Soft Clayey Soil Research Articles

Seismic performance of buildings supported by a shallow doubly-curved shell raft foundation

Foundation transmits loads of superstructure to soil layers. Also, seismic loads are transmitted to the superstructure via the foundation. It has been shown that the characteristics of the foundation affect the seismic response of the superstructure. The influence of shell foundations on the seismic performance of structures has not been investigated in the literature. In this paper, the seismic response of 5, 10, and 15-story steel moment-resisting structures supported by a shallow doubly-curved shell raft foundation is compared to the seismic response of these structures supported by a pile-raft foundation. It was assumed that structures are founded on soft-clayey soil. Soil-foundation-structure systems were analyzed under the influence of four earthquake excitations using fully nonlinear time-history analysis. The numerical results generally show that the maximum displacement decreases while the maximum shear force increases in each story of structures with shell foundation compared to structures with pile-raft foundation. Moreover, the results reveal the better seismic performance of structures supported by shell foundation in terms of the maximum inter-story drift compared to structures supported by pile-raft foundation.

Improvement of Soft Clayey Soil by Bio-polymer

This examination explains the utilization of bio-polymer powder for clayey soil enhancement. The article concentrates around examining the strength attitude of the clayey soils built up with homogenous bio-polymer. Carboxy methyl cellulose was determined as bio-polymer material to build up the normal soft clayey soil. The biopolymer has been added to the soil with two separated rates (0.5 and 3%) by total weight of soil. Different tests were carried out to consider the impact of utilizing this polymer as a balancing out specialist on the geotechnical properties of soil. It was estimated that as the bio-polymer content expands in the soil, the specific gravity decreases, while the optimum water content (OMC) is expanded. The results showed different effects on Atterberg’s limits; by increasing the liquid limit(L.L) and plasticity index(P.I) while the plastic limit decrease. The tests additionally mirrored a huge improvement in the unconfined compressive strength (UCS) of the treated soils. With the increment in biopolymer content, the consolidation index (Compression index Cc and recompression index Cr) decrease.

Modelling the capacity of micropiled-raft foundation rested on soft clayey soil using an artificial neural network approach

ABSTRACT Micropiled-raft foundation shows its ability to solve particular type of foundation problem i.e. building of medium height and weight structures over soft deep-seated clayey soil deposit. Potential of artificial neural network method was used in the study for the assessment of capacity of micropiled-raft foundation under a given settlement in soft clayey soil considering the complex non-linear load-settlement behaviour. Experiments were conducted on micropiled-raft foundation constructed with different variables within a soft clayey soil bed in the test pit in field and a database was prepared from load-settlement graphs those were utilized to develop different ANN models. It was observed from the study that Bayesian Regularization algorithm with 90–10% validation model performs the best. Sensitivity analysis was performed to determine the relative significance of different input variables and a neural interpretation diagram was prepared. An empirical equation was proposed with best fit ANN model and an example illustrated.

Towards the vulnerability assessment of low-code RC frame buildings at precarious slopes subjected to rainfall induced landslide hazard

The presence of capillary pressure in unsaturated soils may, under certain circumstances, significantly affect the stability of a slope and the safety of a structure standing in the vicinity of its crest. More specifically, the change in saturation induced by a rainfall event may directly influence the value of apparent soil cohesion potentially resulting in excessive permanent slope displacements and subsequent structural damages for the structure standing on it. Under these considerations, this study aims at the vulnerability assessment of typical reinforced concrete (RC) buildings on precarious slopes subjected to rainfall induced landslide hazard. The proposed methodology is based on a two-step numerical analysis procedure. First, the permanent absolute and differential ground displacement time histories at the assumed building location within the landslide zone are evaluated performing coupled mechanical-flow analysis of a generic initially unsaturated natural slope configuration considering the employment of different rainfall events of increased intensity at the surface of the slope model. Different soil properties of the surface layer are considered to represent silty and soft clayey soil material. Appropriate analytical relationships between the rainfall intensity and its duration and the computed permanent displacements are extracted. Then, a series of nonlinear static time history analyses are performed for reference low and mid-rise, low-code RC bare and infilled frame buildings located next to the slope's crest to assess their fragility. The buildings’ response assessed using appropriate engineering demand parameters (EDPs) to account for both the global flexural and local shear demand are statistically correlated with predefined damage limit states to construct the fragility functions. To facilitate the applicability of the proposed methodology within a quantitative landslide risk assessment framework, vulnerability curves are finally developed to quantify the expected direct losses in normalised cost terms.

Drained Creep Test and Creep Model Evaluation of Coastal Soft Clay

Prediction of the long-term behavior of soft clayey soils after construction is of paramount importance for civil and geotechnical engineers. Deformations on the bedded layers occur slowly as a result of exposure to additional high level of stresses. In this study, creep tests of soft clay soils from coastal area were conducted to examine long term stress–strain behaviors with varying stress levels in the laboratory under drained constant loading condition. The creep tests showed that drained features would induce viscoelastic creep behavior. The instantaneous stiffness decreases with deviatoric stress, but increases with confining pressure. Then two component models and three empirical models were compared with laboratory creep tests, component models are found more reliable than empirical models for drained creep test, and the Burgers model is more consistent with the test results. But empirical models have less parameters, especially for different deviatoric stress at same confining pressure.

A study on the effects of piled-raft foundations on the seismic response of a high rise building resting on clayey soil

Piled-raft foundations are often used to transfer the structural load to the depth of the soil and tall structures can be constructed on medium to soft soils by utilizing a group of piles. The static effects of a group of piles are quite evident while their dynamic effects are quite unknown and therefore, not considered in the design of the superstructure.In the present research, the performance of pile-raft foundations on the seismic response of a 20-story benchmark building resting on soft clayey soil has been investigated using a 2D finite difference model, namely FLAC. The study has been carried out by analyzing the seismic response of the structure with and without pile-raft foundations, on the surface and inside an excavation.The results show that when the structure is constructed on the surface, piled-raft foundations have a significant beneficial effect on the seismic response of the superstructure, for instance a 40% decrease in the base shear. In the case where the structure is located inside an excavation the use of piled-raft foundations are not noteworthy and do not have a considerable effect.The results of this study give an insight on the effects of pile-raft foundations on the seismic response of a superstructure to overcome the current shortage of information in this area and to better predict the behavior of tall structures in soft soil situations.

Numerical investigation on the performance of stone columns under raft foundation in soft clayey soils

Stone columns are the most common and effective technique used for enhancing the overall strength and performance of soft soils. They are more effective for moderately lightweight structures. This investigation presents a parametric study of stone columns embedded in ground to strengthen the soft clayey soil under stiff raft foundation. This research is based on a computational analysis by creating a foundation finite element model consisting of a group of stone columns that are mounted under rafting using PLAXIS 3D. A certain range of parameters (for example spacing, diameter and angle of friction of stone columns) is considered and it is concluded that the increase in diameter and angle of friction of stone columns can improve the ultimate load bearing capacity of the foundation system. Furthermore, the failure mechanism of this foundation scheme is analysed and a semi-empirical model for the determination of the bearing capacity ratio (BCR) is developed from the results of the parametric analysis.

Effect of Exploration Depth on Microstructural Behavior of Subsurface Soft Clayey Soil for Foundation Construction Purposes

The geomorphological, microstructural pattern and mineralogical configuration of subsurface soils explored from 1-meter, 3-meter and 7-meter depths have been studied for the purpose of foundation materials suitability. Soils samples arehauled from borrow sites to where they are utilized as foundation materials. In very most cases, this exploration is doneat varying depths and soil being an erratic geomaterial change in its important engineering characteristics with depth.This laboratory examination was necessary to establish the microstructural behaviour and pattern of soils when they areexplored from different depths. The samples collected from different depths showed to be A-3 soils according to AASHTOclassification method and poorly graded according to the USCS. Also varying depth of the soil sample was characterizedby a proportional increase in moisture content; this as well applies to the `liquid limit, plastic limit and plasticity indexvalues respectively with an exception in the shrinkage limit, which reduces with increase in depth of soil sample. This can beattributed to the erratic behavior of soil, which makes it change behavior from location to location and from depth to depth,clayey contents changes with depth likewise its desiccation properties. The geomorphology and microstructure of the soilsshow weaker configuration with increased depth of exploration to 7 meters. This shows that for any foundation purposes,soils at both 3 meter and 7-meter depths require treatment to be suitable for construction purposes. Geo-constructions likecompacted earth liner systems, mechanically stabilized earths or backfills, pavement subgrade systems can be constructedwith the studied soils but care must be taken to modify the soils to meet the basic design considerations.

Geotechnical properties of clayey soil improved by sewage sludge ash

ABSTRACT Rapid urbanization has resulted in the production of large quantities of sewage sludge over worldwide. The disposal of sewage sludge in landfills or open areas is not considered as an environmentally friendly solution. Therefore, the use of sewage sludge as ash can provide a better solution in geotechnical applications. Keeping this in view, this study investigates the possibility of using sewage sludge ash (SSA) to improve the geotechnical properties of soft clay soil. The sewage sludge ash (SSA) is attained by burning the sludge for 2 h at 900°C. The tests conducted on the clayey soil are specific gravity, standard Proctor test, sieve analysis, Atterberg limits, CBR test and unconfined compression test. Three curing times were used for the untreated soils and soils treated with sewage sludge ash (SSA) which are 3 days, 14 days and 28 days. The sewage sludge ash (SSA) was mixed with the soil at different percentages by weight of the soil at 10%, 15% and 20% of dry soil weight. The results showed that the sludge ash increases the unconfined compressive strength of the soft soil at 3, 14, 28-day curing time. The bearing capacity of the soil decreases after adding SSA at the first, but curing time led to improve the bearing capacity of clayey soil after adding SSA and the percentage of SSA of 10% gave the optimum value of CBR. The results indicated that a better performance of the unconfined shear strength was obtained at 28-day curing time. The findings of this research indicate that sewage sludge ash (SSA) can be used to improve the soft clayey soil and further reduce the environmental risks associated with this substantial. Implications: Rapid urbanization has resulted in the production of large quantities of sewage sludge over worldwide. The disposal of sewage sludge in landfills or open areas is not considered as an environmentally friendly solution. Therefore, the use of sewage sludge as ash can provide a better solution in geotechnical applications. Keeping this in view, this study investigates the possibility of using sewage sludge ash (SSA) to improve geotechnical properties of soft clay soil. In this paper, Sewage Sludge Ash (SSA) is recycled as a new type of chemical addition to soft clay soil and used as a stabilizer to improve a clayey soil. This study proposes that a percent of the total amount of clay to be reinforced is replaced with sewage sludge ash (sewage sludge ash plus soil) in order to achieve the need of improvement in the geotechnical properties of clayey soil and make use of industrial wastes. The sewage sludge ash (SSA) is attained by burning the sludge for 2 h at 900°C. The tests conducted on the clayey soil are specific gravity, standard Proctor test, sieve analysis, Atterberg limits, CBR test, and unconfined compression test. Three curing times were used for the untreated soils and soils treated with sewage sludge ash (SSA) which are 3 days, 14 days, and 28 days. The sludge ash (SSA) was mixed with the soil at different percentages by weight of the soil at 10%, 15%, and 20% of dry soil weight. The results showed that the sludge ash increases the unconfined compression strength of the soft soil at 3, 14, 28-day curing time. The bearing capacity of the soil decreases after adding SSA at the first, but curing time led to improve the bearing capacity of clayey soil after adding SSA and the percentage of SSA of 10% gave the optimum value of CBR. The results indicated that a better performance of the unconfined shear strength was obtained at 28-day curing time. The findings of this research indicate that sewage sludge ash (SSA) can be used to improve the soft clayey soil and further reduce the environmental risks associated with this substantial.

Dynamic Responses of Reinforced Soil Model Wall on Soft Clay Foundation

This paper investigated the relative seismic response of reinforced soil retaining wall overlying a soft clayey soil layer—applicable to road or railway embankment. A series of 1D shaking table tests, 0.1 to 0.5 g, were conducted on the 1 m high physical model. The scaled physical model was subjected to harmonic sinusoidal input motions at frequencies of 1 Hz, 3 Hz, 5 Hz, 10 Hz, 12 Hz, and 15 Hz. A laminar box was used to enclose the soil during the experiment. The variation of parameters such as base motion excitations; frequencies; and surcharge pressures were studied. The results of this study revealed that these parameters have a significant influence on the model wall and vary along the elevation; impacting pore water pressure as well. It also had an impact on the variation along the depth of the clayey soil layer. Maximum face deformation was observed at the top layer of the wall.

Seismic Analysis of Floating Stone Columns in Soft Clayey Soil

The response of floating stone columns of different lengths to diameter ratio (L/D = 0, 2, 4, 6, 8, and 10) ratios exposed to earthquake excitations is well modeled in this paper. Such stone column behavior is essential in the case of lateral displacement under an earthquake through the soft clay soil. ABAQUS software was used to simulate the behavior of stone columns in soft clayey soil using an axisymmetric finite element model. The behavior of stone column material has been modeled with a Drucker-Prager model. The soft soil material was modeled by the Mohr-Coulomb failure criterion assuming an elastic-perfectly plastic behavior. The floating stone columns were subjected to the El Centro earthquake, which had a magnitude of 7.1 and a peak ground acceleration of 3.50 m/s2. The surface displacement, velocity, and acceleration in soft clayey enhanced by floating stone columns are also smaller than in natural soft clay. The findings of this research revealed that under the influence of earthquake waves, lateral displacement varies with stone columns of various lengths.

Improvement Separation Layer of Disconnected Piled Raft Foundations using Geogrid and Geocell Layers

To control the problems of high stresses and applied moments in the piled raft foundations disconnected piled were used and the piles considered as reinforcement to the soil rather than as structural members, the gap (separation layer) between the piles and the raft can be filled with stabilized granular material which distributes the stresses below the raft and decreases the concentration stresses at the pile heads. Fifteen model tests were performed using three precast concrete pile models embedded within soft clayey soil of undrained shear strength 30kPa. Flexi-Force sensors were used fixed on piles head and the surrounding soil to measure the sharing load transmitted to piles and the surrounding soil. Geogrid and geocell materials were used in different depths and in multilayers to reinforce the separation layer and increase its stiffness. The results show that when reinforcing the separation layer with geogrid at different depths, an increase in depth over the top of the piles reduced the bearing pressure. When used, geocell reinforcement significantly increases in load carrying capacity, and a significant reduction in footing settlement occurs.

Soft soils: A study on their electrical resistivity values and geotechnical properties (porosity, SPT and particle size distribution)

Soft soils pose abundant engineering issues due to its low bearing capacity and shear strength. Comprehensive study on soft soil’s physical properties such as shear strength and ability to store water (porosity) could help in devising the optimum ground improvements and foundations techniques. Therefore, physical properties of soft marine clay in Nibong Tebal were thoroughly studied using 2-Dimensional Resistivity Imaging (2-DRI) method in conjunction with porosity measurements, standard penetration test values (SPT-n) and particle size distribution (PSD) analysis. The 2-DRI profile depicts three lithologies, which are unsaturated topsoil, saturated soft clayey soil and saturated sandy soil in the area. The soft soil extends up to 32 m in thickness where it overlies the sandy layer and could be correlated back to lithology profile from borehole record. Additionally, soil samples were collected at three locations along the survey line for porosity measurements via saturation porosimetry method. The samples demonstrate that the clay layer has a very large porosity range and signifies that the soil will compress tremendously under load. On the other hand, SPT-N values of the soft clay is also very low; thus, could be classed as very soft to soft cohesive soil with very low shear strength as compared to a higher range SPT-n values of the sandy layer. The PSD result also compliments the 2-DRI, porosity and SPT results to show distinct differences between topsoil and the soft clay layer in terms of the presence of fine grains. These results further indicate that the thick upper layer is not capable of bearing immense loads such as high-rise infrastructures due to the soil’s high porosity and low shear strength. Hence, the area must undergo ground remediations prior to any infrastructure developments on the land.

Axial sliding resistance of partially embedded offshore pipelines

This paper presents the results of centrifuge model tests and three-dimensional large-deformation finite-element analysis on axial pipe–soil sliding behaviour of partially embedded subsea pipelines. A three-dimensional re-meshing and interpolation technique with small strain approach was adopted using the Abaqus mesh-to-mesh solution mapping feature with the Cam Clay model. The parameters studied include soil properties, interface friction coefficient, embedment depth and post-lay reduction in vertical load. Embedment depth and post-lay load reduction were found to exercise the strongest influence on the post-consolidation and sliding behaviour. Empirical relationships correlating centrifuge experiments and numerical modelling are proposed for the embedment enhancement factor in terms of the embedment and vertical load ratios, under conditions of very slow sliding, corresponding to the drained condition. For very fast sliding, corresponding to effectively undrained conditions, similar relationships involving embedment and vertical load ratios and interface friction coefficients are also proposed. Finally, the variation of embedment enhancement factor with sliding velocity is expressed in terms of a relative enhancement index, Ψ, which can be adequately described by hyperbolic relationships for the complete range of consolidation history. These relationships provide a basis for the evaluation of the embedment enhancement factor corresponding to an arbitrary sliding velocity, which can be used in routine analysis and design of as-laid underwater pipelines in soft clayey soils.

Experimental Study of Rubble Mound Behavior on the Very Soft Soil Seabed

The construction of rubble mound structures such as a breakwater or access road on a very soft seabed is essential to the development of maritime transportation. This process can result in significant settlement that causes the rock particles to sink into the seabed, leading to loss of material. In the current study, several case studies on breakwaters facing large settlements, which resulted in the use of excessive amounts of rubble, were surveyed. A series of physical models were developed to study the deformation and volume loss of rubble mound breakwaters on very soft clayey soil during construction. It was found that most deformation occurred early in construction. The primary mechanisms influencing settlement were rock penetration into the soft bed, flow of clay material into the porous body of the rubble mound, and lateral deformation of the soil beneath the breakwater, which is associated with soft bed heave at the breakwater toe. During testing of very soft beds, the ratio of material loss to the design weight of the rubble mound increased up to 27%, and the proportion of penetration to total material loss was as high as 56%. The results of the experiments and case studies were used to develop an empirical relation with which to predict settlement.

Fractional Time-Dependent Merchant Model for Coastal Soft Clay

Deng, H.Y.; Dai, G.L., and Azadi, M.R., 2020. Fractional time-dependent merchant model for coastal soft clay. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 825–831. Coconut Creek (Florida), ISSN 0749-0208.Soft clayey soils behave a time-dependent creep property subjected to sustained load. In order to describe the stress-strain-time property of soft clayey soil, a time-based fractional creep constitutive model is proposed based on the Caputo fractional calculus by applying the Abel dashpot in classical component model. The proposed fractional Merchant model is validated by drained creep test of coastal soft clay. The model parameters are obtained by fractional nonlinear fitting in terms of drained creep test results of coastal soft clay. Then the predicted results by the proposed fractional Merchant model and classical component models are also compared and validated with creep test results. It shows that the proposed fractional Merchant model is more approached to drained creep test results than classical component models. In particular, the proposed fractional Merchant model could well reduce the errors in the initial phase of creep compared with the classical model. It is indicated that the fractional Merchant model is superior in predicting drained creep property of coastal soft clay.

Relative relevance of factors affecting the electrokinetic dewatering of soft clayey soils

Electrokinetic (EK) treatment is becoming increasingly important in the geotechnical field, especially for treating fine-grained soils. Above all, dredged sediments (slurries) need to be treated in order to be reutilised. Applying an electric potential difference within the soil, three phenomena take place: electrophoresis, electro-osmosis and electromigration. Negative particles move towards the positive electrode while water and cations move towards the negative electrode. Although the literature is full of cases describing the parameters that affect the EK process, there is a need to understand its limits and fields of application. This paper summarises the results collected from several case studies to understand the influence of some parameters on the efficiency of EK treatment, specifically in terms of dewatering rate. Soil conditions (soil type, pH, pore fluid salinity and water content) and set-up design parameters (electrode materials, configurations and operational mode) are analysed. Finally, parameter ranges for assessing the acceptability of electro-osmotic treatment are proposed. The results show that there are optimum values for the previously mentioned parameters that improve the dewatering and thus enhance the behaviour of the treated soils. EK treatment can be effective when applied on dredged sediments with low salinity.

Seismic Soft Soil-Structure Interaction Using RLBRB-Equipped Strut in Deep Excavations

ABSTRACT This paper presents the applicability of Reduced Length Buckling-Restrained Braces (RLBRBs) in combination with strut elements in deep excavations. Strut members are used as part of the lateral load resisting system. By proposing a new type of RLBRB section, the advantages of RLBRBs are demonstrated in dynamic soft soil-structure interactions. A numerical investigation is carried out to clarify the behavior of RLBRB-equipped strut members in supported deep diaphragm walls in soft clayey soils. The validity of the numerical models is confirmed after comparing the results of the nonlinear dynamic analyses with those of the experimental evidences. Four different excavations with 8 m, 12 m, 16 m and 20 m of clear bay spans and an excavation depth of 14 m are numerically simulated. In order to investigate the seismic analysis under various circumstances, three different accelerograms with various frequency contents are utilized. In the current study, the damping mechanism and the axial load bearing capacity of the RLBRBs in seismic conditions are taken into account in order to dissipate the induced earthquake energy and consequently preserve the local and global stability of the supported deep excavation. In this regard, one- and two-sided RLBRB-equipped struts with pipe-shaped steel cores are applied in a lateral stiffening system. As a result, unlike the conventional struts, the sudden stress changes in the struts are removed. Furthermore, the parameters influencing deep excavation stability are investigated. Basal heave, surface settlement, and lateral deformation of diaphragm walls are determined during geostatic and seismic conditions. Findings of this study provide fundamental principles for designing deep excavations under seismic conditions with efficient strut members. The applicability and effectiveness of the obtained results are also illustrated.

Improvement of Soft Soil by Stone Column Treated with Bentonite

Soft clayey soils cover wide Iraqi areas specially the regions close to rivers and the southern part of this country Heavy weight structures like: highways, dams, multiple story buildings are suffering unacceptable settlement, when constructing on soft soils. The high contamination of water in such soils decrease the effective stress and reduce bearing capacity. The need was appeared to improve such problematic soil by the use of new technique of stone column treated with different percentages of natural bentonite by a series of field tests using full scale concrete footing constructed on soft soil in addition to a laboratory model to investigate settlement with time at constant stress. The soil that used in this study is natural clayey soil, brought from a location south of Diyala governorate, from a farm area. The study includes also: The effect of stone column diameter treated with bentonite on the behavior of footing constructing on soft clayey soil, The effect of stone column length on the behavior of footing on such soils. Results of field and laboratory model tests reviled that the treated model by stone column mixed with 40% bentonite is the ideal one, which reduces the settlement by 55%. In other hand problems of uneven settlements appear when using 60% bentonite as a mix proportion. The Ideal slenderness ratio (Ds/Ls<25%). The effective depth of stone column treated with bentonite is (1/3H).

Effect of the pore fluid salinities on the behaviour of an electrokinetic treated soft clayey soil

Dredging activities of harbours and rivers are becoming very important in many countries all over the world and, as a consequence, the disposal of dredged sediments is a critical concern from an environmental point of view. In order to facilitate the disposal or the reuse of large volume of dredged soils, usually under-consolidated and with a high water content, an electrokinetic treatment can be adopted with the goal to dewater and strengthen the sediments.This paper presents the results of some electrokinetic tests performed on reconstituted clayey specimens at different pore fluid salinities (0.2 < sc < 30 g/l) treated with electrokinetic (EK) technique. The results indicate that the presence of small quantities of salts in the pore fluid enhances the electro-osmotic consolidation. On the contrary, for high salt concentrations of the pore fluid the electro-osmotic dewatering is significantly reduced. The mechanical behaviour of treated specimens has been investigated at the micro (SEM) and macro scale (triaxial and oedometer tests). The experimental results highlighted the relevant and expected contribution of the pore fluid characteristic on the effectiveness of the treatment as ground improvement technique.