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Über dieses Buch

This book comprises select proceedings of the Indian Geotechnical Conference 2020 (IGC2020) focusing on recent developments in the field of transportation geotechnics, scour and erosion, offshore geotechnics, and environmental geotechnology. The contents are useful to academicians, researchers, practitioners and policymakers to understand and tackle the challenges in an efficient manner and to adopt appropriate sustainable geotechnical engineering solutions.

Inhaltsverzeichnis

Frontmatter

Prediction of Stability of an Infinite Slope Using Geospatial Techniques

Two-dimensional (2D) slope stability investigations are the most regularly utilized techniques among the designers because of their effortlessness. Determining the factor of safety against a potential failure is the main objective in predicting the stability of the slope. On the off chance, if the factor of safety is determined to be sufficiently massive, the slope is considered to be steady (safe). On the off chance that it is 1.0 or less, it is perilous. In this study, Variables such as soil water content and land temperature of 20 selected points were estimated during field observation. Samples collected from the site were analyzed in the geotechnical laboratory to determine the field moisture content, cohesion, angle of shearing resistance, and density. The principal parameter, soil moisture (ω), is obtained from the experimental methods for 20 selected points. Then the remote sensing perspective is utilized to calculate the safety factors of the expressway slope stability. Cartosat information was used to infer a few critical variables engaged with the assurance of slope stability. Maps of soil mechanical factors, for example, the cohesion of the soil (c), angle of shearing resistance (ø), and unit weight of the soil (γ) are obtained by correlating with soil moisture (ω) in the model maker. Cartosat-1 Digital Elevation Model (DEM) data is used in determining another significant variable, the slope angle (α). factor of safety (FOS) computations depend on infinite slope stability models for shallow landslides that are computed using SAGA GIS software.

Srirama Dinesh, Chirasmayee Savitha, Arif Ali Baig Moghal

Application of Bi-directional Extreme Learning Machine in Predicting Stability of Slope of Railway Embankment in Seismic Condition

This study presents the application of machine learning technique in predicting the stability of slope of railway embankment. As we know that most of the railway tracks are built on the natural ground surface and the track system is installed on the prepared formation called Permanent Way, constructed either earthwork in formation or earthwork in cutting or in a combination of both. In contrast, the installation of a railway system requires healthy investment as well. Hence, to run the entire system satisfactorily, a detailed analysis on account of the stability of slopes of Permanent Way is always necessary, especially to prevent damages in seismic conditions. For this purpose, Bi-directional extreme learning machine is used for the prediction of factor of safety in seismic conditions. It is interpreted from the results that the developed model is capable enough to predict the factor of safety. The value of R2 was obtained as 0.9983 in both the training and testing phases. The lower values of RMSE (training = 0.0184 and testing = 0.0181) in both phases justify the generalization capability of the model. The finding of this research concludes that the developed model can be used as a simple computational approach in predicting the stability of slopes particularly in the introductory stages of railway Projects.

Abidhan Bardhan, B. Dhilipkumar, Lakshmi Mulagala, Pijush Samui

Risk Assessment and Early Warning System for Landslides in Himalayan Terrain

India is having the highest mountains chain on the earth, and the northward movement of the Indian plate toward china causes continuous stress on the rock geometry furnishing them friable, weak, and vulnerable to landslides. The major hydro geological hazards in these hilly ranges include landslides, and avalanches are unprecedented catastrophes that are experienced in almost all of the country. The remediation method adopted before and after landslides occurrence depends upon the characteristics of the sliding mass, which include the geologic environment and geometry of the landslides. The major existing methods for the prevention and remediation of landslides comprises of construction of piles and restraining structures, modifying slope geometry, grouting rock joints and fissures, rerouting surface and underwater drainage and diverting debris/rock fall pathways, but these methods are strained by cost, landslide magnitude and frequency, and the risk pertaining to human settlements. The recent trends and developments such as landslides zonation mapping, hazards risk mapping, Landslides Early Warning System (EWS), preparation of policies related to mountains land use, and town planning are forged ahead of the existing practices and have positive effects on the cost and societal benefits.

R. K. Panigrahi, Gaurav Dhiman

Numerical Analysis of the Stability of Soil Slope Subjected to Rainwater Infiltration

India is among the top 10 countries with the highest percentage of landslide disaster for the past few years. Among the natural disasters, rainfall-induced slope failure is one of the natural disaster, resulting in loss of human life and damage to public properties. In this study, Finite Difference Analysis (FDA) of unsaturated flow is carried out to investigate the response of slope subjected to rainwater infiltration. The effect of rainfall intensities and duration on pore pressure generation, degree of saturation, slope stability and evolution of strains during rainfall event for homogeneous finite slope is investigated. A parametric sensitive analysis is performed considering different rainfall intensities applied over the soil slope. Results indicate that the rainfall intensity and duration have a negative effect on factor of safety (FOS), significant effect on pore-water pressure, saturation and FOS values.

H. R. Bhanuprakash, Adarsh S. Chatra

Response of Sand at Low Normal Stresses Using Gravity Shear Test

Shallow slope failures have been observed due to loss of strength, infiltration of water, climatic factors, etc. Strength properties of near-surface soils, especially at low normal stresses have rarely been studied. Similar problems occur at the interfaces between geosynthetic and soil/backfill in case of MSW (Municipal Solid Waste) disposal site, as for such materials (soils and geosynthetics), shear response of interfaces becomes significant considering the fact that very low normal stresses act along the potential failure plane. The bond strength for such materials is usually measured either by a direct shear test or a tilt test. Gravity-induced shear test is proposed herein to be performed for conditions of low normal stress. In the present study, a new test set-up was developed and tests have been carried on the sand at different normal stress conditions for relative density of 50 and 75%. Response of granular material at very low normal stresses is thus studied and results presented.

Konda Kiranmai, Kadali Srinivas, Madhav Madhira

Rock Slope Stability Analysis of a Metro Station Excavation

Successful design of rock cut slopes is a product of thorough geotechnical investigation, use of suitable design methods, implementation of appropriate excavation methods and adoption of appropriate stabilization measures. This paper deals with rock slope stability analysis conducted for a metro station excavation as a part of one metro rail project in southern part of India. Kinematic analysis and numerical analysis have been performed considering various conditions of slope failure. An attempt has been made to execute a comparative analysis of various available methods for rock slope stability analysis. Rock support system has been estimated to achieve suitable factor of safety, and a comprehensive design strategy to deal with rock slope stability has also been elucidated in this paper.

R Rajaraman, Gundeti Sumanth Kumar

Design of Core of Earthen Dam by Replacement with Geosynthetics

Earthen dams are embankments constructed from easily available soil in the vicinity of the construction site. The main components of an earthen dam are outer shells and inner core. The core is provided in the center of the dam to reduce the seepage through the embankment. The core materials of earth dams are usually selected based on available burrow areas and mainly from low permeable geomaterials (mostly clay). Many times, it may be difficult to find a suitable clay for the core in the locality of the embankment. In the present study, the effect of the introduction of Geosynthetic Clay Liner (GCL) in the core of the embankment is analyzed. A 33 m high embankment was considered and analyzed for seepage and slope stability analysis. In the present study, a geosynthetic clay liner is introduced in the core in order to reduce the thickness of the clay core. Seepage flow analysis through the embankment is studied with and without a Geosynthetic Clay Liner. Steady and sudden drawdown conditions are also considered in the study. It is observed that the usage of Geosynthetic Clay Liner results in the reduction of seepage flow through the embankment by 22%. Even the core material has been reduced by 13%.

Asif Ali Mohammed, S. Sasanka Mouli, J. Y. V. Shiva Bhushan

Investigation and Design of Remedial Measures for Landslide in Hunthar Veng, Mizoram—A Case Study

The city of Aizawl (Capital of Mizoram) is linked with rest of India through the National Highway-54 (NH-54). The highway near the Aizawl city is prone to landslide (at Km 179.50 on NH-54) and sinking due to haphazard growth of the city on vulnerable slopes and poor drainage system. The Hunthar Veng landslide area is active since 1993 and gets reactivated every year after the monsoon. If the area continues to slide and sink and not treated properly, it is possible that hazard could propagate to a much larger area, thereby putting a greater number of houses and properties at risk. Looking into the danger prevailing in the region, it was decided to focus on strengthening the slope and increase its stability. Slope stability analysis was carried out by considering the seismicity susceptibility. Different ground improvement options like (a) Grouted nails, (b) Removal of debris and installation of grouted Nails and (c) Stepped Slope with Cut-off Wall were considered for stabilising the slope. From the slope stability analysis, it was found that the factor of safety of the slope after applying different measures was not adequate except in one condition, where cut-off walls of large depth, i.e. up to 20 m in depth at a spacing of 2.5-3 m from top to bottom was provided. This solution analytically appears safe but has its own demerits like high cost and time consuming. Therefore, economical and environmentally friendly remedial measures were suggested.

M. Vinoth, P. S. Prasad, Sudhir Mathur, Kishor Kumar

Stability Analysis of Tailings Dam Using Finite Element Approach and Conventional Limit Equilibrium Approach

The probability of failure in tailings dam is generally found to be much greater than the conventional water retaining dams. Slope instability is one of the major reasons, contributing more often to the failure of these tailings dam. Due to this reason, the stability of tailings dam has drawn much attention as significant numbers of tailings dam’s failure have been reported worldwide in the recent years. The present work focuses on evaluating the stability of existing tailings dam by using finite element method (FEM) as well as conventional limit equilibrium methods (LEMs) under static loading conditions. Shear strength reduction (SSR) technique is incorporated (by using 2D finite-element based package RS2) in order to observe the potential modes of failure. Further, Rocscience SLIDE-2D is utilised to evaluate the stability of dam embankments by LEM. The results obtained from the analysis utilizing both LEM and FEM are compared in terms of their global factor of safety (FOS) and strength reduction factor (SRF) respectively. Further, an attempt is made to explore the stability of different types of tailings dam, based on their method of construction (i.e., upstream (U/S) method and downstream (D/S) method). The results obtained from LEM and FEM are found be in good agreement with each other. It is observed that the FOS and SRF values decrease as the height of embankment is raised. In addition, the failure surface is found to be circular in FEM for most of the critical slopes, which supports the assumptions of circular slip surface considered in LEMs based analysis. In addition, D/S slope is found to be more susceptible to failure than the U/S slope, for both U/S and D/S methods of construction.

Surender Singh, Abhishek Kumar, T. G. Sitharam

Stability Analysis of Slopes at a Landslide Prone Area: A Case Study on the Landslide at Madikere, India

The recurring landslides at Madikeri in India during rainy seasons have created fear among people in this area. In 2018, high rainfall was recorded in Makkandur, Kodagu District, located in the Western Ghats of India. This led to severe landslides, floods, and soil displacement. In the present study, the soil in the landslide prone area was analyzed to identify the suitable amendment to improve the slope stability. In-situ and laboratory experiments were conducted on the soil to examine the characteristics of this soil. The soil properties were determined with and without amendments to know the improvement in the factor of safety of the slope. The factors of safety corresponding to two different heights of slopes presented at the site were estimated using the Taylor’s stability number. The stability analysis was also performed using GEO5 software tool. Two amendments, fly ash and rice husk ash, were studied in different proportions and found that there is considerable increase in the factors of safety with the selected additives.

J. Sumalatha

Study of Dry Granular Flow Behaviour with and Without Erodible Layer

Landslides and debris flow possess greater damaging power due to their sudden occurrence and relatively high velocity. Landslide flow behaviour can be interpreted using a granular column collapse model. In the present study, dry granular flow behaviour on the erodible and non-erodible layers is analysed. A granular column collapse model with its spreading surface containing an erodible and non-erodible layer is used in this study. The unique property of granular particles to behave in a heterogeneous manner requires its analysis to be done individually. Therefore, particulate-level simulations are performed with the help of the discrete element method (DEM). Particle trajectories and the interaction forces between the particles in the system are studied at every step. Notable changes are found in the flow behaviour with respect to different aspect ratios. Parameters like bulk coordination number and the evolution of energy of the system are taken into consideration in this study.

S. Sureka, C. Kavinkumar, Rakesh J. Pillai

Numerical Analysis of Buried Pipelines Located in Slopes

Buried pipelines act as lifelines for infrastructural development as they are extensively used as a carrier of essential materials such as oil, natural gas, chemicals, etc. for human need and for industrial growth. The present study deals with numerical investigation of buried pipe in soil slope using PLAXIS-3D. In addition, a footing was also installed to analyze the optimum position of buried pipe, which will have minimum effect on the ultimate bearing capacity of footing. For this analysis, the angle of soil slope is taken as 20°, relative density is taken as 85% and ratio of setback distance to width of footing (b/B) is taken as 2. The typical load deformation curve was generated from PLAXIS-3D software considering different variable parameters to get the optimum position of buried pipe. From the result, it is observed that the footing’s bearing capacity gets increased as the pipe position going away from the stress bulb of footing in a downward direction. The safe vertical depth of buried pipe is taken as 3.5 times the width of footing and horizontal distance of buried pipe from the nearest edge of footing is taken as 2 times the width of footing, where the effect of buried pipes on bearing capacity of footing is less.

Rishi Ranjan, Anil Kumar Choudhary, Awdhesh Kumar Choudhary

Different Sets of Remediation for Mitigation of Landslides in Hilly Terrains of India

The great Himalayan Mountain is a majestic cluster of several numbers of more or less parallel hill ranges intervened by numerous valleys and extended plateaus. The Himalayan landscape, as said by expert geologists, is especially susceptible to landslides. The northward movement of the Indian plates caused continuous stresses on the hill slopes making them weak and prone to landslides. The Himalayan topography, as well as high seismic vulnerability and rainfall in the region, are enlarging the liability to landslides. Landslides or landslips involve a large ground movement due to the gravity forces, which result in total mass wasting of the slope. The landslides are experienced in almost all the national and state highways adjacent to the hill slopes of the Himalayas and hill ranges of India North East, Western Ghats and Nilgiris, Eastern Ghats, Himachal, J&K, Garhwal and Kumaon hill ranges, and Vindhyas. The remedial measures for landslides may be divided into four subcategories; restraint, removal, drainage, and relocation. The retaining structures are designed to retain rock/soil slope that would not naturally be stable at its position. The reinforcement measures include soil nailing and earth reinforcement measures, which involve the insertion of steel rods, metallic strips, geosynthetics, and steel angles to improve the stability of the slope. The reinforcement measures also include the improvement of the mechanical characteristics of the ground through chemical, thermal, or mechanical treatment. The third major remedial measures are drainage measures, which are most effective in a geologic condition that allows interference with the natural water regime. Also, bioengineering techniques in which vegetation is a fundamental part are useful approaches to prevent landslides as they improve slope stability and maintain ecological balance. They are most suitable to be deployed in developing countries because of their cost-effectiveness and environmentally friendly nature. The chosen remedial measures depend upon several factors such as type movement (slide, flow, etc.), type of material (debris, rock, soil, etc.), location of the failure, the process of failures, etc. The several factors that are to be considered before designing and implementing landslides remedial measures will be discussed in the paper. The paper shall be dealt with different sets of remediations such as soil nailing technique, earth reinforced structures, retaining structures, drainage measures, and bioengineering techniques for mitigation of landslides adjacent to roads in Himalayan terrain considering the economic as well as social feasibility, steadiness, and efficiency. Moreover, several advantages and disadvantages of remediation techniques shall be incorporated in the paper.

R. K. Panigrahi

Influence of Fines Content on Stability of Unsaturated Soil Slopes

Natural sands usually consist of considerable fines content (FC) (various proportions of silt and/or clay), the presence of which significantly affects its structure and unsaturated behavior. Soil water characteristic curve (SWCC) is the primary and fundamental tool to address unsaturated soil properties as it relates to the soil suction and the soil water content. However, it is well accepted that the SWCC exhibits hysteresis as it does not follow the same path during desorption and sorption. For a constant value of suction, the soil water content in the desorption is always greater than in the sorption. SWCC considerably changes with the presence of fines in the soil. Therefore, the present study sheds some light on the unsaturated behavior of soil mixtures with varying FC. Ennore sand was reconstituted with various percentages of red soil fines to attain the desired proportions of the soil mixture. The degree of hysteresis between desorption and sorption is presented. The results revealed that increasing the FC in the soil significantly affects the degree of hysteresis. Furthermore, the effect of percentage fines and hysteretic SWCC on the unsaturated infinite slopes has been carried out. It is observed that there is a considerable difference in the factor of safety obtained for the various percentage of fines during sorption and desorption cycles. The present study emphasizes the significance of the influence of FC on the degree of hysteresis of SWCC as it affects slope stability significantly.

Ammavajjala Sesha Sai Raghuram, B. Munwar Basha, Arif Ali Baig Moghal

Stability of Sloped Soil Embankment for Seismic and Tidal Load Combination

The slope of soil embankment near the port is subjected to fluctuation in water level, seismic load, dynamic vehicular load, and superstructure load. So the combined effect of these loading poses a threat to slope stability of soil embankment. In this study, dynamic vehicle load and superstructure load are not considered. This paper presents a common solution which is micropiles for slope stability when sloped soil embankment is subjected to either seismic loading or a combination of seismic and tidal loading. M-C criteria and Geoslope software are used for analysis. Slope stability theories namely Bishop, Fellenius, Janbu, and Spencer are considered for finding factors of safety. JNPT, Mumbai bore log data, Mumbai tidal, and seismic data are used for investigation. Using Bishop’s theory variation in the factor of safety with a surcharge is examined at horizontal seismic coefficients 0.225 and 0.16 (zone III cities), respectively, for seismic loading and combination of seismic and tidal loading. It is observed that a non-linear relationship exists between the factor of safety and surcharge for both cases.

Amritansh Mishra, A. Trivedi

Monitoring of Landslide in Heavy Rainfall Areas Using Low-Cost Microcontrollers

Landslide can be triggered by earthquakes, precipitation, and man-made changes in the soil. These are one of the major disasters due to heavy rainfall in the hilly regions of the southern parts of the country. The main problems when it comes to reducing the casualty from such disaster are the lack of early warning to evacuate the problem-prone area. What is intended here is to propose a system that can record the change in moisture content of the soil and send out an early warning before it reaches the peak when the soil losses its internal friction and starts to slide. The system can send out SOS signals to the authorities so that the evacuation can be initiated. The paper focuses on the calibration and manufacturing of such a system and its robustness. The calibration part includes laboratory studies about the inter-particle relationship of soil with the change in moisture content and the slope of the terrain. Manufacturing involves the development of a microcontroller with sensors and communication devices using open-source platforms which are not yet outdated with the current scenario.

K. S. Beena, O. Varun Menon, P. J. Rooma

An Experimental Study on the Influence of Water-Level Fluctuation on Stability of Slope of Model River Bank Composed of Cohesionless Material

The stability of a slope is utterly governed by soil properties, stress conditions, and slope geometries. Any change taking place of at least one of these factors means slope stability conditions being potentially affected. The objective of this study is as follows: experimental model analysis of the stability of a bank simulating a river bank during post-flood condition, determination of factor of safety by strength reduction method, study of the influence of drawdown rate and ratios on the stability of a bank and lastly to study the variation of pore pressure with water level fluctuation and its effects on stability. In this model, the study of stability of river bank, the effect of shear stress generated by the velocity of water flow has not been taken into account, instead the river bank is subjected to rapid drawdown only, and from the experimental results, we may conclude that the water-level fluctuation is one of the dominating causes of bank failure for cohesionless soil. The effects of drawdown rate and drawdown ratio on the factor of safety reveal that it is drawdown ratio which is taking a leading role to make the river bank unstable rather compared to drawdown rate. And during major bank failures, we observed that the factor of safety of model river bank became minimum.

Md. Firoz Ali, Supia Khatun, Yasser Arafat

Rock Mass Index (RMI) to Estimate the Shear Strength Parameters of the Rockmass: Case Study from Lesser Himalayas, Jammu & Kashmir, India

Rock Mass Index (RMI) is the method of rockmass classification system, which gives emphasis on the block size, joint characteristics and strength of intact rocks to express the UCS of the rockmass. The present work focuses on the applicability of RMI in the context of estimation of shear strength parameters, like angle of internal friction (Φ), cohesion (c), etc., and also the ‘m’ and ‘s’ constants for Hoek–Brown failure criterion from the Anji Khad in Lesser Himalayas of Jammu & Kashmir. Lithology comprises stromatolitic limestone and dolomite of Proterozoic Sirban Group, which has experienced a high degree of deformation due to the major thrusting activity (Reasi Thrust) in the region. The geological map of the area and geostructural scanline surveys has been done for demarcation of different zones (5 zones have been delineated) on the basis of types of discontinuity and degree of jointing. The input data for the calculation of shear strength parameters as well as ‘m’ and ‘s’ constants of the H-B failure criterion were obtained from the characterisation of the joints, which were then processed. The results were very much comparable with the data obtained by in situ shear tests performed in the region earlier. In situ tests are often performed to get the shear strength parameters, but due to their operational difficulties, high cost and timing factors, the tests are not performed regularly which often create information gap and constructional problems in tunnels, the foundation of bridges, etc. Therefore, the method of estimation of shear strength parameters by RMi which is reliable and also cost- and time-effective, can be used extensively.

Pratap Chandra Dhang

The Light at the End of the Tunnel––The Sleemanabad Tunnel

It is a herculean task to build a tunnel in mountainous earth comprised of loose soil, especially when there is no adequate cover on top of the tunnel. Yet in Madhya Pradesh, India, such a project is underway by the Department of Narmada Valley Development. The context is as follows: along the canal of Rani Avanti Bai Lodhi Sagar Dam (Bargi) built on westward Narmada, between the km mark of 104 and 116, canal alignment changes from Narmada alluvium to Ganga alluvium by traversing through 32 to 37 m high mountain range. This region with dense dwellings has important transport channels located along the way such as National Highway NH-7 and Howrah-Mumbai Railway Line. This proposed tunnel project has a strategic goal to serve around 2.45 lakh hectare parched agricultural lands of Jabalpur, Katni, Satana, and Rewa districts. The construction of a 10.00 m diameter and 12.00 km long tunnel started in March 2008 using a Tunnel Boring Machine (TBM). The project was fraught with delays and to fast track the remainder of work, another TBM was deployed from the opposite end of the tunnel.This paper will illustrate the complexity involved in using two TBMs simultaneously, especially given the challenging geological terrain as well the risk on the impact on transportation on ground and analyse the impact on schedule and design of the project.

Surendra Singh Pawar

Static and Dynamic Assessment of Tunnel Rock Supports in Weak Rock

Tunnel rock support design can be very intriguing as it involves a high-risk factor and any improper analysis may lead to severe financial loss. Conventional empirical methods along with the numerical analysis provide a better interpretation of the expected problems during the construction. In this study, an approach has been made to understand the effectiveness of various supports in weak rock conditions. The data from the literature is taken as input for modeling using the finite element software PHASE2 of RocScience for both static and dynamic loading. The performance of the supports has been evaluated in terms of stress distribution, plastic deformation to suggest an optimum support system for the available data. For the continuum model, a rock mass devoid of joints was considered and an equivalent Mohr–Coulomb failure criterion was assumed for it. Joints were introduced in the dis-continuum model by providing interface elements. Dynamic analysis has been performed with the pseudo-static and time response method. The results indicate that the combined use of rock bolts and shotcrete as support provides a reliable support system under various static and dynamic forces in tunnel supports.

Jishnu Choudhury, Vineet Gajamer, Dhritilekha Deka, S. Sreedeep

Numerical Study on the Influence of In-Situ Stress Ratio on Stress and Deformation Characteristics of Rock Tunnel

Numerical study on rock tunnel is to determine the influence of the In-situ stress ratio to understand and estimate the rock state stress, which has become increasingly important. The state of intact stress in rock mass changes while excavating the tunnel. On the other hand, it establishes a new form of stress and deformation in a tunnel. For this study, different in-situ stress ratio values (0, 0.5, 1, 1.5, 2, 3) are considered, and different shapes of the tunnel (circular, elliptical, and D-shaped) are used for analysis. Two other models are used (Mohr–Coulomb and Hoek–Brown Model), and their responses are compared. PLAXIS 3D Finite Element Software is used for Numerical analysis. The result shows that the crown’s deformation is more if the in-situ stress ratio is less, and deformation in the sidewall is more if the in-situ stress ratio is high. Among these three shapes, the elliptical shape shows more deformation for both Mohr–Coulomb and Hoek–Brown models. While comparing the Mohr–Coulomb and Hoek–Brown model, the Hoek–Brown model shows more deformation because it considers the Rock Mass properties like GSI, Disturbance factor, etc., and the failure envelope or strength envelope is not linear. Whereas in the case of Mohr–Coulomb strength envelope is linear.

T. Jegadeesh Kumar, M. Muttharam

Active Earth Pressure Distribution Against Braced Wall Considering Arching Effects

Estimation of active earth pressure against the rigid wall depends on the mode of wall movement. The pressure distribution is non-linear owing to arching effects. Here new formulations of calculating active earth pressure above and below cut level are proposed considering arching effects against braced wall. Horizontal translation as well as rotation about the top of wall is taken into account for above excavation whereas below cut level the wall is tilting around its lower edge. Expressions for earth pressure coefficient, earth pressure distribution and total earth pressure force are provided considering soil parameters like soil friction angle ‘ϕ’, wall friction angle ‘δ’ and cohesion ‘c’, etc. For validation of the proposed formulation, the predicted values are compared with existing case studies. Comparisons between measured and predicted values establish that proposed method satisfactorily predict earth pressure exerted on wall for both cohesive and cohesionless soil.

Kingshuk Dan, Ramendu Bikash Sahu

Investigation on Axial Response of Pile Due to Staged Tunnelling: A Numerical Approach

Estimation of foundation and subsequently, superstructure response is essential to assess the preliminary risk due to tunnelling. Several aspects of pile, tunnel, and soil characteristics influence the pile response during staged tunnelling. The present study investigates the response of a single pile in cohesionless soil through three dimensional finite element analysis. The numerical modeling, tunnel geometry, and properties and the pile parameters investigated are described here. Volume loss of tunnel, vertical load level on the pile, and lateral distance of pile from tunnel longitudinal axis on the axial response of pile have been investigated and reported here. Results of a large number of numerical analyses can identify and quantify the parameters influencing the pile response due to tunnelling. Volume loss of the tunnel significantly influences the axial response of the pile. Lateral and longitudinal influence zone of pile settlement due to tunnelling has been identified and reported here. Working load on the pile significantly reduces the initial design factor of safety due to tunnelling. The results of the present study are useful for preliminary assessment regarding the safety and stability of the existing pile foundations for a range of practical parameters of tunnel and pile.

Manojit Samanta, R. R. Abishek, V. A. Sawant

Comparison of Limiting Equilibrium and Finite Element Analysis for Embedded Retaining Walls

A classic part of geotechnical engineering is the design of embedded retaining walls. They comprise of sheet pile walls, secant pile walls, diaphragm walls, and similar and are important part of many civil structures. Embedded retaining walls commonly comprise steel sheet piling or concrete walls, built as diaphragm walls in slurry trenches or using piling methods. The performance and design of embedded walls have been debated extensively by many authors, whilst codes of practice aim to specify design procedures. This paper compares the results of a limit equilibrium approach with the results of finite element method. The finite element analysis was done in PLAXIS code and soil was modeled as Mohr–Coulomb. The soil was modeled as drained type with zero pore water pressures. The analysis of cantilever wall, single propped wall (CMRL-Case study), and multi-prop wall as given in CIRIA SP 95 for sheet pile cofferdams is done and the results were compared. The compared results show that both the limit equilibrium method used for analysis and the finite element approach gives similar prediction of the maximum bending moment. It also shows that the earth pressures in the passive state are matching at the top, i.e., just below the excavated level, but the earth pressures from the Plaxis decreases as it moves toward the toe.

Tehseena Ali, K. M. Nazeeh

Assessment of Effect of Deep Excavation on Adjacent Structures Using Finite Element Analysis

Deep excavations and its impact on neighboring buildings is one of the most important issues when planning to construct new facility. In metropolitan city, it’s a challenging task for the execution of underground construction due to limited space and high cost of land. Hence, this implies that deep excavation has become necessary for the proper utilization of available space. Therefore, it’s important to make sure that adjacent structures are safe against deep excavation-induced deformation. In this study, a two-dimensional Finite Element Method in PLAXIS 2D has been chosen for the soil–structure analysis of deep excavation supported by contiguous pile wall located in Addis Ababa. For the numerical analysis two constitutive models Mohr–Coulomb and Hardening Soil have been applied in drained effective stress condition. The objective of this study is to investigate the effect of deep excavation on adjacent structures by considering support stiffness, ground water condition, neighboring building distance from face of excavation, and building load. The analysis of this study monitors parameters like maximum lateral wall deflection (δhm), maximum settlement (δvm), angular distortion of the neighboring structures, horizontal strain, and maximum bending moment of contiguous pile wall. Moreover, normalization of lateral wall deflection (δhm/He) and settlement (δvm/He) to the excavation depth (He) and neighboring building distance-excavation (D/He) has been presented. Parametric studies have been carried out by varying parameters of diameter of contiguous pile wall, horizontal anchor spacing, and pre-stress force of anchor. The analysis result has been recorded in terms of lateral wall deflection, ground settlement, and bending moment.

Anand M. Hulagabali, Pankaj Bariker, C. H. Solanki, G. R. Dodagoudar

Performance Evaluation of Controlled Blasting and Prediction of Attenuation Relation for Charnockite Rocks

Blasting is a common method, employed in mines for production and excavation of rock where precision of excavated level is not necessary. However, when important and critical structures are located adjacent to the blasting area and precision is required for the excavated level, controlled blasting technique needs to be adopted for hard rock excavation. Performance of controlled blasting is evaluated using a parameter namely Peak Particle Velocity (PPV) and this needs to be limited to minimize the damage of existing structure and specified by Directorate General of Mines Safety (DGMS) in India. The specific explosive charges were obtained by carrying out site-specific trial blast studies. For a charnockite rocky site located along East Coast of India, site-specific relation and specific charge per delay was established through trial blast studies. Further, controlled blasting was carried out and the PPV values observed were compared with the predicted one. The empirical relation, established during trail blast studies is found to be non-conservative beyond 200 m and site-specific relation is modified with alternate scaling distance formulations. This predicted equation can be used for arriving specific charge per delay and for carrying out controlled blasting in similar geology.

N. Nitheesh, G. Padmanabhan, Sudipta Chattopadhyaya, B. P. C. Rao

Embedded Retention Wall Design Practices Consequences and Measures

Embedded retention walls generally comprise vertical structural members, namely diaphragm walls, secant or contiguous walls, sheet piles or Berlin walls. These structural members are sufficiently embedded into the ground to make excavation pits stable. The stability of embedded walls significantly depends on the passive resistance of the soil. Inappropriate choice and misinterpretation of design soil parameters make the retention system design more complex. Even though a normal retention system falls under “no exceptional risk category” [1], usage of the improper method of analysis makes the wall unstable. A majority of deep excavations are installed in densely populated areas and the consequences of failures are immeasurable. Hence, a practicing engineer must have commendable knowledge of the usage of design parameters and the method of analysis to prevent failures. This paper illustrates parametric study on the performance of the wall focusing on the method of analysis, the effect of the water table, over dig, surcharge, soil stiffness, wall flexibility, and drained and undrained behavior of soil.

Govind Raj, Madan Kumar Annam

Effect of Overburden Pressure and Soil Parameters on Tunnel-Induced Ground Settlement

With the continuous improvement of urban transportation systems, the requirement of the tunnel has increased day by day due to the scarcity of surface space and restricted movements. Mechanized excavation by tunnel boring machine is being extensively used in metro, railway and road tunnels due to comparatively less hazards and relatively faster excavation speed. Therefore, it is essential to have an innovative, cost-effective and safe design of tunnel with appropriate consideration of design methodology and site constraints like existing buildings and other structures. In the design of a tunnel, it is very important to have a proper estimation of ground settlement that is induced due to tunneling. The variation in ground settlement due to varying characteristics of subsurface deposits and tunnel depth, which cause variation of overburden pressure, needs to be addressed properly for tunnel design. Therefore, with this in view, a parametric study has been made for a 6.3 m diameter circular tunnel structure having different depths of 9.7 m, 10.6 m, 12.8 m and 13.6 m, encountering varying soil layers of clayey silt, sandy silt and silty sand. A set of numerical models have been developed to compare the results obtained from an analytical method as well as field data recorded at the project site. The results of the study reveal that ground settlement gradually decreases with an increase of overburden pressure, and thereby, the depth of the tunnel. It is observed that about 9–29% reduction in ground settlement value occurs when overburden pressure, as well as the depth of the tunnel, increases by 10–41%. Also, with the change of soil layer from silty sand to clayey silt, the ground settlement reduces significantly from 14% to 25%, even when the depth of the tunnel remains the same. The findings of the present study may be helpful to the researchers and practicing engineers in the design of tunnels under different subsoil conditions.

Chiranjib Sarkar, Sibapriya Mukherjee, N. Kumar Pitchumani

Seismic Analysis of Shallow Tunnels in Soil Medium

In both urban and national frameworks, tunnels form vital components of the transport and utility systems. They are being constructed in densely populated urban zones and metro cities at an expanding rate to promote rising space and passage requirements. Occurrence of any sort of seismic activity in that particular region may cause damage of these infrastructures. Hence, a careful consideration of the impacts of seismic loadings on the analysis and design of tunnels is required as a part of hazard evaluation. Different closed form analytical approaches exist, such as methods given by Wang and Penzien for seismic analysis of shallow tunnels. Ovaling deformations occur when seismic waves propagate perpendicular to the axis of tunnel and are therefore, designed for the transverse direction. In this paper, these two analytical solutions are used for the analysis of tunnel lining forces, constructed in soft to hard soil with various mechanical properties and constant shear strain. Seismic analysis was carried out by means of selecting eight unique types of soil, very soft clay to highly dense sand. The study indicates a relative error in both analytical methods. It was found that the variations in thrust and bending moment are dependent on the flexibility ratio, thus, it is proposed that the stress distribution is to be considered for analysis and design of tunnels’ lining. It is also seen that the induced circular stress in the tunnel liner is decreased with increasing soil stiffness.

Abdullah Ansari, K. S. Rao, A. K. Jain

Development of Rational Method of Design of Soil Nailing System in Granular Soil

Soil Nailing technique involves installation of driven or grouted nails (steel bars) spaced closely down the slope/excavation in stages to create an in-situ coherent gravity structure to increase the shear strength of soil and restrain its movement. Soil nailed wall in granular soils is likely to have rotation about toe and tend to behave as a reinforced earth wall after construction. Hence in the present paper, an attempt is made to design soil nailing system based on classical Rankine’s earth pressure theory (1857) coupling with coherent gravity analysis of reinforced earth wall design in selected granular soil possessing required minimum cohesion of 7 kN/m2 for adopting soil nailing technique. The design data generated for soil nailed wall is compared with the existing Gassler design method (1996). Soil nailed walls designed for soil retention in excavations of heights varying from 4.5 to 10 m are compared with the Gassler method-based designs. The proposed design methodology yielded L/H ratios of 0.75–1.1 for different heights of soil nail walls in contrast to the L/H ratios of 0.6–0.7 in Gassler's method.

M. Nagalakshmi, C. N. V. Satyanarayana Reddy

Numerical Analysis on Interaction of Single Pile Tunnel System

In past few years, the number of tunnels construction in several populous cities significantly increases for better infrastructure development. In many situations, tunnel alignment must be laid below the high rise buildings, bridges or important civil engineering structures. In such condition, the chances of possible damage to the foundations of these structures are very high. Hence, it is vital to study the tunnel-pile interaction behaviour for the safety and serviceability of the both tunnel and the foundation of the existing structures. In view of this series of numerical analysis are carried out on tunnel-pile interaction behaviour. It is observed that the maximum surface settlement takes place at the centre of tunnel and it decreases with horizontal distance from tunnel centre at Greenfield condition. In tunnel pile condition, different pile behaviour is observed for varying tunnel position with respect to pile. Maximum pile head settlement is found when tunnel is placed just beneath the pile toe position. Reduction in pile capacity is found to be 3.07% and 6.98% when tunnel is placed near the centre of pile length and near the pile toe consequently. This is because of maximum end bearing resistance reduced when tunnel was placed near the pile toe.

Arnab Choudhury, Awdhesh Kumar Choudhary
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