Constitutive Model for Strength Characteristics of Municipal Solid Waste

This paper presents modification of the derivation of a previously proposed constitutive model for the prediction of stress-strain behavior of municipal solid waste (MSW) incorporating different mechanisms, such as immediate compression under loading, mechanical creep, and time-dependent biodegradation effect. The model is based on critical state soil mechanics incorporating increments in volumetric strains because of elastic, plastic, creep, and biodegradation effects. The improvement introduced in this paper is the modified critical state surface and considers five variable parameters for the estimation of stress-strain behavior of MSW under different loading conditions. In addition, an expression for the strain hardening rule is derived, with considerations of time-dependent mechanical creep and biodegradation effects. The model is validated using results from experimental studies and data from published literature. The results are also compared with the predictions of the stress-strain response obtained from a well-established hyperbolic model. (c) 2014 American Society of Civil Engineers.

Macro-Level Assessment of Seismically Induced Landslide Hazard for the State of Sikkim, India Based On GIS Technique

This paper presents a macro-level seismic landslide hazard assessment for the entire state of Sikkim, India, based on the Newmark's methodology. The slope map of Sikkim was derived from ASTER Global Digital Elevation Model (GDEM). Seismic shaking in terms of peak horizontal acceleration (PHA) at bedrock level was estimated from deterministic seismic hazard analysis (DSHA), considering point source model. Peak horizontal acceleration at the surface level for the study area was estimated based on nonlinear site amplification technique, considering B-type NEHRP site class. The PHA at surface was considered to induce driving forces on slopes, thus causing landslides. Knowing the surface level PHA and slope angle, the seismic landslide hazard assessment for each grid point was carried out using Newmark's analysis. The critical static factor of safety required to resist landslide for the PHA (obtained from deterministic analysis) was evaluated and its spatial variation throughout the study area is presented. For any slope in the study area, if the in-situ (available) static factor of safety is greater than the static factor of safety required to resist landslide as predicted in the present study, that slope is considered to be safe.

System reliability analysis of granular filter for protection against piping in dams

Granular filters are provided for the safety of water retaining structure for protection against piping failure. The phenomenon of piping triggers when the base soil to be protected starts migrating in the direction of seepage flow under the influence of seepage force. To protect base soil from migration, the voids in the filter media should be small enough but it should not also be too small to block smooth passage of seeping water. Fulfilling these two contradictory design requirements at the same time is a major concern for the successful performance of granular filter media. Since Terzaghi era, conventionally, particle size distribution (PSD) of granular filters is designed based on particle size distribution characteristics of the base soil to be protected. The design approach provides a range of D15f value in which the PSD of granular filter media should fall and there exist infinite possibilities. Further, safety against the two critical design requirements cannot be ensured. Although used successfully for many decades, the existing filter design guidelines are purely empirical in nature accompanied with experience and good engineering judgment. In the present study, analytical solutions for obtaining the factor of safety with respect to base soil particle migration and soil permeability consideration as proposed by the authors are first discussed. The solution takes into consideration the basic geotechnical properties of base soil and filter media as well as existing hydraulic conditions and provides a comprehensive solution to the granular filter design with ability to assess the stability in terms of factor of safety. Considering the fact that geotechnical properties are variable in nature, probabilistic analysis is further suggested to evaluate the system reliability of the filter media that may help in risk assessment and risk management for decision making.

Joint Strength and Wall Deformation Characteristics of a Single-Cell Geocell Subjected to Uniaxial Compression

Geocells are three-dimensional expandable panels with a wide range of applications in geotechnical engineering. A geocell is made up of many internally connected single cells. The current study discusses the joint strength and the wall deformation characteristics of a single cell when it is subjected to uniaxial compression. The study helps to understand the causes for the failure of the single cell in a cellular confinement system. Experimental studies were conducted on single cells with cell pockets filled up with three different infill materials, namely silty clay, sand, and the aggregates. The results of the experimental study revealed that the deformation of the geocell wall decreases with the increase in the friction angle of the infill material. Experimental results were also validated using numerical simulations carried out using Lagrangian analysis software. The experiment and the numerical results were found to be in good agreement with each other. A simple analytical model based on the theory of thin cylinders is also proposed to calculate the accumulated strain of the geocell wall. This model operates under a simple elastic solution framework. The proposed model slightly overestimates the strains as compared with experimental and numerical values. (C) 2014 American Society of Civil Engineers.

工程地质力学及其应用中的若干问题

工程地质力学是以工程为目的研究地质体变形破坏规律的科学。地质体具有非连续、非均匀、流-固耦合以及未知的初始状态的特性，工程地质力学的关键科学问题包括如何判断地质体的当前状态、描述地质体的力学特性以及分析地质体由连续到非连续的演化过程。工程地质力学研究应当以地学为基础、力学为手段、工程为目的，迫切需要解决的工程问题包括探测地质体的几何和力学特性，给出地质体稳定性的分析方法、地质工程设计依据以及地质灾害的预测预报方法。无论是模型实验还是模拟实验的结果能否回答工程问题取决于对地质条件的认知程度，但是，实验研究可以作为验证数值模拟结果的有力工具；地质调查和现场测量是工程地质力学必不可少的组成部分，地质体的力学分类体现了地学的基础作用，可实现地质环境描述定量化。针对工程需求建立力学模型可主要考虑含结构面岩体、土石混合体以及地质中裂隙流和岩土体的相互作用；实验室岩块实验的试样尺寸应作为地质体多尺度计算模型中的基本尺度。工程地质力学的主要研究内容应当包括给出关键的力学测量参数、研究获得这些参数的方法及相关的仪器：在提出和完善力学模型的同时，应更加注重新的计算方法的验证以及工程应用研究。

三维离散元计算参数选取方法研究

简要分析了岩体力学计算中比较重要的几何参数和物理参数的选取问题.通过对几种离散元方法接触关系的比较,讨论了在不同的计算模型中结构面刚度所代表的物理意义.指出在刚性块体模型中,结构面的刚度是包含了岩块和结构面物理特性的等效刚度,而在可变形块体模型中,只有当块体间的接触弹簧刚度取足够大时,才能客观地反映岩体的特性.太大的接触刚度影响计算的可靠性,为此给出了一种简单的处理方法.通过量纲分析的方法给出了岩体结构振动的阻尼表达式,指出可以通过岩体的振动实验确定阻尼比,并进而给出特征时间.量纲分析得到的特征时间为计算时间步长提供了参考值.最后,介绍了离散元法的计算控制及滑动与失稳的判据.