Liquefaction Problem Research Articles

Modeling of Compaction Grouting Technique with Development of Cylindrical Cavity Expansion Problem in a Finite Medium

The compaction grouting (CPG) method is relatively a new ground improvement technique for mitigating the liquefaction problem. In this technique, a stiff mortar is injected under high pressure that displaces and compacts the surrounding soil. Though the application of the method has been mainly dependent on the field tests, practical experience and empiricism, the compactive mechanism of CPG is not well understood. The objective of the present study is to bring out its compactive mechanism in its densification and confining effect. This paper presents an analytical solution for the process of CPG simulating it as an expansion of a cylindrical cavity in a finite medium. Effect of CPG is quantified as an increase in lateral earth pressure at any stage of applied injection pressure normalized with initial hydrostatic pressure and in terms of a densification factor. Predictions are made to reveal the behavior of CPG-treated soil in three states of density, namely as comparatively loose, medium and dense. Design charts are developed for liquefaction resistance parameter of CPG, RCPG, based on the present model of cavity expansion theory. It has been found that the design methods for CPG-improved ground should account for the coefficient of earth pressure at rest.

Application of UBCSAND to the LEAP centrifuge experiments

UBCSAND is an effective-stress constitutive model for estimating shear-induced deformations resulting from liquefaction. It is a practice-oriented tool that balances simplicity of formulation and use with the ability to address key aspects of the liquefaction problem. This paper discusses the challenges of applying a FLAC-UBCSAND modeling approach to Class-A, B, and C predictions of the LEAP centrifuge tests. Attention is given to typical model calibration procedures and difficulties in using these procedures for the LEAP evaluations. A comparison of the analysis predictions to the centrifuge measurements is provided.

Geotechnical properties of a type of iron ore fines

Accidents and life loss caused serious concern on the liquefaction problem of some solid bulk cargoes such as iron ore fines during transportation at sea. To understand the liquefaction property of a type of iron ore fines, a series of tests, e.g. SEM observation, monotonic loading triaxial test, cyclic loading triaxial test etc. were conducted. Test results show that this unusual material possesses some special properties, for instance, much higher specific gravity Gs (average Gs=4.444) as compared to common materials in geotechnical engineering. SEM observation unveils that the tested iron ore fines has a multi-layer, micro-porous structure which may affect its water retention ability under unsaturated states. The result from the undrained monotonic loading test indicates an angle of internal friction of 45.6o according to the Mohr-Coulomb failure criterion. Interestingly, the peak strength and the residual strength were achieved at values of axial strain of approximately 2.5% and 13%, respectively, regardless of confining pressure among three undrained monotonic loading tests. The undrained response of tested iron ore fines to cyclic loading shows similar characteristics as those of common sands and the liquefaction resistance of this material defined based on the relationship between CSR and number of cycle is not significantly affected by change of confining pressure.

Laboratory tests on cyclic undrained behavior of loose sand with cohesionless silt and its application to assessment of seismic performance of subsoil

Geotechnical earthquake engineering in the recent times has been paying special attention to themes such as liquefaction of sand with cohesionless fines, performance-based design, and seismic mitigation measures for housing areas. Because recent earthquakes in Japan and New Zealand caused many liquefaction problems in residential zones, the above-mentioned issues have become even more important than before. The present study conducted laboratory tests on sand with cohesionless fines in order to show how the seismic performance of loose subsoil is assessed, thus developing a practical methodology of performance-based mitigations. Most experimental data obtained is presented together with interpretations, and the mathematical framework for the performance assessment is described together with an example of specified mitigation methods. It is worth mentioning that the target of this assessment is the residential land of people who cannot afford high costs of testing and analysis, therefore, the methodology is simplified as much as possible.

PREDICTION OF COMPACTION CHARECTERISTICS OF SOIL USING PLASTIC LIMIT

In all kinds of earthwork constructions, the laboratory determination of the compaction characteristics of the soils plays an important role. Soil compaction is defined as the method of increasing the density of the soil by application of mechanical energy. The principal reason for the compaction of the soil is to produce a soil mass which can satisfy the three basic criteria. Firstly, the reduction of subsequent settlement of the soil mass, under working loads. Secondly, for the reduction in permeability which will subsequently avoid built up of large water pressures causing liquefaction problems and is also important for retaining water in case of earth dams. Thirdly, it is used for increasing the shear strength of the soils. But the determination of compaction characteristics in laboratory is laborious. It requires significant time and effort. Hence, there is a necessity for prediction of compaction characteristics with the help of correlating it with index properties of soil which can be determined easily. The plastic limit of soil can be found effortlessly and it bears a good correlation with compaction characteristic, namely optimum moisture content (OMC). In this paper, a study is conducted on nine types of fine grained soils like black cotton soil, red clay, china clay, marine clay, silty clay etc. collected from different parts of Telengana and Andhra Pradesh. And a simple equation has been suggested using regression analysis to obtain the optimum moisture content of a soil from the plastic limit, thereby eliminating the dependence of the proctor test for determination of OMC.

The Acid Modification Method to Reduce the Loess Liquefaction Potential

This paper introduced to the low viscous loess liquefaction problem by acid modification method. The liquefaction test showed that after the modification, the modified loess’s pore water pressures is very smaller then unmodified samples under 50-65Kpa dynamic stress. The modified loess almost no stress reduced after the liquefaction test. It showed that the method can effectively reduce low viscous loess liquefaction potential, and enhance the loess strength.

Seismic liquefaction potential assessed by fuzzy comprehensive evaluation method

Liquefaction of loose, saturated granular soils during earthquakes poses a major hazard in many regions of the world. The determination of liquefaction potential of soils induced by earthquake is a major concern and an essential criterion in the design process of the civil engineering structures. A large number of factors that affect the occurrence of liquefaction during earthquake exist a form of uncertainty of non-statistical nature. Fuzzy systems are used to handle uncertainty from the data that cannot be handled by classical methods. It uses the fuzzy set to represent a suitable mathematical tool for modeling of imprecision and vagueness. The pattern classification of fuzzy classifiers provides a means to extract fuzzy rules for information mining that leads to comprehensible method for knowledge extraction from various information sources. Therefore, it is necessary to handle the soil liquefaction problem in a rational framework of fuzzy set theory. This study investigates the feasibility of using fuzzy comprehensive evaluation model for predicting soil liquefaction during earthquake. In the fuzzy comprehensive evaluation model of soil liquefaction, the following factors, such as earthquake intensity, standard penetration number, mean diameter and groundwater table, are selected as the evaluating indices. The results show that the method is a useful tool to assess the potential of soil liquefaction.

A database for PGA threshold in liquefaction occurrence

Liquefaction exclusion criteria, based on peak ground acceleration (PGA) threshold value, are often included in seismic codes and recommendations. In this note, a rationale approach for setting the threshold is presented and a PGA limit of 0.09g was found. This value is derived from a statistical analysis of the background data used to create some common verification charts for the liquefaction problem.

Simplified probabilistic state concept characterization of sandy soils and application to liquefaction resistance assessment

Probabilistic relationships are developed for the simplified characterization of a sandy soil’s state within the state concept framework. The relationships require knowledge of conventional geotechnical characterization parameters (i.e., median particle diameter, fines content and particle shape) and in situ field data (i.e., SPT N1 values). The salient features of the proposed relationships are illustrated by comparing the reference and in situ states of Toyoura sand, obtained in laboratory tests, with those obtained from the simplified relationships. Sensitivity analyses are utilized to understand the uncertainties in the simplified relationships which have the most significant impact on common problems of flow liquefaction and cyclic mobility resistance of sandy soils. The presented results illustrate that uncertainty in the position of the steady-state line at zero confining stress is the most significant uncertainty in flow liquefaction assessment, followed by in situ void ratio, and slope of the steady-state line. Analyses using the simplified state concept relationships within an elastic-plastic constitutive model illustrate that the in situ relative density is the key uncertainty in cyclic liquefaction resistance. Finally, it is shown that the uncertainty in cyclic liquefaction resistance due to uncertainty in situ void ratio is largely consistent with that obtained from empirical predictions of cyclic liquefaction resistance.

The Analysis for the Dynamic Strength and Vibration Liquefaction of Saturated Sand under Cyclic Loading

Saturated Sand；Cyclic Loading；Dynamic Strength；Vibration Liquefaction Abstract.The liquefaction problem of saturated sand under cyclic loading is essentially a dynamic strength problems,but under the action of load,its strength has a sudden dramatic loss and it is unexpected.so it is different from the general dynamic strength problem.This paper analyzes the dynamic strength of saturated sand under cyclic loading.And its vibration liquefaction mechanism, influencing factors and preventive measures are analyzed and discussed.

Dynamic analysis of ground with rigorous use of strain dependency and its application to seismic microzonation of alluvial plane

Seismic microzonation is one of the most important measures to mitigate earthquake hazards in urban areas. Because the ground motion varies significantly with the subsurface geology, it is needed for microzonation to account as much as possible for the local soil conditions. Noteworthy is that nonlinear deformation properties of soil play essential roles in amplification of strong ground motion. It is desired furthermore to focus on the expected damage extent in addition to the calculated maximum acceleration and/or velocity. The present study first developed a computer code for one-dimensional response analysis of ground that reasonably takes into account nonlinear dynamic soil properties. Second, correlations between the calculated ground motion and damage extent were obtained by examining seismic damages during the past earthquakes. By combining these two issues, seismic microzonation was carried out, and detailed damage distribution was assessed. The product of this study covers not only the damage caused by ground shaking but also liquefaction problem and lifeline damage.

Preparation of fully saturated models for liquefaction study

The degree of saturation significantly influences the liquefaction resistance of sandy soils. In preparation of models for dynamic centrifuge tests and 1g shaking table tests, however, the degree of saturation has not been accurately controlled. A technique to prepare fully saturated model ground for liquefaction study is summarised in this paper, focusing on how vacuum pressure and centrifugal acceleration during the saturation process affect the degree of saturation. A method to evaluate degree of saturation of models accurately is developed first. Then, a total of ten experiments were conducted in which water was introduced to dry sand deposits at different atmospheric pressures at different centrifugal accelerations. It is confirmed that increased acceleration contributes to enhance degree of saturation and reduces time for the saturation process. Two dynamic centrifuge tests on models with different degrees of saturation, one almost fully saturated and the other slightly unsaturated, with the difference in degree of saturation between the two models being 1·5%, were conducted. Differences in excess pore pressure responses between the two models became more significant as the depth increased. It is concluded that a precise control of degree of saturation on the order of 0·1% is important in model tests related to liquefaction problems.

Undrained shear strength response under monotonic loading of Chlef (Algeria) sandy soil

During the last mid-century, the Chlef area was strongly affected by two earthquakes. From the geological context, there were numerous ejections onto the ground level of great masses of sandy soils and large displacements of various forms of some building foundations. These damages are due to soil liquefaction problem. This loss of shear strength can be attributed to many factors. History of recent cases indicates that sand deposited with silt content is much more liquefiable than clean sand. Therefore, a deep understanding of silty sand behavior is needed for the liquefaction assessment of silty sandy soils. Moreover, during seismic shaking, the post-liquefaction behavior of silty sand and, consequently, the stability of structures founded on liquefied soil depend on the steady-state shear strength of soil. The objective of this laboratory investigation is to show the effect of silt contents and the relative density on the mechanical behavior of such soils in monotonic loading. In this context, a series of undrained triaxial tests were performed on reconstituted saturated silty sand samples with different fines content ranging from 0% to 40%. In all tests, the confining pressure was held constant to 100 kPa. The fines content and the global void ratio are expressed by means of the equivalent void ratio. Linear correlations relating the undrained residual shear strength of loose, medium dense, and dense (Dr = 12%, 50%, and 90% before consolidation) sand–silt mixtures to the equivalent void ratio are obtained. The concept of the equivalent void ratio will then be used as a key parameter to express the dilatancy behavior of both clean and silty sand soils. Moreover, from the experimental results obtained, it is clear that the global void ratio cannot be used as a state parameter and may not represent the actual behavior of the soil as well.

Static liquefaction behavior of saturated fiber-reinforced sand in undrained ring-shear tests

The problem of static liquefaction of sand is nowadays a classical soil mechanics subject. Using a ring-shear apparatus, we explore the possibility of fiber reinforcement as a new method to improve the liquefaction resistance of sand. In order to understand the effect of the fiber content and sand density on the static liquefaction behavior of fiber-reinforced sand, a series of undrained ring-shear tests were carried out on saturated samples with different fiber content and sand density, and the test results and mechanisms of fiber reinforcement were then analyzed. The results indicate that the undrained shear behavior of fiber-reinforced loose samples is not greatly influenced by the presence of fiber, but for medium dense and dense samples, the presence of fiber clearly affects their undrained behavior. Untreated specimens showed a continuous decrease in shear resistance after failure, while the specimens treated with fiber showed fluctuations even after shear failure, and these fluctuations become stronger with increasing fiber content. The peak shear strength increases with the fiber content, especially in dense specimens. After shearing, all the fiber-reinforced and untreated dense samples maintained structural stability, while the unreinforced loose samples showed a completely collapse of structure. The presence of fibers may thus limit or even prevent the occurrence of lateral spreading that is often observed in unreinforced sand.

Using evolutionary search to optimise the energy consumption for natural gas liquefaction

Liquefaction of natural gas is a highly energy intensive process. Therefore its energy optimisation is an important matter. Sequential Quadratic Programming (SQP) will often be the preferred method for solving these optimisation problems, but there are some obstacles due to the fact that they use the local shape of the functions. Evolutionary search could be a way of getting around these problems and in this work, evolutionary search methods were combined and adapted to the liquefaction problem. The research focused on how to efficiently use all the function evaluations to obtain robust convergence, leading to the concept of diversity; and secondly how to deal with the infeasible individuals. Tests were performed on a benchmark function to assess the effect of different methods from the literature and the parameters which control them. Finally an application to the process simulator showed satisfactory results which were less than 5% from the assumed optimal solution.

Professor Ioannis Vardoulakis (1949–2009)

Professor Ioannis Vardoulakis (1949–2009)

GIS-based soil liquefaction susceptibility map of Mumbai city for earthquake events

Abstract The problem of liquefaction of soil during seismic event is one of the important topics in the field of Geotechnical Earthquake Engineering. Liquefaction of soil is generally occurs in loose cohesionless saturated soil when pore water pressure increases suddenly due to induced ground motion and shear strength of soil decreases to zero and leading the structure situated above to undergo a large settlement, or failure. The failures took place due to liquefaction induced soil movement spread over few square km area continuously. Hence this is a problem where spatial variation involves and to represent this spatial variation Geographic Information System (GIS) is very useful in decision making about the area subjected to liquefaction. In this paper, GIS software GRAM++ is used to prepare soil liquefaction susceptibility map for entire Mumbai city in India by marking three zones viz. critically liquefiable soil, moderately liquefiable soil and non liquefiable soil. Extensive field borehole test data for groundwater depth, standard penetration test (SPT) blow counts, dry density, wet density and specific gravity, etc. have been collected from different parts of Mumbai. Simplified procedure of Youd et al. (2001) is used for calculation of factor of safety against soil liquefaction potential. Mumbai city and suburban area are formed by reclaiming lands around seven islands since 1865 till current date and still it is progressing in the area such as Navi Mumbai and beyond Borivali to Mira road suburban area. The factors of safety against soil liquefaction were determined for earthquake moment magnitude ranging from Mw = 5.0 to 7.5. It is found that the areas like Borivali, Malad, Dahisar, Bhandup may prone to liquefaction for earthquake moment magnitude ranging from Mw = 5.0 to 7.5. The liquefaction susceptibility maps were created by using GRAM++ by showing the areas where the factor of safety against the soil liquefaction is less than one. Proposed liquefaction susceptibility map of Mumbai city can be used by researchers for earthquake hazard analysis, for the preventive measures in disaster management, for urban planning and further development of Mumbai city and suburban area.

Sensitivity analysis on a multilayer perceptron model for recognizing liquefaction cases

In this paper, a new approach is presented for quantifying the system sensitivity of key parameters influencing the recognition of field liquefaction cases in a multilayer perceptron neural network ( MLP model). A novel index, the average sensitivity factor, SF i , derived from the mathematical formulation of neural network is proposed to quantify the result of the sensitivity analysis. The SF i is a robust index of sensitivity analysis for the MLP model and can be used in the other problems not just in the recognition of field liquefaction problem. A well-trained MLP model is first developed to discriminate between the cases of liquefaction and non-liquefaction. Excellent performance and good generalization is achieved, with the higher recognition rate 98.9% in the training phase, 91.2% in testing phase and 96.6% on the overall cases. Using this model, the SF i values are then calculated and reveal that peak ground acceleration ( PGA) is the most sensitive factor in both the liquefaction and non-liquefaction cases. Earthquake parameters ( M w and PGA), the stress state parameters of the soil layer ( r d , σ V and σ v ′ ), and the soil resistance parameters ( SPT-N, C N , C E and FC) play approximately equal roles. The seismic demand factors ( M w , PGA, r d , σ V , and σ v ′ ) is more sensitive than the liquefaction resistance capacity factors ( SPT-N, C N , C E , and FC) in the two-class liquefaction recognition problem.

Semen quality and age-specific changes: a study between two decades on 3,729 male partners of couples with normal sperm count and attending an andrology laboratory for infertility-related problems in an Indian city

To compare the semen quality and age-specific changes in men between the 1980s and 2000s. Prospective study. Andrology laboratory, University of Calcutta, India. A semen sample was obtained from 3729 men presenting for infertility problems in two distinct decades, that is, between 1981-85 and 2000-2006. Subjects with sperm count >20 x 10(6)/mL without any extreme pathological disorders were selected. Samples having a major liquefaction problem were excluded. A standard World Health Organization procedure for semen analysis was performed that included assessment of volume, sperm concentration, and percentage motility. The motility parameters were further classified into forward progressive motility and nonprogressive motility. The present large-scale study confirms a significant decline in the sperm motility parameters and seminal volume in the present decade. However, no change in overall sperm concentration was noted. A decline was seen in sperm motility with increasing age in both decades. There are significant changes in sperm motility and volume between the two decades, and the age-related changes in semen parameters are also different in the two decades.

Development of a Sampler for Measurement of Gas Content in Soils

The problem of wave-induced liquefaction is an important feature in coastal and marine engineering, and is one of the main research topics in the European Union project Liquefaction around Marine Structures (LIMAS). In this context, the gas content of a soil is one topic of interest, as the presence of gas influences the pore pressure response and the gradient distribution in the seabed during wave action. The main objective of the work described herein has been to develop a new sampler that enables in situ measurement of gas content in the seabed, and at the same time retrieves a representative sample of the soil. The sampler should be able to maintain the natural soil structure and amount of gas in the pores to a high degree, and should primarily be used in sandy and silty materials. The major challenge in the project was to achieve perfect sealing of the sample container after sample shearing. This was finally obtained by use of a ball valve and backpressurized ball-valve housing in the lower end of th...