Liquefaction Hazard Mitigation Research Articles

The Stability Analysis of the Bored Pile Foundation as Liquefaction Hazard Mitigation at the University of Tadulako Reconstruction Project

A Pile foundation is one of the most important structural elements. Pile foundations are used to support buildings when the hard soil layer is located very deep to keep the structure stable and standing when loaded by internal and external forces. The University of Tadulako is located in a moderate liquefaction-prone zone. In planning for rebuilding post-earthquake, where this area suffered massive damage, it was built on loose sandy soil with shallow groundwater levels. As a result, it has a possibility of liquefaction hazards in this area. This study aims to analyze the stability of the bored pile foundation as liquefaction hazard mitigation under service and extreme conditions. The analysis is carried out using two approaches, analytical method and computer-aided numerical simulation using RSPile and GEO5 2019. The type of foundation plan that will be used is the bored pile foundation with a diameter of 0.6 meters with a depth of 10 to 13 meters. The result shows the foundation remains stable under service conditions, but under extreme conditions, the foundation collapsed for type P1.B, and recommended redesign becomes type P1.A. However, after redesigning, the foundation becomes inefficient, and further research is needed on efficient foundation design.

Numerical Modeling of the Effect of Desaturation on Liquefaction Hazard Mitigation

Earthquake-induced liquefaction is always a concern when the soil near the surface of a site is composed of relatively loose saturated sand. One of liquefaction mitigation methods is to induce gas bubbles into the deposit to reduce the degree of saturation. A coupled pore-scale model is presented herein to investigate liquefaction resistance of desaturated granular materials. The multiphase fluid, which mimics the behavior of air and water, is modeled using the multiphase single component lattice Boltzmann method. The solid phase is modeled using the discrete element method. The coupled framework was utilized to study the behavior of a soil deposit with the different degrees of saturation of 100%, 92%, and 82% during an earthquake loading. Based on the results of the simulations performed, liquefaction occurred in the fully saturated granular deposit and was not observed anywhere at depth in the desaturated deposits. It has also been found that reducing the saturation level from 100% to 92% significantly affects behavior. In desaturated deposits, higher average coordination number, lower pore pressure buildup, and slower effective stress decay were observed compared to fully saturated deposits. However, it turned out that a further reduction in the degree of saturation from 92% to 82% does not have a significant impact on the calculated parameters.

Unsaturated Fluid Flow through Granular Soils Treated with Microbial Induced Desaturation and Precipitation

The use of microorganisms to induce desaturation of granular soils via denitrification results in nitrogen and carbon dioxide gas generation, which in turn lowers the degree of saturation of the soil matrix. Given sufficient substrates, the stimulated bacteria will produce enough gas to develop a continuous gas phase. Introducing gas into the soil to reduce the degree of saturation is shown to increase the soil resistance to dynamic loading and helps to mitigate liquefaction. The impact of desaturation on liquefaction hazard mitigation has comparative value to the calcite precipitation phase of the process. Meso-scale tests have been performed on a relatively thin tank of soil to simulate planar flow through a granular soil treated with MIDP.

Mitigation of liquefaction hazard by dynamic compaction — a random field perspective

This paper presents the findings of a case study to quantitatively assess the effect of dynamic compaction (DC) on mitigating liquefaction hazards from a random field perspective. DC is known to increase the density and strength of loose sand deposits, leading to a decrease in liquefaction potentials. Thus, by comparing the liquefaction potentials before and after DC at a given site, the effectiveness of DC in mitigating liquefaction hazards can be quantified. In practice, however, a direct one-to-one comparison is challenging due to limited availability of in situ test data and the fact that the number and location of these data before and after DC are typically different. To overcome these challenges, a random field-based approach is proposed in this study to visualize and quantitatively evaluate the effectiveness of DC across the entire project site. This approach is proven effective in assessing the effects of DC and is validated with liquefaction observations from the 1999 Chi-Chi earthquake.

Assessing effect of dynamic compaction on liquefaction potential using statistical methods – a case study

ABSTRACTThis article is aimed at illustrating the practical use of statistical methods in geotechnical engineering. As an example, the efficacy of dynamic compaction (DC) in the mitigation of liquefaction hazard is studied through a case study of a site in the Chang-Hwa Coastal Industrial Park in Changhua County, Taiwan. Before DC, the soil at the study site, which mainly consists of a layer of hydraulic fill of silty sand to fine sand underlain by recent alluvial plains (Qa), is deemed susceptible to liquefaction. After DC, the soil at the study site is improved such that the liquefaction potential is greatly reduced. The efficacy of DC in reducing liquefaction potential is evaluated quantitatively using the statistical methods, and the effectiveness of these statistical methods, especially when used with visualisation technique, is demonstrated. This provides a basis towards risk-based communication and decision making in the setting of practical applications.

A performance-based approach for design of ground densification to mitigate liquefaction

In performance-based geotechnical earthquake engineering, the required degree and spatial extent of ground densification for mitigation of liquefaction beneath a structure should be determined based on the acceptable levels of performance of foundation. Currently, there is no solution for evaluation of the amount of settlement and tilt of footings constructed on a densified ground which is surrounded by a liquefiable soil. This implies the need for numerical procedures for simulation of seismic behavior of shallow foundations supported on both liquefiable and densified subsoil. In this paper, the dynamic response of shallow foundations on a densified ground is studied using a 3D fully coupled dynamic analysis. For verification of the numerical model, simulation of a series of centrifuge experiments has been carried out and the results were compared with the experimental measurements. After verification of the numerical model, a comprehensive parametric study has been performed to develop a methodology for estimating the effectiveness of subsoil densification in reducing liquefaction-induced settlement of shallow foundations. Range of problem variables were considered in a way that the possibility of bearing capacity failure is low enough. The proposed methodology can be utilized for development of a performance-based design procedure for liquefaction hazard mitigation by soil densification.

Solutions to Sustainability in Construction: Some Examples

Many innovative solutions to sustainability have been developed or adopted in the past in various sectors of construction. Some of those related to geotechnical engineering are presented in this paper. These include the use of biocement as an alternative to Portland cement for soil improvement, the use of bio-desaturation as a method for mitigation of liquefaction hazard, the use of plastic waste to make construction products, and the use of the NEUSpace method for land reclamation in deep water to reduce the usage of fill materials.

Mitigation of liquefaction hazard by dynamic compaction

The tendency to apply soil improvement techniques in comparison with conventional remedial methods has been widely increasing in Iran, especially over the past decade. This is because these techniques are less time-consuming and more cost-effective. The risk of liquefaction at the Caspian Sea Republics Oil Swap (CROS) project site for loose saturated sandy layers down to 13 m was revealed subsequent to completion of the geotechnical investigations. Following a detailed study, dynamic compaction was selected to be the best option, especially for the foundations of the nine oil tanks at the site. To determine the dynamic compaction pattern, including the optimum number of drops, total energy and height of drop, a detailed trial programme was carried out. This included drilling boreholes, cone penetration test and standard penetraiton test performance and trial tamping as well as heave tests. The results were quite satisfactory, and the liquefaction hazard was well mitigated. Because of the lack of time, no ageing effect was investigated. L'approche consistant à appliquer des techniques d'amé-lioration des sols en comparaison avec les méthodes de traitement conventionnelles s'est répandue en Iran, particuliè rement ces dix dernières années. En effet, ces techniques sont plus économiques et permettent de ne pas perdre de temps. Les études géotechniques réalisées sur le site du projet CROS ont permis de révéler le risque de liquéfaction pour les couches sableuses saturées et meubles jusqu'à 13 m de profondeur. Après une é tude détaillèe, il a é té décidé que la compaction dynamique offrait la meilleure solution, en particulier pour les fondations des neufs réservoirs de pétrole sur le site. Un programme d'essais détaillé a été mis en place pour déterminer le profil de compaction dynamique, y compris le nombre optimal de chutes de pilon et l'énergie totale et la hauteur de chute. Il comprenait le creusement de trous de forage, la réalisation de tests de performance CPT et SPT, un damage d'essai et des tests de soulèvement. Les résultats obtenus sont satisfaisants et le risque de liquéfaction a puêtre bien atténué. En raison du manque de temps à disposition, il n'a pas é té possible d'étudier les effets du vieillissement.

LIQUEFACTION-INDUCED SETTLEMENT OF SHALLOW FOUNDATIONS AND REMEDIATION: 3D NUMERICAL SIMULATION

Calibrated Finite Element (FE) simulations are increasingly providing a reliable environment for modelling liquefaction-induced ground deformation. Effects on foundations and super-structures may be assessed and associated remediation techniques may be explored, within a unified framework. Current capabilities of such a FE framework are demonstrated via a simple 3-dimensional (3D) series of simulations. Ground liquefaction and settlement under the action of a surface load is investigated. Liquefaction hazard mitigation is explored by soil compaction and/or increase of permeability below and around the applied surface load. The potential and limitations of numerical simulation are discussed, along with future research needs and challenges towards more reliable practical application.