Numerical analysis of surface subsidence in asymmetric parallel highway tunnels

Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good understanding for prediction of tunnel deformation and surface settlement during the engineering life of the structure. The deformational behaviour, design of sequential excavation and support of any jointed rock mass are challenging during underground construction. We have raised several commonly assumed issues while performing stability analysis of underground opening at shallow depth. For this purpose, Kainchi-mod Nerchowck twin tunnels (Himachal Pradesh, India) are taken for in-depth analysis of the stability of two asymmetric tunnels to address the influence of topography, twin tunnel dimension and geometry. The host rock encountered during excavation is composed mainly of moderately to highly jointed grey sandstone, maroon sandstone and siltstones. In contrast to equidimensional tunnels where the maximum subsidence is observed vertically above the centreline of the tunnel, the result from the present study shows shifting of the maximum subsidence away from the tunnel centreline. The maximum subsidence of 0.99 mm is observed at 4.54 m left to the escape tunnel centreline whereas the maximum subsidence of 3.14 mm is observed at 8.89 m right to the main tunnel centreline. This shifting clearly indicates the influence of undulating topography and in-equidimensional noncircular tunnel.     

河南省煤矿塌陷地复垦模式研究

在调查河南省煤矿塌陷地实际情况的基础上,根据河南省煤矿塌陷地地形地貌特点和区域位置,以尽快恢复被破坏土地的原有生产能力为出发点,系统分析了煤矿塌陷地的特性,通过对不同塌陷地进行比较分析,研究提出了5种不同类型塌陷区的复垦模式和4种不同分区塌陷地的复垦模式。该研究为河南省矿区土地复垦工作的开展提供了科学依据,并可为全国其它矿区土地复垦工作提供借鉴。     

Experimental investigation on the train-induced subsidence prediction model of Beiluhe permafrost subgrade along the Qinghai-Tibet Railway in China

Based on dynamic triaxial test at low temperature of the frozen clay from the Beiluhe permafrost subgrade along the Qinghai-Tibet Railway (QTR), residual deformation laws and dynamic subsidence prediction model of permafrost subgrade under train traffic were studied. First, time history curves of residual strain of frozen soil are obtained and analyzed under different temperatures, frequency, confining pressure and moisture content. And conclusions can be drawn that the axial strain rate is greatly affected by the amplitude of dynamic stress, as well as increases with dynamic to static stress ratio and temperature rising, while it decreases with the raise of frequency and moisture content. Hereby, the power functions were adopted to fit the relationships of axial dynamic strain rate vs. stress ratio, temperature, frequency, and moisture content, respectively. Simultaneously, the permafrost dynamic subsidence mechanism was interpreted rationally and the variation of fitting parameters was discussed. Furthermore, the long-term traffic loading subsidence model was established through observing the axis residual strain time histories of frozen specimens under the longtime cyclic loading and adopting the amendment of vibratory number of times. The model can comprehensively consider the effects of stress state, temperature, moisture content, and confining pressure of frozen soil, as well as the vibratory frequency and vibration number of longtime cyclic loading. Consequently, the model can be applied to the train-induced subsidence forecast investigation of permafrost subgrade. The paper has an important significance for rational safety evaluation on long-term operation of permafrost regions railway such as QTR. Meanwhile, the investigation provides basic data for the further research on dynamic damage constitutive model of frozen soil under train traffic and the gradual improvement of railroading criterion in cold regions.     

地基蠕动滑陷治理措施

通过焦坪变电站地基土层蠕动沉陷的实例，分析了地基土层蠕动沉陷的原因，提出相应治理措施。     

岩溶塌陷区住宅地基钻孔注浆加固处理

铜陵小街地区发生岩溶性地面塌陷,危及住宅区,为此对塌陷区采取钻孔注浆方法进行处理。注入水泥,以充填岩溶洞、裂隙以及土体洞穴,增强土体强度,提高土层的承载力。文中介绍了钻孔注浆参数、施工特点及施工情况,并对注浆效果加以评价。     

济宁市城区地面沉降监测与成果分析

随着社会，经济和都市化的发展，被列为十大地质灾害之一的地面沉降，已引起了人们的广泛关注。介绍了济宁市地面沉降监测方法，并对监测结果进行了统计分析，结果表明：济宁市地区地面沉降明显，相对于1992年最大沉降量为147mm，沉降量大于60mm的面积已达80km^2。     

盐矿水溶开采地表塌陷发生机理及防治措施

水溶开采诱发地表塌陷是盐矿开采中常见的地质灾害现象,具有突发性强、破坏程度大、持续时间长等特点。系统分析了近几十年来盐矿地表塌陷的典型实例,指出溶腔不稳定造成的垮塌、卤水及地下水侵蚀诱发断层活化以及上覆岩土体侵蚀破坏后承载力降低是水溶开采诱发采区地表塌陷主要的三种模式,并揭示了塌陷发展过程中各个因素的相互作用和影响。为防止盐矿塌陷的发生,分别从理论与试验研究、地质勘查、矿井设计以及生产管理等方面提出了相关的建议和措施。     

注充宽条带跳采全采采煤法

常规方法开采煤炭已对地面环境造成了严重的沉陷灾害。村庄等地面设施的压煤和其他低采出率采煤方法又使得大量煤炭资源无法采出。基于此现状提出了注充宽条带跳采全采采煤方法。通过分析开采过程及其影响,此采煤方法可以减缓地表下沉,有效保护矿区地表环境,解决煤矿深部化开采过程中的地面设施压煤问题。同时,对此采煤方法的深入研究,有益于进一步完善我国矿山开采的相关理论和技术。     

Use of the area of main influence to fix a relevant boundary for mining damages in Germany

In 2010, the fracking discussion in Germany caused a number of changes in German law, which came into force in 2016.Especially the production of gas had to be regulated.With the legislation amendment, the Subsidence-Area Mining Regulation has been revised, too.The changes expand the compensation of mining damages, especially to the extraction with drilling from the surface and underground storage.Although the Subsidence-Area Mining Regulation has been revised, the area of main influence(subsidence of 10 cm)remains to determine a relevant boundary for mining damages.The determination and prediction of this boundary above caverns are presented in this paper.In addition, further elements of ground movements and their relevance to mine damages are analyzed.The usage of the area of main influence to fix a relevant boundary for mining damages does not correspond to the relevant elements of ground movements.A limit for differences in subsidence(tilt) or horizontal changes in length should be preferred to describe the relevance of mining damages on buildings.Furthermore, this paper outlines the meaning of using the area of main influence to fix a relevant boundary for mining damages.     

Anthropogenic effects on the subsurface thermal and groundwater environments in Osaka, Japan and Bangkok, Thailand

Anthropogenic effects in both Osaka and Bangkok were evaluated to compare the relationships between subsurface environment and the development stage of both cities. Subsurface thermal anomalies due to heat island effects were found in both cities. The Surface Warming Index (SWI), the departure depth from the steady geothermal gradient, was used as an indicator of the heat island effect. SWI increases (deeper) with the magnitude of heat island effect and the elapsed time starting from the surface warming. Distributions of subsurface thermal anomalies due to the heat island effect agreed well with the distribution of changes in air temperature due to the same process, which is described by the distribution of population density in both Osaka and Bangkok. Different time lags between groundwater depression and subsidence in the two cities was found. This is attributed to differences in hydrogeologic characters, such as porosity and hydraulic conductivity. We find that differences in subsurface degradations in Osaka and Bangkok, including subsurface thermal anomalies, groundwater depression, and land subsidence, depends on the difference of the development stage of urbanization and hydrogeological characters.