Rajagopal Karpurapu

• PhD
• Adjunct Professor at Andhra University

Basal reinforcement of embankments and supporting with piles is one of the most recent solutions for rapid embankment construction on soft foundation soils. This paper uses the Particle Image Velocimetry (PIV) to evaluate the performance of unreinforced and reinforced embankments over soft foundation soils in terms of maximum settlement at the emba...

This paper presents a study on the behavior of two-tiered Mechanically Stabilized Earth walls (MSEW) with varying offset distances under static and seismic loading. From the literature, it is observed that the interaction mechanism between the two tiers and the behavior of tiered retaining walls under static and seismic loading are not addressed ad...

Vertical drains are used widely to accelerate the consolidation of soft clay deposits when preloading is used as a ground improvement technique. One of the essential input parameters required in Barron's theory is the coefficient of horizontal consolidation, ch. The values of ch can be determined by the radial consolidation test, using either a cen...

The geotextile tubes find wide range of applications in coastal protection structures in the form of submerged breakwaters, artificial reefs and the core of sea walls and groins. These tubes are generally arranged in a stacked manner to achieve the required height as per the design requirements of the coastal protection structure. The upper geotext...

Vertical drains are extensively used along with the preloading technique as an effective ground improvement method for soft compressible soils. The installation of prefabricated vertical drains (PVD) in soft clay soils causes disturbance in the soil around them. This disturbed zone is called a smear zone. The smearing in the soil affects the permea...

Non-linear seismic deformation analyses of an earth embankment founded on liquefiable soil were performed using the FLAC 2D and PM4Sand as the constitutive model to simulate the seismic behaviour of loose sand foundation. PM4Sand model was calibrated to the cyclic behaviour of Nevada 120 sand. The untreated embankment-foundation system was subjecte...

The pressure distribution below geocell reinforced foundation beds depends on several factors like height of geocell, weld distance (pocket size), infill material, etc. This paper describes a method to determine the load dispersion mechanism through a geocell layer using a non-contact Digital Image Correlation technique. Series of plate load tests...

Reflective cracks are the major distress in Hot-Mix Asphalt (HMA) Overlays. Among the several mitigation methods adopted to reduce the reflective cracking, the application of geosynthetic layer between the old pavement and the new overlay is widely adopted due to the ease of application. The application of geosynthetics as interlayers reduces the t...

Geocells are three-dimensional cellular expandable mats used to improve the loadcarrying capacity of weak subgrades. The expanded geocell pockets take the shape of a honeycomb connected to their neighbouring pockets. This manuscript deals with the importance of considering the exact shape of the geocell pockets in three-dimensional numerical modell...

Vertical drains are often used to accelerate the consolidation settlement in soft clays subjected to preloading. Even though there are a variety of ground improvement techniques available, prefabricated vertical drains (PVD) in combination with preloading have become a popular method for soft soil problems as it provides an effective solution. Mari...

Geosynthetic encased granular columns are used to effectively stabilize marine soft clay deposits with low undrained shear strength. The present study focuses on assessing the behaviour of geosynthetic encased granular columns in very soft clays using two FE approaches namely 2D axisymmetric and 3D unit cell. The study compares the results obtained...

The use of geocells for support of foundations on weak subgrades has been gaining popularity in recent years. Detailed studies were performed in this work through laboratory tests and numerical simulations to investigate the influence of different parameters on the geocell supported foundations on soft subgrades. A series of large-scale laboratory...

Vertical drains are often used to accelerate the pre-consolidation settlements in soft clay soils. The coefficient of radial consolidation (Cr) is one of the important parameters that governs the rate of settlement. Several researchers have proposed different methods to estimate the coefficient of radial consolidation. This paper attempts to compar...

Granular columns are commonly used to support flexible structures over soft clay soils. The installation of such columns increases both the strength and stiffness of the ground. However, constructing these columns in clay soils having low cohesive strength of about 15 kPa is a challenge due to inadequate confinement. The columns may be encapsulated...

Railways are the primary mode of public transport around the world and play a pivoting role in the day-to-day transportation needs of commuters. Hence, an improved railway track infrastructure demands high-quality control. Excessive settlement in rail tracks is a common failure phenomenon incurring an extra maintenance cost. Installation of railway...

Shallow footings are the most preferred foundations for buildings due to low cost and ease of construction. However, under seismic loads, these foundations may suffer excessive settlements, particularly when there is a risk of soil liquefaction. This paper explores the effectiveness of granular columns in mitigating the liquefaction-induced ground...

This paper discusses the bearing capacity and settlement response of granular columns with and without geosynthetic encasement using the currently available design procedure. The design procedure is modified to include the influence of the geosynthetic encasement. The key parameters influencing the load bearing capacity and settlement are studied t...

A 2D finite element analysis was conducted to obtain the factor of safety against deep-seated failure of embankments resting on granular columns. Two methods, namely individual column method and equivalent area method, are used to compute the safety factor (FOS). The results of the parametric analysis with the prime factors that influence FOS say t...

One of the common distresses observed in asphalt concrete (AC) pavements under repeated vehicular and thermal loadings is cracking. Overlay placement is a quick remedy to rehabilitate these distressed surfaces. Unfortunately, this practice without treating the cracks will not resolve the cracking issue because the existing cracked surface soon prop...

Analysis of the pile driving is extremely important when the pile driving is met with premature refusal. The present study is aimed at analyzing the offshore driven pile met with refusal using the continuum method of numerical analysis.

This paper presents the results from 3-dimensional analysis of offshore driven pipe piles using FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) program. The numerical model was developed with solid elements for both the pile and the surrounding soil. Interfaces are created both on the inside and outside surfaces of the pipe pile along...

This paper addresses the use of geosynthetic encasement provided to granular columns for reducing the settlement of the treated ground. The settlement behaviour is analysed and discussed subsequently by considering the design of a full-scale field problem using the currently available design procedure. The influence of different parameters influenc...

In urban areas scarcity of land to build infrastructure has driven the geotechnical engineers to improve poor subsoil conditions through different techniques. Granular column treatment is one of the most promising ground improvement techniques widely practiced all over the world. This paper discusses briefly the status of research on this topic. Fo...

Reflective cracking is a major cause for premature deterioration of asphalt pavements. Different varieties of geosynthetics are used at the interfaces of surface layers to control the reflective cracks. The significant factors influencing their efficiency are the flexural strength and interfacial bonding. Fracture energy that leads to development o...

Geosynthetic products are routinely used to reinforce pavement overlays to control crack propagation under repeated vehicular and varying thermal loads. Many experimental methods are available to measure the potential of geosynthetic products in controlling reflective cracks. Among all methods, the four-point beam (4PB) fatigue test is commonly use...

The paper aims at comparing the deformation behaviour of unreinforced embankments, basal reinforced embankments and geosynthetic reinforced embankments with floating and end bearing piles. The floating piles were terminated within the soft foundation soil, while the end bearing piles transfer the loads to a hard stratum. Four series of centrifuge m...

In this paper, an attempt is made to analyse the dilative behaviour of dense sand at two different sizes of the direct shear box, i.e., small (60 mm × 60 mm ×30 mm) and large (305 mm × 305 mm × 140 mm). A three-dimensional numerical model is developed using the FLAC3D software to analyse the size effect on dilative behaviour of dense sand along the...

The application of geosynthetics between the cracked asphalt pavement layer and new asphalt layers to retard reflective cracking has gained interest in the past decades. The performance of the interlayer system depends on its capacity to bond between the old and newly laid overlay layers. This study is taken up to evaluate the interlayer bond stren...

Open-ended pipe piles are commonly used for the foundations of offshore jacket platforms, mooring piles, offshore wind turbines and, in general, for pile foundations like micro piles, etc. Driveability of open-ended piles is greatly affected by the formation of soil plug during the driving, particularly in sandy soils. In order to study the behavio...

Reflective cracking is a major phenomenon leading to premature failure of fresh asphalt overlays. Application of a geosynthetic interlayer system to retard reflective crack propagation is a well-known technique. However, this method often fails because of debonding or inadequate interaction between the asphalt and the geosynthetic. Major variables...

Even before the evolution of soil mechanics, the research on mitigating the problems induced by soft soils has started. The granular column is one of the promising ground improvement technique widely accepted as a solution to soft soil problems all over the world. Recently the performance of it is improved by encasing with geosynthetic products lik...

Reflective cracking is a major phenomenon leading to premature failure of fresh asphalt overlays. Application of a geosynthetic interlayer system to retard reflective crack propagation is a well-known technique. However, this method often fails because of debonding or inadequate interaction between the asphalt and the geosynthetic. Major variables...

Vertical drains are widely used to accelerate the consolidation of soft clay deposits when preloading is used as a ground-improvement technique. Barron's theory is generally used for the design of vertical drains. One of the important input parameters required in Barron's theory is the coefficient of horizontal consolidation, ch. A reliable estimat...

A systematic series of slope stability analyses were performed on embankments supported on soft clay soils treated with ordinary granular columns (OGC) and geosynthetic encased granular columns (EGC). The effect of various parameters such as the undrained shear strength of soft clay, friction angle of fill materials and aggregate in granular column...

This paper presents a simple, cost effective and reliable image processing technique for deformation measurement in geotextiles during wide width tensile strength tests. Localised strains are likely to be generated in the geotextiles due to production defects, seams and punctures. Accurate measurement of localised strains will help in better unders...

The Geosynthetic Reinforced Piled Embankment Systems provide cost economic solutions for the construction of high embankments even on very soft clay soils. They are fast to construct and enable the usage of marginal locally available soils to help in sustainable growth of infrastructure. These systems consist of cement concrete columns acting as pi...

The introduction of geosynthetics has drastically changed the manner of geotechnical practice. The challenges posed by the uncertainty of soil properties are easily overcome by the intelligent use of geosynthetics. The geosynthetics are applied practically in all areas of geotechnical engineering including the construction of steep slopes, retainin...

In urban areas scarcity of land to build infrastructure has driven the geotechnical engineers to improve poor subsoil conditions through different techniques. Granular column treatment is one of the most promising ground improvement techniques widely practiced all over the world. This paper discusses briefly the status of research on this topic. Fo...

In this paper an attempt is made to analyze the dilative behaviour of dense sand at two different sizes of the direct shear box, i.e. small (60 mm⨯60 mm⨯30 mm) and large (305 mm⨯305 mm⨯140 mm). A three-dimensional numerical model is developed using the FLAC 3D software to analyze the size effect on dilative behaviour of dense sand along the top and...

In urban areas scarcity of land to build infrastructure has driven the geotechnical engineers to improve poor subsoil conditions through different techniques. Granular column treatment is one of the most promising ground improvement techniques widely practiced all over the world. This paper discusses briefly the status of research on this topic. Fo...

Construction of embankments on soft soil or sludge is a challenging task due to the inferior strength of the foundation soil and excessively large total as well as differential settlements. If the embankment is constructed as part of an engineered landfi ll project, it becomes even more challenging because of the requirement of leak-proof lining sy...

Granular columns installed below the embankments are subjected to combined action of vertical and lateral loading depending on their location. The columns installed near the centerline of the embankments are primarily subjected to vertical loading while those near the toe are subjected to predominant lateral loading. In this paper analyses are carr...

Accurate measurement of various properties of geosynthetics is important for proper quality control and design procedure. Among all the mechanical properties, tensile strength of geosynthetics is one of the important parameter required for design purposes. Current testing procedures available in the laboratory are not capable of measuring the local...

This paper compares the results of laboratory studies carried out to determine the engineering properties, response under cyclic loading and the microstructure of soft clay after subjecting it to preloading by surcharge and vacuum. The samples for these tests were prepared at different initial consolidation pressures of 25, 50 and 100 kPa under K0...

Stone columns installed in very soft clay soil (cu<15 kPa) do not have sufficient lateral capacity to resist the large shear deformations near the toe of embankments, and can thus lead to deep seated failure of supported structure. In this paper a stone column supported embankment is modeled using FLAC3D to simulate the deep seated failure and to e...

This paper presents the experimental and numerical procedure for analyzing the shear load capacity of Geosynthetic Encased Stone Columns (GESC). Past studies have mainly focused to understand the vertical load capacity of GESC. However, these columns may also be subjected to significant amount of shear loading such as near the toe of high embankmen...

The main objective of the research project focuses on understanding the behaviour of granular columns subjected to lateral loading. To achieve the objective, experimental studies were carried out using the large direct shear box in which stone columns of two different diameters (50 mm and 100 mm) and three different configurations (single, triangul...

Asphalt pavements are layered structures designed to carry road traffic loads for a designed time period. The performance of this layered structure depends upon the bond interaction between the layers. Improper design due to the wrong interpretation of factors influencing the performance of pavements results in the development of distresses. The mo...

Vertical drains are extensively used to accelerate the consolidation of soft clay deposits when preloading is used as a ground improvement technique. Barron's theory is widely adopted for the design of vertical drains. One of the important input parameter required in Barron's theory is the coefficient of horizontal consolidation ch. The reliable es...

Reflective cracking is the phenomenon of propagation of cracks from an existing cracked pavement surface into and through the newly laid overlay due to the load or temperature induced stresses or both. The reflective cracking mechanism is a complex phenomenon due to the large number of parameters that influence the propagation of cracks. For this r...

Construction sites consisting of soft soils may require ground improvement to prevent excessive settlements or bearing capacity type failures and shear movements, which results in construction delays and premature failures. Among the various ground improvement techniques, the Geosynthetic Reinforced Piled Embankment Systems (GRPES) provide a practi...

Conventional finite element method (FEM) relies on deterministic values to represent structural and load parameters and it does not have the capability of considering random parameters in response evaluation of the structures. In the context of stochastic computational mechanics, uncertainty modeling using random finite element method (RFEM) has by...

The performance of unpaved and paved roads are improved with the inclusion of the geosynthetics. Many design procedures are developed to quantify the improvement and cost effectiveness. High cost of geosynthetics and unavailability of product makes the synthetic geotextile an overburden for the rural economy. The environmental impacts and disposal...

Granular columns are primarily designed to carry vertical loads. Depending on column length and support conditions granular columns undergo various types of failure under vertical load. Failure mechanisms of granular columns under vertical loading are reasonably well understood. The granular columns can be subjected to large lateral loads due to ho...

Pile foundations are used to account for huge vertical, uplift and lateral loads due to live loads, dead loads, earthquake, wind, impact, waves and lateral earth pressure etc. Uniform cross section piles are commonly used in the practice. Other best alternate, to cylindrical piles are tapered and stepped piles. Some researchers have studied the beh...

Pile foundations are used to account for huge vertical, uplift and lateral loads due to live loads, dead loads, earthquake, wind, impact, waves and lateral earth pressure etc. Uniform cross section piles are commonly used in the practice. Other best alternate, to cylindrical piles are tapered and stepped piles. Some researchers have studied the beh...

Geosynthetic reinforced piled embankment systems (GRPESs) have proven to be an effective and economical technique to address the problems posed during the construction of embankments on soft soils. In this paper, the predictions of the performance of GRPESs from three modeling approaches [axisymmetric, three-dimensional (3D) column, and full 3D mod...

Reflective cracking is one of the major distresses found in asphalt overlays. Bituminous materials are weak under tensile or shear loading. Due to repeated loading as well as due to varying climatic conditions, the cracks and joints in the existing pavements reflect to the overlay. The introduction of a rein-forcing materials which has better tensi...

The main objective of the research project described in this paper is to quantify the response of woven geotextile encased stone columns subjected to lateral loads. This objective is achieved using a set of large direct shear tests in which stone columns of two different diameters (50 mm and 100 mm) and two different configurations (triangular and...

Many of the pavement structures fail well before their design life owing to the poor quality of construction materials, inadequate compaction, inadequate preparation of the subgrade, overloading, etc. Two options are available to improve the longevity of the pavement. The first option is by increasing the thickness of different pavement layers and...

Preloading coupled with vertical drains is a successful ground improvement technique for soft clay deposits. Though surcharge in the form of sand pile is conventionally used, vacuum consolidation is also an option. This paper presents a case study on ground improvement using vacuum consolidation technique carried out near the shoreline in the city...

This paper studies the effect of the type of pile on the behaviour of basal reinforced pile supported embankments constructed on soft clay. The performance of embankment supported on both end bearing piles and floating piles was studied. 3D column models were used for carrying out the parametric studies to examine the development of arching mechani...

In the recent years, the geosynthetics have been used in combination with columnar systems to support embankments over soft soils. The application of the geosynthetics in the embankment fill above the columns enhances the load transfer from the soil to columns, reduces the total and differential settlements and also found to be economical. This pap...

The use of stone columns is one of the proven ground improvement techniques for improving the load carrying capacity of soft clay deposits. When the stone columns are installed in soft clays, there is a possibility of intrusion of fine clay particles into the column which reduces the shear strength of the stones resulting in reduction in capacity....

Laboratory model tests in geotechnical engineering are routinely performed in small concrete or steel test tanks to examine the bearing capacity of footings, lateral earth pressures on retaining walls, behavior of reinforced foundation soils, and more. Results from these model tests are influenced by the shear forces generated on the sidewalls. The...

This paper examines the influence of rock socket lengths on the lateral response of piles embedded in homogeneous sandy soil overlying rock. A 3-D finite element based numerical analysis has been used to investigate the performance of piles due to socketing into the rock. Parametric studies have been carried out for understanding the behaviour of p...

Many of the pavement structures fail well before their design life owing to the poor quality of construction materials, inadequate compaction, inadequate preparation of the subgrade, overloading etc. Two options are considered during the design of a pavement structure in order to improve the longevity of the pavement. The first option is by increas...

Stone columns are often considered as an excellent ground improvement technique adopted to improve the load carrying capacity and reduces the settlement characteristics. However the load carrying capacity mainly depends on the undrained shear strength of surrounding soils. Reinforcement in the form of encasement is usually provided around the stone...

Construction of infrastructure facilities in coastal areas is quite challenging due to the problems posed by the low bearing capacity and high compressibility of the foundation soils in those areas. Several researches have shown that Geosynthetic Reinforced Piled Embankment Systems (GRPES) is an attractive solution for such problems. In this paper,...

The geosynthetics reinforced soil retaining walls are popular in most road and railway projects. When the height of these walls exceed a certain limit, it is preferable to use multiple tiers to achieve economy and good aesthetics. This paper discusses the details of the analysis and construction of two retaining walls of height up to 44 m in 4-tier...

The influence of initial conditions, i.e. stress state and void ratio, on the liquefaction resistance of silty sands under two-way cyclic loading is investigated in this paper. Using a cyclic triaxial test device, a series of undrained stress-controlled cyclic triaxial tests was performed on reconstituted specimens of sand and sand mixed with 15, 3...

This paper presents the reliability analysis of reinforced retaining wall using finite element method. Response surface approach is used to approximate the performance function and a first-order reliability method (FORM) is used to evaluate the reliability index. In the analysis, displacement response of the reinforced retaining wall is considered...

A recent technique of pile installation of pre-cast piles without noise or vibration is the use of pile jetting. Water jets at high pressures are used to drive the piles that temporarily liquefy the soil thus allowing the pile to penetrate into the ground under their self-weight. This technique is utilized under conditions where control of construc...

To study the effect of non-plastic fines on liquefaction resistance of Gujarat sand, the cyclic triaxial tests have been carried out on sand-silt mixtures with fines content varying from 0 to 50%. The specimens were prepared by moist tamping under compaction procedure at different relative densities. Stress controlled, undrained tests have been per...

The stone columns (or granular piles) are increasingly being used as ground reinforcement elements for supporting a wide variety of structures including buildings and flexible structures. The stone columns derive their load capacity from the confinement offered by the surrounding soil. In very soft soils this lateral confinement may not be adequate...

Geosynthetic reinforcement is often adopted in steep sloped embankments to reduce the land take. The behaviour of traffic supporting steep sloped reinforced soil embankments subjected to repeated loading were investigated through non linear finite element analysis. Application of locally available low friction fill soil is explored. Attempt was mad...

This paper presents the finite-element simulations of the behavior of strip footings resting on sand beds, with different density of soil, reinforced with geocells of different dimensions. The strength and stiffness of sand confined with geocells is represented by an equivalent composite model developed from triaxial compression tests. The addition...

Geosynthetics are polymeric materials subjected to creep. Creep is an important factor. Studies on creep are few as they are expensive and time consuming. Hence, extrapolation for the design life becomes a necessity. This is achieved by modeling the behavior by means of chain models and superposition techniques. The current study utilizes the True...

One common approach for treatment of soft clay soils is the installation of stone columns. The load capacity of the stone columns depends very much on the shear strength of the surrounding soft clay soil. The stone columns help in both reduction of settlements and accelerated pre-consolidation of clay soil deposit. However, in case of extremely sof...

The use of stone columns (otherwise called granular piles) has proved to be an economical and technically viable ground improvement technique for construction on soft clay soils. Though the stone columns are designed to carry vertical compressive loads, soil movements occurring in the field conditions may cause shear deformations in the stone colum...

This paper presents an equivalent continuum method for simulating the behaviour of geocell reinforced sand foundation beds, using finite element technique. An equivalent composite model is used for numerically simulating the improvement in the strength and stiffness of sand confined with geocells. Shear strength of geocell encased sand is derived f...

The traditional factor of safety does not account for the variability and uncertainty of the different parameters considered in the analysis. On the other hand, the reliability approach considers the possible variations in the design parameters and gives more realistic estimates of the safety of the structure and the possible risk of failure. In th...

Synopsis: The burgeoning demand for raw materials in road infrastructure development projects in India can be minimized by use of innovative techniques based on new developments in geosynthetics. New generation 3D cellular confinement systems (geocells) offer improved structural reinforcement for road construction that not only reduce pavement thic...

Pile foundations are often subjected to combined vertical and lateral loads. The current design practices assume that the effect of these two loads is independent of each other. Hence, the pile design is carried out separately for vertical and lateral loads. The laboratory and field test data on the lateral response of piles under the combined acti...

The degradation of strength and stiffness of clayey soil under cyclic loading conditions is of serious concern in geotechnical engineering. This degradation behaviour depends on the initial properties and the loading conditions imposed on the soil. An attempt has been made in this paper to model the response of soil under cyclic loading using the c...

Pile foundations are often subjected to both vertical and lateral loads. The current design practices assume that the effect of these two loads is independent of each other and hence the pile design is carried out separately for vertical and lateral loads. The conventional methods for analysis of piles based on sub-grade reaction methods also do no...