Liquefaction Mitigation Research Articles

Coupled smoothed particle hydrodynamics-discrete element method simulations of soil liquefaction and its mitigation using gravel drains

In this paper, a fully Lagrangian particle-based method for coupled fluid-particle interaction is utilized to evaluate liquefaction of saturated granular soils subjected to dynamic base excitations. The discrete element method (DEM) is employed to model the solid particles and the fluid motion is simulated using the smoothed particle hydrodynamics (SPH). A coupled SPH-DEM scheme is achieved through local averaging techniques and well-established semi-empirical formulas for fluid-particle interaction. A key feature of the employed technique is that it does not presume undrained conditions for the granular deposit and allows for spatial fluid movements within the deposit. The responses of loose and dense granular deposits to seismic excitation are first analyzed. As expected, the loose deposit exhibited significant pore pressure development and liquefaction while the dense deposit barely showed any considerable buildup of pore pressure and did not liquefy. Liquefaction of the loose deposit resulted in significant surface settlement while that experienced by the dense deposit was within tolerable limits. A liquefaction mitigation technique through the installation of gravel drains was then introduced to the loose deposit and its effect on mitigating pore pressure buildup was examined. Results of conducted simulations show that the installation of gravel drains effectively reduced pore-pressure buildup and, for the most part, the soil maintained its strength. However, the drains did not reduce the overall surface settlement of the deposit to acceptable levels.

The Effect of Lightweight Expanded Clay Aggregate on the Mitigation of Liquefaction in Shaking Table

Non-conventional materials are often applied to dissipate the energy of dynamic loads and mitigate liquefaction. In this study, the effect of Lightweight Expanded Clay Aggregate (LECA) on the mitigation of liquefaction was examined using shaking table tests. LECA, a common lightweight material, was added to saturated sand in a range of 0–20% to study the variation of excess pore water pressure (EPWP) generation, as well as the acceleration response of the soil. Based on the obtained results, the addition of 5% and 10% LECA to saturated sand resulted in a significant decrease in the generation of EPWP, while higher LECA content led to an increase in the generation of EPWP. The mechanisms behind such behaviors contradict the effects of increasing the damping of the soil mixture and reducing the effective initial stress as a function of overall mixture density. Adding 5 and 10% LECA reduces EPWP because aggregates accelerate the dissipation of EPWP during and after vibration. As the percentage of LECA increases by 15% and 20%, excess pore pressure ratio increases. The cause of this may be the reduction of effective initial stress leading to reduced soil density in higher-LECA contents. 10% LECA is presented as the threshold for changing the liquefaction behavior of sand-LECA mixtures. This study concludes that adding LECA to sand samples increases the rate of dissipation of EPWP, but also leads to a significant decrease in initial effective stress.

State of the Art Review of Emerging and Biogeotechnical Methods for Liquefaction Mitigation in Sands

Abstract Earthquake-induced liquefaction causes soil to exhibit fluidlike behavior due to a sudden increase in pore water pressure and a concurrent decrease in effective stress. The liquefaction ca...

Parametric investigation of effectiveness of high modulus columns in liquefaction mitigation

In this paper, an extensive parametric study is carried out in order to examine the effectiveness of high modulus columns (HMCs) in liquefaction mitigation using a nonlinear three-dimensional (3D) finite-element (FE) software. For this purpose, a hypothetical liquefiable soil profile of 20 m thick is modeled and parametric analyses are performed by considering different area replacement ratios, shear modulus ratios, improvement depth (slenderness) ratios and input motion intensities. The results of the parametric analyses are evaluated by examining shear stress reduction, shear strain distribution, peak surface acceleration, maximum horizontal acceleration, factor of safety against soil liquefaction, excess pore water pressure ratio, surface settlements, lateral displacements and response spectra. Comparative analyses between unimproved liquefiable soil and improved soil are performed to show the influence of high modulus columns on the response of liquefiable soil. The seismic performance of liquefiable soil reinforced with HMCs is specifically investigated by focusing on the shear strain and shear stress distribution between liquefiable soil and high modulus columns. Therefore, the analysis results are discussed in terms of assumption of shear strain compatibility by comparing the modified equations for shear stress reduction factors suggested in the literature with the one developed in this paper. Additionally, the reliability of the current design methodology for evaluating shear reinforcement of HMCs is discussed by showing effects of shear strain compatibility and incompatibility on the values of factor of safety against liquefaction and recommendations are made related to the use of HMCs in engineering practice.

Undrained Dynamic Response of Partially Saturated Sands Tested in a DSS-C Device

AbstractLiquefaction-induced seismic vulnerability is still a major problem in geotechnical engineering applications. To address this issue, various liquefaction mitigation techniques have been pro...

Experimental Evidence of the Effectiveness and Applicability of Colloidal Nanosilica Grouting for Liquefaction Mitigation

AbstractThe low viscosity and the ability to control solidification rate make colloidal nanosilica grout an excellent ground-improvement solution which is functional for different engineering purpo...

In-Ground Gravel–Rubber Panel Walls to Mitigate and Base Isolate Shallow-Founded Structures on Liquefiable Ground

AbstractThe effectiveness of a new liquefaction mitigation strategy is investigated experimentally for newly constructed shallow-founded structures: an in-ground gravel–rubber (GR) panel wall syste...

Numerical Investigation of Stone Column Improved Ground for Mitigation of Liquefaction

Installation of a stone column in loose soil is one of the robotics ground enhancement techniques that reduce the risk liquefaction and related ground deformation. However, the experimental investigation is costly and it is time-consuming to check the feasibility of this technique for the evaluation of ground subsidence and fluctuations in excess pore water pressure concerning different area ratios of a high modulus column. This paper presents a numerical investigation into shallow foundations underlain by a stone column as a liquefaction countermeasure. The Biot's consolidation equations are coupled with stress equilibrium equations in finite element modeling for cyclic loading conditions. The critical state model based on generalized plasticity theory was applied to model the nonlinear behavior of soil. The unknown displacement and pore pressure are evaluated using code written in FORTRAN 90. The granular column installation effect is also considered to predict displacements and excess pore pressure (EPP) at each time step. With the introduction of a granular column, considerable reductions were observed in displacements and EPP. The results underline the effectiveness of granular column installation as an effective measure in the mitigation of liquefaction.

Static liquefaction behavior of short discrete carbon fiber reinforced silty sand

Saturated silty sand is more likely to cause landslide due to static liquefaction behavior. In this study, easily dispersible short synthetic carbon fibers (CF), with larger aspect ratio and smaller diameter (7 μm) compared with conventional polypropylene fibers, were used to improve the liquefaction resistance behavior of silty sand. A series of triaxial tests under different confining pressures were carried out on reinforced samples with different fiber contents (0.2, 0.5, 1.0%) and lengths (3, 6, 10 mm). The properties of stress and strain relationships, development of pore water pressure, effective stress path, liquefaction brittleness index, critical state line and volumetric strain were examined. The results from undrained tests showed that both the peak and post-peak deviator stresses of CF reinforced samples did not show a regular increase with fiber length. The 6 mm CF fiber showed the best reinforcement effect at a confining pressure of 100 kPa while 3 mm CF fiber achieved the best results at a confining pressure of 200 kPa. CF-reinforced sand was confirmed to be an effective liquefaction mitigation method compared with the method using conventional polypropylene fibers. This study provides an effective improvement method in particular to prevent a geological hazard in backfilling engineering projects.

Seismic analysis of stone column improved liquefiable ground using a plasticity model for coarse-grained soil

This paper presents the seismic analysis of stone column (SC) improved liquefiable ground using a three-dimensional (3D) plasticity model with unified description of coarse-grained soil (CGS). The model is a modification of an existing plasticity model for large post-liquefaction deformation of sand, with improvements on the formulation for strength characteristics exhibited by CGS. According to requirements of FLAC3D User-Defined-Model (UDM), the model is implemented into the finite difference code FLAC3D, for which a method synchronizing the mapping centres and sharing necessary internal variables of subzones is developed to resolve the computational stability issue caused by the mixed discretization technique of FLAC3D. The model is validated against monotonic/cyclic and undrained/drain laboratory tests under 8 different stress paths and initial states on a gravel material and Toyoura sand. A centrifuge shaking table test on SC improved liquefiable ground is simulated adopting the model. The results show that the constitutive model and analysis method are effective in reproducing the liquefaction behaviour of CGS ground under seismic loading. Parametric analysis for liquefaction mitigation effects of SCs is further conducted, highlighting the importance of densification and maintaining drainage efficiency of SCs. Results show that the SC’s effective improvement area is approximately 2–3 times its diameter.

Liquefaction resistance of sand amended with biochar

Biochar is a solid carbon material produced by heating organic biomass in the absence of oxygen through a process known as pyrolysis. Scientists and policy makers have recognised its potential role in carbon sequestration, reducing greenhouse gas emissions, renewable energy, waste mitigation and as soil amendment. To date, most studies related to biochar application to soil have focused mainly on the agronomic benefits, while little attention is paid on its effects on soil properties from geotechnical point of view. Considering that biochar can be produced from biomass, its use would fit satisfactorily the current trends of recycling wastes for ground improvement and liquefaction mitigation. To address this, the effect of adding various proportions by weight of biochar, derived from poultry litter, on the liquefaction resistance of sand is investigated through undrained cyclic triaxial tests. The findings suggest that, contrary to other earlier published reports using another type of biochar, adding poultry litter biochar to sand decreases its liquefaction resistance in a similar manner as adding non-plastic fines. The results highlight the fact that the type of biochar used as soil amendment is important in determining whether the liquefaction resistance of the host sand will improve or not.

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.

Numerical Evaluation of Liquefaction Resistance for Desaturated Sands

AbstractDesaturation has been a cost-effective and straightforward ground improvement method for liquefaction mitigation. Recent advancements in geotechnical numerical simulations have allowed for ...

Seismic Performance Evaluation of Improved Jet Grouted Grid Form with Horizontal Slab in Liquefaction Mitigation

A chain event of the 2016 Kumamoto earthquakes caused considerable geotechnical damage related to liquefaction in many places around Kumamoto plain. Many low-rise houses and traditional Japanese style houses, which were constructed on shallow foundation, suffered differential settlement and tilting due to liquefaction. To mitigate the building damages due to the liquefaction, a new countermeasure method of jet grout grid form with a horizontal slab is introduced in this study. The effectiveness of the proposed technique was evaluated through physical modelling and numerical modelling. As a part of the physical modelling, a set of 1 g shaking table tests for unimproved case and improved case were performed, in which the mitigation effects of the grid form with a horizontal reinforcing slab were examined based on the acceleration, excess pore water pressure ratio as well as ground settlement. Numerical simulation was also performed for assessing the effect of improved method on soil-structure interaction and building settlement during the earthquake. The physical and numerical results confirmed that the grid form with horizontal slab reinforced method is effective in settlement control and offers favorable contribution in liquefaction mitigation.

Electric Conductivity Probes to Study Change in Degree of Saturation - Bench Top Laboratory Tests

Sand characteristics such as liquefaction susceptibility can be affected as a result of change in degree of saturation of sand. New liquefaction mitigation technique by inducing partial saturation in sands is introduced by Yegian et al in 2007[1]. This technique requires to monitor changes in degree of saturation of sand. By nature, changes in degree of saturation of sand can lead in changes in its electric conductivity. Electric conductivity is the property of a material that represents its ability to conduct electric current. Fully saturated sand can conduct electric current better than sand with lower degree of saturation. Therefore, the change in measured electric conductivity can be used to calculate the change in degree of saturation of sand. In 1942, Gus Archie [2] expressed that the electric conductivity of soil is a function of its porosity, degree of saturation, tortuosity and electric conductivity of pore fluid. Using Archie’s law electrical conductivity can be related to the degree of saturation in sands. Typically, electric conductivity probes and meters are instruments which are used to measure electric conductivity. Using electrical conductivity probes, sets of bench top tests were conducted on Ottawa sand to study the relation between degree of saturation and electric conductivity in sand. Partial saturation in sands were created by pouring dry sand into sodium percarbonate solution with a known initial concentration. By nature, sodium percarbonate in water, generates oxygen gas bubbles in time. The changes in electric conductivity in the specimen were measured using electric conductivity meters and probes. In addition, changes in degree of saturation of the specimen were measured using soil phase relations equations. Measured electric conductivity data and calculated degree of saturations were correlated to explore relation between electric conductivity and degree of saturation. This paper presents results of bench top tests, and suggests a relationship between, final degree of saturation of sand and initial concentration of sodium percarbonate solution

Measurement of sand grain distribution to gauge liquefaction risks at six key coastal west sumateran sites

It is well known that earthquake-induced liquefaction can cause remarkable damage to buildings. A recent disaster involving liquefaction in Palu damaged buildings and infrastructure and has become the focus of many researchers. Detailed study of liquefaction is necessary in order to have a good understanding and direct mitigation efforts for the future. In this study, the liquefaction potential of sands with various grain size distributions was analyzed. The research was experimental using a laboratory sieve shaker. The samples were taken from six areas near important facilities. From this, the relationship between grain distribution and liquefaction potential could be plotted and this information could become an important input for liquefaction mitigation efforts in sandy sediment areas.

State-of-the-Art of Colloidal Silica-Based Soil Liquefaction Mitigation: An Emerging Technique for Ground Improvement

In the booming field of nanotechnology, colloidal silica (CS) has been introduced for ground improvement and liquefaction mitigation. It possesses a great ability to restrain pore pressure generation during seismic events by using an innovative stabilization technique, with the advantages of being a cost-effective, low disturbance, and environmentally friendly method. This paper firstly introduces molecular structures and some physical properties of CS, which are of great importance in the practical application of CS. Then, evidence that can justify the feasibility of CS transport in loose sand layers is demonstrated, summarizing the crucial factors that determine the rate of CS delivery. Thereafter, four chemical and physical methods that can examine the grouting quality are summed and appraised. Silica content and chloride ion concentration are two effective indicators recommended in this paper to judge CS converge. Finally, the evidence from the elemental tests, model tests, and field tests is reviewed in order to demonstrate CS’s ability to inhibit pore water pressure and lower liquefaction risk. Based on the conclusions drawn in previous literature, this paper refines the concept of CS concentration and curing time being the two dominant factors that determine the strengthening effect. The objective of this work is to review CS treatment methodologies and emphasize the critical factors that influence both CS delivery and the ground improving effect. Besides, it also aims to provide references for optimizing the approaches of CS transport and promoting its responsible use in mitigating liquefaction.

Comparison on seismic response of rectangular closed diaphragm wall and pile group in sloping liquefiable deposit

This paper presents fully coupled solid-fluid nonlinear dynamic finite element (FE) model on OpenSees platform to study the response of rectangular closed diaphragm wall (RCDW) subjected to earthquakes. Soil seismic behavior was simulated by the PDMY02 soil model available in OpenSees and soil-RCDW interaction was captured by the zero length elements with PyLiq1, TzLiq1 and QzSimple1materials. Then, the FE numerical model was validated by data measured from centrifuge experiments. The validated numerical model was used to investigate the different seismic response between RCDW and pile group in sloping liquefiable deposit. The numerical simulation results showed that: a) Compared with pile group, RCDW can mitigate liquefaction in soil core subjected to earthquakes; b) RCDW was able to resist soil lateral spreading more effectively; c) The shear strain of soil core was restrain by RCDW which resulted in slow generation of excess pore water pressure. Therefore, RCDW had the advantage of liquefaction mitigation; d) Pile group had more deformation displacement, RCDW had more rigid displacement, resulted from the different stiffness and structural integrity between RCDW and pile group; e) Finally, it can be concluded that RCDW may be more suitable choice applied in the sloping liquefiable ground.

Blast-induced liquefaction in silty sands for full-scale testing of ground improvement methods: Insights from a multidisciplinary study

In the engineering geology field increased attention has been posed in recent years to potential liquefaction mitigation interventions in susceptible sand formations. In silty sands this is a major challenge because, as the fines content increases, vibratory methods for densification become progressively less effective. An alternative mitigation technique can be the installation of Rammed Aggregate Pier® (RAP) columns that can increase the resistance of the soil, accounting for its lateral stress increase and for the stiffness increase from soil and RAP composite response. To investigate the influence of these factors on liquefaction resistance, full-scale blast tests were performed at a silty sand site in Bondeno (Ferrara, Italy) where liquefaction was observed after the 2012 Emilia-Romagna earthquake. A multidisciplinary team of forty researchers carried out devoted experimental activities aimed at better understanding the liquefaction process at the field scale and the effectiveness of the treatment using inter-related methods. Both natural and improved areas were investigated by in-situ tests and later subjected to controlled blasting. The blast tests were monitored with geotechnical and geophysical instrumentation, topographical surveying and geological analyses on the sand boils. Results showed the RAP effectiveness due to the improvement of soil properties within the liquefiable layer and a consequent reduction of the blast-induced liquefaction settlements, likely due to soil densification and increased lateral stress. The applied multidisciplinary approach adopted for the study allowed better understanding of the mechanism involved in the liquefaction mitigation intervention and provided a better overall evaluation of mitigation effectiveness.

Effect of distribution pattern of DSM columns on the efficiency of liquefaction mitigation

Liquefaction during earthquakes can result in severe damage to structures, primarily from excess pore water pressure generation and subsoil softening. Deep Soil Mixing (DSM) is a common method of soil improvement and is also used to decrease shear stress in liquefiable soils to control liquefaction. The current study evaluated the effect of Deep Soil Mixing (DSM) columns and implementation of different column patterns on controlling liquefaction and decreasing settlement of shallow foundations. A series of shaking table physical modelling tests were conducted for three different distribution patterns of Deep Soil Mixing (DSM) columns (i.e.: square, triangular and single) with a treatment area ratio of 30%. The treatment was applied to a liquefiable soil under a shallow model foundation. The results showed that the excess pore water pressure decreased 20% to 50% in comparison with the unimproved soil, depending on the Deep Soil Mixing (DSM) column pattern used. For improved soil, the shallow foundation settlement was about 10% that of the unimproved soil in the best case. The increase in soil shear stiffness after use of the Deep Soil Mixing (DSM) columns was compared with the results of existing practical relations to increase soil shear strength.