Ground Improvement Techniques and Geosynthetics

Geopolymer soil column is one of the advancements in Ground improvement techniques. The study is aimed at the comparison of Geopolymer soil column and untreated sand in the load carrying capacity and settlement behavior of footing resting on loose sand. The effects of Geopolymer soil column and untreated sand are investigated by conducting experimental studies. The parameters involved in this study include soil column spacings and curing periods. A load test was carried out on a model footing resting on sand with Geopolymer soil column and untreated sand. Load test is repeated on the footing with Geopolymer soil column at varying curing periods of 7, 14, and 28 days. The load-settlement curve for different curing periods day were compared. It was observed that the Geopolymer soil column has high bearing capacity improvement factor compared to untreated sand. Settlement also considerably reduced while using Geopolymer soil column. A parametric study has been carried out to compare the settlement of Geopolymer soil column and untreated sand by finite element modelling using PLAXIS 2D Software and the results are agreeable with the experimental results.

Micropiles support loads individually, as group or as a network. In cases of groups and networks, the micropiles and the surrounding soil will form a composite block to resist the applied loads. This may lead to a group capacity or network capacity that is different from the total capacity of individual piles consisting of the group or network. The group effect of piles in granular soil has been studied by many researchers, the results of which so far have been inconsistent. Therefore, it is difficult in practice to compare the performance of micropile groups from one test program with other, without considering all the factors together. This work consists of a model experimental study of group behaviour in sand. In this paper three important parameters, namely length-to-diameter ratio (L/D), spacing of piles and relative density of sand were considered. For this purpose 12 micropile groups with each group arranged in a square grid of four piles, with centre-to-centre spacing of 2D, 4D, and 6D and with L/D ratio of 20, 35, 50, and 65 were installed in sand bed having relative density of 50%. The group effect of ultimate total resistance on contractive (loose) sand was studied by installing the same number of micropile groups in sand having relative density of 30%. Similarly the group effect on dilative (dense) sand was studied by installing another twelve groups in sand having a relative density of 80%. The model micropile groups were subjected to axial compressive loading. The group efficiency came out to be high at 4D spacing for the entire different L/D ratio for the loose and the medium dense sand. Positive group effect was observed in most cases but in case of micropile group in 80% relative density, mostly negative group effect was observed. Most importantly the group efficiency was found to be a function of L/D ratio, spacing of the micropile groups and relative density of sand.

Natural soil samples were treated and cured with lime, enzyme and enzymatic lime. The cured samples were subjected to various laboratory tests. The optimum dosages were calculated based on the results of Unconfined Compressive Strength Tests. Later samples were mixed with optimum dosages and compacted in Proctor moulds and were subjected to CBR tests at different stages of curing. Significant improvement was observed in enzymatic lime stabilized soils over lime stabilized and enzyme stabilized soils. CBR tests were also done by varying the percentage of clay in the soil specimens. In all tests enzymatic lime stabilized soils exhibited superior improvement of properties.

Soft clay consolidation is an important aspect to be considered for large construction projects undertaken in or near coastal areas. Pre-fabricated Vertical Drain or PVD has gained considerable importance in accelerating soft clay consolidation for major civil engineering construction projects worldwide, as it is economical with proven efficiency. However, there is still some confusion and uncertainty in selecting the right type of PVD for a particular project as well as the design procedure to be adopted. As a result, specification for PVD in many cases are made without considering many factors which may influence the performance of such drains for a project. This paper considers the PVD design theory and evaluates various parameters which influence PVD performance such as soil, soil disturbance due to installation, PVD materials, etc., and recommends a procedure for PVD design and selection of PVD and installation method for a project.

Heaving of expansive soil is a crucial phenomenon due to their excessive volume changes with variation in moisture regime, which in turn leads to substantial distress to the structures built on them. The main objective of this study is to evaluate the effectiveness of micropile and performance of geotextile to resists upward movement of structures built over expansive soil. For this study, the expansive clay compacted in a steel box of size 50 cm × 50 cm × 50 cm to a depth of 20 cm and analyzed with two different methods to control heaving of soil. Firstly, four micropiles of 16 and 20 mm in diameter were inserted into the soil with and without frictional resistance. The micropiles were fastened to the corners of footing of size 15 cm × 15 cm × 0.5 cm, with nut and bolt system. Further, Geotextiles were reinforced below the footing at a vertical spacing of 0.1B and 0.3B as single and double layers. Then the soil was saturated with water and the upward movement of model footings (swelling) was monitored with time. Test results showed that maximum heave reduction was 79% for 20 mm diameter micropiles with frictional resistance.

Underground voids may develop due to natural causes and due to human activity. The presence of underground void can cause severe instability to foundation and damages to the structure. In this paper the effect of an underground void on the load-settlement behaviour of a strip footing is investigated by carrying out a series of laboratory scale load tests. The parameters varied for the study are depth of void below the footing and eccentricity of void from the centre of footing. It is observed that the effect of void is considerable only when it is within a critical depth and eccentricity. The results of loading tests are compared with those obtained from finite element analyses for validation. The addition of Foundation bed and Reinforced foundation bed improves the load-settlement behaviour of the soil with void. It is observed from the results of finite element analyses that the presence of underground void can cause stress concentration inside the soil mass which leads to failure. The stress concentration factor around the void on the side nearer to loading is more than that on the farther side. Also with increase in depth parameter the stress concentration factor goes on decreasing. The distribution of internal stress and location of stress concentration depends upon the relative positions of the footing and void.

This paper investigates the influence of properties of infill material on the load-settlement behaviour of geocell mattresses by carrying out a series of laboratory scale-load tests on a model strip footing resting on clay reinforced with confined geocells. The parameters varied include aspect ratio of the aperture of geocell, infill materials and relative density of the infill material. The infill materials used in this study are sand, 6 mm aggregates and 12 mm aggregates. The experimental results are compared with the results obtained from Finite Element Analyses carried out using the software Plaxis 2D. It is observed that the load-settlement behaviour is considerably influenced by the properties of infill material. An increase in grain size of the infill material considerably improved the load-settlement response of the geocell. However an increase in the aspect ratio of the aperture of the geocell caused a reduction in bearing capacity. It is also observed that an infill material of sand, compacted to a relative density of 88% gives better improvement than 6 mm aggregate.

An experimental study was carried out to investigate the application suitability of randomly distributed glass fiber-reinforced cohesive soil as subgrade material. Glass fiber of 20 mm length with varying fiber contents (fc = 0.25, 0.5, 0.75 and 1% by dry weight of soil) was used as reinforcement. The effects of fiber content variation on compaction parameters of soil, and the effect of fiber content and soaking time variation on CBR strength were investigated. The soaking time was varied from 4 to 40 days. The CBR and secant modulus were calculated at different penetration depths ranging from 2.54 to 12.7 mm. Test results have shown that the glass fiber content has insignificant effect on the OMC and MDD of the soil. The CBR strength is found to increase with penetration depth up to 7.62 mm penetration and thereafter remains almost constant at all fiber contents. The CBR strength and secant modulus of soil have improved significantly with fiber content up to an optimum fiber content value of 0.75%, and decrease with increase in soaking time at any fiber content. The maximum improvement in CBR strength is found out as 2.48, 2, and 1.5 times for 4, 20, and 40 days soaking for 0.75% fiber inclusion. It has been found that the glass fiber-reinforced soil can be extensively used as subgrade material.

Experiments were conducted on model strip footings resting on clay soil reinforced with horizontal layers of strip reinforcement with and without end plate anchors. Load and corresponding settlements were measured and results presented in the form of pressure–settlement curves. Model strip footing was a rigid steel plate while galvanized iron sheet strips of 1 mm thickness were used as reinforcement with 16% coverage. Anchor plates were attached on either side of strip reinforcement. Tests were conducted for three arrangements of reinforcement, i.e., length increasing with depth, constant length, and length decreasing with depth. Bearing capacity increased by 38 and 370% respectively compared to unreinforced soil for without and with anchor conditions. Maximum increase was observed for the case of constant length of reinforcement. Provision of end anchors increases the bearing capacity significantly and permits use of shorter reinforcement with low coverage ratio.

The challenges to develop or strengthen the weak soil always prompted the need for further research investigation to develop a new, eco-friendly, and sustainable method of ground improvement. The MICP (microbially induced carbonate precipitation) technique is one such method in which metabolic pathways of microorganism are utilized to form calcite precipitation inside the soil matrix leading to improve the engineering properties of soil. Ureolysis or urea hydrolysis is the most efficient process among all MICP methods of carbonate generating reaction, as it has the potential to produce large amount of calcite (CaCO3) within a short period of time. This study aims to investigate the effectiveness of MICP technique on fine grained soil as clayey sandy silt or loam in improving its shear strength. In this study, three species of urease positive, alkaliphelic aerobic bacteria, namely Sporosarcina pasteurii, Bacillus megatarium, and Morganella morgani were used for ureolysis and microbially induced calcite precipitation. Quantitative analysis of calcite precipitation in the soil samples was done by Piper method. The target soil was mixed with each microorganism individually before it was compacted into the mould. In the experimental programm, four different treatment conditions were considered for each types of microorganism such as (1) untreated, (2) treated with cementation reagent (mixture of 0.5 M CaCl2 and 0.5 M urea), (3) treated with bacteria only and (4) treated with both bacteria and cementation reagent. These experiments revealed that all these three types of microorganism can induce sufficient amount of calcite precipitation that can result in measurable improvement of the strength of soil.

The engineering behavior of soil is affected by the presence of organic content in the soil. Previous studies have shown that organic content in clay is a key factor which affects the index properties, unconfined compressive strength and compaction behavior. Fly ash stabilization of clay is a commonly used stabilization method in pavement construction. Presence of organic content affects the stabilization of clay using fly ash, because organic content influences the pH of clay and hence the pozzolanic reaction is also affected. Kaolinite clay with different organic content (9–5%) is stabilized using Class C fly ash. The variation in index properties, unconfined compressive strength and compaction behavior of clay with different organic contents which is stabilized with fly ash is presented. Optimum fly ash requirement is also affected by the presence of organic content in clay. The optimum fly ash content for stabilization of kaolinite with different organic content is also presented in this paper.

Fly ash and sand, both the materials have been added in the percentages of 10, 20, 30, 40, 50 and 60% with the clayey-silt soil by dry weight. Modified Proctor compaction was chosen for the California bearing ratio (CBR) tests and applied to soil-fly ash and soil–sand mixes. Un-soaked and soaked CBR of the soil are found as 54.50 and 3.90% respectively under modified Proctor compaction. Both fly ash and sand improved the CBR of the clayey-silt soil but addition of sand show the better result under both un-soaked and soaked conditions. However, the addition of 40% sand to the soil shows the maximum un-soaked CBR value as 70.07%. An addition of fly ash decreases the unconfined compressive strength (UCS) of the clayey-silt soil and increases in UCS observed at 40 and 20% addition of sand to the soil at standard and modified Proctor compaction respectively. The addition of both fly ash and sand to the soil increase the shear strength of the clayey-silt soil at standard Proctor compaction. Depending on availability of the material either fly ash or sand, it can be said that strength of the weaker clayey-silt soil can be improved using any of the additives.

The main objective of this investigation is to present the variations in index and engineering properties of expansive soil such as liquid limit, plastic limit, compaction characteristics, CBR and shear strength parameters when it is mixed with different percentages of Quarry dust (0, 5 and 10%) and Ferric chloride by dry weight of soil. Quarry dust has been chosen, as it is problematic to the environment and public due to its improper disposal. Quarry dust exhibits high shear strength, good permeability which is highly beneficial for its use as a geotechnical material. Ferric Chloride can be used because of its capability to easily exchange cations and ready dissolvability in water. Initially, expansive soil is mixed with different percentages of Quarry dust and Optimum percentage of Quarry dust were determined on the basis of Compaction and CBR tests. From the test results, it is observed that up to the addition of 5% of Quarry dust there is an increase in strength parameters such as Maximum Dry Density and California Bearing Ratio beyond that it is not effective. This investigation is further carried out by mixing Ferric chloride varying from 0 to 2% with an increment of 0.5% to the Quarry dust treated expansive soil (at its optimum 5%) and same series of experiments were conducted. From the results, it is observed that at optimum percentages, i.e. 5% Quarry dust and 1% ferric chloride, there is a marked improvement in the strength characteristics of soil.

Stabilization of problematic soils using waste materials is a solution to waste disposal and can be cost-effective as well as sustainable. English Indian Clays Ltd, one of the largest clay producers, generates huge amount of waste sand during Kaolin processing and poses the problem of disposal of this waste. Hence a study is conducted on the feasibility of utilizing this waste material in improving the properties of soil in conjunction with lime. The study involved experimental investigations to characterize subgrade soil (highly compressible silty soil found in Changanaserry, Kerala) and waste sand. An effort was made to study the effect of waste sand, individually and combined, on compaction behavior, Atterberg limits, California Bearing Ratio and Unconfined Compressive Strength of soil, so as to assess its usefulness for modifying the soil. Waste sand of varying proportions was used to replace soil. It was found that the properties of subgrade improved considerably on replacing soil with waste sand. For the optimum soil–waste sand mixture, further improvement in its strength was attained by treating it with lime. The results showed a marked improvement in the strength of the mix on treating with lime and with increase in curing period.

Vegetation has been used globally for centuries to control soil erosion on slopes. It is widely recognized that vegetation contributes to slope stability, but to an unquantifiable degree. Vetiver grass (Chrysopogon zizanioides) is being utilized to reduce the soil erosion and strengthen the slopes. Vetiver roots are massive, fine-structured, and grow fast and deep. With an average tensile strength of 85 MPa, which approximates to one-sixth of that of mild steel, Vetiver root is compared to as ‘living soil nail’. Roots of trees and other vegetation increase the shear strength of soil by root reinforcement. The difference between shear strength values of root-permeated soil and root-free soil sheared under the same conditions gives the shear strength increase caused by the roots. This paper presents the investigation on increase in shear strength of soil by Vetiver roots. Using a custom made large-scale in situ direct shear test apparatus, in situ direct shear tests were conducted at different depths on a soil plot with one-year-old Vetiver grass planted at 0.15 m spacing in an equilateral triangular pattern. The tests prove that the Vetiver grass roots increase the shear strength of soil by up to 139% at 0.15 m depth and up to 47% at 0.75 m depth.

This paper discusses the use and efficacy of rice husk ash (RHA) as a stabilizing additive to problematic expansive soils. RHA is an agricultural industrial waste. It is abundantly available and therefore needs to be effectively disposed. The paper presents experimental results obtained from tests conducted on RHA-clay blends. Liquid limit, plasticity index, free swell index (FSI), compaction characteristics, strength parameters, and CBR were determined on the expansive clay specimen to which RHA was added in different quantities such as 5, 10, 15, 20… 50% by dry weight of the soil. Test results indicated that FSI and PI decreased with increasing RHA content. Further, CBR and angle of internal friction increase while cohesion decrease.

Use of stone columns for ground improvement in clayey soil is a common practice. Due to the high cost and scarcity of stone in some areas, jhama (over burnt brickbats) are being used as an alternative to stones. It is intended in the present study to compare the load carrying capacity of stone columns with that of jhama columns through laboratory tests and to conclude whether the jhama columns can be an alternative to stone columns. Model tests were carried out on 50 mm diameter and 400 mm long columns embedded in soft clay in a tank of size 1 m × 1 m × 1 m. The load-settlement plots were studied to observe the difference in behaviour of a stone column and a jhama column in terms of bearing capacity and mode of failure. A numerical analysis using Plaxis-2D was also carried out to observe the load-settlement behavior of all the models. A good agreement of experimental and analytical results was observed.

Layout and configuration of reinforcement play a vital role in improvement of geosynthetic reinforced foundation soil. In the present study, laboratory performance of square footing resting on geosynthetic reinforced sand bed of given density is analyzed. The configuration of the reinforcement is altered by varying parameters such as number of reinforcing layers and vertical spacing of reinforcement. The concept of pressure bulb is used while designing the layout of reinforcement. By this method, breadth of the reinforcement varies with depth corresponding to the breadth of pressure bulb at the particular depth. The effect of breadth of reinforcement is compared in every case by providing uniform breadth of reinforcement. Aluminum angles are used as anchors in the reinforcement. Presence of anchors improves the foundation soil by the development of passive resistance. The rate of improvement is studied by varying the position and height of anchors. It is observed that, reinforcement increases the bearing capacity and reduces the settlement at a particular load. Providing reinforcement breadth with respect to pressure bulb gives comparable results with the reinforcement of uniform breadth. The influence of breadth of reinforcement is more pronounced in case of single layer of reinforcement. The improvement in bearing capacity is about 2.8 times with the inclusion of reinforcement and about 3.9 times with the inclusion of anchors. By the inclusion of anchors at various positions, a layer of reinforcement can be reduced.

Geosynthetic encapsulated granular trenches (EGT) have found to improve the load carrying capacity of strip footings situated on weak soil under monotonic load. Granular trench is a two-dimensional plane strain variant of stone column. The EGT is formed by wrapping a geosynthetic around the granular trench. In the investigation reported herein, repeated load behaviour of EGT supported strip footings situated on earth embankments was studied. Repeated load tests were carried out on model strip footings resting on granular trenches with and without encapsulation. A cyclic hydraulic actuator with control and data acquisition facilities was used. River sand was used to prepare the embankment and 6 mm aggregate was used as the fill for the trench. Geogrid reinforcement was used for encapsulation. Non linear finite element simulations were carried out to arrive at the optimum dimensions of the EGT under monotonic loading. The optimum dimension thus obtained was used for repeated load studies. Influence of magnitude and frequency of repeated loading were investigated through experiments. Details of test setup, experimental programme, observations and results are discussed in the paper. It was found that the EGT system effectively improves the bearing capacity of footings situated on earth embankments under repeated loading.

The quantification of the kinetics of short-term clay–lime interactions is a key step for optimizing the parameters during lime stabilization of fine-grained soils, and also for predicting the long-term performance of lime treated soil matrix. The existing scientific literatures often believed that monitoring of consistency limits as well as compaction characteristics of lime treated soils yield significant amount of information regarding their physico-mechanical behaviour. However, apparently limited extent of works has been carried out to assess the role of clay mineralogy and pore fluid chemistry on inherent variations in plasticity and compaction characteristics. Further, no definite single conclusion could be drawn from the previous studies conducted to comprehend the plausible mechanisms of stabilization occurring in the lime treated soils during short-term and long-term interaction periods.In order to enhance the current understanding, this study primarily focused on the critical evaluation of plasticity properties and compaction characteristics variations of lime treated soils with respect to change in pore fluid chemistry (such as pH and concentration of lime). The study employed soils with quite diverse physico-chemical and mineralogical compositions so as to highlight the role played by the clay mineralogy in governing the extent of short-term improvement that can be mobilized by lime treatment. Based on the significant observations gathered from experimental works, attempts have been made to elucidate the possible short-term mechanisms of lime stabilization which also contribute to long-term strength and durability of lime treated soil.

This paper presents the instrumentation and back analyses conducted to assess the field performance of ground improvement works in one of the port development projects along Mumbai coast. Ground improvement using Prefabricated Vertical Drains (PVD) with Preloading in excess of 90 ha reclamation of land was carried out to improve the soft estuarine deposit below the seabed. The marine clay along the Mumbai coastline was found to be very soft with undrained shear strength less than 5–7 kPa at the top of the mud. Extensive geotechnical campaigns were carried out to comprehend the variations in the geotechnical properties of the clays. The PVD design was conducted based on various design parameters derived from the investigation data. As the coefficient of horizontal consolidation (ch) values were found to be crucial in the estimation of rate of consolidation over time, various radial consolidation and cone dissipation tests were carried out. The ch values from these tests were observed to be in the range of 1.8–5.2 m2/yr, which yielded the design value of around 3 m2/yr. Extensive instrumentation and monitoring were conducted using multilevel magnetic extensometers, settlement gauges and piezometers to back calculate the field ch values. The back calculated field ch values were in the range of 3.7–4.7 m2/yr with smear diameter ratio of 2.5 and smear permeability ratio around 3–4. The back analyses helped to apply suitable corrections in the design parameters in the field, thereby accounting for the parametric variations in the field and also effectively mitigating the geotechnical risks.

This paper deals with the discharge and absorption capacity tests conducted in the laboratory on newly developed and fabricated four different types of prefabricated vertical drains (PVDs) made from combination of both natural and polymer geotextiles, commercially available polymer-based PVD and natural PVD. The newly developed PVDs are made from single-layer nonwoven polyester sheath as filter wrapped around a core of coir ropes or coir mats and single-layer nonwoven jute sheath as filter wrapped around a core of cardboard or corrugated polyester, designated as composite prefabricated vertical drains (PC–PVD, PN–PVD, JC–PVD, and JP–PVD). The natural PVD is made from single-layer nonwoven jute wrapped around a core of coir ropes. The rubber membrane-confined short term discharge capacity tests were conducted at different compressive stresses and hydraulic gradients. The test results of the composite PVDs are compared and discussed, with the results from polymer-based PVD and natural PVD.

Clay soils inherit certain problems due to its properties such as plasticity, volume change, low strength, etc. To overcome these problems an attempt has been made in the present study to determine the utility of organic waste in stabilization of clay which has been obtained from Sunnam Cheruvu area of Nadergul, Hyderabad. Organic wastes have been considered due to their economical and environmental advantage. Ash of sugarcane pulp, wood, and coconut shell have been considered to investigate their potential in stabilizing the clay soil in pursuit of obtaining a cheaper and effective stabilizer. Laboratory experimentation was done to evaluate the differential free swell and unconfined compressive strength (UCC) for various percentages of ash contents. Curing of stabilized soil samples for 7 and 28 days were considered. Stabilization also required addition of lime to control swell. The results show that the swell and strength properties of samples were improved with the addition of various ash contents and also with curing period. Therefore it is concluded that sugar cane pulp ash, wood ash and coconut shell ash have a good potential in improving the properties of clay soil.

In this paper an experimental investigation was conducted to study the effects of lime and plastic fiber on split-tensile strength and toughness properties of a soft soil. The specimens were prepared and tested at three different percentages of lime (i.e. 3, 5 and 9% by weight of the dry soil) and four different percentages of fiber content (i.e., 0.5, 1, 1.5, and 2% by weight of the dry soil). It was found that lime content, curing duration and fiber content has a significant influence on the split-tensile strength and toughness of the lime-stabilized-fiber-reinforced soil. The test results indicated that lime amendment enhanced the split-tensile strength up to 5% of lime beyond that it shows an adverse effect. Moreover, the inclusion of discrete plastic fiber with lime-stabilized soil further enhanced the spilt-tensile strength and toughness of the treated soil. This improvement is up to 1.5% of fiber beyond that effectiveness of the reinforcement reduced. Therefore, 5% lime with the inclusion of 1.5% plastic fiber is the optimum combination to improve the soft soil. With this combination of lime and fiber at 28 days curing, the split-tensile strength shows an increase of 20 times compared to parent soil. This improvement of the treated soil enhanced the pavement life and stability of the other geotechnical structures.

Stability of anchored geosynthetics in landfill covers and liners depends on the efficiency of anchorage of reinforcement at berms and top of landfills. Pull-out tests can give an insight into the anchorage behaviour of geosynthetics. A review of literature for horizontal and inclined pull-out apparatus has been done and reported in this paper. A large number of pull-out apparatus have been developed for horizontally embedded geosynthetics. However none of these are suitable for the study of geosynthetics embedded in anchor trenches. For inclined pull-out apparatus, only two studies have been reported so far. Both the apparatus facilitate modelling of anchor trenches, but both of them had limitations. From the comparative study, it is concluded that there is a need to develop a universal pull-out system for study of behaviour of geosynthetics embedded in anchor trenches. An optimal solution could be obtained from a hybrid design of the two inclined pull-out apparatus and ASTM recommendations.

Flexible pavement system laid on the expansive soil subgrades show signs of continuous distress in the form of cracking, unevenness, rutting, etc., during its service period. Extensive laboratory, model, and field studies have been carried out by various researchers have shown promising results with the utilization of industrial by-products, i.e., quarry dust, rice husk ash, blast furnace slag, flyash, etc., for the stabilization of expansive subgrade. These materials offer two folded advantage of effective utilization and solution for their safe disposal. In this present work, an attempt has been made to study the efficacy of flyash in stabilizing the expansive soil subgrade. Laboratory experimentation was conducted for finding the optimum content of flyash required for treating the expansive soil. Model flexible pavement systems are prepared in circular tanks with different untreated and flyash treated subgrade layers. Tests are conducted to study their cyclic load responses. The experimental results show that model flexible pavement with 10% flyash treated subgrade is showing low heaving and low settlement to the applied cyclic loading. The coefficient of elastic uniform compression, representing variation of elastic rebound of the model pavements is assessed for model pavements.

Expansive soils, such as black cotton soils, are a worldwide problem. Construction on this soil has been drawing the attention of practicing engineers and researchers for many years. With changes in moisture regime, expansive soils are subjected to erratic changes in volume. In monsoon, predominantly they take up water and swell but in summer, they tend to shrink on evaporation of water, thus posing the problem of alternate cycles of swelling and shrinkage. This behavior of expansive soils is attributed to the presence of mineral-montmorillonite, which has an expanding lattice. Many researches, all over the world, are working to evolve more effective and practical treatment methods, to mitigate the problems posed to the construction of pavements on expansive soil sub grade. Stabilization is one of the effective methods adopted to improve the characteristics of expansive soils. Of late, good stabilizing agents like lime, cement and metakaolin are employed extensively in soil stabilization for building foundations or pavement sub-grades. Keeping in view the research findings outlined above, in the present work, experimentation was carried out to investigate the efficacy of different additives, Viz., Lime, Metakaolin and Lime + Metakaolin combination, in stabilizing the expansive soil sub grade, thereby, improving the strength and reducing swelling potential of stabilized soil.

Soil strata is highly varying in nature and it is a challenging task for Geotechnical engineers to come up with the most suitable foundation system that is safe during static and dynamic loadings. In this paper, a case study on ground improvement using sand columns at Puri in Odisha is discussed. The strata at site comprised mostly fine sands of low SPT-N values with some intermittent clay seams at intermediate depths. The water table was also encountered at very shallow depths at the location. The geotechnical profile of the boreholes was analyzed on the guidelines of Seeds and Idris and it was observed that the liquefaction potential of the soil layers is prominent and ground improvement is inevitable up to a depth of 10.5 m below existing ground level in view of stability of structures. The selective methods like vibro compaction, dynamic compaction were considered to be the suitable methods for the ground improvement. However, as the liquefiable layer is 10–11 m deep from ground level, provision of sand column is found to be the best alternative to reach those depths. In this method, the natural sand is densified with displacement method so that the relative density of the sand will be enhanced to avert the liquefaction risk. It was proposed to use Raft foundation with supporting ground improvement. Field tests such as sand column test, Pre and post DPTs, SPTs tests were carried out at site for assessing the extent of improvement and the results for the same are briefed in this paper.

Expansive soils lack the required engineering properties for use in pavement subgrades, and as a foundation supporting layer under buildings. In the present study red mud, a byproduct of bauxite industry is stabilized with lime and in turn is used to stabilize the expansive soil. Compaction studies and unconfined compressive strength studies were conducted in order to see the efficacy of these materials in improving the strength of the soil. Red mud is stabilized with 4% lime and lime-stabilized red mud is added to the expansive soil in different percentages varying from 10 to 50% in increments of 10%. Tests are also conducted on soils stabilized with lime-stabilized red mud and flyash, adding them in equal quantities along with 4% lime. The results show that red mud as well as red mud–flyash improves the geotechnical properties of the soil.

Two different laboratory tests, i.e., California bearing ratio (CBR) and permeability have been conducted on fly ash both in unreinforced and reinforced with nonwoven geotextiles. CBR test is conducted on fly ash and the values are 11.23 and 16.27% at 2.5 and 5 mm respectively. After reinforcement provided in three different layers, i.e., two layers in middle with fly ash layer in between, one layer each in middle and bottom, and one layer each in top, middle and bottom, the CBR values increases within the ranges between 11.72–17.58% at 2.5 mm and 17.5–22.46% at 5 mm penetration. However, the most improved (i.e., increased) values are observed when reinforcement is provided in three layers at equal interval. The permeability (k) value of well compacted fly ash is 3.30 × 10−7 m/s. The permeability value decreases after reinforcement has been provided in different layers and within the ranges 8.14 × 10−8 to 9.8 × 10−8 m/s and the most improved (i.e., decreased) values are observed in three layers reinforcement at equal interval. The modified permeability value minimizes the seepage of water through a fly ash embankment. So the fly ash and reinforced fly ash can be used as a structural fill and embankment materials.

Nowadays it is common practices to strengthening the soft subgrade by using waste materials. Granulated blast furnace slag (GBFS), an industrial waste may be used to stabilize soft clay sub-grade. In the present study, an attempt has been made to evaluate the effect of GBFS contents on California bearing ratio (CBR) value of clayey soil GBFS mixture. Three types of clayey soil and one types of GBFS has been used in the present investigation. Soaked CBR test has been performed with varying GBFS content (0–50%) for above three types of soil. From the experimental outcomes it has been found that with increase in GBFS content the soaked CBR values increases and reaches a maximum value at certain GBFS content after that it decreases. The optimum value of GBFS content is 30% irrespective of types of soil when it has been compacted at OMC and MDD of the respective mixture. Based on the experimental data a nonlinear power model has been developed to predict the CBR value of soil GBFS mixture in terms of GBFS content and CBR value of the respective soil alone.

In this paper, results obtained from a series of large-scale repeated load model tests are presented. Repeated load tests were conducted on geocell reinforced and unreinforced dense sand layers overlying weak sub-grades to understand the general behavior of reinforced unpaved roads. The height of the weak sub-grade was always maintained and the height of the dense sand layer was varied according to the heights of the geocell mattress used. The relative densities of the weak sub-grade and dense sand were maintained at 30 and 75% respectively. The loading was applied through a circular steel plate which replicates the traffic loading applied through a sophisticated double acting linear dynamic actuator attached to a 3.5 m high reaction frame. Results from each case are presented, and different views on the results are discussed with the experimental tests. It was inferred that the rutting on the pavement surface can be reduced to about 35% by providing nominal size of the geocell mattress in base layers over weak sub-grades. The results are also quantified through a non-dimensional factor, called traffic benefit ratio (TBR), defined as a ratio of number of load cycles applied on reinforced section to the number of load cycles applied on unreinforced section at the same settlement. It was found that the TBR can be increased as high as 15 with geocell reinforcement at a settlement ratio of 5%.

Cochin marine clay is usually associated with substantial difficulties, since these soils are sensitive to deformation and possess very small shear strength, which may lead to structural damages during the execution and throughout the lifetime of any structure. The foundations require strengthening of soil to carry the loads imposed over soft strata. Out of several techniques available for improving the load carrying capacity of soft clay strata, stone columns are ideally suited for structures with widespread loads with higher permissible settlements. Cementing agents are used in the pores of granular piles to improve the load-carrying capacity of soft soils. This paper presents the results of studies made on the influence of cementing agents such as cement, lime, flyash, and their combinations on load carrying capacity of soft soils.

This paper deals with transmissivity test conducted in laboratory on newly developed coir latex composite to be used as separator in flexible pavement. The coir latex composite is developed by treating coir fibre of varying fibre length, woven coir geotextile and nonwoven coir geotextile with optimum latex content (50%). Transmissivity of the composite is measured under varying hydraulic gradient and normal pressure using a specifically designed apparatus to simulate field condition. Transmissivity of the coir latex composite seems to decrease with increase in hydraulic gradient as well as with increase in normal pressure. The results are compared under test conditions without using the composite as well as with coir geotextiles without latex treatment.

Geosynthetic reinforced granular piles are commonly used in engineering practice to enhance the bearing capacity, reduce settlements and to increase the rate of consolidation of very soft clays. In the present paper, laboratory model tests have been carried out on vertical–horizontal combined reinforced floating granular piles installed in soft clay. A 75 mm diameter and 375 mm length single granular pile was formed by simulating unit cell concept. Geotextile and geogrid were used over the full length of granular piles as vertical encasement and horizontal strips respectively. Geogrid strips of 65 mm diameters were placed at three different centre to centre spacing of 25, 50, and 70 mm. Vertical load–settlement relationship of untreated clay bed, unreinforced and reinforced granular pile treated ground were obtained under short-term loading. The influence of reinforcement was examined in term of ultimate load intensity of granular piles compared to untreated ground. Model tests indicated significant improvement in the load carrying capacity of granular piles due to the incorporation of geosynthetic.

In agriculture-based country like India road network plays a major role. The life and maintenance of roads mainly depend on the strength of both sub-base and subgrade of soil and traffic intensity. In India about 20% of the total area is covered by Black cotton soil. Because of the high swelling and shrinkage characteristics under varying water contents Black cotton soil poses problems in road construction and maintenance. This paper presents experimental results illustrating the behavior of Black cotton soil stabilized with Ground Granulated Blast furnace Slag (GGBS) and GGBS-lime mix. In order to estimate the strength of the stabilized soil, tests such as Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) tests were performed. Tests were conducted on soil-GGBS mix for GGBS dosages 3, 6, 9, and 12% by weight of dry soil and soil-GGBS-Lime mix with 2 part GGBS and 1 part Lime for dosages 3, 6, 9, and 12% by weight of dry soil. Tests were conducted on both unsoaked and soaked samples, unsoaked samples were cured for 7 and 28 days whereas soaked samples were cured for 3 days and soaked for 4 days. The effect of binder content, curing period and soaking on the UCS and Elastic modulus were studied and subsequently the effect of binder content on CBR values were also studied. With the increase in binder content and curing period the strength of the treated soil was found to be enhanced. Soaking resulted in the decrement of the strength of the stabilized soil. From the experimental results it is clear that GGBS-lime mix is a superior binder content than GGBS for the improvement of black cotton soil, when used as a sub-base material in flexible pavement.

The various methods are in practice for improving the properties of soil which are neither economical nor eco-friendly. The microorganisms, nutrients, biological processes may prove to eco-friendly solution to soil improvement. This paper aims to review different microbial, their microbiological processes and their geotechnical applications to enhance the properties of soil. The microbial improves different geotechnical properties of soil. The microbiological processes include calcite precipitation, mineral transformation and different pathways. The properties of cohesionless soil or cohesive soil can be improved using microbes. This paper review, the geotechnical applications of cementation of sands to enhance bearing capacity, soil erosion control, groundwater flow control, and remediation of soil and groundwater impacted by metals and radionuclides.

Coir fibre–polymer composite being economical and ecofriendly, can be considered as a best alternative for the geosynthetic composite. The use of coir fibre–polymer composites can be extended to ground improvement and can be used as a separator in flexible pavement. This paper deals with the long-term performance in terms of strength criteria of natural fibre composite sheets for use as separator in flexible pavements. The study was confined to three types of composites: coir fibre latex composite sheet, woven coir mat and woven coir mat latex composite sheet. In the study the strength characteristics were studied using the California Bearing Ratio (CBR) test method. The tests were conducted at an interval of one month for a period of four months to study the time dependent strength variation on natural fibre composites. A system of soil, aggregate and composite is used for CBR test. The soaked CBR values for various composites developed are studied and compared for their strength characteristics. Several results show that with time the residual strength increases initially and converges to a certain value, after which the rate of deterioration decreases at a small value. Among the three types of composites, woven coir mat latex composite is expected to give better results in terms of strength characteristics.

The knowledge of the rate at which the settlement of clay layer takes place is very important in the design of vertical drain. The coefficient of consolidation, whether it is vertical or radial drainage (cv or cr) plays an important role in the design of vertical drains and it controls accurate prediction of rate of consolidation of soil. This paper presents an overview of different methods used in the past for finding the coefficient of consolidation, using vertical drainage (cv), as well as with vertical drains (cr) based on free strain approach as well as equal strain approach. It is noted that free strain approach is complex; a large number of methods were developed based on equal strain approach. In this paper, these methods for the determination of cv and cr are summarized and compared. This review will be useful for researchers or practicing engineers for estimating the rate of settlement in the clay layer with/without drains.

Ground improvement through fiber-reinforced soil has been in practice in the recent past. However, with increasing concern for sustainable development, researchers are encouraged to investigate alternative forms of reinforcement than the mainstream synthetic fibers. Coir fibers have been in practice as an alternative natural fiber for ground improvement. In this study, fibers extracted from a local coconut plantation were used to improve the strength characteristics of a local hill soil. The strength characteristics of the soil-coir fiber composite have been compared with the same soil reinforced with synthetic polypropylene fiber. The study investigates the strength variation and change in ductility of both soil-fiber composite with respect to bare soil. The fiber percentage added to soil was selected at 0.5, 0.75 and 1% of the dry weight of soil. A series of unconfined compressive strength (UCS) tests were conducted to ascertain the strength characteristics of the soil. The reinforcement strength results of the soil-coir fiber composite show the efficacy of using such a natural fiber to improve the soil strength characteristics.

Ash ponds cover up enormous stretches of valuable land and accounts environmental problem. Adaptation of appropriate in-place stabilization technique may bring about enhancement in the geotechnical properties of the ash deposit as a whole, transforming it into a worthy construction site. In this present experimental program, large-scale laboratory model test tank of diameter 105 cm with 120 cm height has been filled with ash slurry at 70% water content with a centrally installed chemical column of sodium hydroxide (1% of NaOH by dry weight of the ash in the bed) having a diameter of 20 cm. Undisturbed samples were collected from different radial distances of 15, 25, 35, and 45 cm after curing periods of 7, 30, 60, and 90 days and the in-situ water content, dry density, unconfined compressive strength, and hydraulic conductivity were measured. This method has been found more efficient in increasing the unconfined compressive strength and reducing hydraulic conductivity of the ash deposits in addition to altering other geotechnical parameters like in-situ water content and dry density. A substantial strength increment was noticed up to a radial distance of 2D (where D is the diameter of the chemical column) from the center of the column.

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. Focus is on the recent advancement of encasing these columns with geosynthetic products to enhance their performance in load bearing capacity and reducing the foundation settlements. This paper is divided into analytical, experimental, numerical and field studies on the aspect of encased granular columns (EGCs) which have been published in the past three decades. The primary objective of this study is to compile the above said aspects of EGCs into one single source of information to interested researchers in this field. Lot of studies have been conducted mainly on the laboratory aspects of EGCs. Very few attempts have been made by researchers to study the mechanism of granular columns at full-scale levels through field tests. Finally a brief summary with necessary discussions is provided on the efforts made so far in studying the behavior of EGCs.

Erosion and flood are the two major problems of lower plain reach of Jiabharali River and hence become a matter of concern due to its devastating impact on life and property. The River Jiabharali carries substantial quantity of silt along with discharge of 4429.73 cumec. Due to deposition of sediments, the sand chars forms in the river bed at random, creating spill channels making bank erosion more vulnerable. River also has a natural gradient to shift its courses towards the western side and there is formation of offshoot channels after each flood, thereby widening its waterway and making the problem more intense. This paper describes the case study where Geosynthetics materials and Gabions are used in erosion control and flood protection measures at two different reaches (Dikoraijan and Kurukani) along the Jiabharali River by construction of bank revetment with launching apron and raising and strengthening of embankment at places which are prone to floods. The project is located in the Sonitpur District of Assam from Ch: 9490 m (Dikoraijan) to 14,397 m (Kurukani). The laboratory investigations undertaken for Geosynthetics materials and Gabions for the above project are presented in this paper along with advantages of using Geosynthetics materials.

This paper presents static and cyclic behavior of geofoam specimens of 100 mm cube and 15 kg/m3 density (D). To understand cyclic behavior of Geofoam, a factor “R”, defined as ratio of combined axial static and cyclic stress component to the yield strength of geofoam, is used in cyclic uniaxial compression (CUC) tests. CUC tests are conducted at three frequencies (f) of 0.5, 1 and 3 Hz, R values of 0.4, 0.6, 0.8, 1 and 1.2, and for 5000 cycles. Static tests on geofoam exhibited a bi-linear axial stress–strain response. From CUC tests, it is noted that effect of number of cycles is insignificant on cyclic modulus, and effect of testing frequency on cyclic modulus is found marginal, for lower values of R. As the value of R increases, the cyclic axial strain increases, which decreases cyclic modulus of geofoam, irrespective loading frequency and number of cycles. Previous studies, while modeling Geofoam behavior, assumed positive values of Poisson’s ratio and linear regression models relating Poisson’s ratio and density of geofoam. In contrary, the present study revealed that Poisson’s ratio of geofoam not only depends on its density, but also strongly influenced by number cycles and axial strain of geofoam, and can also take negative values.

In this study, an attempt has been made to investigate the influence of flyash columns (FACs) on the expansive soil using different percentages of flyash and calcium carbide residue (CCR) to reduce heave of expansive soil bed. Puzzolanic activity of the binder admixture has been studied by replacing the columns admixture by sand in the vertical columns in the soil specimen. Conventional Oedometer tests have been performed. Free swell index (FSI) and particle size distribution tests have also been conducted as post-tests. It has been observed that swell properties considerably reduce with vertical fly ash columns in the expansive soil bed.