Liquefaction-induced Settlement Research Articles

Application of EPR-MOGA in computing the liquefaction-induced settlement of a building subjected to seismic shake

Accurate prediction of the liquefaction-induced settlement ( $${S}_{\mathrm{lc}}$$ ) is an essential requirement for a good design of buildings resting on liquefiable ground and subjected to seismic shake. However, prediction of the $${S}_{\mathrm{lc}}$$ is not straightforward process and it requires advanced soil models and calibrated soil parameters that are not readily available for designers/practitioners. In addition, the available empirical models to estimate the $${S}_{\mathrm{lc}}$$ have been developed using either classical regression analysis or multivariate adaptive regression splines and such techniques produce complicated models. Also, these empirical models have been developed utilizing results of numerical modelling. To overcome these limitations, novel model has been developed in this paper utilizing robust regression analysis driven by artificial intelligence called the evolutionary polynomial regression analysis. The new model has been developed using centrifuge results (real laboratory measurements) and can be easily used to accurately estimate the liquefaction induced settlement. The developed model scored a mean absolute error, root mean square error, mean, standard deviation of the predicted to measured values, coefficient of determination, $$a20 - \mathrm{index}$$ , and EPR coefficient of determination of 2.12 cm, 2.84 cm, 1.06, 0.19, 0.98, 0.77, and 97%, respectively, for the learning data and 1.73 cm, 3.31 cm, 0.99, 0.17, 0.97, 0.75, and 97%, respectively, for the examination data. The developed model has also been used in a parametric study to provide an insight into the sensitivity of the $${S}_{\mathrm{lc}}$$ to the foundation width, building height, pressure applied on the foundation, thickness and relative density of the liquefiable layer, and earthquake intensity. The results obtained from the parametric study are reasonable and in agreement with previous studies in the literature. Thus, the developed model can be employed to optimize designs and to reduce design costs as it does not require complicated analyses and/or expensive computational facilities.

Calculation of the settlement of pile foundations taking into account the influence of soil liquefaction

Pile foundations are considered one of the most common foundation solutions for the construction of buildings and structures in difficult geotechnical conditions, including in seismic areas. However, during earthquakes specific processes often occur that negatively affect the interaction of piles with the surrounding soil. Soil liquefaction is one of the most difficult problems in geotechnics. Many historical cases show that buildings and structures on pile foundations are collapsed completely when the surrounding soil liquefies. One of the reasons is the increase in settlement of the foundation after soil liquefaction.Unlike the liquefaction potential assessment, or liquefaction-induced settlement of structures on shallow foundations, which are discussed by many researchers, the settlement of pile foundations after soil liquefaction has not been studied extensively. This paper presents the calculation of the settlement of pile foundations in different cases, with and without taking into account the influence of soil liquefaction, based on the hypothesis that the additional downward loads due to self-compaction of the liquefiable soil layers have an effect on piles. The analysis method in this study refers to the finite element method via PLAXIS 3D software. Finally, a brief comparison of the calculation results in the different considered cases is presented. The comparison shows how much the foundation settlement can increase if the influence of soil liquefaction is taken into account based on the suggested hypothesis. This paper provides a useful calculation and importance of further researches of liquefaction-induced settlement of pile foundations for seismic design.

Effect of air injection on pile and pile group behavior in liquefiable soil

Soil liquefaction during large earthquakes causes serious damage to structures built on foundations. In recent years, artificially injecting small amounts of air into liquefaction-susceptible soils has been proposed as a newly developed and cost-effective liquefaction mitigation method. Nevertheless, the liquefaction response of piles through this method has not been investigated so far. A series of 1g shaking table tests were conducted in this research to evaluate the liquefaction response of pile and pile group in air-injected partially saturated soils. The results have shown that air injection effectively reduces the liquefaction-induced settlements of pile and pile group. Also, this method has relatively reduced the excess pore pressure ratio. According to visual results and bending moments in piles, the depth of a liquefied soil layer decreases in air-injected partially saturated soils. Also, the deformation of soil structure is observed to decrease by injecting air into the samples. Despite these effects, larger accelerations are transmitted to the surface of the soil and consequently to the structure, and larger bending moments are applied to the piles in air-injected partially saturated samples. It was observed that at the low confining pressure, the effectiveness of this method is not a function of air injection duration.

A Simple and Sustainable Prediction Method of Liquefaction-Induced Settlement at Pohang Using an Artificial Neural Network

Conventionally, liquefaction-induced settlements have been predicted through numerical or analytical methods. In this study, a machine learning approach for predicting the liquefaction-induced settlement at Pohang was investigated. In particular, we examined the potential of an artificial neural network (ANN) algorithm to predict the earthquake-induced settlement at Pohang on the basis of standard penetration test (SPT) data. The performance of two ANN models for settlement prediction was studied and compared in terms of the R2 correlation. Model 1 (input parameters: unit weight, corrected SPT blow count, and cyclic stress ratio (CSR)) showed higher prediction accuracy than model 2 (input parameters: depth of the soil layer, corrected SPT blow count, and the CSR), and the difference in the R2 correlation between the models was about 0.12. Subsequently, an optimal ANN model was used to develop a simple predictive model equation, which was implemented using a matrix formulation. Finally, the liquefaction-induced settlement chart based on the predictive model equation was proposed, and the applicability of the chart was verified by comparing it with the interferometric synthetic aperture radar (InSAR) image.

Dynamic soil-structure interaction analyses of two important structures affected by liquefaction during the Canterbury earthquake sequence

The 2010–2011 Canterbury earthquake sequence produced significant damage in Christchurch. Much of the observed damage was related to soil liquefaction. The availability of building information, performance observations, survey data, geotechnical data, and ground motions recordings in Christchurch produced several well-documented case histories that provide insights to liquefaction-induced building settlement. Two case histories of important structures built atop fluvial soil deposits with sand and gravel layers are analyzed. One building was the third tallest building in Christchurch before the earthquakes, and the other building is an architectural landmark. Both structures were sited near the Avon River in zones of minor-to-moderate lateral spreading. Nonlinear dynamic soil-structure-interaction effective stress analyses are performed using the program FLAC with the PM4Sand constitutive model calibrated with laboratory tests or established simplified liquefaction procedures. The results show good agreement between observed and calculated responses of the ground and structure for the Canterbury earthquake sequence. Dynamic analysis identified several potential mechanisms contributing to the observed performance. Its use is encouraged to estimate shear-induced liquefaction building settlement.

Multivariate adaptive regression splines model for prediction of the liquefaction-induced settlement of shallow foundations

Buildings with shallow foundation are vulnerable to liquefaction-induced settlement during an earthquake. Accurate settlement evaluation is an important step in earthquake damage mitigation. This paper presents a simplified approach to estimate the liquefaction-induced settlement of buildings with shallow foundations. The multivariate adaptive regression splines (MARS) algorithm is adopted. The validated finite difference method is used to produce artificial data that consider various properties of the soils, structures and ground motions. A relative importance analysis is conducted to quantify the effect of each input parameter and their coupled interactions on the liquefaction-induced settlement. The accuracy of the established model is demonstrated through centrifuge test results available in the literature.

Liquefaction-induced settlements of residential buildings subjected to induced earthquakes

The paper evaluates the dynamic performance of existing residential houses affected by gas-extraction-induced earthquakes in an area of low tectonic seismicity where structures have not been designed against earthquake loading. The foundation consists of narrow spread footings (width, B < 0.7 m), while the seismic demand is characterized by low intensity. Nonlinear, effective stress, fully coupled, dynamic soil-structure interaction analyses were performed to develop estimates of liquefaction-induced settlements for buildings on narrow spread footings, founded in a range of soil conditions, with ground motions and structural characteristics that are typically encountered in the study area. The results verify patterns observed in recent studies for slab foundations and shed light on new mechanisms. For the low magnitude earthquakes considered in this study, the total foundation settlements were found to be relatively limited, although simplified liquefaction triggering calculations would sometimes predict low factors of safety against liquefaction. A simplified equation was developed from regression of the numerical analyses results to derive estimates of liquefaction-induced settlements for residential buildings that was adopted in the latest update of the relevant seismic building code.

Prediction of seismic compression of saturated sand considering the ground motion characteristics and variable permeability

A one dimensional shear beam numerical model was firstly established to calculate the seismic compression in free-field site of saturated sand by using OpenSees program. Based on the established model, the influence of permeability coefficient on the liquefaction-induced settlement of saturated sand was investigated by introducing a variable permeability coefficient model. The modified model was verified by comparison with results from centrifuge model test. The correlation between seismic compression and seismic load parameters was studied, and a velocity spectrum intensity (VSI) based prediction function was proposed to estimate the compression of saturated sand by considering both the characteristics of seismic motion and the sand properties. The results show that the modified variable permeability model significantly improves the accuracy of the simulation results. Direction of seismic motion has a significant effect on the seismic compression and excess pore water pressure of sand, and the simplification of using one-dimensional load in a certain direction to represent the two-dimensional loads underestimates the seismic compression of sands. The proposed VSI-based prediction function provides a means for estimating seismic compression of saturated sand, and the prediction accuracy improves with increasing the relative density of sand.

Assessment Supporting the Use of Outcropping Rock Evolutionary Intensity Measures for Prediction of Liquefaction Consequences

This study evaluates a variety of intensity measures (IMs) for predicting the liquefaction-induced residual settlement and tilt of shallow-founded structures. We use data from both numerical and physical (centrifuge) models of soil-foundation-structure systems. The relative quality of these IMs is quantified in terms of efficiency, sufficiency, and predictability. We consider both scalar and vector-valued IMs and evaluate the relative performance of IMs recorded at different locations (outcropping rock, within rock, far-field, and foundation) from nonlinear and equivalent-linear simulations. Cumulative absolute velocity (CAV) at outcropping rock is the optimum IM for predicting foundation settlement, while either outcropping rock CAV, peak ground velocity, or peak incremental ground velocity is optimum for predicting permanent foundation tilt. Vector IMs offer improvements to efficiency and sufficiency but may be impractical to predict.

Estimation of settlement after soil liquefaction for structures built on shallow foundations

Soil liquefaction can occur when the strength and stiffness of soil are reduced by changes in the stress condition, and the settlement of structures can be affected by this phenomenon following an earthquake. To evaluate the liquefaction-induced settlement of structures, a simple equation that proposed the concept of equivalent viscosity of soil-water mixture is adopted. In this study, comprehensive finite element analyses are conducted and a viscosity chart is proposed that enables prediction of the liquefaction-induced settlement value. To accommodate different site conditions, several corrections are made based on experimental data obtained from literature; such corrections are found to be effective for proficiently estimating the liquefaction-induced settlement under differing conditions.

Experimental Study on Seismic Response Characteristics of Liquefiable Soil Layers

ABSTRACT This study evaluates the effect of excess pore water pressure (EPWP) in liquefiable sand sub-layers on the seismic response of the soil profile. A series of shaking table tests were conducted to evaluate the liquefaction performance of a loose to dense subsurface sandy layer on the site effect phenomena. The results confirmed that the liquefied subsurface layer could attenuate or amplify the main characteristics of the seismic site response from 10% to 60%, primarily depending on the level of EPWP and soil softening in the layer. It is important to consider the detrimental effects of liquefaction-induced settlement in these estimations.

Influence of inherent anisotropy on the seismic behavior of liquefiable sandy level ground

Inherent anisotropy is a crucial aspect to consider for an improved understanding of the strength and deformation characteristics of granular materials. It has been the focus of intense investigation since the mid-1960s. However, inherent anisotropy’s influence on ground seismic responses, such as liquefaction, has not been extensively studied. In this paper, inherent anisotropy’s influence on ground seismic responses is examined through a series of dynamic centrifuge model tests on liquefiable level sand deposits. During the model setup, five different deposition angles (0, 30, 45, 60, and 90 degrees) were achieved using a specially designed rigid container. The models were exposed to tapered sinusoidal input accelerations and the recorded results were fully investigated. It was found that deposition angle-caused inherent anisotropy significantly influenced the excess pore pressure responses during the shaking and dissipation phases. The amount of excess pore pressure build-up and the high excess pore pressure duration increased with the deposition angle, while the dissipation rate decreased as the deposition angle increased. The inherent anisotropy also influenced liquefaction-induced ground settlement, with volumetric strain increasing along with the deposition angle. With respect to response acceleration, inherent anisotropy’s effects depended on the amount of excess pore pressure build-up (i.e., degree of liquefaction). In view of these results, it was concluded that a sandy ground, deposited at a higher angle (i.e., closer to 90 degrees), is more susceptible to liquefaction and that inherent anisotropy’s influence should be considered when evaluating the liquefaction potential and performing effective stress analyses.

Key Trends in Liquefaction-Induced Building Settlement

AbstractDynamic soil-structure interaction effective stress analyses are performed to identify key trends in the settlement of buildings with shallow foundations affected by soil liquefaction. Over...

A Centrifuge Study of Seismic Structure-Soil-Structure Interaction on Liquefiable Ground and Implications for Design in Dense Urban Areas

Current practice in seismic design often assumes free-field conditions for the estimation of liquefaction-induced building settlement. This is inaccurate, as a structure places additional stresses on the soil, resulting in changes to the spatial and temporal occurrence of liquefaction, accelerations, and deformations. Further complications arise in dense urban environments where closely spaced structures may interact through structure-soil-structure interaction (SSSI). Previous studies have shown that SSSI may have positive or negative effects on the response of adjacent structures in terms of permanent settlement, rotation, and flexural deformations. However, little is known regarding how to maximize the benefits of SSSI with minimal risk of adverse consequence. In this study, centrifuge tests were conducted on both isolated and closely spaced structures to identify how the building separation and ground motion characteristics affect the response of adjacent structures founded on a layered, liquefiable soil profile. Results indicate that properly planned configurations and interactions may be employed in combination with traditional mitigation strategies to improve the settlement-rotation response of adjacent structures, while also reducing the demand imposed on the superstructure.

Key predictors of structure settlement on liquefiable ground: a numerical parametric study

Excessive building settlement and tilt on liquefiable soils has led to significant damage in previous earthquakes. The state-of-practice for evaluating liquefaction-induced building settlement still primarily relies on semi-empirical free-field relationships that have repeatedly been shown as unreliable and inaccurate during field and physical model studies. This is because these methods ignore the presence of the building, soil-foundation-structure interaction, and some of the dominant mechanisms of deformation near buildings. In a comprehensive numerical parametric study, the dynamic response of the soil-foundation-structure (SFS) system was assessed with a wide range of soil, structure, and ground motion characteristics. The primary objectives were: first, to identify the key predictors of foundation settlement and study their relative importance and interdependence; and second, to provide a comprehensive and mechanistically-sound dataset for the future development of a probabilistic predictive model of building settlement. The numerical simulations involved fully-coupled, 3-dimensional, nonlinear dynamic analyses of the SFS system, previously validated using centrifuge experimental results. For the conditions considered, the key predictors of building settlement were identified as the cumulative absolute velocity (CAV) of the outcropping rock motion, the relative density of, thickness of, and depth to the liquefiable layer(s), presence of a low-permeability cap, followed by foundation length-to-width ratio, embedment depth, contact area, and bearing pressure. The structure’s inertial mass and height/width ratio as well as the initial fundamental period of the structure and site were comparatively less influential. The relative importance and influence of most input parameters were shown to depend on ground motion intensity (e.g., CAV) and soil relative density.

Liquefaction-induced settlement and tilting of buildings with shallow foundations based on field and laboratory observation

In order to examine relative importance of key parameters affecting liquefaction-induced settlement and tilting of buildings with shallow foundations, earthquake reconnaissance studies and centrifuge experiments were made and their results were compared with those of similar previous studies. It is shown that: (1) The liquefaction-induced relative settlement and tilting of shallow foundations tend to increase with increasing contact pressure and ground settlement, and with decreasing groundwater table depth and thickness of the non-liquefied crust; (2) The tilt angle of the building also tends to increase with increasing eccentric mass and distance ratio; and (3) The safety factors against vertical load and dynamic overturning moment are key indicators to estimate liquefaction-induced damage to buildings with rigid shallow foundations.

Effect of Cone Penetration Conditioning on Random Field Model Parameters and Impact of Spatial Variability on Liquefaction-Induced Differential Settlements

AbstractThe prediction of liquefaction-induced damage to structures can be aided in part by an understanding of the magnitude of inherent spatial variability of the underlying liquefaction-suscepti...

Modification of the liquefaction potential index to consider the topography in Christchurch, New Zealand

In recent years, many have mapped the liquefaction potential index (LPI) to describe the liquefaction hazard at regional scale. Several investigators have calibrated the LPI to field observations of liquefaction-induced ground failure after a number of major earthquakes; the significance of LPI values and their correlation with the severity of liquefaction-induced ground failure can vary greatly depending on the calibration. In this study, the LPI was computed at more than 1200 cone penetration test soundings across the Christchurch area, New Zealand, using peak ground accelerations from the 2011 Christchurch Earthquake. Based on detailed field observations of liquefaction-induced ground failure after the earthquake, it was shown that the LPI has potential for discriminating between areas with no liquefaction-induced ground failure hazard and areas that may experience liquefaction-induced ground oscillations and settlement; however, the LPI performed poorly at sites where severe ground failures occurred, especially at sites that experienced lateral spreading. As many researchers have found a positive correlation between lateral spreading and the proximity and depth of a nearby free-face (i.e., a steep topographic depression, river channel, etc.), a new LPI framework was proposed that includes a parameter named the free-face ratio (FFR). FFR was shown to have a significant correlation with field observations of lateral spreading in Christchurch. It was shown that by incorporating FFR into the LPI framework, modified LPI values are positively correlated with the severity of field observations of liquefaction-induced ground failure in Christchurch. It was also shown that maps can be produced based on LPI and FFR, and such maps rarely underpredict the liquefaction-induced ground failure hazard, unlike maps based on the unmodified LPI.

Modeling added spatial variability due to soil improvement: Coupling FEM with binary random fields for seismic risk analysis

A binary mixture homogenization model is proposed for predicting the effects on liquefaction-induced settlement after soil improvement based on the consideration of the added spatial variability between the natural and the treated soil. A 2D finite element model of an inelastic structure founded on a shallow foundation was coupled with a binary random field. Nonlinear soil behavior is used and the model is tested for different mesh size, model parameters and input motions.Historical evidence as well as physical and numerical modeling indicate that improved sites present less liquefaction and ground deformation. In most cases this improvement is modeled as homogeneous; however, in-situ measurements evidence the high level of heterogeneity in the deposit. Inherent spatial variability in the soil and the application of some soil improvement techniques such as biogrouting and Bentonite permeations will necessary introduce heterogeneity in the soil deposit shown as clusters of the treated material in the natural soil. Hence, in this study, improvement zones are regarded as a two-phase mixture that will present a nonlinear relation due to the level of complexity of seismic liquefaction and the consequent settlement in a structure. This relation is greatly affected by the mechanical behavior of the soils used and the input motion. The effect on the latter can be efficiently related to the equivalent wave period as the proposed homogenization model depends on the stiffness demand of the input motion.

6th Ishihara lecture: Simplified procedure for estimating liquefaction-induced building settlement

Significant settlement and damage may occur due to liquefaction of soils beneath shallow-founded buildings. The primary mechanisms of liquefaction-induced building settlement are shear-induced, volumetric-induced, and ejecta-induced ground deformation. Volumetric-induced free-field ground deformation may be estimated with available empirical procedures. Although challenging to estimate, ground failure indices and experience can be used to estimate roughly ejecta-induced building settlement. Nonlinear dynamic soil-structure interaction (SSI) effective stress analyses are required to estimate shear-induced ground deformation. Results from over 1300 analyses identified earthquake, site, and building characteristics that largely control liquefaction-induced building settlement during strong shaking. A simplified procedure is developed based on the results of these analyses to estimate the shear-induced component of liquefaction building settlement. The standardized cumulative absolute velocity and 5%-damped spectral acceleration at 1s period capture the ground shaking. The liquefaction building settlement index, which is based on the shear strain potential of the site, captures in situ ground conditions. Building contact pressure and width capture the building characteristics. Field case histories and centrifuge test results validate the proposed simplified procedure. Recommendations and an example for evaluating building performance at liquefiable sites are shared.