Shear Strength Of Soft Clay Research Articles

Large-deformation study of T-bar penetration in spatially variable sediments

The T-bar penetrometer is extensively used in offshore field investigation and laboratory testing to evaluate the undrained shear strength of soft clay because of its reliability and repeatability in measurements. However, most previous studies on T-bar penetration have adopted a deterministic approach and focused solely on homogeneous soils, neglecting the geological uncertainty caused by the spatial variability of soil. To remedy this situation, this study aimed to investigate the effect of soil spatial variation on the T-bar penetration process in soft clay by employing large deformation random finite element modeling. The findings indicate that the variability in soil strength substantially modifies the flow pattern and failure mechanism of the soil, consequently influencing the penetration resistance factor of the T-bar. It was observed that the resistance factors follow the log-normal distribution. A relationship between the probability of failure as well as the factor of safety was determined, allowing for a clear assessment of the reliability level associated with varying factors of safety. To allow for this effect, a practical framework is developed to correct T-bar penetration data to estimate soil strength.

LOAD VERSUS SETTLEMENT BEHAVIOR OF SOFT CLAY REINFORCED WITH CEMENT STABILIZED RECYCLED ASPHALT PAVEMENT-LATERITIC SOIL COLUMN

In this paper, the performance of cement stabilized recycled asphalt pavement (RAP)-Lateritic column inclusion in soft clay was investigated via a physical model. The load-settlement response and bearing capacity of the composite ground was studied at various cement contents (0%, 1% and 3%) and at 30% RAP replacement ratio. The soft clay was consolidated in the PVC mold in a diameter of 150 mm and 300 mm high while the stabilized RAP-lateritic soil column with a diameter of 50 mm was used as a column at the center of the soft clay. The results showed that the bearing capacity of the composite ground significantly increased with the increased shear strength of column. The purposed bearing capacity equation derived from the unconfined compressive strength of column and undrained shear strength of soft clay was found to predict the bearing capacity of the composite ground satisfactorily.

Undrained shear strength of soft clay reinforced with encapsulated stone dust columns

PurposeThe stone dust column was used to strengthen the sample and had a significant effect on improving the shear strength of the kaolin clay. The application of stone columns, which can improve the overall carrying capacity of soft clay as well as lessen the settlement of buildings built on it, is among the most widespread ground improvement techniques throughout the globe. The performance of foundation beds is enhanced by their stiffness values and higher strength, which could withstand more of the load applied. Stone dust is a wonderful source containing micronutrients for soil, particularly those derived from basalt, volcanic rock, granite and other related rocks. The aim of this paper is to evaluate the properties of soft clay reinforced with encapsulated stone dust columns to remediate problematic soil and obtain a more affordable and environmentally friendly way than using other materials.Design/methodology/approachIn this study, the treated kaolin sample's shear strength was measured using the unconfined compression test (UCT). 28 batches of soil samples total, 12 batches of single stone dust columns measuring 10 mm in diameter and 12 batches of single stone dust columns measuring 16 mm in diameter. Four batches of control samples are also included. At heights of 60 mm, 80 mm and 100 mm, respectively, various stone dust column diameters were assessed. The real soil sample has a diameter of 50 mm and a height of 100 mm.FindingsTest results show when kaolin is implanted with a single encased stone dust column that has an area replacement ratio of 10.24% and penetration ratios of 0.6, 0.8 and 1.0, the shear strength increase is 51.75%, 74.5% and 49.20%. The equivalent shear strength increases are 48.50%, 68.50% and 43.50% for soft soil treated with a 12.00% area replacement ratio and 0.6, 0.8 and 1.0 penetration ratios.Originality/valueThis study shows a comparison of how sample types affect shear strength. Also, this article provides argumentation behind the variation of soil strength obtained from different test types and gives recommendations for appropriate test methods for soft soil.

Effect of strain-softening and strength anisotropy on the undrained bearing capacity of non-associated clay

The bearing capacity of soils is critical in the design and analysis of foundations. The classical solutions derived from methods of characteristics and bound theories are based on the rigid plasticity and associated flow rule, which may not be realistic for natural soils. The undrained shear strength of soft clays exhibits strain-softening and anisotropic behaviour in laboratory tests, which creates complexity when choosing appropriate strength parameters in the conventional design process. In addition, the stress–strain characters are non-associative and path dependent, which also affects the bearing capacity of soils. This paper investigates two classical stability problems (i.e. deeply embedded pile/pipe section and rigid strip footing) using finite-element analysis and the MIT-E3 soil model, and demonstrates the effects of stain-softening and strength anisotropy on the undrained bearing capacity of soils. The computed results are compared with analytical solutions and finite-element limit analyses, as well as those from finite-element analysis using conventional soil models. These findings have strong practical implications in predicting the bearing capacity of foundations and interpreting in situ tests.

Numerical Assessment of Jackup Spudcan Foundations by varying Angle of Spud in 3d Fem in Geotechnical Engineering

A jack-up structure is a bottom-mounted floating unit having an adjustable hull and movable legs. Particular jack-up structures are more susceptible to hazards under environmental loads during their operation and life cycle in the ocean. Authors attempted here to evaluate vertical load carrying capacity of soil and predicting its behaviour. Simulation of loaddeformation behavior under axial compression has been carried out for advancing research. The entire study has been carried out using three-dimensional finite element-based software Plaxis 3D A.E. 2017. The geometrical variation of substructure spud can have an inverted spud at the centre bottom from 1200 to 1800 studied for knowing behaviour under axial compression, axial tension and lateral forces. The simulated numerical model is used to develop empirical expressions for axial capacities estimation. The numerical analysis results indicate that spud can have an inverted angle of cone 1300 which is most beneficial under the static combined vertical, moment and horizontal loading (3D loading) in marine clay. The axial load carrying capacities in compression, tension and lateral loading follow the same sequence in ascending order from 1800,1750, 1500, 1300 and highest in 1200. Stiffness and undrained shear strength of soft clay contribute more than the diameter of the spud and embedment depth in compression and tension.

Behavior of the geotextile reinforced dykes on sand-overlying-clay deposit

An extensive investigation on the performance of large geotextile mat dykes on stiff-over-soft soil deposits is carried out undertaken through numerical simulation in this paper. The large mat is reinforced by geotextiles with a new type of arrangement, i.e. non-uniform geotextile reinforcement. The numerical model is validated against centrifuge test data and other previously testing results, prior to conduct parametric study. It is found that large geotextile reinforced dykes on sand overlying clay fails through a global mechanism that the whole dam sank downwards together. It is found that the thickness of the sand layer, the width of the dyke base, and the shear strength of soft clay are the key influence factors on the stability of the dyke. A design flow chart is then proposed to quantity the performance of the geotextile mat dyke with non-uniform reinforcement, in terms of predicting allowable dyke fill height and the corresponding safety factor, which can be employed to provide refer for its design and construction.

Enhancing the Life Cycle of the Jack up Structure by Applying Alternative Foundation Methodologies in Geotechnical Engineering

A jack-up structure is a bottom-mounted floating unit having an adjustable hull and movable legs. Particular jack-up structures are more susceptible to hazards under environmental loads during their operation and life cycle in the ocean. Authors' attempts here to enhance its life cycle and sustainability in shallow to deep waters by correctly accessing soil behaviour and predicting its load carrying capacity. Here the numerical analysis of the substructure has been attempted. Simulation of load-deformation behavior under axial compression has been carried out for advancing research. The entire study has been carried out using three-dimensional finite element-based software Plaxis 3D A.E. 2017. The geometrical variation of substructure spud can have an inverted spud at the centre bottom from 120 0 to 180 0 has been studied for knowing behaviour under axial compression, axial tension, and lateral forces. The simulated numerical model is used to develop empirical expressions for axial capacities estimation. The numerical analysis results indicate that spud can have an inverted angle of cone 130 0 is most beneficial under the static combined vertical, moment, and horizontal loading (3D loading) in marine clay. The axial load carrying capacities in compression, tension, and lateral loading follow the same sequence in ascending order from 180 0 ,175 0 , 150 0 , 130 0 and highest in 120 0 . Stiffness and undrained shear strength of soft clay contribute more than the diameter of the spud and embedment depth in compression and tension.

Effects of biopolymers on the liquid limit and undrained shear strength of soft clays

Effects of biopolymers on the liquid limit and undrained shear strength of soft clays

Experimental Evaluation of the Reference, Shear-Rate Independent, Undrained Shear Strength of Soft Clays

Abstract The soil’s undrained shear strength is affected by the rate of shearing. This dependency can be inferred from mechanical laboratory testing at different operation rates or from using diffe...

Assessing the undrained strength of very soft clays in the SPT

The log of a SPT in very soft clay may simply indicate a zero blow-count, or present information on the penetration – under self-weight – of the composition (sampler, rods and hammer) as recommended by some standards. The second type of information is often disregarded by design engineers due to the lack of a standard procedure for measuring these penetrations or because the test is regarded as not sensitive enough to give an indication on the undrained shear strength of soft clays. The penetration under the composition’s selfweight, however, can indicate the magnitude of Su, which, along with other more specific and sensitive tests, can help in assessing the spatial distribution of clay consistency in a large deposit. A proposed test procedure and interpretation had been given in an earlier technical note. This note presents an extended formulation and an evaluation of Su via the SPT at a construction site in Rio de Janeiro, including comparisons with results of piezocone and vane tests. The values of Su obtained with the SPT lie between the profiles given by vane tests, corrected by Plasticity Index, and the Critical State Theory, the latter representing a lower bound to the clay strength.

Improvement of shear strength and compressibility of soft clay stabilized with lime columns

Soft clay improvement using lime columns is an effective and economic method; which used mainly for enhancing the engineering properties of soft soil, reducing settlement and increasing shear strength. Improvements in engineering properties of soft clay can be achieved instantaneously with small additions of lime to soft soils. However, the effectiveness of this improvement depends on the quantity and type of lime as well as the mineralogical composition of soil. In this paper, the behavior of soft clay improved with lime columns has been studied. A series of large scale direct shear box tests were carried out with different number of lime columns, diameter, and different curing periods. Experimental study was carried out on both single and a group of lime columns. The results showed that the group of columns increased the shear resistance of soft clay soil with lesser horizontal deformation. Shear strain decreased by 28% and 47% in case of using 1 and 4 lime columns respectively after 7 days curing. Meanwhile, increasing the lime column diameter was found to increase the shear strength of soft clay and improve its compressibility. Finally, the shear strength was found to be increased by 53% when using a single lime column, while when using a group of 4 lime columns with diameter/length (D/L) ratio equals 0.28, the shear resistance is duplicated compared to the case of soft clay without lime columns.

Investigation of the mechanical behavior of soft clay under combined shield construction and ocean waves

This study aims to investigate the mechanical behavior of soft clay under both shield construction and long-term dynamic wave loading in the practical construction of breakwaters to protect coastal power plants. Continuous rotation of the principal stress axis due to cyclic wave loading is reproduced by altering the control loads (that is, axial load, torque, inner cell pressure, and outer cell pressure) in a hollow cylindrical shear apparatus (HCA). In the HCA, the confining pressure is progressively reduced to replicate the stress release induced by ground loss during shield construction. The HCA test results show that both long-term wave loading and shield construction significantly affected the dynamic stiffness of soft clay. Under the combined effects of wave loading and shield construction, the post-cyclic shear strength and stiffness of the soft clay are reduced more significantly compared to the isolated effect of wave loading, especially at lower confining pressure. The degradation of the dynamic secant modulus, Ed, and the initial tangential modulus, Ei, is indicated to be synchronous at the end of the cyclic loading test, which implies the unique disturbance of the combined action of shield construction and dynamic wave loading on the microstructure of soft clay considered in this study. Based on the experimental observations, a simple and effective constitutive model is also developed to reproduce the degradation of stiffness and shear strength of soft clay induced by shield construction and dynamic wave loading.

Analysis of thermal power plant fly ash and lime in increasing shear strength of soft clay

Soil is the basic foundation for any civil engineering structures. It is required to bear the loads without failure. In some places, soils are weak which cannot resist the oncoming loads. Soft clay is known to have low strength and high compressibility. Utilization of additive is a method that can be applied to increase shear strength of soft clay. This study was conducted to determine the effectiveness of mixing fly ash, lime and soft clay with different percentage in order to increase the strength. A series of laboratory test were conducted in determining the physical properties, compaction and shear strength on soft clay soil. The soil samples; both disturbed and undisturbed were obtained from the vicinity of Politeknik Sultan Idris Shah (PSIS). Two tests carried out are compaction and direct shear strength. From the results, the highest strength of soft clay was at 69 kPa by mixing soil with 12% fly ash + 4% lime.

The shear strength of soft clay reinforced with single and group crushed brick column

Soft Clay is often known to be a problematic soils in construction because of its low strength and high compressibility characteristic. Before construction begins, ground improvement needs to be done to improve the soil bearing capacity so that the superstructure can be placed on top of it and reduce settlement and consolidation. In this study, the soft clay is going to be reinforced with crushed brick column which is part of construction waste produced during construction stage to achieve sustainable construction. This study was aimed to investigate the effectiveness of single and group crushed brick column in improving the shear strength by using laboratory scale model. Kaolin is being used as soil sample while crushed brick as the reinforced column. Few laboratory tests are conducted to determine the properties of kaolin clay and crushed brick. Unconfined Compression Test (UCT) also used to test the shear strength of the reinforced kaolin samples The improvement of shear strength of single crushed brick column with area replacement ratio of 4.00% (10mm column diameter) are 3.34%, 4.60% and 1.07% at sample penetration ratio, Hc/Hs of 0.6, 0.8 and 1.0 respectively while for area replacement of 10.24% (16 mm column diameter) are 7.56%, %, 16.37% and 4.97% at the same penetration ratio.. The result shows that the improvement shear strength for height penetration ratio of 1.0 is 13.33% which was the highest, while 0.6 and 0.8 are 12.31% and 9.79% respectively for group crushed brick columns with diameter 10mm. The improvement of shear strength is highest for height penetration ratio of 1.0 with 16.10% improvement which was slightly higher than 0.6 and 0.8 which were 13.49% and 11.35% respectively in sample reinforced with grouped columns with diameter 16mm. It can be concluded that the shear strength of soft clay could be improved by installation of single and group crushed brick column.

Behaviour of the Undrained Shear Strength of Soft Clay Reinforced with Natural Fibre

The term soil reinforcement is conventional since decades ago for the stabilization of soft ground such as of clay and peat. Numerous research has arisen in the utilization of natural fibres as the reinforcement materials. Cost reduction, increment of sustainability awareness and eco-friendly environment are some of the advantages when using natural fibres to stabilize soft ground. A research study was carried out to evaluate the strength of the soft soil when unreinforced and reinforced using natural fibres. The findings on the experimental investigation of the study will be presented in this paper. Crushed coir fibres were used to reinforce an intermediate plasticity soft clay where both materials were collected locally in Brunei Darussalam. The crushed coir fibres were added at 0.5%, 1.0%, 1.5% and 2.0% to the dry weight of the sample. A series of an unconsolidated undrained Tri-axial test was conducted on the unreinforced and reinforced samples where the behaviour of the samples were observed and compared. The results indicated that inclusion of fibres affects the soil’s undrained shear strength. It was observed that increasing the percentage inclusion increases the undrained shear strength of the soil, up to a certain amount. Further increment of fibres, however, does not show further improvement in the undrained shear strength.

STRENGTH OF SOFT CLAY REINFORCED WITH 10 MM SINGLE CRUSHED COCONUT SHELL (CCS) COLUMN

Stone column can be used as a ground improvement technique where a portion of soft soil is replaced with granular material such as stone or sand. The benefit of using stone columns in low strength soil has been proven as an efficient method to improve the bearing capacity and reduce settlement of soft soils. This study aims to investigate the improvement in shear strength of soft clay by embedded with a single crushed coconut shell (CCS) column. The cost of soil improvement can be reduced because of CCS is a waste material. This paper was done by determining the physical and mechanical properties of kaolin and CCS as well as the effect of height penetration ratio of a single CCS column on shear strength characteristics. Unconfined Compression Test (UCT) was conducted for 4 batch kaolin samples including a control sample in order to determine the shear strength. Each batch involved four samples to find the accurate value. The research variables are the height of crushed coconut shell column which is 60 mm, 80 mm and 100 mm where the column penetration ratio is 0.60, 0.80 and 1.00 respectively. A total of 16 unconfined compression tests had been conducted on kaolin sample with dimensions of 50mm in diameter and 100 mm in height. The increment of shear strength by embedded with crushed coconut shell columns is 19.02 %, 34.76 % and 24.34 % for with 4 % area displacement ratio at column penetration ratio of 0.60, 0.80 and 1.00 respectively. From the results obtained, the relationship between shear strength increases is influenced by the height of the column. The maximum column height (full penetration) does not generate the highest strength and it proves that critical column length theory is true in this study.

The effect of gypsum plafond waste on shear strength of soft clay soil

One type is soft clay soil which has a low compressibility and high water content that causes the carrying capacity of the soil to be low. In this research, soil improvement was carried out chemically by soil stabilization method using a mixture of gypsum plafond waste with a percentage of 5 %, 10 %, 15 %, 20 %, and 25 % in a laboratory scale. Soft clay samples used for the study were taken in the Pakjo area of Palembang, South Sumatra. The use of gypsum plafond waste as a mixture was expected to increase the shear strength of soft clay. Tests carried out include testing Direct Shear. Based on the USCS classification, the soil was classified as CH and based on AASHTO classification was A-7-6. The value of wop is 22 % (optimum moisture content) and the value of γdmax is 1.74 gr/cm3 (maximum dry weight). The maximum cohesion (c) value is 24.20 kPa from 15 % mix of gypsum plafond waste (WPG15) sample. For the maximum value internal friction angle (ϕ) is 16.36 °C from 5 % mix of gypsum plafond waste (WPG5) sample. The maximum shear strength (τ) is 26.57 kPa from 5 % mix of WPG15 sample.

Effect of Pore Fluid Concentration on Shear Strength of Soft Clay

Consolidated quick direct shear tests were conducted on bentonite and mixed bentonitekaolin soils with different concentrations of sodium chloride solution. The physical mechanism of the pore fluid concentration effect was explained at the micro level on the basis of micro forces among particles. The test results indicated that the shear strength of bentonite and bentonite-kaolin noticeably varied with increase in sodium chloride solution concentration, especially under high vertical stress. The friction angle increased with the pore fluid concentration, but the cohesion decreased. With increase in pore fluid concentration, the electric double-layer repulsion among soil particles decreased, thereby increasing the effective contact stress at the mineral-mineral contact and leading to increased consolidation settlement and a lower water content under vertical stress. This means a larger shearing resistance at the mineral-mineral contact point and a thinner absorbed water layer at the mineral-water-mineral contact point, leading to a greater friction angle and a lower cohesion.

Modelling the degradation of penetration resistance during cyclic T-bar tests in a Gulf of Mexico clay

Installation and repetitive movement during the operation of a pipeline causes remolding and softening of the surrounding soil. Similar effects can occur around foundations during their operating life. The degradation of the undrained shear strength of soft clays near the seabed is a critical component of the design of subsea facilities, including pipelines and shallow foundations. This paper presents a two-stage strength degradation model based on the framework developed by Hodder et al. (2010) for repeated vertical movement of a cylindrical object (T-bar penetrometer) embedded in a soft Gulf of Mexico (GOM) clay. The model is compared with the behavior observed in four box cores sampled in the Gulf of Mexico, in which 8 cyclic T-bar penetrometer tests were performed. By varying the parameters in the strength degradation model, its applicability for GOM clay is examined, and the effects of the location of cycling within the box core and parameter variability between box cores relative to the average parameters are explored.

SHEAR STRENGTH OF SOFT CLAY REINFORCED WITH ENCASED LIME BOTTOM ASH COLUMN (ELBAC)

Soft clay soils are problematic soil that causes bearing capacity failure and excessive settlement, leading to severe damage to buildings and foundation. In this study, bottom ash is used to replace the natural aggregate while quicklime is used to increase the bonding between bottomash particles. This research is aimed to investigate the role of single encased lime bottom ash column (ELBAC) in improving the shear strength by using laboratory scale model. Kaolin is being used as soil sample while lime bottom ash as the reinforced column and the column is encased with non-woven geotextile. Laboratory tests are conducted to determine the physical properties of bottom ash, kaolin clay, and quicklime sample. Unconfined Compression Test (UCT) also used to test the shear strength of the reinforced kaolin samples. There are 21 kaolin samples being tested in this study and the dimension of the specimen used is 50mm in diameter and 100mm in height. However, there are two different types of the diameter of single lime bottom ash column being used which are 10mm and 16mm. The heights of the column are 60mm, 80mm and 100mm. The improvement of shear strength of single encapsulated lime bottom ash column with area replacement ratio of 4.00% (10mm column diameter) and 10.24% (16mm column diameter) are 43.58%, 50.00%, 49.17% and 38.08%, 42.67%, 32.75% at sample penetration ratio, Hc/Hs of 0.6, 0.8 and 1.0 respectively. It can be concluded that the shear strength of soft clay could be improved by the installation of the single encapsulated lime bottom ash column.