Clayey Soil Deposits Research Articles

Seismic Response of Pile Foundations in Clayey Soil Deposits Considering Soil Suction Changes Caused by Soil–Atmospheric Interactions

Seismic Response of Pile Foundations in Clayey Soil Deposits Considering Soil Suction Changes Caused by Soil–Atmospheric Interactions

Consolidation mechanism of high-water-content slurry during vacuum preloading with prefabricated vertical drains

Vacuum preloading combined with prefabricated vertical drains (PVDs) has been widely used to improve soft clayey soil deposits. However, the consolidation deformation of high-water-content slurry under vacuum pressure is still not fully understood. In this study, the displacement field of the slurry during vacuum preloading was directly observed using the particle image velocimetry (PIV) technique. The test results showed that the displacement field of the slurry could be divided into three different zones that reflect distinct consolidation patterns. In zones I and III, the slurry was predominantly compressed along the horizontal and vertical directions, respectively, whereas in zone II, compression occurred in both vertical and horizontal directions. In particular, the slurry elements in zones I and II underwent horizontal extension prior to horizontal compression. The study also visualized the boundary of the soil column and provided an equation for the relation between soil column thickness and consolidation time, which could provide a reference for the theoretical consolidation calculations related to soil columns.

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.

Siesmic Response of Single Pile Soil Structure Interaction Effect of Cordera bridge foundation

The response of single pile foundations to the dynamic loads is considered in this paper. The behaviour of such foundation is important specifically in case of earthquake excitation through the supporting soil medium. An axisymmetric finite element model has been implemented to simulate the behaviour of pile in relatively clayey soil deposit using Abaqus software including the soil structure interaction effect soil system. Eight node axisymmetric quadrilateral element CAX8R used to simulate the soil continuum. Contact behaviour between the single pile part and the part of soil was simulated using the ‘surface to surface’ contact method with master-slave concept. Furthermore, the pile behaviour material has been simulated with a linear elastic model while, soil material has been simulated with an elasto-plastic model “Mohr-Coulomb failure criterion”. Two different excitation have been adopted during the analysis: El-Centro and Ali-Algharbi earthquakes in order to investigate the effect of various intensities. The results of the analysis demonstrate alteration in the relative displacement and stresses along the pile with different soil layer and different stiffness with both earthquake excitations.

A method to predict the torsional resistance of suction caisson with anti-rotation fins in clay

Suction caisson foundations have been increasingly employed as a primary solution to support the offshore fixed- or mobile-structures. Due to harsh environment and complex force transferring of offshore structures, they are still being developed as to satisfy increasing requirements in strict working scenarios. One of emerging challenges is a torsion-governing failure, which has been observed in the oil and gas industry (i.e. significant multiple-inline-force-induced torsion) and in the renewable energy field (i.e. non-coplanar tensile force induced torsion). This paper introduces a novel suction caisson foundation, with anti-rotational fins assembled on the outer skin of caisson. By a comprehensive numerical study, the evolution from local to global failure as the fin numbers from single to multiple, is examined in the clayey soil deposit with effects of soil strength heterogeneity, fins dimension, installation process and foundation-soil interface considered. Based on these, a set of methods to estimate the ultimate torsional capacity of such novel caisson is proposed, which starts from the gain in capacity for a single fin, and evaluate the changes of gains in capacity as fin numbers, then identify the optimised anti-rotational capacity. Finally, three key parameters (i.e. the required fin numbers, the available anti-rotational capacity and the optimised anti-rotational capacity) with some critical considerations, recommendations and implications have been concluded for design practice.

Study on Effect of Ground Improvement on Lateral Load Carrying Capacity of Pile using Developed Simplified Soil–Pile Stiffness Matrix

In this present study, a Beam on Nonlinear Winkler Foundation approach has been utilized to study the effect of ground improvement on deformation characteristics of laterally loaded pile. Fourth-order governing differential equation of pile deformation has been solved, and a simplified pile–soil stiffness matrix has been developed. The optimum depth (from ground surface) up to which engineering properties of soil require to be improved has been ascertained using a computer code developed in MATLAB utilizing the developed soil–pile stiffness matrix. This optimum depth can be defined as the depth beyond which the improvement in engineering properties of soil (e.g., deformation modulus) has negligible effect on deformation characteristics of laterally loaded pile. Optimum depth has been suggested for different slenderness ratios of piles installed in soft-to-medium-stiff clayey soil deposit, and statistical equations have been developed to find the optimum depth of ground improvement for different pile slenderness ratios (L/D) and relative stiffness (Ep/Es) of pile. The study reveals that the optimum layer improvement ratio (L1/L) reduces with the increased pile slenderness ratio (L/D) and increases with the increased relative stiffness (Ep/Es) of pile. Design charts have been proposed to get a preliminary estimation of lateral pile capacity in virgin clay as well as improved clay for different layer improvement ratios (L1/L).

Response of urban single and twin circular tunnels subjected to transversal ground seismic shaking

The response of tunnels subjected to ground seismic shaking is commonly evaluated, disregarding the existence of other structures in the near area. However, significant interaction phenomena may take place between the tunnel and existing structures in dense urban environments, altering the seismic response of the tunnel compared to the one predicted for ‘green field’ conditions. This study aims at investigating the effect of heavy buildings on the response of urban single or twin circular tunnels, when subjected to severe ground seismic shaking in the transversal direction. For this purpose, a numerical parametric study was conducted on representative tunnel-soil-buildings systems, employing the finite element code ABAQUS. Several configurations were examined, including single or twin circular tunnels, embedded in clayey soil deposits. The high-rise buildings were simulated as equivalent single degree of freedom oscillators (SDOFs), founded on rigid raft foundations. Salient parameters that affect the seismic response of tunnels, namely (i) the burial depth of the tunnels, (ii) the number of buildings-SDOFs and their position relative to the axis of the tunnel and (iii) the soil properties and response during ground shaking were investigated within this parametric study. The computed responses of the investigated configurations, in terms of (i) lining deformations, (ii) dynamic earth pressures and seismic shear stresses developed along the perimeter of the tunnels and (iii) dynamic lining forces, were compared with the cases where the buildings-SDOFs at the ground surface were neglected. The effect of buildings-SDOFs was quantified by means of response ratios μ, defined as the ratio of the maximum envelope value of the response parameter computed at critical lining section at the presence of the buildings-SDOFs, to the relevant value estimated for green-field conditions. The response ratios were plotted against the flexibility ratios, F, of the investigated soil-tunnel systems, highlighting the effects of the salient parameters mentioned above on the interaction phenomena. Generally, the consideration of the buildings-SDOFs at the ground surface resulted in an increase of the response of the tunnels, compared to the one predicted for ‘green field’ conditions, both in terms of tunnel deformations and dynamic earth pressures and soil dynamic shear stresses around the tunnel, as well as in terms of dynamic lining forces, with the effect being generally higher for shallow tunnels.

Assessment of an alternative to deep foundations in compressible clays: the structural cell foundation

The new type of deep foundation for buildings on saturated, compressible-low strength clayey soil deposits, branded structural cell essentially consists of a rigid concrete top slab, structurally connected to reinforced concrete peripheral walls (diaphragms) that enclose the natural soil. Accordingly, as the initial volume of the confined soft clays within the lateral stiff diaphragms will remain constant upon loading, the hollowed structural cell will be “transformed” into a very large cross-section pillar of unit weight slightly higher than that of the natural soft clayey soil. This type of foundation seems to be a highly competitive alternative to the friction pile-box foundations (widely used in Mexico City clays), due to its economic and environmental advantages. Economies result, for example, from the absence of huge excavations hence sparing the need of earth retaining structures. Further savings result from appreciably smaller concrete volumes required for building the structural cell than the friction pile-box foundation; moreover, the construction time of the former is much shorter than that of the latter. Regarding the impact to the environment, less air contamination follows from the fact that both traffic jams and soil excavation lessen appreciably. Considering these facts and others regarding scheduling, it was decided to replace 48-friction pile-box foundations specified in the master plan project by this new type of foundation. The overall behavior of these cell foundations over a five-year period is fared from close visual observations and their leveling during the first three years after their construction.

Holocene Deposits in Saga Plain: Leaching Mechanism and Soil Sensitivity

The Saga Plain in Japan contains a 10–30 m thick Holocene clayey soil deposit with a natural water content generally more than 100% and a liquidity index (I L ) larger than 1.0. Most of this is a marine deposit known as the Ariake clay formation. Using salinity in the pore water of this deposit as an index, the mechanism of post-depositional salinity leaching from the Ariake clay formation has been investigated. This has been achieved using current measurements of the salinity distribution in the deposit and the groundwater flow velocity in an underlying Pleistocene gravelly sand layer, together with advection–diffusion analyses. It is suggested that diffusion together with possible rainfall percolation and/or upward seepage flow from the Pleistocene gravelly sand layer was the main mechanism causing salinity leaching. Detailed analysis of the test results from four boreholes indicates that for the locations where the activity of the clay minerals was less than 1.25, salinity leaching probably accounts for the observed low undrained shear strength (<0.5 kPa) of remoulded soil samples, high values of the sensitivity (S t ), and the formation of a quick clay.

Deformation behaviour of clay under repeated one-dimensional unloading–reloading

The deformation of clayey soil under repeated cycles of unloading and reloading has been investigated in oedometer tests using both undisturbed and reconstituted Ariake clay samples. The test results indicate that even for repeated unloading–reloading in the overconsolidated stress range, the deformation of the soil sample is not purely elastic and there is an accumulation of permanent deformation. Based on the test results, a model has been proposed for predicting unloading–reloading-induced deformation. The proposed model has been used to simulate the behaviour of a clayey soil deposit in the Saga Plain, Japan, in response to groundwater fluctuation. Good agreement between the simulation and the field measurements indicates that the proposed model can be used to predict land subsidence induced by groundwater fluctuations.

Consolidation analysis of clayey deposits under vacuum pressure with horizontal drains

A method has been developed for the consolidation analysis of dredged mud or clayey soil deposits containing strip-type, prefabricated horizontal drains (PHDs), based on either the axisymmetric or plane strain unit cell theory. An approximate consolidation theory has also been proposed for a surface soil layer subjected to vacuum pressure applied through the PHDs at a shallow depth from the surface. The proposed method and the consolidation theory have then been applied to the analysis of a field project in Japan involving dredged mud consolidated by vacuum pressure with PHDs. By comparing the field-measured and analyzed results in terms of water content distributions with depth and the thickness variation of the deposit, the usefulness of the proposed method has been demonstrated.

Settlement prediction and behaviour of pile foundations in deep clayey soil deposits

A new measurement technique is used to determine the settlement of bridge pile foundation and the thickness of deep compressed soft layer. The finite element Plaxis 3D foundation program is used in the analysis with a proposed empirical equation to modify the input parameters represented by the soil compression modulus. The results of the numerical analysis using the proposed empirical equation provide insight to the settlement analysis of pile groups in soft clayey soils; consequently, the finite element Plaxis 3D program can be a useful tool for numerical analysis. The numerical analysis is modified by adjusting the calculation of compression modulus from those obtained under pressure between 100–200 kPa by which the results of the settlement are modified and thus matching the realistic measurements. The absolute error is 3 mm which is accepted compared with the last researches. This scenario can be applied for the similar problems in the theoretical applications of deep foundations.

Determination of Relationships Between Menard Pressuremeter Test and Standard Penetration Test Data by Using ANN model: a Case Study on the Clayey Soil in Sivas, Turkey

An extensive site characterization study, consisting of 70 Menard pressuremeter tests and 77 standard penetration tests was undertaken on the clayey soil deposit of high plasticity prior to the construction of 4 Eylul Dam’s water treatment plant which provides water supply to Sivas (Turkey). It is aimed to investigate the possible relationships between standard penetration and pressuremeter parameters for the clayey soil in Sivas. To obtain the accurate empirical equations, nonlinear regression analysis between standard penetration blow counts, pressuremeter modulus, and limit pressure were undertaken. An artificial neural network model was developed for accurate estimation of corresponding pressuremeter data based on the measured values. The measured data and calculated performance values were used at the design of Levenberg–Marquardt based multi-layer perceptron artificial neural network model. Calculated values were compared to the predicted values using the statistical error analysis. The relationship between limit pressure and undrained shear strength obtained from the conducted unconfined compression strength tests is also presented. The proposed equations are compared with those obtained from previous studies. The paper concludes that the presented equations based on the nonlinear regression analysis may be valuable for similar soils and beneficial to the practitioners for comparing, evaluating and reciprocal conversion of the parameters obtained from standard penetration and pressuremeter tests.

A strategy to address the task of seismic micro-zoning in landslide-prone areas

Abstract. As concerns landslide prevention and mitigation policies at the urban scale, the ability of Geographical Information Systems (GIS) to combine multi-layered information with high precision enables technicians and researchers to devote efforts in managing multiple hazards, such as seismically induced instability in urbanized areas. As a matter of fact, many villages in the Italian Apennines, placed near high-energy seismic sources, are characterized by active sliding that are seasonally remobilized by rainfall. GIS tools can be useful whether accurate Digital Elevation Models (DEM) are available and detailed mechanical and hydraulic characterization of superficial deposits over significant portion of the urban territory is undertaken. Moreover, the classic methods for estimating the seismic-induced permanent displacements within natural slopes are drawn from the generalization of Newmark's method. Such method can be applied to planar sliding mechanism that can be considered still valid wherever shallow landslides are generated by an earthquake. The failure mechanism depends on the mechanical properties of the superficial deposits. In this paper, the town of Castelfranci (Campania, southern Italy) has been studied. This small town, hosting two thousand inhabitants, suffers from the seasonal reactivation of landslides in clayey soil deposits due to rainfall. Furthermore, the site is seismically classified by means of the peak ground acceleration (PGA) equal to 0.246 g with respect to a 475 yr return period. Several studies on the evolution of slopes have been undertaken at Castelfranci and maps have been drawn at the urban scale not taking into any account the seismic hazard. This paper shows possible seismically induced hazard scenarios within the Castelfranci municipal territory aimed at microzonation of level 2, by estimating the slope permanent displacements comparable to those caused by the strongest historical seismic event that hit this area: the 1980 Irpinia earthquake. To this aim, geotechnical characterization of local soils collected over the last 25 yr by local technicians have been used to predict possible permanent displacements by means of Newmark's sliding block approach. Two simplified relationships relating peak ground acceleration and Arias intensity to permanent displacements have been used and compared. Although similar results are drawn, the two analyses point out the most hazardous sectors of the Castelfranci urban area.

Behaviour of Two Closely Spaced Strip Footings Placed on a Stiff Clay Bed under Cyclic Loading

Abstract Foundations are sometimes placed very close to each other because of space limitations or to limit the footing loads or to accommodate certain structural details. When footings are placed at close spacing, they interact with each other and the behaviour of each individual footing is altered compared to that of a single isolated footing. Also, foundations are often subjected to cyclic live loads in addition to self-weight of the structure causing change in soil performance below it. The design of foundations placed close to each other and subjected to cyclic loading is very complex as both of the phenomena (i.e., footing interference and cyclic load) affects the behaviour of foundation soil. The presence of clayey soil deposits in the construction site adds further uncertainty to this problem because there is no consensus among the researchers regarding interfering footing behaviour on clay. To uncover the actual behaviour of two closely spaced surface strip footings on clay deposits under cyclic loading, small-scale experimental studies with footings placed at two different spacings were carried out in the Civil Engineering laboratory at the University of New South Wales (UNSW@ADFA). The study shows that the application of low-frequency cyclic load improves the bearing capacity and stiffness of foundation soil (clay), irrespective of the interfering footing spacing. Also, the permanent deformation of interfering footings placed at closer spacing is found to be smaller compared to that of footings placed at wider spacing.

On the deformation behaviour of strip footings during the construction process of an adjacent diaphragm wall in soft clayey ground

AbstractThe installation process of diaphragm walls in soft clayey soil deposits can produce considerable deformations on the adjacent ground, affecting the serviceability of nearby structures. This article highlights the influence of the stepwise D‐wall construction process on the development of settlements of neighbouring strip footings. For the simulation of the construction process, a three‐dimensional finite element model of a plain diaphragm wall section and an adjacent footing is assumed. The stress‐strain behaviour of the ground is described by an advanced constitutive model, which especially takes into account the rheological properties of the soft clay, like creep, relaxation and a rate‐dependent stiffness. Numerous calculations are performed, considering the impact of the panel geometry and the installation sequence of the diaphragm wall. Furthermore, the loading as well as the bending stiffness of the strip footing is varied. With respect to the serviceability of the footing, recommendations for the D‐wall construction are finally given, aiming at a prevention oriented construction technique.

Evolution of the factor of safety following excavation in clay

Numerical analyses have been performed to study the evolution of the factor of safety following the excavation of a cut in clay. The analyses consider variable thickness of the clayey soil deposit under the excavation. The results show that, for a given clayey soil, there is a relation between the time for full dissipation of excess pore-water pressure from the soil mass following the excavation and the geometry of the cut (Htot/Hexc). The analytical results agree reasonably well with pore pressure measurements made in excavations in clay deposits from eastern Canada. This suggests that time to reach full pore pressure equilibration following the excavation of a cut in homogenous clayey soil deposits can be predicted when knowledge of the coefficient of swelling–consolidation is available. Lastly, results obtained in the present study show that 50% of the difference between the short- and long-term factors of safety may be lost at values as low as about 8% of the time to reach equilibration of pore pressures. This means that the time during which one can rely on the short-term strength of the clayey soil following the excavation may be relatively short, especially for soft clays.

The influence of the construction process on the deformation behaviour of diaphragm walls in soft clayey ground

AbstractConventional numerical predictions of deep excavations normally neglect the construction process of the retaining structure and choose the earth pressure at rest as initial condition at the beginning of the simulation. The presented results of simulation and measurements during the construction process of the Taipei National Enterprise Center show, that such an assumption leads to an underestimation of the horizontal wall deflection, the surface ground settlements as well as the loading of the struts in case of normally to slightly over‐consolidated clayey soil deposits. The stepwise installation process of the individual diaphragm wall panels results in a substantial modification of the lateral effective stresses in the adjacent ground. Especially the pouring process of the panel and the fresh concrete pressure causes a partial mobilization of the passive earth pressure and a distinct stress level increase in the upper half of the wall. As a consequence of the increased stresses prior to the pit excavation, up to 15% greater ground and wall movements are predicted. Moreover, the increased stress level due to the installation process of the diaphragm wall leads to substantial higher strut loadings during the excavation of the pit. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Design and behaviour of a geosynthetic reinforced retaining wall and bridge abutment on a yielding foundation

There has recently been an increase in the use of geosynthetic reinforced soil structures to support bridge abutments and approach roads in place of traditional pile supports. In this respect, reinforced soil walls offer a cost effective alternative to, and have been found to reduce the “bridge bump” effect associated with, pile supported abutments. The paper focuses on the numerical analysis of a hypothetical 6 m high geosynthetic reinforced soil wall supporting a bridge abutment and approach road constructed on a 10 m thick yielding clayey soil deposit. The results of the numerical analysis are compared to current design methodologies to examine the effect of the yielding soil foundation on the behaviour of the wall and abutment. The study includes the examination of both the internal and external stability of the wall, and focuses on methods of improving the external stability.

Evaluation of advanced constitutive modelling for cemented clayey soils: A case history

In this paper, the settlement analysis of the raft foundation of a sugar silo founded on a cemented clayey soil deposit is re-examined by using an advanced constitutive model for natural soils recently published in the literature. The model, combining a kinematic hardening framework with a bounding surface plasticity approach, appears to be an attractive compromise between relative analytical simplicity and ability to reproduce the main features of the mechanical behaviour of cemented soils. The model has been implemented in a finite difference code in order to analyse the boundary value problem; the available experimental data obtained during the geotechnical investigation of the site were used in order to calibrate the model. The numerical analyses showed that the adopted model was found to be successful in capturing the main features exhibited by the measured load-settlement curve of the sugar silo.