Settlement Response Research Articles

Nonlinear soil response under non-uniform seismic excitation from multi-point shaking table tests

The soil response to large earthquakes is strongly nonlinear, which has a significant influence on the performance of buried infrastructure as well as input motion to superstructures. This paper reports on uniform and non-uniform multi-point shaking table tests to elucidate the effect of soil non-linearity on free-field soil response. Emphasis was placed on investigating the effect of the non-uniform seismic excitation in different directions on the soil response. The tests were conducted on scaled sand deposits enclosed in a suspension continuum soil box using three shaking tables that can induce uniform and non-uniform seismic excitations. Quantitative analyses were performed to study the ground motion response characteristics and variation of free-field soil characteristics underground motions with different intensity, frequency content and directions. The analyses evaluated the soil dynamic characteristics and their variation with strain level, as well as soil acceleration and settlement responses. The results demonstrated that the soil nonlinear behavior is influenced by the ground motion intensity, direction (longitudinal or transverse) and uniformity. Non-uniform ground motion may lead to more pronounced changes of soil structure, which would decrease the soil profile natural frequency and increase its damping ratio. The variation of soil shear modulus with strain also reflected the soil plastic response. The longitudinal excitation had a more pronounced effect on the soil vertical settlement compared with the transverse excitation. However, non-uniform excitation had a minor effect on the soil vertical settlement.

Load–Settlement Response and Bearing Capacity of a Surface Footing Located Over a Conduit Buried Within a Soil Slope

Abstract Engineers often face challenges when designing foundations that are located over buried structures. This paper presents a laboratory model test investigation of the load–settlement respons...

A study of the effects of foundation uplift on the seismic loading of wind turbine tower and shallow foundation using a new dynamic Winkler model

In this study, the effects of foundation uplift on the seismic loading of wind turbine tower and shallow foundation are investigated. A dynamic Winkler model is proposed for the dynamic response analysis of shallow foundation supported structures and is named as QzSimple4, in which PySimple3 is applied to replace the elastoplastic component in QzSimple2 for the compression under the foundation and the gap model in QzSimple1 is assembled to capture the foundation uplift. The proposed model agrees well with the q-z experimental backbone curves and reasonably captures the acceleration responses of the bridge deck and the settlement-rotation responses of the shallow foundation under various excitation levels. However, QzSimple2 model strongly overestimates the q-z backbone curves in terms of linear range and ultimate bearing capacity, which leads to obviously overestimate some acceleration responses of the bridge deck and significantly underestimate the settlement responses of the shallow foundation. Finally, a systematical study is performed to investigate the effects of foundation uplift on the seismic loading by using the proposed Winkler model and the equivalent linear sway-rocking model. The foundation uplift occurs under severe earthquakes. Without considering the foundation uplift, the moment on the wind turbine tower is slightly overestimated, while that on the shallow foundation is significantly underestimated for the large soil stiffness. This is one reason why the shallow foundations at Aso-Nishihara wind farm were damaged during the Kumamoto earthquake.

Load bearing and settlement characteristics of Geosynthetic Encased Columns under seismic loads

Ordinary stone columns and Geosynthetic Encased Stone columns are used in remediation of soft soils with low bearing capacities. Primary objective of granular columns is to provide structural support to the overlying foundation layers. Given that the granular columns implemented in soft soil conditions support a large portion of the surcharge pressure, developing an understanding of settlement response and pressure bearing characteristics of granular columns under seismic loading conditions is of paramount importance. This study aims to present experimental findings of granular column load bearing response under simulated seismic loads and the effects of lateral boundary conditions on column behavior. In order to mimic the seismic behavior of columns supporting a sustained surcharge load, two different large-scale experimental assemblies are used in 1-g shaking table tests. The assemblies used were a laminar box and a rigid box which were intended as physical analogies for free-field and rigid boundary conditions. The reinforcement strains, pressure concentration on column heads, and settlement of the unit cells enhanced with granular columns with varying reinforcement stiffnesses are studied. The relationship between unit cell settlement and two important earthquake intensity measures namely, Arias Intensity and Shaking Intensity Rate, are also investigated.

Centrifuge model studies on the settlement response of geosynthetic piled embankments

The paper aims at comparing the deformation behaviour of unreinforced embankments, basal reinforced embankments and geosynthetic reinforced embankments with floating and end bearing piles. The floating piles were terminated within the soft foundation soil, while the end bearing piles transfer the loads to a hard stratum. Four series of centrifuge model tests were conducted at gravity g = 40, using the 4.5 m radius large beam centrifuge facility at the Indian Institute of Technology Bombay. The tests were performed at constant pile spacing, and the embankment was constructed using an in-flight sand hopper. The deformations were measured using Linear Variable Differential Transformers (LVDTs). A digital image analysis technique was employed to arrive at the surface displacements, displacement vectors, and displacement contours. The geogrid reinforced embankments resting on end bearing piles and floating piles showed 88% and 44% lesser settlements respectively, compared to the unreinforced embankments. The geogrid reinforcement helps to distribute the load uniformly. A deep-seated slope failure was observed for unreinforced embankments. The piled embankments proved to be a practical solution for construction without prolonged waiting periods for pre-consolidation of the foundation soil.

Settlement of a railway embankment on PVD-improved Karakore soft alluvial soil

This paper presents a case history of the settlement performance of a railway embankment built on a Prefabricated Vertical Drain (PVD) improved soft alluvial soil of Karakore area, Wollo province, north-east of Ethiopia. The embankment was constructed on Awash - Kombolcha - Haragebaya (AKH) railway project for the purpose of preloading so as to facilitate the consolidation settlement in a short period of time; and it was monitored for more than 750 days. Numerical predictions of Class A and Class C (based on back-calculation procedure) were performed using Plaxis 2D. The soft soil creep (SSC) model was employed for the soft soil layers, while the Mohr-Coulomb (MC) model was used for the drainage and fill layers. The predictions were compared with the field monitoring settlement data. Quite a reasonable agreement was achieved from the finite element modelling of Class C prediction when the prediction was compared with the actual field settlement values. Parametric sensitivity studies were carried out to examine the influence of parameters on the rate and magnitude of settlements. The results of the numerical predictions and parametric studies have been discussed in detail. The soil on the flood plain area of Karakore is found to be very soft to soft alluvial deposit and formed over Tertiary Eocene stiff clay. The variable conditions of the soil formation and deposition highly dictated the deformation and excess pore water pressure behaviour of the soft subsoil sediment. The parametric sensitivity study showed that, following the compression index, the initial void ratio, the hydraulic conductivity, and the OCR highly influenced the settlement responses of PVD-improved soft alluvium soil respectively.

Choosing the right home: settlement responses by larvae of six sea urchin species align with hydrodynamic traits of their contrasting adult habitats

AbstractOcean organisms as diverse as seaweeds and sea cucumbers exhibit life cycles in which dispersal occurs primarily via microscopic larvae or spores, with adults exhibiting limited or even no dispersal. In benthic animals, the larval stage concludes with irreversible settlement into the benthos. The decision of where and when to settle is thus one of substantial import. Prior work has shown that settlement in two shoreline echinoids (a sea urchin and a sand dollar) is unexpectedly sensitive to an environmental feature (intense fluid turbulence) that can be considered as a signal to larvae of their arrival in the neighbourhood of the hydrodynamically energetic habitats in which these taxa live as adults. Here, we used a comparative approach to explore the evolution of turbulence responsiveness in late-stage echinoid larvae. We examined three pairs of closely related sea urchins that differ in the energetic exposure of their adult habitats and found that larval responsiveness to turbulence was more pronounced in urchins that settle in more hydrodynamically exposed locations. These results raise the possibility that evolutionary differences in larval responsiveness to environmental indicators of appropriate adult habitat might reinforce or even provide a mechanism for vicariance in the ocean.

Physical Modeling of Stone Columns in Unsaturated Soil Deposits

Abstract This article focuses on evaluating the load–settlement response of circular footings on unsaturated soil layers improved with stone columns using 1-gravity (1-g) physical modeling experiments. The initial (preloading) conditions in the soil layers were varied by compaction to the same dry density but different initial degrees of saturation. An effective stress analysis calibrated using direct shear experiments was found to satisfactorily predict the measured bearing capacities of unimproved soil layers, considering a change in failure mode for soil specimens at certain initial degrees of saturation. As the bearing capacity of the unsaturated soil layers increased, the amount of improvement gained by incorporating stone columns decreased. Bulging deformations of the stone column exhibited a close relationship with the bearing capacity, with smaller amounts of bulging in soil layers with low initial degrees of saturation that also have high bearing capacity. The stress concentration ratio increases with increasing initial degree of saturation, indicating that stone columns carry a greater fraction of the applied footing stress for soil layers closer to saturated conditions.

Analysis of rigid pavements on ground improved by geosynthetics and stone columns

Stone columns and geosynthetics have been widely used as effective stabilisation techniques to improve the load–settlement response of foundations. In view of this, an analysis of rigid pavements resting on geosynthetic-reinforced granular bed–stone column improved subgrade soil has been carried out. A detailed idealisation of the problem has been done using elements of Kelvin–Voigt body, Pasternak shear layer and Winkler springs, respectively, to simulate the behaviour of subgrade soil, granular fill and stone columns. A non-linear constitutive relationship for these elements has been considered. Governing differential equations for the soil–pavement system have been developed by modelling the geosynthetic as a rough elastic membrane and the pavement as a thin plate. These equations have been written in their finite-difference form and solved using the lower–upper (LU) decomposition method with the help of appropriate boundary conditions. A detailed parametric study to depict the influence of various factors affecting the pavement behaviour has been carried out. Quantitative evaluation of this influence has been done to enable the deflection and bending moment in the pavement and the tension mobilised in the geosynthetic layer to be obtained.

Mohr-Coulomb and Hardening Soil Model Comparison of the Settlement of an Embankment Dam

In this study, numerical analysis of an embankment dam was carried out to predict settlement behavior with the use of the Mohr-Coulomb Model (MCM) and of the Hardening Soil Model (HSM). The MCM was applied to all material zones of the dam and the HSM was used for four major material zones that occupied significant volume. The settlement response of the dam was similar for MCM and HSM for three material zones (clay core, sandy gravel and random fill), each having a modulus of elasticity (MOE) in the range of 25000 to 50000kPa. However, it was found that after the end of the construction, the MCM showed about 57% and 50% more settlement as compared to HSM when MOE of sandy siltstone varied from 70000 to 125000kPa respectively. The results regarding the dam settlement predicted with the HSM are in agreement with the findings in previous studies.

Mechanisms beneath rectangular shallow foundations on sands: vertical loading

This paper details analysis of deformation behaviour of silica and carbonate sands under a rectangular foundation subject to uniaxial vertical load based on results from a series of centrifuge model tests. A multiscale particle image velocimetry/digital image correlation (PIV/DIC) technique was used to record and analyse the foundation tests with high resolution and measurement precision. Cone penetrometer and pressuremeter tests provide in situ soil characterisation of the tested sand sample in the centrifuge environment. The soil behaviour is analysed through foundation load–settlement response and the observed soil deformation measurements. Different soil deformation mechanisms and strain behaviours were observed in the different sands tested, and the particle shape effect is considered, with data from scanning electron microscopy, to explain the differences. The results and analyses contribute towards better understanding of different soil behaviours under shallow foundations in different sands.

Effect of aspect ratio of footings on settlement response of geosynthetic-reinforced granular fill-soft soil system

In this paper, a simple mathematical model is used to study the effect of aspect ratio of footings on settlement response of unreinforced or geosynthetic-reinforced granular fill-soft soil system. The length-to-width ratio (aspect ratio) of footings is varied from 1.0 (square) to 3.0 (rectangular). The foundation model is formulated for single layer of reinforcement. Parametric studies are carried out for a range of shear modulus values of granular fill and ultimate bearing capacity values of soft soil. It is observed that the aspect ratio has significant effect on settlement response and mobilised tension in geosynthetic layer. Both settlement and mobilised tension below the loaded area increase with an increase in the aspect ratio of footing for a particular loading intensity with constant width of the footing and constant soil parameters. The effectiveness of the reinforcement in terms of settlement reduction decreases due to increase of aspect ratio. The settlement decreases with an increase in ultimate bearing capacity of soft soil or shear modulus of granular fill. However, the rate of reduction of settlement with an increase in ultimate bearing capacity or shear modulus decreases as the aspect ratio increases.

Soil Interaction of Building frame Resting on Clayey Soil: Effect of Change of Aspect ratio

In General the framed structures are analyzed by considering that their bases are totally rigid (or) hinged. However, depending on relative rigidities of soil foundation and super structure the foundation undergoes deformation. In structural design the designers ignore the settlement response of the framed structure. The distribution of load on column and moment in framed structure transmitted to the foundation in the substructure has a crucial role in structural stiffness. Hence the analysis of the single bay single storied building frame resting on soil (CLAYEY SOIL) is taken for present study. The numerical analysis is carried out using ANSYS R16.0 by assuming that the base of the frame is resting on Soil (CLAYEY SOIL). The constant column height of 3M, while beam length varies of 6M,12M, &18M and their respective aspect ratio’s of 2,4&6. And for each aspect ratio the modulus of sub-grade reaction for clayey soil varies from 0.01 to 0.050N/mm3. The conventional analysis which assumes that the frame is resting on rigid support is carried out using ANSYS R16.0 by assuming the fixed base for the columns in the building frame when modulus of sub grade reaction varies from 0.01 to 0.050 N/mm3. The following conclusions have been drawn from the study, The percentage difference of shear force and bending moment in the beam, The axial load, shear force and, bending moment values in the column, and The bending moment values (Mx)&(Mz) in the shell and footing settlements in the shell for various aspect ratios of the frame obtained from both conventional and finite element analysis are not having considerable difference. Comparing numerical analysis which considers soil interaction with the conventional method, the conventional analysis is shown higher values SF and B.M in the beam, footing and columns. In conventional analysis it is assumed that the footings are resting on a rigid medium so footing settlements are zero. While observing the footing settlements in reality they undergo with some settlement therefore these settlement values are observed for numerical analysis which are used for the design to satisfy codal requirements.

Stacked pile solution for axial load–settlement analysis of driven piles in multi-layered soils

The load–settlement (Q–s) response of deep foundations is influenced by the soil stiffness. One of the most common methods of installing these foundations is the process of driving, which changes the in situ soil stress and stiffness regime. The stiffness further reduces in a nonlinear manner as the loads and shearing strains increase within the soil. The decay in the stiffness of the soil surrounding an axially loaded pile varies with depth. While a variety of methods is available to predict the nonlinear Q–s response of piles in relatively simpler soil profiles, only select methods can handle the case of multi-layered soils, where the stiffness properties vary between layers. As an alternative, the Randolph analytical pile solution is exploited for (i) developing a new modulus reduction scheme from the back-analysis of load tests on driven piles that also accounts for plasticity of the soil, (ii) devising a methodology for generating modulus reduction curves for individual layers of a multi-layered system, and (iii) formulating a stacked pile model with integration of modulus reduction curves for an improved solution. The back-analysis process accounts for the installation effects on the in situ soil stiffness. A step-wise flowchart and example applications of the methodology are also presented.

Numerical Study of Stiff Diaphragm Walls Used to Improve the Performance of Rocking Foundation Systems

ABSTRACT This research explores the effectiveness of the use of stiff diaphragm walls next to a rocking foundation through numerical simulation. This improvement technique is used as a means to increase in subsoil peripheral confinement and reduce rocking-induced settlement. The numerical model was verified by the centrifuge test of rocking shallow foundations on clay under cyclic loading. A parametric study was conducted to explore the effect of three stiff wall shapes on the performance of a rocking system. The general conclusion of the parametric investigation is that the use of stiff diaphragm walls reduced the sinking-dominated settlement response of the rocking system.

Stochastic analysis of foundation immediate settlement on heterogeneous spatially random soil considering mechanical anisotropy

The study presents a probabilistic immediate settlement analysis of shallow foundations resting on an anisotropic soil layer of spatially random properties. To this end, a rigid foundation of quite negligible slippage has been considered. Stochastic finite element method along with the numerous Monte Carlo simulations is implemented to explore the potential influence of mechanical anisotropy on the elastic settlement of a single spread footing. The analysis is also performed for the differential undrained settlement response of a pair of shallow foundations. Exploiting variable stochastic properties for the soil elastic modulus, including covariance, scale of fluctuation and cross-anisotropy ratios, several realizations of the respective soil stiffness measure are adopted, leading to the consequential corresponding realizations of the shallow foundation settlement. The results of the numerical simulations show that the increase in the elastic modulus anisotropy ratios leads to a dramatic reduction in the induced foundation settlement. Furthermore, it was observed that with the increase in the auto-correlation distance for the soil elastic modulus, the discrepancies between the evaluated settlements using deterministic and stochastic analyses grow more phenomenal. The computed settlements of the footings, considering the substantial effect of soil anisotropy, are also observed to be greater when a stochastic analysis is employed.

The Origins of Trypillia Megasites

The Trypillia megasites of Ukraine are the largest known settlements in 4th millennium BC Europe and possibly the world. With the largest reaching 320ha in size, megasites pose a serious question about the origins of such massive agglomerations. Most current solutions assume maximum occupation, with all houses occupied at the same time, and target defence against other agglomerations as the cause of their formation. However, recent alternative views of megasites posit smaller long-term occupations or seasonal assembly places, creating a settlement rather than military perspective on origins. Shukurov et al. (2015)'s model of Trypillia arable land-use demonstrates that subsistence stresses begin when site size exceeded 35ha. Over half of the sites dated to the Trypillia BI stage - the stage before the first megasites - were larger than 35ha, suggesting that some form of buffering involving exchange of goods for food was in operation. There were two settlement responses to buffering:- clustering of sites with enhanced inter-site exchange networks and the creation of megasites. The trend to increased site clustering can be seen from Phase BI to CI, coeval with the emergence of megasites. We can therefore re-focus the issue of origins on why create megasites in site clusters. In this article, we discuss the two strategies in terms of informal network analysis and suggest reasons why, in some cases, megasites developed in certain site clusters. Finally, we consider the question of whether Trypillia megasites can be considered as 'cities'.

Time Dependent Settlement Response Model of Tested Piles in Coastal Region of Nigeria

Time Dependent Settlement Response Model of Tested Piles in Coastal Region of Nigeria

Observations and analysis of wide piled foundations

Available case histories on observations on full-scale piled rafts show that the settlement response to applied load can be modeled as that for an Equivalent Pier due to compression of the piles and the soil matrix plus that of an Equivalent Raft for compression of soil layers below the pile toe level. Interior piles engage the soil from the pile toe level upward in contrast to a single pile, which engages it from the ground downward. Piles and soil, combined as a pier, have strain compatibility, which determines the distribution of load between the piles, the contact stress, and the load-transfer movement of the piles. The responses between the interior and perimeter piles differ. Particularly so in non-subsiding and subsiding environment, because perimeter piles can be subjected to downdrag and drag forces, while neither downdrag nor drag force will affect the interior piles. In non-subsiding environment, it is advantageous to make perimeter piles shorter, while in subsiding environment perimeter piles best be longer. The load distribution across the raft is also governed by the degree of rigidity of the raft and by the difference in dishing at the pile toe level and in the dishing of the actual raft.

Predicting the stress-strain behaviour of zeolite-cemented sand based on the unconfined compression test using GMDH type neural network

Stabilizing sand with cement is considered to be one of the most cost-effective and useful methods of in-situ soil improvement, and the effectiveness is often assessed using unconfined compressive tests. In certain cases, zeolite and cement blends have been used; however, even though this is a fundamental issue that affects the settlement response of a soil, very few attempts have been made to assess the stress-strain behaviour of the improved soil. Also, the majority of previous studies that predicted the unconfined compressive strength (UCS) of zeolite cemented sand did not examine the effect of the soil improvement variables and strain concurrently. Therefore, in this paper, an initiative is taken to predict the relationships for the stress-strain behaviour of cemented and zeolite-cemented sand. The analysis is based on using the unconfined compression test results and Group Method of Data Handling (GMDH) type Neural Network (NN). To achieve this end, 216 stress-strain diagrams resulting from unconfined compression tests for different cement and zeolite contents, relative densities, and curing times are collected and modelled via GMDH type NN. In order to increase the accuracy of the predictions, the parameters associated with successive stress and strain increments are considered. The results show that the suggested two and three hidden layer models appropriately characterise the stress-strain variations to produce accurate results. Moreover, the UCS values derived from this method are much more accurate than those provided in previous approaches. Moreover, the UCS values derived from this method are much more accurate than those provided in previous approaches which simply proposed the UCS values based on the content of the chemical binders, compaction, and/or curing time, not considering the relationship between stress and strain. Finally, GMDH models can be considered to be a powerful method to determine the mechanical properties of a soil including the stress-strain relationships. The other novelty of the work is that the accuracy of the prediction of the strain-stress behaviour of zeolite-cement-sand samples using the GMDH models is much higher than that of the other models.