跨越走滑断层黏土地层动力响应离心机试验研究

地震中基岩走滑断层活动引起跨断层地下结构物破坏,上覆土层的非一致响应机制尚不明确,隐伏裂缝影响规律认识不足。基于可模拟走滑断层活动的层状剪切箱,针对黏土地层展开两个离心机振动台试验,对比上覆土体中隐伏裂缝的影响。试验结果表明,当地层中不存在隐伏裂缝时,基岩走滑断层错动对两盘地层的非一致振动的影响不显著。当地层中存在隐伏裂缝,错动盘一侧土体的振动加速度幅值随振动循环次数的增加逐渐减小,固定盘和错动盘两侧土体出现非一致振动响应,固定盘一侧土体产生的超静孔压大于错动盘一侧。隐伏裂缝对土体非一致振动响应的影响范围受限于其在地层中的分布范围,探明隐伏裂缝上断点的埋深具有重要工程意义。     

基于有效应力法的静压桩时变承载力研究

基于天然饱和黏土地基中静压沉桩扩孔问题的弹塑性解,以沉桩结束后桩周土体的应力状态为初始条件,推导了桩周孔压消散的解析解。在此基础上,考虑桩周土体再固结过程中的土体松弛效应,提出了采用有效应力计算天然饱和黏土中静压桩时变承载力的理论方法。通过已有离心模型试验和现场试验结果对该方法进行了验证,研究了沉桩结束后静压桩承载力随固结时间的变化规律。结果表明,提出的理论方法合理考虑了土体的原位力学特性、沉桩效应及沉桩结束后土体有效应力的变化,因而可以较好地预测静压桩的时变承载力。该研究成果为合理确定黏土中静压桩承载力提供了理论依据,具有一定的理论和工程意义。     

陡倾煤层开采条件下上覆山体变形破坏物理模型试验研究

大型岩质滑坡是中国西南岩溶矿区的主要地质灾害类型,其破坏和成灾过程具有复合性。以我国重庆武隆鸡冠岭滑坡为例,通过离心物理模型试验研究了地下开采条件下陡倾灰岩斜坡的变形失稳机制。试验时随着煤层模型板被拔出,上覆岩层在拟重力作用下开始出现位移与层间错动,当煤层模型被拔出150 mm时,模型山体发生显著破坏。试验结果表明:陡倾灰岩斜坡在长期重力作用下,会出现弯曲倾倒的变形,随着地下煤层逐渐采空,上覆陡倾层状岩体失去支撑,岩层层面分离并产生拉张裂缝,岩体变形加剧发生倾倒破坏,并对煤层下部的稳定岩体形成挤压,下伏稳定岩体发生剪切破坏,最终导致鸡冠岭以倾倒-滑移的复合模式整体失稳。这一研究对中国西南山区大型岩质滑坡的早期识别与失稳机制分析具有指导意义。      

北京山区工程勘察风险特征与防范措施研究

北京山区工程地质条件复杂,岩土工程勘察中存在或潜在着诸多风险,能否全面查清山区工程建设场地的工程地质条件,认清风险影响因素,对工程建设的安全至关重要。识别风险源,有助于提高对勘察风险的理解和掌握。本文试对北京山区岩土勘察风险的主要影响因素进行分析,并提出对应的防范措施,希望能为北京山区工程建设安全提供一些参考和帮助。     

Stratovolcano stability assessment methods and results from Citlaltépetl,Mexico

Citlaltépetl volcano is the easternmost stratovolcano in the Trans-Mexican Volcanic Belt. Situated within 110 km of Veracruz, it has experienced two major collapse events and, subsequent to its last collapse, rebuilt a massive, symmetrical summit cone. To enhance hazard mitigation efforts we assess the stability of Citlaltépetl's summit cone, the area thought most likely to fail during a potential massive collapse event. Through geologic mapping, alteration mineralogy, geotechnical studies, and stability modeling we provide important constraints on the likelihood, location, and size of a potential collapse event. The volcano's summit cone is young, highly fractured, and hydrothermally altered. Fractures are most abundant within 5–20-m wide zones defined by multiple parallel to subparallel fractures. Alteration is most pervasive within the fracture systems and includes acid sulfate, advanced argillic, argillic, and silicification ranks. Fractured and altered rocks both have significantly reduced rock strengths, representing likely bounding surfaces for future collapse events. The fracture systems and altered rock masses occur non-uniformly, as an orthogonal set with N–S and E–W trends. Because these surfaces occur non-uniformly, hazards associated with collapse are unevenly distributed about the volcano. Depending on uncertainties in bounding surfaces, but constrained by detailed field studies, potential failure volumes are estimated to range between 0.04–0.5 km³. Stability modeling was used to assess potential edifice failure events. Modeled failure of the outer portion of the cone initially occurs as an "intact block" bounded by steeply dipping joints and outwardly dipping flow contacts. As collapse progresses, more of the inner cone fails and the outer "intact" block transforms into a collection of smaller blocks. Eventually, a steep face develops in the uppermost and central portion of the cone. This modeled failure morphology mimics collapse amphitheaters present at many of the world's stratovolcanoes that have experienced massive failure events.Editorial responsibility: H. Shinohara     

Spatial variation of cone tip resistance for the clay site at Texas A&M University

The cone tip resistance data available for the clay site at Texas A&M University, USA (one of the National Geotechnical Experimentation Sites) are used to show how the spatial variation of a soil property can be quantified. It is suggested that the first step in quantifying the spatial variation of a soil property should be the identification or selection of the statistically homogeneous soil layers. A new simple procedure is suggested to identify statistically homogeneous layers in a soil profile. Through examples it is shown that the procedure works extremely well in identifying the statistically homogeneous layers. For the chosen statistically homogeneous layers, the spatial variation of cone tip resistance with depth is quantified in terms of a constant mean or a mean trend, variance/standard deviation/coefficient of variation or a variance around the mean trend, and a correlation or variogram function. Correlation distances in the depth direction were found to be between 0.1 and 0.5m for the two soil layers investigated. It was shown that the correlation distance decreases in the presence of a global mean trend for the soil property. In such cases, it is important to note that a part of the correlation is automatically included in the mean trend function.     

Geotechnical properties of cemented paste backfill from Cannington Mine,Australia

Paste fill is the newest form of backfill material in the spectrum available to international mines and is made from full mill tailings. Tailings have an effective grain size of approximately 5 μm and are combined with a small portion of binder and water to make paste. It is deposited into the voids created by mining which are referred to as stopes. The empty voids are approximated as vertical rectangular prisms, with plan dimensions of 15–40 m and heights of 100 m or more. Backfilling of mined stopes provide an increased level of local and regional stability to the ore body, as well as providing a suitable and economic dump of mining related waste. Paste is a relatively new technology in the mining industry and a review of the physical properties and mechanical fill behaviour was considered pertinent.     

Geotechnical Characteristics of Copper Mine Tailings: A Case Study

Waste management issue in mining industry has become increasingly important. In this regard, construction of tailings dams plays a major role. Most of the tailings dams require some kinds of remedial actions during their operational lifetime, among which heightening is the most common. In the first stage of the remedial provisions for Sarcheshmeh Copper Complex tailings dam in Iran, it has been decided to use hydrocyclone method to provide suitable construction material due to the high cost associated with using borrow materials for heightening of the dam. To undertake this project a series of laboratory experiments was performed to determine the copper ‘original tailings’ and ‘cycloned materials’ geotechnical characteristics to evaluate the applicability of the cycloned materials for construction purposes. Different laboratory experiments were conducted to determine the grain-size distribution, Atterberg limits, specific gravity, maximum density, shear strength parameters, consolidation coefficient, and hydraulic conductivity. The results were compared with those of similar mines to check whether they follow the trends observed in other copper tailing materials elsewhere. Variation of the cohesion and internal friction angle versus different compaction ratios were studied in order to determine realistic shear strength parameters for tailing dam stability analysis. In this study, using oedometer test, a mild linear relation between void ratio and the consolidation coefficient has been found for tailings materials. By considering the effects of void ratio and weight of passing sieve #200 materials, a new relationship is proposed that can be used for estimating the copper slimes hydraulic conductivity in seepage analysis of tailings dams.     

Modeling of a Multiply Jointed Voussoir Beam in the Centrifuge

Summary The mechanics and kinematics of a multiply jointed Voussoir beam have been studied based on the response of small scale beams tested in the centrifuge. The model beams were made up of six blocks, confined between fixed abutments. The tests included monitoring of beam deflection, development of axial thrust and distribution of strain within the beam. The models were subjected to accelerations of up to 90 g, depending upon the beam geometry. Two different beam geometries were considered. The test data were analysed in the light of pseudo analytical algorithms accepted in the analysis of singly jointed Voussoir beams. The data show that small translations and rotations of the block at the beam-abutment interface are required for a stable compression arch to set up in the beam. The computations and physical models indicate that the development of thrust is in linear proportion with the applied acceleration and is independent of beam thickness. The distribution of strains along the beam leads to the conclusion that the depth of the compression arch varies from the total beam thickness, to approximately one half of the beam thickness, under stable conditions. The data should be of considerable use to researchers looking to calibrate/validate numerical techniques used in describing the response of discontinuous rock masses.