Soft Soil Deposits Research Articles

Microzonation models for Montreal with respect to $$\hbox {V}_\mathrm{S30}$$ V S 30

The development of seismic microzonation maps is now a prerequisite for performing advanced seismic hazards and seismic risk assessments in urban areas. Current microzonation procedures are based on classifying site response in soil categories based on $$\hbox {V}_\mathrm{S30}$$ . In many practical cases, information on shear wave velocity is sparse and analysts must resort to other sources of information to develop zonation maps over large regions. For Montreal, Canada, a geostatistical approach combining a large dataset of boreholes, $$\hbox {f}_{0}$$ data from the H/V method, and a limited number of shear wave velocity measurements is proposed. Predictive equations are developed with the different types of information and partly used to create three different $$\hbox {V}_\mathrm{s30}$$ models: A first model based on the total thickness of soft soil deposits (One Layer Model), a second model based on stratigraphy obtained from borehole data (Four Layers Model) and a third model (Composite Model) that combines data from the previous two models with data from seismic surveys. Variability and uncertainty associated with the choice of the models are described and estimated using a second moment analysis. The composite model which combines borehole, $$\hbox {f}_{0}$$ and Vs data is shown to be the most accurate compared to models derived only from borehole and Vs data (an average reduction of 40 % of the squared error) and shows good agreement with the geological map for clay and sand locations with soils classes C and D (54 % agreement on average). This approach opens new perspectives for $$\hbox {V}_\mathrm{s30}$$ microzonation in urban areas when budgets for Vs surveys are limited.

Effects of Soil Plasticity on Seismic Performance of Mid-Rise Building Frames Resting on Soft Soils

In this study, the effects of Plasticity Index (PI) variation on the seismic response of mid-rise building frames resting on soft soil deposits are investigated. To achieve this goal, three structural models including 5, 10, and 15 storey buildings are simulated in conjunction with a clayey soil representing soil class Eeaccording to the classification of AS1170.4–2007 (Earthquake actions in Australia) and then varying the Plasticity Index. Structural sections of the selected frames were designed according to AS3600–2009 (Australian Standard for Concrete Structures) after undertaking dynamic analysis under the influence of four different earthquake ground motions. The frame sections are modelled and analysed, employing finite difference method adopting FLAC 2D software under two different boundary conditions: (i) fixed base (no Soil-Structure Interaction), and (ii) flexible base considering soil-structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted and the results in terms of maximum lateral displacements and inter-storey drifts for the above mentioned boundary conditions are obtained, compared, and discussed. Base on the results of the numerical investigations, it becomes apparent that as the Plasticity Index of the subsoil increases, the base shears of mid-rise building frames resting on soft soil deposits increase, while the lateral deflections and corresponding inter-storey drifts decrease. It is concluded that reduction of the Plasticity Index could noticeably amplify the effects of soil-structure interaction on the seismic response of mid-rise building frames.

Lateral displacement of PVD-improved deposit under embankment loading

ABSTRACT: The likely range of values of the maximum lateral displacement of the ground caused by embankment loading of a soil deposit improved by the installation of geosynthetic prefabricated vertical drains (PVDs) was investigated. This involved a study of 18 field cases and an empirical equation for predicting the maximum lateral displacement is proposed. The proposed equation considers the effects of the embankment load, loading rate, and the deformation, consolidation and strength properties of the soft subsoil. Combining the proposed equation with a previously established equation for predicting the lateral displacement of soft soil deposits under the combined action of embankment and vacuum pressure loading provides a method for estimating the likely range of values of the maximum lateral displacement of a PVD-improved deposit under embankment loading with or without the application of vacuum pressure. It is suggested that the proposed method can be used as a design tool in geotechnical practice.

Assessment of the Elastic-Viscoplastic Behavior of Soft Soils Improved with Vertical Drains Capturing Reduced Shear Strength of a Disturbed Zone

AbstractSoil disturbance induced by the installation of vertical drains reduces the horizontal soil permeability and shear strength in the disturbed zone. Thus, the soil disturbance contributes to the reduced overconsolidation ratio (OCR) of the soil in the vicinity of drains, influencing soil deformation. Although a significant amount of research has been conducted on the effect of permeability variations in the smear zone, the influence of the reduced shear strength in the smear zone on the ground behavior has not been investigated. In this study, a numerical solution adopting an elastic-viscoplastic model with nonlinear creep function in combination with the consolidation equations has been developed. Moreover, the effects of shear strength variation in the disturbed zone on the time-dependent behavior of soft soil deposits improved with vertical drains and preloading have been studied. The applied elastic-viscoplastic model is based on the framework of the modified Cam-clay model, capturing soil creep...

Consolidation behavior of soft deposits considering the variation of prefabricated vertical drain discharge capacity

This paper is primarily focused on why and how to consider the varied discharge capacity during simulations of consolidation via prefabricated vertical drains (PVDs) for soft soil deposits. First, the existing studies regarding discharge capacity are summarized and discussed. These studies conclude that the discharge capacity of PVDs at sites vary with the confining pressure and consolidation time. Next, a series of analytical solutions that consider the variation of discharge capacity with ground depth, consolidation time or both simultaneously are presented and compared. Applications of these solutions and of the newly introduced parameters are described. Then, a well-documented case history on ground treatment with PVDs is analyzed, in which the parameters related to the time-dependent discharge capacity were obtained from laboratory tests. A comparison between a classical solution and the newly presented method indicates that consideration of the varied discharge capacity in the consolidation theory can better predict the consolidation process of PVD-improved ground.

Field Experiments for Monitoring the Dynamic Soil–Structure–Foundation Response of a Bridge-Pier Model Structure at a Test Site

Summary results from a series of field experiments at a test site in Greece are presented, involving an in situ instrumented bridge-pier model built on realistic foundation conditions, to study the dynamic behavior of structure-foundation-soil system. It was attempted to link the variation of its dynamic characteristics to certain changes in its structural system, including the development of structural damage. This measured response was next utilized to validate numerical tools capable of predicting influences arising from such structural changes as well as from soil–foundation interaction. This bridge-pier model was supported on soft soil deposits allowing the study of structure–foundation–soil interaction effects during low-to-medium intensity artificial excitations. The in situ experiments provided measurements that were used to verify fundamental analytical solutions for soil–structure interaction. They were also used to validate numerical simulations that were developed to predict the response of the studied structure and thus, back-evaluate modeling assumptions. The obtained accuracy of the numerical predictions must be partly attributed to sound knowledge of the mechanical properties of the pier model and of the soil, not necessarily the case in all practical applications. It is evident that more complex finite-element models can improve the quality of the prediction only in cases where their parameters can be defined equally well. A special study further focused on the radiation of the waves generated by the vibration of the bridge-pier model through the soil medium. It is deemed that this comprehensive experimental investigation of soil–structure interaction provides measurements of the system response and enhances our understanding of the physical phenomenon as a whole.

A case study in evaluating the status of consolidation of a soft soil deposit by incomplete piezocone dissipation tests using laboratory and field data

By using the piezocone penetration test (PCPT or CPTu), one can develop not only a better understanding of the soil stratification, but also an understanding of soil behavior parameters related to soil compressibility, as well as soil strength. This paper describes a case study that utilizes incomplete piezocone dissipation test to estimate status of consolidation of a soil deposit. Incomplete pore pressure dissipation record of PCPT is extrapolated on an inverse time scale (1/t method) to estimate the “in situ” pore pressure and “residual excess” pore pressure. No case study has been reported in open literature where this methodology has been utilized to estimate the status of consolidation of the soil deposit. In this paper, the 1/t method was verified using dissipation data from rigorous calibration chamber tests and field test data.

Soil-structure interaction vs Site effect for seismic design of tall buildings on soft soil

In this study, in order to evaluate adequacy of considering local site effect, excluding soil-structure interaction (SSI) effects in inelastic dynamic analysis and design of mid-rise moment resisting building frames, three structural models including 5, 10, and 15 storey buildings are simulated in conjunction with two soil types with the shear wave velocities less than 600 m/s, representing soil classes De and Ee according to the classification of AS1170.4-2007 (Earthquake actions in Australia) having 30 m bedrock depth. Structural sections of the selected frames were designed according to AS3600:2009 (Australian Standard for Concrete Structures) after undertaking inelastic dynamic analysis under the influence of four different earthquake ground motions. Then the above mentioned frames were analysed under three different boundary conditions: (i) fixed base under direct influence of earthquake records; (ii) fixed base considering local site effect modifying the earthquake record only; and (iii) flexible-base (considering full soil-structure interaction). The results of the analyses in terms of base shears and structural drifts for the above mentioned boundary conditions are compared and discussed. It is concluded that the conventional inelastic design procedure by only including the local site effect excluding SSI cannot adequately guarantee the structural safety for mid-rise moment resisting buildings higher than 5 storeys resting on soft soil deposits.

Calibrating partial factors for Danish railway embankments using probabilistic analyses

High costs are connected with upgrading railway embankments throughout Denmark using the partial factors for geotechnical design calibrated for general application. One way to reduce the costs is reliability-based calibration of the partial factors to a reasonable safety level taking into account the specific design situations and uncertainties relevant to railway embankments. A reliability-based design has been investigated, resulting in an optimal partial factor for the considered subsoil. With a stochastic soil model to simulate the undrained shear strength of soft soil deposits, the partial factor is calibrated using asymptotic sampling for the reliability assessment. The calibration shows that the partial factor can be reduced significantly compared to the value specified in the Danish National Annex to DS/EN 1997-1 (2007), Eurocode 7.

Development and mechanical strength properties of a new lightweight soil

The time-dependent settlement of soft soil poses serious maintenance problems to developments along coastal and riverside areas that encounter thick, soft soil deposits. To overcome this problem, therefore, a lightweight material called Air-Trapped Soil (ATS) was developed. ATS was prepared using sand produced at a factory, so its quality is highly stable. To determine the characteristics of the developed ATSs, a series of unconfined compressive and split tensile tests were conducted, and the compressive and tensile strength characteristics of the lightweight ATSs of various combinations of cement-air bubble-sand were determined. In addition, the relationship between the compressive and tensile strengths was determined. This result shows that the mechanical strength characteristics of the ATS significantly depend on the quantity of air bubbles in the ATSs.

Numerical Simulation of Bored Pile on Foundation Pit Support in Soft Soil Deposits

To the supporting method of bored cast-in-place piles on foundation pit support in soft soil deposits, using the finite element method and considering the interaction between pile group, respectively, bored piles with compound foundation and entitative beam element are numerically simulated in two ways; Compared two kinds of method to calculate the displacement effects of adjacent pipeline to the actual monitoring data, the results show that using entitative beam element are adopted to simulate the piles is more reasonable.

Computation of ground motion amplification in Kolkata megacity (India) using finite-difference method for seismic microzonation

This paper presents the ground motion amplification scenario along with fundamental frequency (F0) of sedimentary deposit for the seismic microzonation of Kolkata City, situated on the world’s largest delta island with very soft soil deposit. A 4th order accurate SH-wave viscoelastic finite-difference algorithm is used for computation of response of 1D model for each borehole location. Different maps, such as for F0, amplification at F0, average spectral amplification (ASA) in the different frequency bandwidth of earthquake engineering interest are developed for a variety of end-users communities. The obtained ASA of the order of 3–6 at most of the borehole locations in a frequency range of 0.25–10.0 Hz reveals that Kolkata City may suffer severe damage even during a moderate earthquake. Further, unexpected severe damage to collapse of multi-storey buildings may occur in localities near Hoogly River and Salt Lake area due to double resonance effects during distant large earthquakes.

Interpretation of density profile of seabed sediment from nuclear density cone penetration test results

The nuclear density cone penetration test (ND-CPT) is used to investigate the wet density (ρ) of soft soil deposits under the sea. In the ND-CPT, the density is determined by the count rate ratio (Rρ) of the gamma rays detected by the detector to the gamma rays from the source. Thus, the ND-CPT measures the average wet density of the material within a spheroid volume around the central point of the source and the detector, which is designated as ρc. The measured ρc values are considerably different from the actual ρ of the seabed sediment because the density varies significantly with depth. We designate the layer of seabed sediment in which the density increases rapidly with depth as the “upper layer” and the layer below it as the “lower layer”. A method is proposed to deduce the actual ρ profile from the measured ρc profile. The upper and the lower boundaries of the upper layer of the seabed sediment can be directly determined from the measured ρc profile as well as the distance (2b) between the gamma ray source and the detector. Based on the results of a back analysis of the measured ρc profile at Isahaya Bay, Ariake Sea, Japan, the density distribution in the upper layer of the seabed sediment can be approximated as a square root function of depth. Comparisons of the measured ρc profiles, obtained using the ND-CPT, and the actual ρ profiles, deduced by the proposed method, show that the actual ρ are obviously different from the measured ρc near the upper and the lower boundaries of the upper layer of the seabed sediment. The thickness of the upper layer of the seabed sediment at Isahaya Bay lies in the range of 0.05–0.55m.

Settlement Behavior of Embankment Reinforced with High Strength Geotextile at the Interface

The behavior of embankment constructed on soft soil deposits has been always discussed by geotechnical engineers and researchers for solve the excessive settlement problems of the geotechnical structure. For solving and minimizing the problems, the geotextile have been introduced recently in market for reinforcement system. This paper presents the results on the settlement behavior of the HSG embankment reinforced by high strength geotextile from the full-scale instrumented embankment and their comparison to the numerical prediction results. The trial embankment has been constructed on the designated place at Research Centre for Soft Soil (RECESS), UTHM, Batu Pahat, Johor, Malaysia. The embankment installed with several of the geotechnical instrumentations to measure the settlement behavior has been analyzed. Finite element results generated from PLAXIS Version 8 software are then compared to the monitoring results. Based on the research findings, high strength geotextile could sustain and minimize the excessive settlement during construction period of 141 mm and 458 mm for post construction period.

Liquefaction Potential for Kolkata City

This paper presents the liquefaction potential of densely populated Kolkata city, which is situated on the world's largest delta island with very soft and thick alluvial soil deposits. Due to presence of soft alluvium deposits at shallow depths, soil resistance against liquefaction is expected to be less. Additionally, large thickness of soil layers may amplify the ground shaking resulting in high seismic demand on the soil. Here in this study, variation of factor of safety against liquefaction is evaluated with depth at different locations in Kolkota city. The study founds striking results that the Kolkata city soils are less prone to liquefaction even though there is significant ground amplification due to presence of thick soil deposits.

Influence of mix uniformity on the induced solidification of dredged marine clay

Ground improvement with soil solidification has been widely applied and has proven to be an effective pre-treatment of soft soil deposits. The solidification procedure usually involves addition and thorough mixing of hydraulic binders with in situ soils, consequently transforming the soft materials into a stronger and stiffer stratum for load bearing. Much has been done on the binder’s effectiveness and resulting enhanced properties of the soils, but not as much has been reported of the factors governing in situ mixing efficiency in producing uniform mixtures. While advancement in machinery and computerization of operations have significantly improved soil mixing, individual factors contributing to the process can be further examined to refine the effectiveness. This paper describes a series of laboratory tests, mainly unconfined compressive strength tests complemented with X-ray computer tomography, conducted on cement-stabilized dredged Kawasaki clay of different uniformities. A number of factors affecting uniformity were examined, namely the water/cement (WC) ratios, number of cement layers in the initial state as well as the number of mixing cycles adopted. Test specimens were prepared based on a systematic combination of these factors to enable a comprehensive cross-analysis of the results. It was found that the clay’s initial consistency was markedly altered by cement addition, which resulted in either enhanced or reduced workability of the mixture. While increased mixing vigor could apparently overcome poor distribution of binder in the mixture, the resulting strength remained very much affected by the WC ratio, suggesting dependency of the mixture’s overall uniformity on a combination of the factors.

Investigation of field-installation effects of horizontal twin-jet grouting in Shanghai soft soil deposits

This paper presents a case study of an investigation into the responses of the surrounding ground to the horizontal twin-jet grouting method (HTJGM) in soft soil deposits of Shanghai. During the field test, the variation of pore-water pressure, lateral earth pressure, lateral displacements of the subsurface soils, and ground surface heave induced by the installation of five horizontal jet-grouted columns were monitored. The monitoring results indicate that the excess pore-water pressure reached 4 to 6 times the undrained shear strength of the soils, while maximum lateral displacements and ground surface heave were up to 80 and 17 mm, respectively. The influence range due to the installation of jet-grouted columns was between 15 and 20 times the nominal column radius. The development of prediction methods for lateral displacements and ground surface heave induced by the HTJGM installation process are presented and discussed. Results from the investigation suggest that the proposed prediction methods can be used to provide reasonable estimates of ground response and influence range of horizontal jet grouting.

Lateral seismic response of building frames considering dynamic soil-structure interaction effects

In this study, to have a better judgment on the structural performance, the effects of dynamic Soil-Structure Interaction (SSI) on seismic behaviour and lateral structural response of mid-rise moment resisting building frames are studied using Finite Difference Method. Three types of mid-rise structures, including 5, 10, and 15 storey buildings are selected in conjunction with three soil types with the shear wave velocities less than 600m/s, representing soil classes Ce, De and Ee, according to Australian Standard AS 1170.4. The above mentioned frames have been analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction), and (ii) flexible-base (considering soil-structure interaction). The results of the analyses in terms of structural lateral displacements and drifts for the above mentioned boundary conditions have been compared and discussed. It is concluded that the dynamic soil-structure interaction plays a considerable role in seismic behaviour of mid-rise building frames including substantial increase in the lateral deflections and inter-storey drifts and changing the performance level of the structures from life safe to near collapse or total collapse. Thus, considering soil-structure interaction effects in the seismic design of mid-rise moment resisting building frames, particularly when resting on soft soil deposit, is essential.

Shear strength behavior of cement treated marine clay

The in-situ deep cement mixing method is an established technique for improving the strength and reducing settlement of soft soil deposits. In practice, upon completion of the cement treatment, the improved ground will be left for curing over a specific period of time, before commencement of construction activities. In the case of deep mixing, curing takes place under the overburden pressures, at deeper depths. Studies on the influence of curing stress on the stress-strain and strength characteristics of cement stabilized clays are limited. The role of curing stress on the strength behavior of the cement treated soil is studied in this paper. Consolidated undrained triaxial compression tests performed on cement treated samples cured with and without stress are mainly focused. Marine clay from Ennore, near Chennai, India, excavated at a depth of 1.5 m was selected for the study. The range of cement contents selected were 10%, 15% and 20% with curing time of 28 days. The curing stresses adopted were 0, 50, 100 and 200 kPa. Additional tests were also conducted to study the effect of lower cement content of 5% and the effect of higher confining pressures.

Free Field Surface Motion at Different Site Types due to Near-Fault Ground Motions

Seismic hazards during many disastrous earthquakes are observed to be aggravating at the sites with the soft soil deposits due to amplification of ground motion. The characteristics of strong ground motion, the site category, depth of the soil column, type of rock strata, and the dynamic soil properties at a particular site significantly influence the free field motion during an earthquake. In this paper, free field surface motion is evaluated via seismic site response analysis that involves the propagation of earthquake ground motions from the bedrock through the overlying soil layers to the ground surface. These analyses are carried out for multiple near-fault seismic ground motions at 142 locations in Mumbai city categorized into different site classes. The free field surface motion is quantified in terms of amplification ratio, spectral relative velocity, and spectral acceleration. Seismic site coefficients at different time periods are also evaluated for each site category due to near-fault ground motions from the acceleration response spectra of free field surface motion at each site and the corresponding acceleration response spectra at a reference rock outcrop site.