Parameter identification for lined tunnels in a viscoplastic medium

This paper is dedicated to the identification of constitutive parameters of elasto‐viscoplastic constitutive law from measurements performed on deep underground cavities (typically tunnels). This inverse problem is solved by the minimization of a cost functional of least‐squares type. The exact gradient is computed by the direct differentiation method and the descent is done using the Levenberg–Marquardt algorithm. The method is presented for lined or unlined structures and is applied for an elastoviscoplastic constitutive law of the Perzyna class. Several identification problems are presented in one and two dimensions for different tunnel geometries. The used measurements have been obtained by a preliminary numerical simulation and perturbed with a white noise. The identified responses match the measurements. We also discuss the usage of the sensitivity analysis of the system, provided by the direct differentiation method, for the optimization of in situ monitoring. The sensitivity distribution in space and time assess the location of the measurements points as well as the time of observation needed for reliable identification. Copyright © 2002 John Wiley & Sons, Ltd.     

Wind velocity and sand transport on a barchan dune

We present measurements of wind velocity and sand flux performed on the windward side of a large barchan dune in Jericoacoara, northeastern Brazil. From the measured profile, we calculate the air shear stress using an analytical approximation and treat the problem of flow separation by an heuristic model. We find that the results from this approach agree well with our field data. Moreover, using the calculated shear velocity, we predict the sand flux according to well-known equilibrium relations and with a phenomenological continuum saltation model that includes saturation transients and thus allows for nonequilibrium conditions. Based on the field data and theoretical predicted results, we indicate the principal differences between saturated and nonsaturated sand flux models. Finally, we show that the measured dune moves with invariant shape and predict its velocity from our data and calculations.     

石香肠构造研究综述

石香肠构造是一种传统的线状构造，由于其在区域构造应力场方面的研究意义及其所包含的流变学信息和控矿意义等一直吸引着研究者的关注。简述了近几十年来石香肠构造在形态学研究上的进展，分析了其在理论研究上的成果，概括了其在应用研究方面的现状，并对当前及今后石香肠构造的研究方向提出了建议。     

晋城市王坡煤矿铁路专运线柏树底隧道下伏采空区治理

采空区是煤层开采所致。在煤矿开采的同时，也要做好对采空区的处置，消除其对上部建筑物稳定和安全的不良影响。晋城市王坡煤矿柏树底隧道下伏采空区，涉及6个煤矿，开采规模大小不等，开采时间长短有别。其顶板基本为自然跨落方式，上覆岩层软硬相间，致使采空区至今尚未完全塌陷冒落，处于不稳定状态。其上部裂隙带比较发育，向上逐渐减弱直至地表，直接关系到覆岩工程地质的稳定性。本文介绍了王坡煤矿柏树底隧道下伏采空区的基本情况，环境地质条件，工程地质评价，分析了采空区对铁路隧道工程的危害，论述了采用全充填压力注浆治理采空区的工艺步骤和质量检验方法。     

高压下玄武岩浆的不混溶及其对双峰式火山岩的成因意义

我们在温度850～1300℃,压力1.0～3.0GPa和含约2%水的条件下的碱性玄武岩熔融实验产物中发现在高于2.0GPa压力下玄武岩熔融后的淬火产物中存在着两种不同成分的玻璃,其中一种呈褐色,另一种为浅色或无色.玻璃的电子探针分析结果表明,褐色玻璃具有相对高的MgO、FeO和相对低的SiO2、K2O、Na2O含量及Na2O＞K2O的特征.熔体的不混溶间隙与温度无明显关系,但与压力关系密切,即在大于2.0GPa的压力条件下两种玻璃的不混溶间隙突然增大.因此,由不混溶作用形成的双峰式火山岩应来自大于2.0GPa的上地幔,且是能够提供酸性端员物质以及快速上升的构造环境.这与双峰火山岩可以产生于大陆裂谷环境或主要产于俯冲带的弧后拉张环境而不是岛弧前缘一致.     

南京市玄武湖水下交通隧道环境地质评价

玄武湖地下交通隧道既在城市,又在水下,环境地质条件极为复杂,是一种脆弱环境下的典型的地质工程。本文对玄武湖地下交通隧道的环境地质条件特别是水文地质条件进行了评价,预测了可能出现的如水污染、地面沉降、地面塌陷、巷道突水等环境地质问题,并提出了相应的防治对策。     

PLS法与隧道围岩稳定性分类

围岩稳定性是隧道工程支护设计的基本参数,采用偏最小二乘回归法,综合考虑多因变量影响因素,对隧道围岩稳定性分类进行回归建模,并取得较好效果.     

穿黄隧洞束窄河道对河段水沙特性的影响分析

利用建立的平面二维非恒定水流泥沙数学模型,在上游来流为10000年一遇的特大洪水过程情况下,就初步拟定的南水北调中线穿黄方案之一的孤柏嘴线路3 0km隧洞工程方案,穿黄隧洞束窄河道对河段水流流态、泥沙运动及河床变形的影响进行了计算和分析比较。计算结果表明,在该洪水过程情况下,穿黄隧洞束窄河道对河段水沙运动特性有一定影响,但影响不大。     

Temporal variations of shear-wave splitting in field and laboratory studies in China

Observations of shear-wave splitting at seismic stations above a swarm of small earthquakes on Hainan Island, China, and other examples world-wide, suggest that the time-delays of split shear-waves monitor the build up of stress before earthquakes and the stress release as earthquakes occur. Rock physics experiments on marble specimens also show variations of shear-wave time-delays with uniaxial pressure analogous to the field observations. The rock experiments show an abrupt decrease in time-delays immediately before fracturing occurs. Similar precursory behaviour has been observed before earthquakes elsewhere, and is believed to be important for two reasons. Precursory changes in shear-wave splitting could be used for short-term forecasting, but of greater importance may be the information such behaviour provides about the source processes in earthquake preparation zones.     

Estimation of fundamental periods of shear‐wall dominant building structures

Shear‐wall dominant multistorey reinforced concrete structures, constructed by using a special tunnel form technique are commonly built in countries facing a substantial seismic risk, such as Chile, Japan, Italy and Turkey. In spite of their high resistance to earthquake excitations, current seismic code provisions including the Uniform Building Code (International Conference of Building Officials, Whittier, CA, 1997) and the Turkish Seismic Code (Specification for Structures to be Built in Disaster Areas, Ankara, Turkey, 1998) present limited information for their design criteria. In this study, consistency of equations in those seismic codes related to their dynamic properties are investigated and it is observed that the given empirical equations for prediction of fundamental periods of this specific type of structures yield inaccurate results. For that reason, a total of 80 different building configurations were analysed by using three‐dimensional finite‐element modelling and a set of new empirical equations was proposed. The results of the analyses demonstrate that given formulas including new parameters provide accurate predictions for the broad range of different architectural configurations, roof heights and shear‐wall distributions, and may be used as an efficient tool for the implicit design of these structures. Copyright © 2003 John Wiley & Sons, Ltd.