of first step of initial impounding of Kol Dam reservoir has already been completed in the month of March-April 2014. After monsoon period, reservoir impounding was restarted in October 2014 and likely to be completed soon. In this paper, analyses of the data of monitoring instruments obtained from the earth and rockfill dam during depletion after first phase of reservoir impounding has been presented. A comparison of the readings obtained during first step of impounding till El. 560m in March-April 2014 and that obtained during re-impounding till El. 560m have been made in this paper.
Behaviour of reinforced soil structures depends on the material properties of soil and geosynthet... more Behaviour of reinforced soil structures depends on the material properties of soil and geosynthetics. Apart from individual properties of soil and reinforcement, the interaction between reinforcement and soil also plays important role in deciding the behaviour of reinforced soil structures. The modelling of the interface characteristics is a very important aspect in developing a correct numerical model for predicting the performance of reinforced soil structures. For simulating the interface behaviour a linearly elastic model with Mohr–Coulomb criterion is commonly used. Experimental observations made from direct shear tests usually show that the force–displacement relationship is non-linear till a peak is attained, beyond which softening behaviour is observed. In this paper a constitutive model appropriate for geosynthetic interfaces has been implemented in FLAC3D and used to simulate the shear stress displacement behaviour of different sand–geotextile interfaces. In the present study, shear stress–displacement behaviour of interfaces of different types of sands and geotextiles (monofilament woven, multifilament woven and nonwoven) have been considered for simulation. The simulated curves using the FLAC3D showed very good agreement with the experimental data over the complete stress-displacement ranges.
During construction and initial reservoir impounding, performance of an earth and rock-fill dam i... more During construction and initial reservoir impounding, performance of an earth and rock-fill dam is required to be closely and frequently monitored for safety of the dam. During construction stage, rate of construction of earth and rockfill dam has to be manoeuvred i.e. increased or decreased on the basis of the instrumentation results to achieve safe construction. Similarly, during initial reservoir impounding, instrumentation results are of paramount importance and have a consequential impact on the decisions regarding future rate of filling, to enable safe impounding of dam. Koldam Hydro Electric Power Project is located on Satluj River in Bilaspur district of Himachal Pradesh in India. The project envisages utilization of a drop in head of about 140m by constructing a 167m high (from the deepest foundation level) rockfill dam and a dam toe surface power house with an installed capacity of 800 MW. Earth and Rockfill dam of Kol Dam HEPP has an elaborate monitoring instruments network for monitoring the health of the various structures viz. earth and rock-fill dam, spillway, galleries and foundations. Around 500 electronic and mechanical instruments have been installed and the performance of these structures is being monitored through this monitoring network. In the present paper, instrument network of only earth and rock-fill dam has been presented. Koldam HEPP is in final stages of construction and first stage of initial impounding has already been completed in the month of March-April 2014. Analyses of the data of monitoring instruments obtained during first stage of reservoir impounding and associated safety aspects have been discussed in the paper.
In direct shear testing of soil-geosynthetics interface, apart from properties of soil and geosyn... more In direct shear testing of soil-geosynthetics interface, apart from properties of soil and geosynthetics, the test apparatus greatly influences the behaviour of interface. In this study, experiments have been conducted using a modified direct shear box in which geotextile is placed over rigid smooth substrate. The effects of allowing stretching the geotextile over smooth substrate on performance of geotextile-sand interface were evaluated through laboratory tests. Locally available natural river sand and two differently textured geotextiles have been used for the study. To investigate the influence of condition of substrate on the sand-geotextile interface behaviour, the results for smooth substrate are compared with the data available in literature, for the rough substrate. The study showed that condition of substrate significantly influences the shear stress-displacement behaviour of interface and interface friction angle.
The behavior of soil-geosynthetics interfaces depends on the different properties of soil includi... more The behavior of soil-geosynthetics interfaces depends on the different properties of soil including particle size, particle shape, density, gravimetric water content, degree of saturation and properties of geosynthetics including structure, texture, etc. This paper pertains to the study of the influence of particle shape of sand on the sand-geotextile interface behavior. Experiments were conducted using a conventional size direct shear box modified for interface testing. In the present study, two different natural sands (one having angular particles and other having rounded particles) and two different geotextiles have been used. The study showed that particle shape significantly influences the interface behavior, especially the post-peak behavior.
Being a flexible structure, earth and rockfill dams are very suitable in high seismic zones. Kol ... more Being a flexible structure, earth and rockfill dams are very suitable in high seismic zones. Kol Dam HEPP envisaged a 163 m high central core earth and rockfill dam. The project site is situated in Himachal (Himalaya) and is prone to large magnitude earthquakes. This paper pertains to the estimation of earthquake induced permanent displacements of the earth and rockfill dam using Newmark's block sliding methods. In the present analysis, a synthetic acceleration time history has been used. The study showed that dam will not suffer any damage when subjected maximum credible earthquake but may undergo large deformation if subjected to a hypothetical large earthquake with PGA of 1g.
The response of double-faced wrap-around reinforced soil retaining walls subjected to strip loadi... more The response of double-faced wrap-around reinforced soil retaining walls subjected to strip loading on the surface has been studied by conducting small-scale model laboratory tests. Model reinforced soil walls were constructed using Kalpi sand as backfill material and geotextiles as reinforcing elements. In the present study, two different multifilament geotextiles were used. Strip loading was applied at the centrally placed footing on the surface of the wrap-around reinforced soil walls. The influence of the number of reinforcing layers and overlap length on load deformation behaviour, ultimate bearing pressure and initial tangent modulus of the footings on double-faced reinforced soil walls was studied. The lateral deformations of wrap-around wall facing with settlement of the footing are also presented.
The paper presents the results of experimental studies with regard to the response of small scale... more The paper presents the results of experimental studies with regard to the response of small scale model strip footings resting on the surface of wrap-around reinforced soil retaining walls constructed using locally available sand as backfill and geotextile as reinforcing elements. Number of reinforcing layers and footing size were varied to find their influence on the bearing capacity and load deformation (both vertical and lateral) characteristics of the walls. It is found that the ultimate bearing capacity of the footings and initial tangent modulus increases with increase in the number of reinforcing layers but the initial tangent modulus decreases with increase in footing size.
The paper pertains to a study regarding the response of strip footings resting centrally on the s... more The paper pertains to a study regarding the response of strip footings resting centrally on the surface of model double-faced wrap-around vertical soil walls. Experiments were performed in the laboratory on small-scale model geosynthetic-reinforced, double-faced, vertical soil walls constructed with sand backfill and wrapped facing using varying spacing, overlap length of reinforcement layers and footing widths to study their effects on its load–deformation behaviour. Then a plane-strain finite element simulation of the model walls was performed, using commercially available Plaxis software, to predict their behaviour under strip loading. Backfill sand and reinforcements were modelled as elastic-perfectly plastic and linearly elastic material, respectively. Comparison of the predicted bearing capacity of the footing resting on these walls and the horizontal displacement of the wall face showed reasonable agreement with the experimental data.
Apart from other factors, the performance of geosynthetic reinforced soil structures depends also... more Apart from other factors, the performance of geosynthetic reinforced soil structures depends also on the characteristics and behavior of the interface between soil and geosynthetic. Experiments were conducted in a direct shear test apparatus to study the shear force–displacement behavior at the soil–geotextile interface using two differently textured woven geotextiles. Analyzing the data so obtained a non-linear constitutive model has been presented for predicting both the pre-peak and the post-peak interface behavior. The predictions made by the developed model are found to be in good agreement with experimental data obtained from direct shear tests.
The paper pertains to the behavior of small-scale model studies on strip footings subjected to ve... more The paper pertains to the behavior of small-scale model studies on strip footings subjected to vertical loading resting on the surface of a wrap around reinforced vertical soil walls with sand backfill. Finite element analysis (using Plaxis 2D version 8 software) of the soil wall was also made to find its response and the predicted values were then compared with experimentally observed values. Effect of the number of reinforcement layers on the overall response was studied. Comparison of the predicted horizontal displacement of the vertical wall face and bearing capacity of the footing resting on the same showed reasonable agreement with the experimental data.
The paper deals with an important practical problem related to construction of ash dykes using fl... more The paper deals with an important practical problem related to construction of ash dykes using fly ash. In most of the thermal power plants fly ash is disposed off in the form slurry pumped to an artificially created pond. When the pond is full with the ash the capacity of the pond is increased by raising the height of the dyke using upstream or down stream method of construction. Due to constraint of land, upstream method of construction is more commonly used, which involves construction of dyke resting on bottom ash in the pond. Before laying the foundation top 1-2 m of bottom ash is removed and then the construction is started on top of it. This results in unloading and reloading of bottom ash. In this work an attempt is made to study the strength behavior of ash in over consolidated state. The experimental study indicates that there is appreciable difference in the strength and both total and effective stress parameters increase when the over consolidation ratio increases. The peak stress at failure is also observed to be higher for higher over consolidation ratio. Consideration of increased parameters will result in more economical design of ash dykes constructed by using fly ash.
Liquefaction of saturated soils during earthquake often had been a major cause of damage to struc... more Liquefaction of saturated soils during earthquake often had been a major cause of damage to structures. Since beginning the liquefaction studies were concentrated on sandy soils, as the sandy soils are known to be more susceptible to liquefaction. However, observations from some sites in China and Loma-Prieta earthquakes show that soils with high plastic fines are also susceptible to liquefaction. Isotropically consolidated undrained cyclic triaxial tests were conducted on undisturbed samples of silty clay soil and results of these tests are used to verify the methods based on SPT data. Slow cyclic tests were performed to investigate the development of pore pressure and cyclic strength, as reliable pore pressure measurement is only possible in slow cyclic triaxial test for clayey soils. The site was than characterized for liquefaction by a computer program developed.
The N-value was obtained for the same site by conducting Standard Penetration Test. Test results were verified using methods reported by Tokimatsu & Yoshimi (1983) and Ishihara (1993). The simplicity of the methods and application of the methods to the fine-grained soils are the main criteria for selection of the field methods. The computer program also provides characterization of site using these methods.
In book: Proceedings of the Indian Geotechnical Conference 2019, 2019
Particularly, for granular soils, several correlations are available in the literature for predic... more Particularly, for granular soils, several correlations are available in the literature for predicting the coefficient of permeability of soils as a function of particle size, properties of pore fluid, void ratio, shape of particles, etc. In this paper, a comparative study of some of the existing predictive models is presented to examine how far these are applicable to natural sands. With the above in view, coefficients of permeability of two different types of sands (sub-angular Ganga sand and rounded Ennore sand) were found out with varying void ratios by constant head laboratory test. The laboratory test data is compared with various predictive models available in the literature. This study highlights the fact that there exists no unique relationship that would be the panacea for predicting the coefficient of permeability values for all types of soils. The expressions as given by Kozeny–Carman, Taylor and Chapuis are rational and scientific. These may be used for quick predictions of the coefficient of permeability, but the coefficients and parameters appearing in these equations need to be properly determined specific to the concerned soil.
In book: Geotechnical Characterization and Modelling, Proceedings of IGC 2018, 2018
The paper is mainly focused on the strain rate effect on shear strength of sands in direct shear ... more The paper is mainly focused on the strain rate effect on shear strength of sands in direct shear test. Experimental investigations on two sands, one with rounded smooth grains (Ennore standard sand) and another with angular grains (Ganga sand), were carried out with a view to investigate the difference in shear strength of the sands at different shear strain rates. From the test results, it was found out that friction angle depends largely on gradation and particle angularity. Angular well-graded particles give the highest friction angle, and the rounded uniform particles give the least. Angle of shearing resistance increases with increasing the strain rate. For these two sands, relationships have also been established for prediction of peak friction angle as a function of relative density and rate of shearing strain.
SYNOPSIS Energy Storage Technologies are the need of the hour. With more and stricter carbon emis... more SYNOPSIS Energy Storage Technologies are the need of the hour. With more and stricter carbon emission norms combined with ambitious targets for the green power a niche is getting created for Energy Storage Technologies. Such technologies are absolutely essential keeping in mind the fact that output from all the current generation renewable energy sources such as solar or wind are fluctuating in nature. Today there are plenty of energy storage technologies available including battery storage, flywheel, molten salt, compressed air, pumped storage etc. But most of them (excluding pumped storage and battery bank) are in initial state of technological development. Battery Storage looks promising but only when used in electric vehicles, emergency situations or grid stability. But for large Grid size energy storage the pumped storage plants still proves to be the best bet in terms of economy, reliability & technical maturity. Sea Water Pumped Storage is a type of artificial pumped storage scheme which harness coastal mountainous topography and abundant seawater. A sea water pumped storage provides a simple solution for storing electrical energy minus the problems associated with the conventional hydro plants of obstructing natural freshwater flow, high cost of building dams, water availability etc. Such type of plants can be very useful in an island type condition and remote areas. India which has almost 3500 km coastline and islands dotted with mountainous topography such plants of the scale of MW to Few MWs can be readily built. In this paper, the merits and demerits of various types of energy storage technologies have been discussed. We have also done a study which demonstrate the importance of energy storage in an Island (isolated grid condition) where they become an absolute necessity if renewable energy is added substantially. Further, a preliminary techno economic study is presented for construction of a typical sea water pumped storage plant at any suitable site (inland or in an Island) in India.
This study undertook stability analysis of nailed soil slopes using the limit-equilibrium method ... more This study undertook stability analysis of nailed soil slopes using the limit-equilibrium method (LEM) and considering a three-dimensional (3D) rigid-body rotational failure mechanism with the assumed slip surface being a part of a sphere. The moment equilibrium of the 3D wedge formed by the slope surface and the slip surface along with the nails embedded in it were analyzed as a whole. A specific-purpose computer code was written for factor-of-safety (FS) computation; the developed computer code is capable of analyzing an unreinforced slope and a nailed slope. The critical slip surface and the corresponding minimum FS value of the unreinforced slope were initially determined, taking into account all possibilities of failure (base failure, slope failure, and toe failure). For the critical slip surface so obtained, nails were then introduced at desired positions, and the FS value for the nailed slope was then estimated with the developed procedure. The developed method and computer code were verified by comparing the FS values of some benchmark problems [two-dimensional (2D) and 3D] obtained by the proposed method with those reported in the literature. The critical slip surfaces obtained from the proposed method were also compared with some of the benchmark problems. A parametric study was conducted to determine the effects of the inclination and spacing of the nails on the FS values.
In storage type hydroelectric projects, proper diversion of river inflow is one of the major work... more In storage type hydroelectric projects, proper diversion of river inflow is one of the major works which require extensive planning not only for construction period but also during first reservoir filling. Owing to the inherent flexible nature of earth and rockfill dams, the process of first reservoir impounding gains critical importance in case of these type of dams. In order to avoid development of undue stresses within the dam body due to internal readjustment during first reservoir impounding, the first reservoir impounding is carried out slowly, in a controlled manner and under close surveillance. Koldam Hydro Electric Power Project is located on Satluj river in Bilaspur district of Himachal Pradesh in India. The project utilizes a drop in head of about 140m by constructing a 167m high (from the deepest foundation level) rockfill dam and a dam toe surface power house with an installed capacity of 800MW. The design of the Koldam project is such that it will also arrest the silt flow from upper reaches and thus increase the life of Bhakra Dam by almost 18 years and therefore the spillway was placed at higher level and cannot be used for controlling the reservoir filling till 144m height of dam. For achieving the controlled first reservoir impounding of 167m high Earth and Rockfill dam of Kol Dam HEPP, a low level outlet named Bottom Outlet had been envisaged. This structure has been constructed inside one of the two diversion tunnels constructed at Koldam HEPP. Owing to the factors like high operating head (approx. 135m), the limited working period and the tough conditions inside the tunnel, construction and operation of Bottom Outlet was always going to be a challenge, requiring dynamic planning and midcourse review of some design aspects. First reservoir impounding of Koldam HEPP has been completed in June 2015 with effective utilization of Bottom Outlet for controlling the reservoir impoundment rate. Present paper discusses the various aspects viz. design, planning, challenges faced and midcourse corrections necessitated thereof in the Bottom Outlet.
In present study, finite element simulation of footing on full-scale model double-faced wall has ... more In present study, finite element simulation of footing on full-scale model double-faced wall has been done using plane strain software Plaxis. The construction of the wall was done in stages, which is simulated in the model wall. After construction, footing is placed on top using plate element and load is applied. The finite element analysis predictions are compared with the experimental results. FEM based predictions of load-deformation behaviour of footing on large-scale model reinforced soil wall are in excellent agreement with experimental data. The predictions of deformation of facings are found to be conservative but the pattern of tilting of footing was in good agreement with the experimental observations.
There are three distinct phases of monitoring in the lifetime of an earth and rockfill dam. viz. ... more There are three distinct phases of monitoring in the lifetime of an earth and rockfill dam. viz. construction, first reservoir filling and operation stage. During construction stage, rate of construction of earth and rockfill dam may require modifications on the basis of the instrumentation results to achieve safe construction. During initial reservoir impounding, instrumentation results are of paramount importance and have a consequential impact on the decisions regarding future rate of filling, to enable safe impounding of dam. During normal period of operation these instruments are required to monitor the behaviour of dam due to fluctuation in reservoir levels or even in steady state conditions. Koldam Hydro Electric Power Project is located on Satluj River in Bilaspur district of Himachal Pradesh in India. The project has 800MW installed capacity and a 167m high (from the deepest foundation level) rockfill dam which creates a head of about 140 m. Earth and Rockfill dam of Kol Dam HEPP has an elaborate monitoring instruments network for monitoring the health of the various structures viz. earth and rock-fill dam, spillway and galleries. First phase of first step of initial impounding of Kol Dam reservoir has already been completed in the month of March-April 2014. After monsoon period, reservoir impounding was restarted in October 2014 and likely to be completed soon. In this paper, analyses of the data of monitoring instruments obtained from the earth and rockfill dam during depletion after first phase of reservoir impounding has been presented. A comparison of the readings obtained during first step of impounding till El. 560m in March-April 2014 and that obtained during re-impounding till El. 560m have been made in this paper.
Behaviour of reinforced soil structures depends on the material properties of soil and geosynthet... more Behaviour of reinforced soil structures depends on the material properties of soil and geosynthetics. Apart from individual properties of soil and reinforcement, the interaction between reinforcement and soil also plays important role in deciding the behaviour of reinforced soil structures. The modelling of the interface characteristics is a very important aspect in developing a correct numerical model for predicting the performance of reinforced soil structures. For simulating the interface behaviour a linearly elastic model with Mohr–Coulomb criterion is commonly used. Experimental observations made from direct shear tests usually show that the force–displacement relationship is non-linear till a peak is attained, beyond which softening behaviour is observed. In this paper a constitutive model appropriate for geosynthetic interfaces has been implemented in FLAC3D and used to simulate the shear stress displacement behaviour of different sand–geotextile interfaces. In the present study, shear stress–displacement behaviour of interfaces of different types of sands and geotextiles (monofilament woven, multifilament woven and nonwoven) have been considered for simulation. The simulated curves using the FLAC3D showed very good agreement with the experimental data over the complete stress-displacement ranges.
During construction and initial reservoir impounding, performance of an earth and rock-fill dam i... more During construction and initial reservoir impounding, performance of an earth and rock-fill dam is required to be closely and frequently monitored for safety of the dam. During construction stage, rate of construction of earth and rockfill dam has to be manoeuvred i.e. increased or decreased on the basis of the instrumentation results to achieve safe construction. Similarly, during initial reservoir impounding, instrumentation results are of paramount importance and have a consequential impact on the decisions regarding future rate of filling, to enable safe impounding of dam. Koldam Hydro Electric Power Project is located on Satluj River in Bilaspur district of Himachal Pradesh in India. The project envisages utilization of a drop in head of about 140m by constructing a 167m high (from the deepest foundation level) rockfill dam and a dam toe surface power house with an installed capacity of 800 MW. Earth and Rockfill dam of Kol Dam HEPP has an elaborate monitoring instruments network for monitoring the health of the various structures viz. earth and rock-fill dam, spillway, galleries and foundations. Around 500 electronic and mechanical instruments have been installed and the performance of these structures is being monitored through this monitoring network. In the present paper, instrument network of only earth and rock-fill dam has been presented. Koldam HEPP is in final stages of construction and first stage of initial impounding has already been completed in the month of March-April 2014. Analyses of the data of monitoring instruments obtained during first stage of reservoir impounding and associated safety aspects have been discussed in the paper.
In direct shear testing of soil-geosynthetics interface, apart from properties of soil and geosyn... more In direct shear testing of soil-geosynthetics interface, apart from properties of soil and geosynthetics, the test apparatus greatly influences the behaviour of interface. In this study, experiments have been conducted using a modified direct shear box in which geotextile is placed over rigid smooth substrate. The effects of allowing stretching the geotextile over smooth substrate on performance of geotextile-sand interface were evaluated through laboratory tests. Locally available natural river sand and two differently textured geotextiles have been used for the study. To investigate the influence of condition of substrate on the sand-geotextile interface behaviour, the results for smooth substrate are compared with the data available in literature, for the rough substrate. The study showed that condition of substrate significantly influences the shear stress-displacement behaviour of interface and interface friction angle.
The behavior of soil-geosynthetics interfaces depends on the different properties of soil includi... more The behavior of soil-geosynthetics interfaces depends on the different properties of soil including particle size, particle shape, density, gravimetric water content, degree of saturation and properties of geosynthetics including structure, texture, etc. This paper pertains to the study of the influence of particle shape of sand on the sand-geotextile interface behavior. Experiments were conducted using a conventional size direct shear box modified for interface testing. In the present study, two different natural sands (one having angular particles and other having rounded particles) and two different geotextiles have been used. The study showed that particle shape significantly influences the interface behavior, especially the post-peak behavior.
Being a flexible structure, earth and rockfill dams are very suitable in high seismic zones. Kol ... more Being a flexible structure, earth and rockfill dams are very suitable in high seismic zones. Kol Dam HEPP envisaged a 163 m high central core earth and rockfill dam. The project site is situated in Himachal (Himalaya) and is prone to large magnitude earthquakes. This paper pertains to the estimation of earthquake induced permanent displacements of the earth and rockfill dam using Newmark's block sliding methods. In the present analysis, a synthetic acceleration time history has been used. The study showed that dam will not suffer any damage when subjected maximum credible earthquake but may undergo large deformation if subjected to a hypothetical large earthquake with PGA of 1g.
The response of double-faced wrap-around reinforced soil retaining walls subjected to strip loadi... more The response of double-faced wrap-around reinforced soil retaining walls subjected to strip loading on the surface has been studied by conducting small-scale model laboratory tests. Model reinforced soil walls were constructed using Kalpi sand as backfill material and geotextiles as reinforcing elements. In the present study, two different multifilament geotextiles were used. Strip loading was applied at the centrally placed footing on the surface of the wrap-around reinforced soil walls. The influence of the number of reinforcing layers and overlap length on load deformation behaviour, ultimate bearing pressure and initial tangent modulus of the footings on double-faced reinforced soil walls was studied. The lateral deformations of wrap-around wall facing with settlement of the footing are also presented.
The paper presents the results of experimental studies with regard to the response of small scale... more The paper presents the results of experimental studies with regard to the response of small scale model strip footings resting on the surface of wrap-around reinforced soil retaining walls constructed using locally available sand as backfill and geotextile as reinforcing elements. Number of reinforcing layers and footing size were varied to find their influence on the bearing capacity and load deformation (both vertical and lateral) characteristics of the walls. It is found that the ultimate bearing capacity of the footings and initial tangent modulus increases with increase in the number of reinforcing layers but the initial tangent modulus decreases with increase in footing size.
The paper pertains to a study regarding the response of strip footings resting centrally on the s... more The paper pertains to a study regarding the response of strip footings resting centrally on the surface of model double-faced wrap-around vertical soil walls. Experiments were performed in the laboratory on small-scale model geosynthetic-reinforced, double-faced, vertical soil walls constructed with sand backfill and wrapped facing using varying spacing, overlap length of reinforcement layers and footing widths to study their effects on its load–deformation behaviour. Then a plane-strain finite element simulation of the model walls was performed, using commercially available Plaxis software, to predict their behaviour under strip loading. Backfill sand and reinforcements were modelled as elastic-perfectly plastic and linearly elastic material, respectively. Comparison of the predicted bearing capacity of the footing resting on these walls and the horizontal displacement of the wall face showed reasonable agreement with the experimental data.
Apart from other factors, the performance of geosynthetic reinforced soil structures depends also... more Apart from other factors, the performance of geosynthetic reinforced soil structures depends also on the characteristics and behavior of the interface between soil and geosynthetic. Experiments were conducted in a direct shear test apparatus to study the shear force–displacement behavior at the soil–geotextile interface using two differently textured woven geotextiles. Analyzing the data so obtained a non-linear constitutive model has been presented for predicting both the pre-peak and the post-peak interface behavior. The predictions made by the developed model are found to be in good agreement with experimental data obtained from direct shear tests.
The paper pertains to the behavior of small-scale model studies on strip footings subjected to ve... more The paper pertains to the behavior of small-scale model studies on strip footings subjected to vertical loading resting on the surface of a wrap around reinforced vertical soil walls with sand backfill. Finite element analysis (using Plaxis 2D version 8 software) of the soil wall was also made to find its response and the predicted values were then compared with experimentally observed values. Effect of the number of reinforcement layers on the overall response was studied. Comparison of the predicted horizontal displacement of the vertical wall face and bearing capacity of the footing resting on the same showed reasonable agreement with the experimental data.
The paper deals with an important practical problem related to construction of ash dykes using fl... more The paper deals with an important practical problem related to construction of ash dykes using fly ash. In most of the thermal power plants fly ash is disposed off in the form slurry pumped to an artificially created pond. When the pond is full with the ash the capacity of the pond is increased by raising the height of the dyke using upstream or down stream method of construction. Due to constraint of land, upstream method of construction is more commonly used, which involves construction of dyke resting on bottom ash in the pond. Before laying the foundation top 1-2 m of bottom ash is removed and then the construction is started on top of it. This results in unloading and reloading of bottom ash. In this work an attempt is made to study the strength behavior of ash in over consolidated state. The experimental study indicates that there is appreciable difference in the strength and both total and effective stress parameters increase when the over consolidation ratio increases. The peak stress at failure is also observed to be higher for higher over consolidation ratio. Consideration of increased parameters will result in more economical design of ash dykes constructed by using fly ash.
Liquefaction of saturated soils during earthquake often had been a major cause of damage to struc... more Liquefaction of saturated soils during earthquake often had been a major cause of damage to structures. Since beginning the liquefaction studies were concentrated on sandy soils, as the sandy soils are known to be more susceptible to liquefaction. However, observations from some sites in China and Loma-Prieta earthquakes show that soils with high plastic fines are also susceptible to liquefaction. Isotropically consolidated undrained cyclic triaxial tests were conducted on undisturbed samples of silty clay soil and results of these tests are used to verify the methods based on SPT data. Slow cyclic tests were performed to investigate the development of pore pressure and cyclic strength, as reliable pore pressure measurement is only possible in slow cyclic triaxial test for clayey soils. The site was than characterized for liquefaction by a computer program developed.
The N-value was obtained for the same site by conducting Standard Penetration Test. Test results were verified using methods reported by Tokimatsu & Yoshimi (1983) and Ishihara (1993). The simplicity of the methods and application of the methods to the fine-grained soils are the main criteria for selection of the field methods. The computer program also provides characterization of site using these methods.
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Papers by Dr. Anubhav _
Koldam Hydro Electric Power Project is located on Satluj river in Bilaspur district of Himachal Pradesh in India. The project utilizes a drop in head of about 140m by constructing a 167m high (from the deepest foundation level) rockfill dam and a dam toe surface power house with an installed capacity of 800MW. The design of the Koldam project is such that it will also arrest the silt flow from upper reaches and thus increase the life of Bhakra Dam by almost 18 years and therefore the spillway was placed at higher level and cannot be used for controlling the reservoir filling till 144m height of dam. For achieving the controlled first reservoir impounding of 167m high Earth and Rockfill dam of Kol Dam HEPP, a low level outlet named Bottom Outlet had been envisaged. This structure has been constructed inside one of the two diversion tunnels constructed at Koldam HEPP. Owing to the factors like high operating head (approx. 135m), the limited working period and the tough conditions inside the tunnel, construction and operation of Bottom Outlet was always going to be a challenge, requiring dynamic planning and midcourse review of some design aspects.
First reservoir impounding of Koldam HEPP has been completed in June 2015 with effective utilization of Bottom Outlet for controlling the reservoir impoundment rate. Present paper discusses the various aspects viz. design, planning, challenges faced and midcourse corrections necessitated thereof in the Bottom Outlet.
The N-value was obtained for the same site by conducting Standard Penetration Test. Test results were verified using methods reported by Tokimatsu & Yoshimi (1983) and Ishihara (1993). The simplicity of the methods and application of the methods to the fine-grained soils are the main criteria for selection of the field methods. The computer program also provides characterization of site using these methods.
Koldam Hydro Electric Power Project is located on Satluj river in Bilaspur district of Himachal Pradesh in India. The project utilizes a drop in head of about 140m by constructing a 167m high (from the deepest foundation level) rockfill dam and a dam toe surface power house with an installed capacity of 800MW. The design of the Koldam project is such that it will also arrest the silt flow from upper reaches and thus increase the life of Bhakra Dam by almost 18 years and therefore the spillway was placed at higher level and cannot be used for controlling the reservoir filling till 144m height of dam. For achieving the controlled first reservoir impounding of 167m high Earth and Rockfill dam of Kol Dam HEPP, a low level outlet named Bottom Outlet had been envisaged. This structure has been constructed inside one of the two diversion tunnels constructed at Koldam HEPP. Owing to the factors like high operating head (approx. 135m), the limited working period and the tough conditions inside the tunnel, construction and operation of Bottom Outlet was always going to be a challenge, requiring dynamic planning and midcourse review of some design aspects.
First reservoir impounding of Koldam HEPP has been completed in June 2015 with effective utilization of Bottom Outlet for controlling the reservoir impoundment rate. Present paper discusses the various aspects viz. design, planning, challenges faced and midcourse corrections necessitated thereof in the Bottom Outlet.
The N-value was obtained for the same site by conducting Standard Penetration Test. Test results were verified using methods reported by Tokimatsu & Yoshimi (1983) and Ishihara (1993). The simplicity of the methods and application of the methods to the fine-grained soils are the main criteria for selection of the field methods. The computer program also provides characterization of site using these methods.