Soft Clay

In this study, the effects of a road subgrade stabilized using black carbon on the rigid road pavement
thickness and cost were investigated. For this purpose, pure soil was subjected to sieve analysis, hydrometer,
consistency limits and pycnometer tests to determine its engineering properties. Afterwards, stabilized mixture
samples were prepared by adding black carbon in five different ratios (2.5, 5, 10, 15 and 20%) to the soil. Pure
and stabilized samples were subjected to the standard proctor test, maximum dry unit weights and optimum
water contents were determined. Mixture samples prepared were subjected to unconfined compression and CBR
tests after 28 days of curing period. Rigid road pavement thickness and cost were analyzed according to the
AASHTO method using the data obtained. According to the test results, it was observed that the highest
compressive strength was obtained from the mixture with 10% black carbon and the CBR value of the mixture
at this ratio increased by 2.87 times compared to the pure soil. As a result, thanks to the soil stabilization using
10% black carbon, it was determined that the pavement thickness reduced by 3 cm and the rigid pavement cost
by 9.68%.

Abstract: In this study, the effects of subgrade soil improved by the usage of metakaolin on the layer thickness and construction cost of
a rigid road designed on it were investigated. First, soil classification tests were conducted to determine the soil class, and several
laboratory tests were performed to identify soil properties. Then, standard proctor tests were applied to soil samples prepared by
adding 3%, 6%, 9%, 12%, and 15% metakaolin by weight. Subsequently, unconfined compressive strength tests were conducted on the
samples prepared with different proportions of metakaolin after a curing period of 28 days. As a result of the tests, the highest strength
was obtained in samples containing 12% metakaolin. Then, after 28 days of curing, the California bearing ratio test was applied to the
samples prepared without additives and with 12% metakaolin, resulting in a 227.56% increase in strength value. After the
experimental studies, pavement layer thickness and cost were investigated according to the rigid pavement design guidelines
recommended by the American Association of State Highways and Transportation (AASHTO). As a result of the calculations, it was
determined that the subgrade improved with 12% metakaolin reduced the rigid pavement layer thickness by 29.17% and the cost by
2.68%.

This paper present an experimental study results on the strength of fibrous peat soil stabilized using Waste Paper Sludge Ash (WPSA). Basically WPSA is a finely waste product resulting from the incinerating of waste paper and considered as lightweight waste materials with silts size. According to ASTM C618, WPSA classified as class-C fly ash because containing more than 10% lime (CaO) possesses some cementitous and pozzolanic, resulting in the selfcementing characteristics. Since class-C WPSA is self-cementing, activators such as lime or cement is not required and WPSA acting as single additives. The peat soil been used in this study been collected from Southern of Peninsular Malaysia and classified as fibrous peat containing high organic with highly acidic and classified as H4 based on degree humification according to the Von Post scale. The purpose of study is to determine the compressive strength development at curing periods of peat stabilized with WPSA. The first objective of this study is to determine the optimum concentration percentage of WPSA used to stabilize fibrous peat. The second objective is to determine the strength development of fibrous peat soil stabilized at the optimum concentration of WPSA at 0day, 14days and 28 days of curing periods. This is the laboratory study involved the unconfined compressive strength test (UCT) of peat soil stabilized at the optimum concentration of WPSA and the result are compared to the untreated peat soil. The laboratory result shows that the optimum concentration of WPSA to stabilize the fibrous peat soil is about 7% at the 290kPa of the maximum compressive strength. Instead, addition of 7% WPSA showed the increment of compressive strength compared to the untreated peat soil from 0day to 28 days of curing periods respectively. This Vol. 13, Bund. B 1614 study shows that the peat soil can be stabilized using WPSA and giving an effective result to enhance peat soil strength for long periods.

Screw piles are widely used in a variety engineering applications supplying stability against compression, overturning moment, uplift tension, and horizontal loads. Screw pile is a famous solution for support light structures, roads and rail signs which have relatively low-capacity foundation. In this study, the behavior of circular (10) mm solid screw pile models embedded in a bed of soft clay soil covering a layer of sandy soil has been studied. The 200 mm thick sand layer was compacted in a steel container with a diameter of 300 mm into four sublayers. The sandy soil layer was compacted at a relative density of 70%. The 300 mm thick soft clay soil bed with Cu (30) kPa was compacted in six sub-layers on the sandy bottom layer. Model tests are carried out with screw piles with a length of 300 mm, 350 mm and 400 mm and a helix diameter of 30 mm. Also, single and double helix and different S/Dh ratio were used for these piles and a comparative study between screw piles and ordinary piles (without helices) is accomplished. This study revealed that introducing screw pile of double helix increases its bearing capacity in soft clay soil by up to a (4-8) % as compared to a single helix screw pile. The results showed that the behavior of screw pile essentially depends on the geometric properties of the pile. According to the achievements, compressive load capacity of screw piles depends on embedded length, spacing ratio (S/Dh) and number of helical plates.

Results from laboratory model tests performed on circular footing are presented in this paper to understand the performance of geocell reinforced expansive soil. Naturally occurring expansive soil was used in this study as subsoil. Geocells of chevron pattern fabricated from geotextile made up of polypropylene were used to reinforce the soil bed. The parameters studied in this testing program were the placement depth of the geocell mattress, pocket size of geocell and the height of geocell mattress. Contrary to other researchers; the improvement in the performance of reinforced bed is evaluated at a settlement level equal to the failure settlement of unreinforced soil bed. The performance of reinforced bed is evaluated through two non-dimensional factors viz. bearing capacity improvement factor (If) and settlement reduction factor (PRS%). Test results indicated that with the introduction of geocell as reinforcement, a substantial improvement in bearing capacity and decrease in footing settlement can be achieved. Bearing capacity of reinforced bed increases by more than 200% and 81% reduction in footing settlement was achieved by using geocell mattress of optimal dimensions and placing it just below the footing base.

One of the main hydraulic properties of unsaturated soils is the Soil-Water Characteristic Curve (SWCC). It is essential to understand, predict soil water storage and determine the hydraulic and mechanical behaviour of soils. These curves can be obtained by direct and indirect measurements. The measurements to obtain these curves are expensive, delicate to perform and can be really slow for fine soils, so predictive models become necessary. In order to make a numerical model, a couple of identification tests were carried out to obtain the physical properties of each sample among the four subgrade materials collected in the regions of Dakar and Thies (Senegal). The measurement tests of the matric suction were then conducted depending on the nature of the material (fine-grained soil or coarse-grained soil) and allowed to draw the SWCC of each soil. Among numerous predictive models developed for SWCC in the last decades; this study used the Perera model to fit the SWCC of four (04) subgrade materials, which did not give a satisfactory coefficient of correlation (R 2 = 58% and a relatively low sum of the squared residuals (SSR)). This leads to modifying the Perera model to better fit the SWCC on the basis of an understanding of the effect of each parameter on the shape of the SWCC. The proposed modified model was validated by checking the adjusted R 2 , minimizing the SSR in order to approach at most the experimental air entry value. The modified model works pretty well on coarse-grained and fine-grained soils. This modified model of Perera provided a very good correlation R 2 equal to 99.98, 98.74, 99.64, and 99.73 for the sandy soils (Sebikotane and Keur Mory) and the Marley and Clayey soils of Diamniadio, with a minimal SSR obtained compared to Perera's and Hernandez model.

The settlement of foundations is usually predicted by the oedometric method and/or by the pressuremeter method. However, the settlement of a foundation can be predicted from Boussinesq formula via the Young modulus, especially in the absence of oedometric or pressuremeter data. This paper aims at, firstly, a highlight on the conditions for the applicability of oedometric and pressuremeter methods, and, secondly, a possible comparison between estimated settlements by the two methods. Such a comparison is still a matter of debate between the soil engineers, especially those who are faced to the design of foundations projects. Here in, it is out of interest the validity of results obtained from the oedometric or pressumeter test, it is assumed that the available data are reliable, well-defined according to standards, both for carrying out the experiments and for the treatment method in order to retain the oedometric or pressuremeter characteristics. Concluding remarks are justified based on the analysis and discussion of two case histories.

Paper deals with the problem of foundation on the soft soil in seismic active regions. In these regions special measures for foundation and sub-base preparation must be taken. Our company deals a lot with soil improvement in loose and soft soils with high ground water levels. The special technique for soil improvement using geosynthetics is developed. The foundation on this soil is problematic and the soil characteristic must be taken into consideration in the early phase of the structural design. The whole structure, taking into consideration the structure stiffness, must be modeled and examined in static and dynamic loads. Structure is modeled by Plaxis software, with subsoil and improved tampon layer and geosynthetics layer(s) between the subsoil and tampon layer. The earthquake response for real earthquake input is analyzed. The stresses, strains and deformations are analyzed in soil and synthetics layers. Experiences not only from analysis but from constructions of the improvement from several sites are discussed and illustrated in the paper. As a result of our analysis and long years of theoretical and practical experience the recommendations for shallow foundations soil improvement are given.

Settlement of base ground due to imposed load is a concern for any Geotechnical Engineer. For the serviceability of subgrade of an embankment, the prediction of embankment settlement is a critically important issue. Calculation of settlement, especially differential settlement, ensures the design grade of the embankment. This study includes the settlement of an embankment at Kanchpur Bridge, Bangladesh, which is a location where the embankment was made on soft soil. The actual field settlement data is compared by the finite element method with the PLAXIS-2D numerical modelling software. Hardening Soil Model and Soft Soil Model have been used in this simulation as constitutive models. Reasonable agreements were obtained from the finite element analysis compared to the actual field monitoring data. Moreover, variations in total deviatoric strains for both models were also illustrated in this paper.

Properties and characteristics of soft clays are presented. Because several problems are faced, when projects construction is intended on soft clays, several improvement techniques can be adopted. Preloading with or without vertical drains, vacuum consolidation and reinforcement by columns are currently used to enhance properties of soft clays. Also, rigid inclusions and geotextiles may be used. The principles and basic criteria for the design of all these techniques are explained. Comparison between advantages of improvement techniques is carried out by illustration of typical case histories.

This paper presents an experimental study carried out on undisturbed cored samples of Tunis soft soil extracted at 17.25 m depth at the lagoon of Sejoumi. Three series of oedometer tests were performed: the first one was a standard test on Tunis soft soil, the second one was performed on the same soil improved by a prefabricated vertical drain Mebradrain 88 (Mb88) type during which vertical drainage was prevented. The third series comprised similar tests to those of series two, during which horizontal and vertical drainage were allowed. The assessment of Carillo's theory was studied by quantifying the effect of radial and vertical consolidation from the observed global degree of consolidation of improved Tunis soft soil specimens by geodrains. The rate in decrease of coefficients c r and k r was greater than that recorded for coefficients c v and k r , respectively. Using the Carillo's theory, a lower degree of consolidation which starts from 10 % is obtained; however, when using simple approximate methods by considering recorded measures from series 3, higher degrees of consolidation starting from 70 % were obtained.

This paper studies the prediction of behaviour of foundations resting on a soil reinforced by sand and stone columns. The preliminary design is based on an optimized improvement area ratio predicted by the methodology proposed by Bouassida & Carter (2014). The prediction of the behaviour of the reinforced soil is predicted by numerical computations carried out by Plaxis V9.2D and FLAC3D codes in plane strain and axisymmetric conditions. A Tunisian case history of oil tank is investigated. When assuming the linear elastic behaviour for constituents of reinforced soil, it is noted that the predictions of settlements given by Columns 1.01 software are in good agreement with numerical results obtained by Plaxis and FLAC3D codes. Comparison between those approaches shows the validity of results using the Columns 1.01 software. By adopting the Mohr-Coulomb failure criterion for columns material and the hardening soil model for soft clay, the evolution of long term settlement predicted by Plaxis code showed the acceleration of the consolidation of the compressible soft clay due to the enhanced drainage property of column material.

Geosynthetic reinforcement in earth structures has been used extensively over the last two decades. Extensive research has been carried out to investigate solutions to enhance the lateral stability of pile foundations. This research is motivated by the need to install piles in sites characterized by soft subsurface soil conditions, and often times, in seismic active areas. This research work explores an innovative use of geosynthetics to enhance the lateral performance of pile foundations. The static and seismic soil-structureinteraction behaviors of geosynthetics-reinforced pile foundation systems were evaluated using a series of reduced scale physical model tests performed on a shaking table in a 1G environment. A laminar shear box containing a pile foundation model supporting a single degree of freedom structure installed in different soil bed models was used in the experiments. The soil models included: a layer of synthetic clay (Modified Glyben) underlain by a sand layer (simulating a base case of soft soil); a layer of synthetic clay sandwiched between a sand layer and an aggregate layer (simulating the case of conventional ground replacement for the top soft soil); and a layer of synthetic clay sandwiched between a sand layer and a geosynthetic-reinforced aggregate layer (simulating the case of ground replacement of the top soft soil combined with geosynthetic reinforcement using a microgrid mesh). A series of sine-sweep, harmonic and scaled earthquake tests have been performed to identify the amplification and resonance conditions of the foundation system and to identify various aspects of seismicsoil-pile-geosynthetic reinforcement interaction effects. Lateral static load tests of this system were performed using a one directional load system that was fixed on the laminar shear box. The dynamic and static tests were simulated employing numerical models developed using the finite element program Plaxis 3D. The results of both static and dynamic tests showed that the microgrid reinforcement improved the lateral performance of the pile foundation and reduced the vibration amplitudes of the supported structure. The numerical analysis results were in close agreement with the dynamic and static experimental results. The results of a parametric study for the investigated foundation configuration and seismic loading demands showed that the requirements for engineered iii backfill can be reduced by more than 50% and the lateral seismic response can be reduced by 50% by using geosynthetic reinforcement.

Site specific empirical correlation models are proposed to estimate the compression index of inorganic marine clay at Kwangyang new port in Korea using 468 consolidation data. Regression analysis is carried out to make correlations in estimating compression index using both single and multiple soil parameters. Soil parameters used, include natural water content, void ratio, liquid limit, plasticity index, the passing percentage of 2 m and specific gravity. Finally, it is found that the compression index predicted by simple multiple regression equations involving the natural water content, the natural void ratio and liquid limit can reasonably evaluate the real soil compression index.

This article first introduces a new method of characterization of expansive clays after oedometer test results performed on intact saturated clay specimens. On the presumed expansive clays specimens, oedometer tests are preceded by the free swelling test from which the swelling pressure is measured. From current oedometer test results carried out on expansive and non-expansive clays, the ratio of compression index (C c) by the swelling index (C s) was determined. A threshold value of the ratio C c /C s was identified to distinguish between expansive clay specimens and non-expansive clay specimens. Second, a novel mitigation method of the swelling phenomena was validated by performing oedometer tests on expansive clay specimens preceding the measurement of swelling pressure. Oedometer tests performed on a 53% thickness clay specimen overlaid by a 47% thickness of sand showed a significant reduction of the swelling pressure compared to that measured on a full expansive clay specimen. The mitigation solution reduced the swelling effect by placing a compacted granular layer as an interface between the expansive clay and the foundation. This solution has been adopted and approved in forthcoming a lightweight building construction at the Faculty of Sciences of Tunis City.

Three projects of end of studies which are related to soil mechanics pathology case histories were undertaken by students at civil engineering department of National Engineering School of Tunis. The two first projects dealt with Joumine and Sidi Saâd earth dams cases. For Joumine dam, concrete slabs of the spillway have been affected by serious disorders. The first disorder is related to the swelling nature of soil foundation of concrete slabs. The second disorder is attributed to high excess pore pressure responsible of slabs up risings. As solution the jet grouting technique was designed to eliminate high pore pressure in the soil foundation of slabs. For Sidi Saâd dam disorders were attributed to high active soil pressures exerted on retaining walls of the spillway. As solution anchored cables were adopted to improve the stability of concrete walls. The third project dealt with four engineering structures crossing Tunis La Goulette express route. All approach slabs were affected by differential settlements due to the existence of highly compressible thick soft clay layers. As solution three soil improvement techniques (rigid inclusions, stone columns prefabricated vertical drains) were compared to stop non admissible consolidation settlements. For each case history, the methodology to diagnose causes of disorders is first presented, second, the utilized approaches, especially those involving finite element codes usage, are highlighted, finally proposal of remedies to re establish suitable exploitation of projects are exposed. This paper well illustrates the great importance for under graduated students, when preparing their works of end of projects, to more understand fundamentals in soil mechanics in parallel with treating serious problems of pathology of case histories.

Tunis soft clay being known as one of the most problematic soils has poor mechanical characteristics, high compressibility and exhibits fragile shear strength. This paper considers the geotechnical characterization of Tunis soft clay by compiling results from in situ and laboratory tests. Accordingly, some correlations are suggested. The assessment of observed behaviour of Tunis soft clays in the zone of interchange ramps was investigated. The follow up of ramps behaviour was performed for a period of three months. The evolution of settlement was monitored by rod settlement, hydraulic settlement and multi-points settlement. A plane strain model was built for numerical investigation conducted by Plaxis software to simulate the behaviour of the ramp's embankment. Hardening Soft Soil Model (HSM) and Soft Soil Model (SSM) were adopted for the soft clay layer. The results showed an agreement between the predictions of the two models of the behaviour of the soft clay. Using measured settlement the adopted behaviour for Tunis soft clay is justified.

Among all of the slope stability methods, use of stone columns and geosynthetic elements can be a good way for stabilizing. One of the efficient ways in order to reinforce earth slopes is Geogrid Encased Stone Column (GESC). This technique can dramatically increase bearing capacity and decrease settlement rate. The aim of this paper is experimentally to investigate a comparison between the behavior of Ordinary Stone Column (OSC) and GESC for reinforcing of sand slopes. The slope was constructed using raining technique and reinforced using GESC. The slope saturated through precipitation and loading procedure applied. The obtained results compared and verified with 3D Finite Difference Method (3DFDM). Both experimental and numerical analyses indicated that location of GESC in middle of the slope increases the bearing capacity of slope crown 2.17 times than OSC.

The paper reviews research investigations conducted on Tunis soft clay that is classified as problematic soil. Results obtained from an experimental study carried out on undisturbed Tunis soft clay specimens are presented and interpreted. On the basis of experimental results, the paper discusses which constitutive law can describe at best the observed behavior of Tunis soft clay. The elastoplastic behavior modeled by the hardening soil model is then justified upon the validation of numerical results of oedometer and triaxial tests carried out on undisturbed soft clay specimens. Stage construction of embankment built of Tunis soft clay was analyzed by the FE code Plaxis 2D. This case study well illustrated the need for practicing ground improvement techniques to neutralize the inherent long-term settlement induced in soft clay.

This paper presents results of experimental tests on soil specimens reinforced by stone columns. The experimental investigations have been conducted by setting up a laboratory scale model. The main objective is to evaluate the effects of various reinforcing materials and stone columns configurations on the axial deformation during a vertical loading test of cylindrical samples of unreinforced and reinforced soil. The findings have been compared to existing experimental results proposed in literature. The specimens of soil consisted in an analogic material of poly-dispersed glass beads with a grain size smaller than 50 µm. Two reinforcing materials have been considered as ballasts: crushed sand and coarser granularity glass beads (0.7 -1.0 mm). The results show that the material type and spacing between columns in a triangular or square configuration can greatly affect the reinforcement efficiency. The proposed results are applicable to predict the improvement of granular soils of medium density when subjected to the vibrocompaction technique.

This paper presents a case history of an eight-metre-deep basement excavation in soft silty clay deposits in Santos, São Paulo, Brazil. The site consisted of a five-metre-thick sand layer overlying a twelve-metre-thick, soft clay layer, underlain by dense sands. A comprehensive geotechnical investigation, including CPTU, DMT, and laboratory testing, informed the initial design, which employed Plaxis for a five-metre-deep diaphragm wall-supported excavation. However, a subsequent unauthorised excavation of an additional three meters triggered significant wall displacements, necessitating emergency measures. The authors conducted additional Plaxis analyses to investigate this, modifying only the excavation depth while preserving the original soil models and parameters. The remarkably close agreement between predicted and observed wall displacements validated the accuracy of the numerical modelling approach. This case study underscores the critical importance of rigorous geotechnical design and the potential consequences of unanticipated excavations. The findings highlight the efficacy of Plaxis in predicting the geotechnical behaviour of deep excavations in soft clay conditions.

Highway pavement design using soft clay soil as a subgrade is always a great challenge and can cause problems such as roadbed instability and soil settlement. To overcome this problem, the knowledge of the subgrade soil characteristic should be studied first because it needs to be considered during the design phase of pavement. This study was conducted to investigate the engineering properties of soft clay that can be used as potential subgrade material. Some soil laboratory tests were performed to establish the engineering properties of the soft clay. From the standard proctor compaction test, the results revealed that the maximum dry density and optimum moisture content are 1.58 Mg/m 3 and 20.15 %, respectively. The finding from the soil-water characteristic curve (SWCC) test indicates that the SWCC did not present a residual suction. The compression modulus and pre-consolidation pressure obtained from the compacted soil sample for the consolidation test are higher than the undisturbed soil sample. Based on triaxial test results, the effective cohesion acquired from the compacted soil sample is greater than the undisturbed sample. This research provides a reference for the study of soft clay engineering characteristics.

Rapid infrastructure expansion, including high-speed railroads, freight corridors, and highways, has led to extensive construction activities across both rural and urban regions. This growth poses a significant challenge for researchers and engineers worldwide, who continuously seek innovative solutions to enhance weak soils, ensuring they meet the demands of various engineering structures. The stability of embankment foundations, particularly when built on soft soil masses, is often compromised due to the inherent characteristics of such soils, including high compressibility, plasticity, sensitivity, low shear strength, and poor permeability. This paper provides a comprehensive review of the challenges encountered during the construction of embankments on soft ground and offers recommendations for effective remedial measures. This review highlights critical considerations such as settlement, slope stability, and soil bearing capacity by analyzing the various factors that influence embankment stability through a systematic approach that incorporates past experimental and numerical studies. Common ground improvement techniques have been identified as effective solutions, such as preloading combined with Prefabricated Vertical Drains (PVD) and using lightweight fill materials. The insights gained from this study can assist engineers and consultants in developing design strategies and innovative solutions to address the challenges posed by land scarcity and problematic soils.

In traditional design of piled foundations with large caps, the superstructure loads are assumed to be carried by piles only and contact between the pile cap and ground surface is purposefully avoided. On the other hand, a raft if used, may provide high load carrying capacity without the possibilities of shear failure of the supporting soil but the resulting settlement will be beyond the permissible limit. Allowable pressure on supporting soil is governed by loads corresponding to the tolerable settlements. As a result, on soft soils, for heavily loaded structures, piles are generally adopted foundations, however at a high cost. In such cases, increasing application of piled raft foundations are being made for economic reasons. In this paper, based on nature of the subsoil profile and field tests on pile, a simplified design approach considering the load sharing mechanism of piles and raft is proposed. Due considerations are given to the site conditions, raft-soil, pile-soil and pil...

A constitutive framework for the simulation of the time-dependent behaviour of soft structured clays has been developed from the combination of a number of existing modelling approaches. The formulation accounts, in a natural way, for timedependent phenomena such as loading rate dependency, stress-relaxation, ageing, and creep deformations under constant load. In addition, the effect of structure is accounted for. To demonstrate the potential of the proposed approach, a specific model based on this framework is described and applied to the simulation of a number of relevant laboratory tests from the literature.

Disturbance encountered when testing soft soils both in laboratory and in-situ conditions makes the determination of the undrained shear strength, Su, very challenging. This paper introduces a new tool called "Cylindrical Penetrometer" (CP) to measure the undrained shear strength of soft soils. Description of this tool is given, and the related shear test procedure is detailed. The proposed tool offers the advantage to avoid the disturbance of soft soils before the commencement of the CP test. From recorded measurements and based on considerations of the existing shear tests, a specific method of determination of Su is proposed. The experimental program included laboratory tests by using two sizes of the CP. The recorded results from CP tests, performed on a reconstituted Tunis soft clay, were compared with those obtained from direct shear tests, vane tests, and a consolidated undrained triaxial test. A fair agreement was found between the Cylindrical Penetrometer results with those obtained from the current shear tests.

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Using stone columns technique is a method of improving weak soil such as soft clay, silt and loose sand that have shown good performance and compatibility with the environment. Columns create a composite material with a lower overall compressibility and greater shear strength than the primitive soil. In this study, it’s tried to find the optimum parameter for reinforcing weak soil. These optimum parameters in addition to creating good resistance conditions to poor soil in terms of horizontal displacement and vertical settlements are more efficient than other models with respect to economical aspect. Variable parameters examined in this study consisted of length and diameter of sand columns under surcharge load of 50 kPa on rigid foundation. three-dimensional models analyzed with Abaqus (14-4-6) software. Evaluating the results of models, in this study it’s illustrated that encased sand columns have improved settlement and bulging in clay soil for approximately 66% and 62%, respectively and the effective length of columns has been determined. It can be concluded that geosynthetic encasements have a good effect on improving the performance of group sand columns and can be used with a few number of columns with shorter diameters by encasing them together with the optimum material that have appropriate stiffness.

A group of finite element analyses was carried out to investigate into the ultimate bearing capacity of the square footing on sand with and without geogrid reinforcement. Simulations were conducted with dimension of 12*12*6m to construct 3D media. The parameters investigated are the effect of the depth of single layer of geogrid, number of geogrid layers within the reinforced zone and length of reinforcements. Influence of all these parameters on the bearing capacity improvement of square footing and its settlement is studied by comparing with the simulation on
un-reinforced sand. The results proved that the reinforcements had a considerable effect on the ultimate bearing capacity of the square footing on a sand bed. Based on the finite element analyses, optimum values of geogrid parameters for maximum reinforcing effect are discussed and suggested.

This paper presents the results of geotechnical and mineralogical investigations on lime-treated soft clay soil from Idku City, Egypt, where high organic matters of about 14% exist. Lime was added in the order of 1, 3, 5 and 7% by weight and laboratory experiments after 7, 15, 30 and 60 days were conducted including the mineralogical and microstructural examinations, grain size analysis, plasticity limits, unconfined compressive tests, vane shear tests and oedometer tests. The results indicate that soft clay soil of high organic content of 14% can be stabilized satisfactorily with the addition of 7% lime. The results also demonstrate that the changes in the mineralogical contents and soil fabric of high organic lime-treated soft clay improve soil plasticity, strength and compressibility.

Earth pressure on buried pipes structure depends not only on soil type, shape and dimension of structure but also on depth, shape and dimension of excavated holes and other factors such as structure load, underground water level. Based on the selected and modified computational scheme with self-established program, the earth pressure on pipe structures according to the construction condition is evaluated and analysed. It is recommended to choose the buried depth for structure in “cut and cover” excavation method so that the influence of earth pressure is reasonably steady from the buried point downward. The replacement of backfill material to cohesive material partially can help to reduce significantly the earth pressure on the buried structure. In addition, evaluation of the the degree of approaching to limit state in surroundings in bored tunnelling excavation allows for analysing the stability in various geological conditions according to the appearance of plastic zone. The resea...

This paper reports the results of model tests on the settlement behaviour of strip footing resting on geocell reinforced sand during cyclic loading. Model tests were carried out in a steel tank with interior plan dimensions of 380 mm x 300 mm, and 400 mm in height. The soil used was uniform beach sand and it was compacted to a relative density of 70%. The geocell mattress was constructed using triax geogrid in a chevron pattern. Tests were conducted by first subjecting the strip footing to an initial sustained static load and then superimposing additional predetermined cyclic loads. Based on the observed test results, the nature of variation of the permanent settlement of the foundation with the amplitude of cyclic load and frequency are presented in this paper.

The design of rail tracks is often challenged by the high compressible behaviour of soft estuarine clays under cyclic loading. In the coastlines of NSW and QLD in particular have very soft clays characterised by low bearing capacity and excessive settlement. Due to the ongoing pressure by the community to acquire high speed rail for greater commuter efficiency and faster heavy haul for improved mining and agriculture productivity, the need for detailed studies involving moving loads with high cyclic frequencies is paramount. In this study, apart from the general non-linear stress strain behaviour of soft subgrade soil, how the physical and mechanical properties are affecting the soft soil in terms of developing excess pore water pressure and axial strains under cyclic loading. The rates of degradation of the soil stiffness, the final resilient modulus and the damping ratio related to hysteresis have also been considered. Detailed experimental efforts and outcomes support the conclus...

The installation of vibro replacement stone columns in any soil causes significant changes to the stress regime around each probe location. In soft clays, the principal effects are caused by a cavity expansion mechanism as the probe is introduced into the soil and the stone column constructed. This paper presents observations of changes in soil volume and pore water pressure during stone column installation. The implications for the most suitable column construction techniques and the soil strength limiting column construction arising from the observations are discussed. The data presented are also of interest to those validating numerical models of stone column installation, and issues relevant to the practical application of numerical modeling are considered.

The limit equilibrium method (LEM) was used to back analyze the per- formance of three full-scale test embankments constructed over soft Bangkok clay. The control embankment was unreinforced while the other two embankments were rein- forced with multiple layers of low-strength geotextile and with a single layer of high- strength geotextile, respectively. The analyses results confirmed the embankment per- formance

Evaluating the actual diameter of jet grouted columns plays a significant role in determining the success of the jet grouting technology. An acoustic monitoring system capable of directly recording the sounds due to the erosion of soil from the jet grouting, detected at different distances from the jet nozzle was used to determine the diameters of the jet grouted columns. Although this acoustic monitoring system has been utilized by a number of researches in the world, further jet grouting acoustic data from various sites and soils are required to establish an acoustic database for future jet grouting work to estimate the effective diameters of jet grouted columns formed in the particular site. However, this system was first introduced in Thailand on Bangkok soils. Therefore, this study was conducted for the MRTA Orange Line Project in Bangkok, Thailand, to determine the effectiveness of this system on the Bangkok soils. The average threshold peak amplitudes and the standard deviations calculated from the acoustic data of trial test columns were used to define the effective diameters of jet grouted columns formed in the Bangkok soils for the future jet grouting practices. It was concluded that the acoustic monitoring system could be effectively used to assist in the large diameter jet grouting technique for the Bangkok soils.

A high-speed railroad foundation with a fine-grained subgrade can potentially build up excessive pore water pressure under cyclic loading from the operation of the train. The generation of the excess pore water pressure in the foundation clay could result in progressive shear failure at a stress level less than its shear strength under static loading conditions. In this study, both static and cyclic undrained triaxial tests were conducted for the Bangkok soft clay. The cyclic triaxial tests were conducted under two loading frequencies of 2 and 4 Hz. Normally consolidated (NC) and over-consolidated (OC) Bangkok soft clays were tested to investigate the behavior of the soils under cyclic loading. The threshold stresses for the NC and OC clays under cyclic loading were determined in the study. The effect of the load frequency, deviator stress level, and stress history of the soil on the threshold stress was evaluated in this study. This study shows that the shear strengths of the NC and OC Bangkok soft clays under cyclic loading could reduce up to approximately 20 and 30%, respectively, compared to those obtained from the monotonic compression tests. This study also concluded that the frequency does not significantly affect the threshold stresses or plastic strain. KEYWORDS: cyclic loading, soft clay, high-speed train, excess pore water pressure, and threshold stress of hysteresis could represent the soil's elastic behavior when soil called "Kaolin clay."

Principles related to the stabilization of soft clay using the vacuum preloading method is well presented in the literature. However, a limited number of studies have focused on the horizontal deformations of the nearby non-treated area due to vacuum preloading. In this study, an evaluation of the horizontal deformation within the non-treated area was conducted for a ground improvement site in Bangkok, Thailand. The term "Influence Distance (ID)" was introduced in this study and is defined as a lateral distance from the edge of the treated zone to a point where horizontal displacement is negligible. Numerical modeling was conducted to study factors related to PVD configuration and soil profiles/properties that could influence the ID. The numerical modelling results show that the ID increases significantly when the PVD length changes from 8 m to 20 m. Furthermore, it is indicated that the new design technique that gradually reduces PVD lengths towards the edge of the treated zone, could reduce the ID significantly compared to the regular design approach with a constant PVD length. The effect of the permeability and stiffness of the medium stiff clay layer located on the top of the soft clay layer on horizontal displacements was also investigated. It was concluded that the presence of the low-stiff and high-permeable medium stiff clay layer results in higher horizontal displacements. An influence chart was developed using the results of the numerical modeling to estimate the ID values. This influence chart was validated using the records of case histories in Bangkok. It is recommended that practising engineers can use this chart to predict the influence zone during a preliminary design stage of a vacuum preloading project.

The undrained shear strength is a critical design parameter in the design of soilcement columns for ground improvement projects. This paper presents an evaluation of undrained shear strength in soil-cement columns constructed with the dry mixing method for Bangkok soft clay. The relationships between undrained shear strength and design parameters including cement content, total water-cement ratio, curing time, and natural moisture content were established using machine learning (ML) techniques in this study. Soil samples of soilcement column (SCC) were obtained from two sites including the AIT site and Highway No. 35 site. Different varieties of cement contents were mixed using the dry method to prepare laboratory SCC samples with curing times of 7, 14, and 28 days. The SCC samples were utilized to develop models including the multivariate regression (MLR) model, random forest (RF) model, and artificial neural network (ANN) regression model for prediction of the undrained shear strength. The coefficient of determination (R 2), mean absolute error (MAE), and root mean square error (RMSE) were used as performance detectors for different models. It was found that R 2 values for all models ranged from 0.70 to 0.99 for the training data and from 0.5 to 0.94 for the testing data. A linear equation using the MLR model to predict undrained shear strength was proposed using cement content, natural moisture content, and curing time as the primary parameters. Various graphs to predict undrained shear strength were also proposed using the RF and ANN models.

This study first demonstrates the microstructural changes of soft Bangkok clay at a real construction site following vacuum PVD modification of soft clay at a − 9-m elevation obtained from Thailand's Suvarnabhumi Airport. In contrast to the undisturbed soil and the first-improvement soil, the second vacuum PVD improvement transformed the face-to-face orientation of the soil structure into edge-to-face flocculated particles. This approach also greatly affected the inorganic NaCl salts leaching from the pore water, resulting in stronger bonding with less soil permeability and an improved consolidation of soil structure. The repulsive interactions between the soil particles lowered the average liquid limit and plastic limit values, which contributed to the edge-to-face flocculation of the soil particles and greatly increased the shear strength. Vacuum PVD with a second improvement is a highly effective solution for raising the settlement rate and minimizing the settlement time to improve soft clay with low strength and high compressibility.

This paper aims at presenting a numerical study of the behaviour of Tunis soft soil improved by vacuum consolidation combined with geodrains. An experimental investigation was carried out on reconstituted samples of Tunis soft soil (TSS) initially extracted from the centre of Tunis city at 35 m of depth. Three consolidation tests were carried out in a cell of 126mm inner diameter and 290-mm height, the first one included a consolidation test by preload stress (q = 100 kPa). In the second test, vacuum consolidation tests (p v =100 kPa) were performed. The third test comprised a vacuum consolidation test combined with the preload (p v =50 kPa and q = 50 kPa). Simulation of those tests by the finite-element PLAXIS-2D code was implemented in axisymmetric conditions. Soft soil model was used to describe the behavior of Tunis soft soil (TSS). During this simulation, a parametric study was performed by varying the horizontal permeability k h of TSS. Then, by comparing the numerical results to the recorded data in laboratory, it has been verified that the numerical predicted settlements are higher than those measured during the performed laboratory tests. Further, numerical results confirmed that when the coefficient k h increases, the consolidation is complete in a shorter time. This work highlighted the usefulness of combining the vacuum pressure and geodrains improvement techniques to improve the behaviour of Tunis soft soil.

L'objectif de ce travail consiste à étudier le comportement des argiles molles de Tunis et la détermination des caractéristiques physiques et mécaniques relevantes. En effet, l'identification des paramètres physiques, minéralogiques, sédimentologiques et ...

A comparative study of soil-water characteristic curves (SWCCs) for compacted lateritic soil ̶ Bacillus coagulans (B. coagulans) mixtures for municipal solid waste (MSW) application was studied. Soil treatment was performed at approximately about one-third pore volume of the microbes (i.e., B. coagulans) for suspension densities of 0, 1.5×108, 6.0×108, 1.2×109, 1.8×109 and 2.4×109cells/ml, correspondingly. Soil specimens were prepared at optimum moisture content (OMC) of British Standard light (BSL) compaction energy. Cementation reagent was applied on the compacted soil and permitted to penetrate until partial saturation was achieved. A set-up of pressure plate extractor was employed to measure the volumetric water content, θ (VWC) in the laboratory for varying matric suctions with a minimum of 10 kPa up to a maximum of 1,500 kPa. The unsaturated hydraulic conductivity (UHC) and VWC were assessed using Brooks - Corey (BC) and Fredlund - Xing (FX) models. Largely, BC and FX models o...

The objective of this project was to characterize the properties of crushed recycled concrete (RCA) and asphalt pavement (RAP) as unbound base without being stabilized, to assess how RCA and RAP behave in the field and to determine how pavements can be designed using RCA and RAP. Issues to be considered include variability in material properties, purity of material, climatic effects, how to identify and control material quality, and leaching characteristics. This project included laboratory specimen and large-scale model tests and evaluation of field data from MnROAD test sections constructed using recycled materials. To identify the characteristics of RAP and RCA typically available in different parts of the country, samples were obtained from eight states: California, Colorado, Michigan, Minnesota, New Jersey, Ohio, Texas, and Wisconsin covering a geographically diverse area. A conventional base course was used as a control material. The extensive investigation undertaken on RCA and RAP indicate that these materials are generally suitable for unbound base course applications and they show equal or superior performance characteristics compared to natural aggregates in terms of stiffness, freeze-thaw and wet-dry durability, and toughness. Their typical compositional and mechanical properties and their variability are defined in this study providing a basis for design considerations. Their relative differences from natural aggregate such as temperature sensitivity, plastic deformations, and water absorption and retention characteristics are also well established. It is noted that some RAP may be sensitive to temperature change that may lead to rutting. This aspect needs to be considered in design.

Review of literature in the field of soil-pile raft-structure interaction indicates that considerable research effort was rendered towards to achieve accuracy in dynamic soil structure interaction (DSSI) model. Interestingly, limited results are available for design response of whole structural system. It is relevant to mention that pile damage (bending) has become a cause of distress in structures. In this context, an effort is devoted in the present paper to see whether DSSI have an adverse effect on elastic as well as inelastic behaviour in superstructure and foundation. This becomes possible through adopting a simplified substructure based DSSI modelling approach. Main focus of the present work is nonlinear seismic response of the whole structure with emphasis on consideration of material nonlinearity in both pile and soil which may contribute in salient design inputs towards performance based design of the whole structural system. Study reveals that consideration of DSSI condition results in inelastic deformation of superstructure and it exhibits marginal increase at higher stories. On the other hand significant increase in deformation at ground storey columns is observed if pile is restricted to deform within elastic range. In fact, initiation of smaller inelastic deformation of pile will lead to further increment in storey displacement, while such storey deformation will gradually decrease with higher inelastic range of deformation in piles and may be beneficial for superstructure system. Hence, designing of pile members with high ductility may reduce the seismic risk of failure of superstructure system. This physical insight may be an important consideration for performance based seismic design of structures.

Subsurface investigations are planned and executed to evaluate soil and rock conditions at project sites and to obtain relevant properties needed for analysis and design of structures. There are various field and laboratory tests used to characterise subsurface soil conditions. All tests have their own advantages and limitations. An extensive subsurface exploration programme was implemented for sections of two existing roadways experiencing continuing settlements which, as a result, require periodic pavement patching and resurfacing. The subsurface investigations involved drilling and soil sampling; field testing including SPT tests and CPT soundings; and various laboratory testing to assess conditions at the two roadway sections. The results show that CPT estimated N 60 values on average agree well with the SPT measured N 60 when all soil types are considered, but there is a significant scatter in the data. CPT estimated N 60 values for sandy soils were higher than the SPT measured N 60 values in nearly all cases, while CPT estimated N 60 values were lower than the SPT estimated N 60 values in the majority of cases for cohesive soils. The results also show that there is a good correlation between the average CPT-N 60 /SPT-N 60 ratios with respect to CPT soil behaviour type, SBT.

Subsurface investigations are planned and executed to evaluate soil and rock conditions at project sites and to obtain relevant properties needed for analysis and design of structures. There are various field and laboratory tests used to characterise subsurface soil conditions. All tests have their own advantages and limitations. An extensive subsurface exploration programme was implemented for sections of two existing roadways experiencing continuing settlements which, as a result, require periodic pavement patching and resurfacing. The subsurface investigations involved drilling and soil sampling; field testing including SPT tests and CPT soundings; and various laboratory testing to assess conditions at the two roadway sections. The results show that CPT estimated N 60 values on average agree well with the SPT measured N 60 when all soil types are considered, but there is a significant scatter in the data. CPT estimated N 60 values for sandy soils were higher than the SPT measured N 60 values in nearly all cases, while CPT estimated N 60 values were lower than the SPT estimated N 60 values in the majority of cases for cohesive soils. The results also show that there is a good correlation between the average CPT-N 60 /SPT-N 60 ratios with respect to CPT soil behaviour type, SBT.

A series of bearing capacity tests were conducted with an eccentrically (e/B = 0, 1/12, 1/6, 1/3) loaded model surface (Df/B = 0) and shallow (Df/B = 0.25) strip footings (B = 80 mm) resting close to reinforced finite sand slopes to investigate ultimate loads, failure surfaces, load–displacement curves, rotation of footing, etc. The experimental set-up used to run the tests consists of a tank, model footing, sand, and a loading mechanism. A single woven geotextile strip sheet was placed horizontally below the footing’s base at a depth of half of the footing’s width. Ultimate loads decreased with increasing eccentricity. This decrease is due to a combination of eccentricity and slope. The use of geotextile reinforcement increased ultimate loads in comparison with unreinforced cases. Failure surfaces were not symmetrical, primary failure surfaces developed on the eccentricity (slope) side, and secondary failure surfaces developed on the other side. Lengths of failure surfaces decrease...