Numerical assessment of liquefaction mitigation effects on residential houses: Case histories of the 2007 Niigata Chuetsu-offshore earthquake

In this study, the effectiveness of liquefaction countermeasures for residential houses was explored using a fully coupled dynamic effective-stress finite element procedure. Numerical analyses were conducted on two wooden houses that were damaged to different degrees due to dune liquefaction during the 2007 Niigata Chuetsu-offshore earthquake. House A, which was only improved by horizontal drainage pipes to lower the ground water level, was completely destroyed; however, house B, which was improved by a horizontal drainage system, soil–cement mixtures, and steel-pipe piles, was slightly deformed. Numerical results show that the effects of the sand dune slope on the damage to the two houses were somewhat different. For house B, it was found that the steel-pipe piles were more effective. Two countermeasures generally led to a greater degree of reduction in both lateral and vertical displacements of house B than only a single countermeasure employed. In addition, the combined implementation of steel-pipe piles and soil–cement mixtures was the most effective among the cases with two countermeasures.     

Comparative analysis on soil engineering classifications of China and America

Based on China National Standard of Soil Engineering Classification (GB/T 50145-2007) and the Unified Soil Classification System of American Society for Testing Materials (ASTM D-2478), two kinds of soil laboratory engineering classification methods were discussed and analyzed from the aspects of the definition in particle fraction, classification of soil type and evaluation standard for soil gradation. There is a same limit of fine grains fraction in the two standards, and there are three main types of soil in GB/T 50145-2007 and two in ASTM D-2487. Different evaluation standards of gradation are put forward for gravels and sands in ASTM D-2487. Same criteria of A line, B line and controlling value of plastic index are in the plasticity chart of both standards.     

Geotechnical Properties of River-fed Sediments Compared with Glacier-fed Sediments

This paper discusses the influence of sedimentary environment and geological setting on geotechnical and physical properties of resulting sedimentary deposits. For this study, two different geological settings were considered, one is a river-fed and the other is a glacier-fed sedimentary environment. For both sedimentary environments, various geotechnical properties were considered and compared. These include plasticity, activity, compressibility, undrained shear strength and sensitivity. Results indicate that physical and geotechnical properties of sediments deposited in these two settings are significantly different. These differences are then interpreted in terms of the various mechanisms involved in submarine slope failure initiation in river-fed versus glacier-fed sedimentary environments.     

Determining the effects of depositional processes on consolidation behavior of sediment using shear-wave velocity

Abstract

Compression behavior of sediments is crucial to geological engineering applications for ascertaining the deformation characteristics of the particular depositional environments. Unfortunately, obtaining the geotechnical parameters required to assess the compression behavior of sediments can be a costly and time-consuming undertaking. This study developed a general prediction equation that simulates the compression behavior of sediments. This developed equation is an exponential decline model that relates an increase of the shear-wave velocity to an increase of the mean effective stress. Consequently, the decrease of void ratio is presented as a continuous function of the shear-wave velocity. For this research, laboratory-derived sediment samples created to mimic actual sediments were isotopically consolidated during a consolidated undrained triaxial compression tests. The samples were prepared in the laboratory by mixing different percentages of fines and controlling the ratio of clay-to-silt fractions. Shear-wave velocity tests were performed during this consolidation testing using bender elements. The experimental constants needed for the prediction equation were well correlated to the depositional factors specifically characterized by percent fines, silt percent, and liquid limit that define better complexity of depositional processes.     

Culture environment and hatchery of origin influence growth,condition and feeding organ morphology in the Pacific oyster Crassostrea gigas in South Africa

South Africa lacks a commercial oyster hatchery. To inform the sourcing of seed for future hatchery establishments, we compared half-sib Pacific oyster Crassostrea gigas cohorts from hatcheries in Namibia and Chile. We measured oyster growth, mortality, condition and feeding organ morphology in Algoa Bay (AB, Eastern Cape) and Saldanha Bay (SB, Western Cape), South Africa, from July 2011 to June 2012. Within SB, 14.3% of mean daily sea temperatures exceeded this species’ thermal optimum of 19 °C, compared to 50.5% in AB. Food abundance (mean daily chlorophyll a concentration) in SB (7.8 mg m^–3) was double that in AB (3.9 mg m^–3) where, presumably to increase particle clearance rates in a relatively phytoplankton-poor environment, oysters had larger gill:palp surface area ratios. Plankton fatty acid profiles (indicators of food quality) differed between locations. In AB, instantaneous growth rates differed between cohorts, and trends varied seasonally. Within both locations, condition index was usually higher in Chilean oysters, whereas shell density was higher in Namibian oysters. In AB only, Chilean seed suffered substantially higher summer mortalities than Namibian seed, suggesting that the latter are more suited to temperatures in AB. AB should also be assessed for culture of the indigenous oyster species that occur there.     

落锥法确定粉土液限和塑限的试验研究

针对部分细粒土进行了室内落锥法确定液限和塑限的试验研究,试验结果表明：对于一些细粒土在双对数坐标上圆锥下沉深度与含水率之间的关系并非线性关系,无法依据线性关系确定液、塑限;采用规程建议的3个含水率范围有时根本无法获得有效试验数据,采用规程建议的3个含水率范围确定得到粉土的液、塑限试验结果的可靠性有待商榷;采用直线段试验数据确定的液、塑限进行分类可能出现相互矛盾甚至错误的结果。进一步试验结果表明：对于黏粒含量高于13 %的粉土,由于其抗剪强度以凝聚分量为主,落锥法适用,所测塑性指数能够反映其可塑性;对于部分黏粒含量低于13 %的粉土及外观接近粉土的粉砂,由于其抗剪强度以颗粒间摩擦分量为主,落锥法不再适用,所测塑性指数不能反映其可塑性。     

Numerical analysis of deformation behaviour of quay walls under earthquake loading

In the last 50 years, there have been many incidences of failure of gravity quay walls. These failures are often associated with significant deformation of liquefiable soil deposits. Gravity quay wall failures have stimulated great progress in the development of deformation-based design methods for geotechnical structures. In this paper, the effective-stress analysis method has been used in conjunction with a generalised elasto-plasticity constitutive model implemented into a finite element procedure. Various monotonic and cyclic triaxial paths are simulated in order to demonstrate the capabilities of the constitutive model. The FEM is validated by back analysis of a typical Port Island PC1 caisson type quay wall, which was damaged during the 1995 Hyogoken-Nanbu earthquake. The numerical results are compared with the observed data obtained consisting of seaward displacement, settlement and tilting. In addition, both the influence of permeability, on the generation of pore water pressure and the influence of the relative density of the backfill and foundation layers, on the residual deformation of gravity quay walls are investigated.     

滨海软土非线性流变模型及其工程应用研究

基于室内一维固结蠕变试验,研究了天津滨海淤泥质软黏土的蠕变变形规律,建立了反映滨海软黏土的非线性流变本构模型,确定了模型中的各个参数。通过此本构模型推导出天津软黏土的沉降计算公式,利用该公式对天津滨海地区北塘水库大坝软土堤基进行了沉降计算和分析,计算值与实测值比较吻合,证明了流变模型的合理性,同时也说明在软土地基沉降计算中,考虑非线性流变性状的影响是必要的。并对天津滨海新区软土长期蠕变沉降作出预测。     

基于损伤塑性模型的砌体墙体非线性有限元分析

为了研究砌体墙体用钢结构加固后的力学性能,需要提供较准确的砌体墙体非线性计算,考虑到砌体与混凝土的材料性质具有相似性,将混凝土损伤塑性模型经修正后应用于砌体数值模拟,实现对砌体墙体的非线性有限元分析。通过与水平加载试验结果对比,验证了有限元模型的正确性。探讨了损伤塑性模型中的粘性系数、膨胀角、砌体本构关系中的初始弹性模量、受拉应力应变关系对计算结果的影响。结果表明：粘性系数和膨胀角对抗剪承载力、峰值位移及下降段性能均有较大影响,而对初始刚度影响很小;随着初始弹性模量的增大,砌体墙体抗剪承载力随之提高,但峰值位移无明显变化;受拉应力应变方程中待定系数的取值,对抗剪承载力及峰值位移影响较大。     

Bearing capacity of non-associative coaxial granular materials by upper bound limit analysis and finite elements

In this paper, an upper bound estimate of the limit load on non-associative coaxial granular materials is presented. The kinematic approach of the upper bound limit analysis has been utilised. The failure mechanism is assumed to coincide with the direction of the shear bands at every point throughout the body. The shear band orientation in non-associative coaxial materials, i.e. those with the same major principal stress and major principal strain increment directions, can be found based on the angle of dilation and the major principal stress direction. Therefore, having known the stress field at limiting equilibrium, the orientation of the shear bands and hence, the failure mechanism can be obtained. In this study, the stress field is first determined by the method of stress characteristics. Then, the finite element interpolation technique is used to interpolate the stress field and to find the orientation of the shear bands at every point within the field. Once the failure mechanism and the stress state at every point along velocity discontinuities have been found, the upper bound limit analysis has been performed to estimate the limit load.