土石坝边坡稳定性分析的温控参数折减有限元法

将土石坝渗流的有限元计算和坝坡稳定分析的强度折减有限元法相结合,对土石坝坝坡的稳定性进行分析。考虑渗流作用时,首先采用有限元法计算坝体渗流场,通过迭代计算出稳定渗流的逸出点和浸润线位置,并根据水力梯度计算坝体所受的渗透力;然后将渗流分析所确定的渗流力与土体自重、浮力、地震力等荷载共同施加在坝体上,采用温控参数折减有限元法计算土石坝坝坡的临界失稳状态及其所对应的安全系数。分析结果表明,采用此方法进行土石坝坝坡稳定分析是合理的,且大大提高了计算效率     

土体本构模型对强度折减法分析基坑整体稳定性的影响

运用有限元强度折减法对基坑工程进行整体稳定性分析时,已有研究主要采用摩尔-库伦模型对土体进行模拟,由于摩尔-库伦模型给出的基坑变形曲线与实测不符,故据此得到的基坑整体稳定安全系数也不甚合理。采用Plaxis硬化模型模拟开挖过程,在强度折减分析中采用特征点位移突变对基坑整体稳定性进行收敛判断,通过分析对比所选取的不同特征点的位移与折减系数的关系曲线,提出采用挡墙内侧开挖面附近土体作为收敛判断的判别点较为合理,其安全系数的取值与采用极限平衡法得到的结果比较接近,而摩尔-库伦模型所得到的计算结果则偏大。最后分析了基坑宽度、基底软土层厚度、挡墙插入深度和挡墙刚度等因素对基坑整体稳定性的影响,并比较了采用这两种不同土体本构模型对分析结果的影响     

Gas emission prediction and recovery in underground coal mines

Strata gas can be released and captured from non-active and active gas resources either from virgin or relaxed strata, both prior to and when mining activities take place. The high and irregular gas emissions associated with high production longwall mining have provided a need to optimise the methods used to predict these gas levels and the ventilation requirements for gas dilution. A forecast of gas emissions during development drivage and longwall mining indicated possible gas and ventilation problems requiring the introduction of various gas drainage techniques and in maintaining the necessary air quantities in ventilation systems to satisfy the statutory gas limitations for various coal production rates. Although there are sound principles used in world-recognised methods of gas emission prediction, a new approach developed from long-term practical experience in underground gassy coal mine practices and gas-rock mechanics studies appear most suitable for local conditions and mining systems in use. The Lunagas ‘Floorgas' and ‘Roofgas' geomechanical and gas emission models offer an effective solution to these problems. Both programs are the most advanced engineering, numerical tools available to calculate gas source contributions to total gassiness and improve the accuracy and quality of gas control, gas capture technologies and ventilation system design.     

塔北油区岩石声发射全过程曲线类型及特征

本文讨论了岩石试样在加载全过程中的声发射特征、不同岩石声发射全过程曲线的分类以及类型的确定方法;对新疆塔里木盆地北部油区井下和地表试样进行了统计、分类,确定出该油区泥岩、砂岩声发射全过程曲线存在Ⅰ、Ⅲ两种类型;白云岩、灰岩、玄武岩声发射全过程曲线具有Ⅰ型特征。      

21世纪黄河下游防洪减灾对策

黄河是受人类活动强烈影响的河流,随着人类活动对流域环境的影响日趋增强,进入黄河下游的水沙条件发生了重大改变,防洪出现了许多新情况、新问题。黄河水资源进一步开发利用,下游牵断流及小水时间逐年延长,黄河将无有效输沙水量,如果来沙不能控制,现行河道的行洪能力和寿命将始终是中国的忧患。小浪底水库２００１年投入运用后,对黄河下游又将强烈堆积。２１世纪社会经济发展对黄河下游防洪减灾提出了更高要求,根据多年对黄     

关于中国煤层瓦斯区域分布的几点认识

据１９９４￣１９９６年连续３年的统计,全国煤矿瓦斯灾害伤亡人数占煤矿伤亡总人数的４０％以上,瓦斯涌出规律、瓦斯涌出量预测、瓦斯突出预测仍是煤矿安全技术的难题,在加强对瓦斯灾害综合治理的同时,把瓦斯作为煤层气资源积极进行开发利用,是当前的研究方向,瓦斯区域分布规律研究可以概括为建立在煤层瓦斯生成条件、保存条件基础上的高斯赋存量,高瓦斯涌出量,低瓦斯赋存量,低瓦斯涌出量区域分布规律研究;建立在高瓦斯赋     

阳城煤矿瓦斯地质规律研究

运用沉积学、构造地质学、煤地质学、数学分析等相关学科和方法,综合分析瓦斯涌出量的地质构造、顶底板岩性、上覆基岩厚度等地质因素,对阳城地区瓦斯含量、涌出量进行量化预测,并作出其全井田瓦斯含量、涌出量的等值线图。研究表明,阳城井田属低瓦斯矿井,瓦斯含量的变化主要与煤层埋深有关,随着煤层上覆基岩厚度以及煤层埋深的增高,瓦斯含量与涌出量在区内由北向南有增高趋势。     

Implementing low-cost landslide risk reduction: a pilot study in unplanned housing areas of the Caribbean

Landslides pose a serious physical and environmental threat to vulnerable communities living in areas of unplanned housing on steep slopes in the Caribbean. Some of these communities have, in the past, had to be relocated, at costs of millions of dollars, because of major slides triggered by tropical storm rainfall. Even so, evidence shows that: (1) risk reduction is a marginal activity; (2) there has been minimal uptake of hazard maps and vulnerability assessments and (3) there is little on-the-ground delivery of construction for risk reduction. This article directly addresses these issues by developing a low-cost approach to the identification of the potential pore pressure changes that trigger such slides we seek to address these three commentaries directly. A complex 45–60° slope site in St Lucia, West Indies was selected as a pilot for a modelling approach that uses numerical models (FLAC and CHASM) to verify the need for surface water management to effectively reduce landslide risk. Following the model confirmation, a series of drains were designed and constructed at the site. Post-construction evidence indicates the methodology to be sound, in that the site was stable in subsequent 1-in-1 to 1-in-4 year rainfall events. A critical feature of the approach is that it is community-based from data acquisition through to community members participating in construction.     

Electromagnetic emissions during dilating fracture of a rock

A lot of experiments on electromagnetic emissions (EMEs) have been reported under axial compressive fracture, shear fracture, indentation fracture and stick–slip (friction) in lab and blasting in situ, but there are rare reports on the in-lab experimental work on EMEs during dilating fracture of a rock which is helpful in studying and understanding EMEs related to slow earthquakes and the earthquakes due to volcanic activities and water level changes of reservoirs. Therefore, in the present paper in order to check whether there are detectable EMEs during dilating fracture of a rock in lab, dilating fracture experiments were conducted. The dry cuboid specimens of initially intact granodiorite and limestone were tested inside magnetic field free space (MFFS) at room temperature. We arranged evenly 20 EME antennas whose resonance frequencies range from 2.5 kHz to 540 kHz close to rock specimens. Our experimental results strongly indicate that detectable EMEs could generate during dilating fracture of a rock. They were recorded only associated with some but not all phases of fracture. Their waveforms often took on the trend that a peak arrived at first and then attenuated sharply and followed by a series of low-amplitude oscillations. The electromagnetic (EM) signals after eliminating the effects of EME antennae via deconvolution had the maximum peak-to-peak amplitudes of about 80.0 mV and 40.5 mV for granodiorite and limestone, respectively. Their main spectral components often concentrated in the band of several kHz to ∼60 kHz and of several kHz to ∼280 kHz. The emission of electrons and charged particles from fracture surfaces and/or micro-fracture electrification could be possible mechanisms for our experimental results.     

基于小波包变换的不同强度煤样的声发射特性

为了研究在单轴压缩下不同强度煤样的声发射特征,利用RMT-150C型岩石力学伺服试验系统和CDAE-1型声发射检测仪,对硬煤、中硬煤和软煤煤样进行实验研究。为了解决煤样在声发射实验中存在的各种信号干扰和信号处理方面的问题,运用小波包变换对煤样的声发射信号进行了分解、去噪和重构。研究结果表明：经过处理之后的声发射信号能够更清晰地反映硬煤、中硬煤和软煤煤样在单轴压缩下失稳破坏的变化特征。软煤、中硬煤和硬煤的声发射信号特征各不相同,随着煤样强度的增加,煤样失稳破坏时声发射累计能量和累计计数逐渐减小,煤样在受力过程中声发射能量和计数的峰值也逐渐减小,并且在峰值处释放的能量也逐渐减小。