深圳市龙岗中心城区岩溶发育区渗透变形试验研究

土层的渗透破坏是龙岗区塌陷（土洞）形成的重要因素，通过在现场取原状样和室内人工配制扰动样的方法，进行室内渗透变形试验，对龙岗区岩溶塌陷成因进行详细分析，深入探讨地下水渗透破坏对岩溶塌陷的影响。在监测区内选取3类主要土层：黏土、粉质黏土、中砂，共设置了11组土样进行室内扰动土渗透变形试验。试验结果表明，土体发生渗透塌陷破坏与土体性质、颗粒级配、土层结构、土体内部空腔大小、土体下部透水基岩孔洞大小以及外部水力梯度等有密切关系。     

湖南宁乡大成桥地区岩溶地面塌陷分布特征及影响因素分析

湖南宁乡大成桥地区至2012年产生岩溶地面塌陷484处。文章通过对地质环境条件及岩溶地面塌陷时空分布特征的分析,总结出本区岩溶地面塌陷的分布特征和影响因素:（1）岩溶发育区发生塌陷428处,占总数的88.5%;冲沟地形中发生岩溶地面塌陷339处,占70%;覆盖层厚度小于10 m区发生塌陷335处,占总数的69.2%;双层结构区发生塌陷266处,占总数的55%,分布密度为7.82处/km2;冲洪积成因土体产生塌陷404处,残积土中产生塌陷80处;(2)岩溶地面塌陷在雨季的4-7月发生281处,占总数的58%;2001-2006年平均每年产生塌陷20处,2007-2012年平均每年产生塌陷54处,逐年增加趋势明显;（3）484处岩溶地面塌陷全部分布在煤炭坝疏干排水形成的降落漏斗范围之内;（4）本区地质环境极为脆弱:岩溶发育,覆盖层厚度较薄、力学性质差且双层结构土广泛分布于冲沟及冲积平原,是产生塌陷的内在因素;矿区疏干排水是主要诱发因素,降雨分布不均、地表水渗漏及河道整治对塌陷产生起促进作用。      

广州夏茅村岩溶地面塌陷成因机理与塌陷过程分析

研究区内已发岩溶地面塌陷灾害严重,地质环境条件极其复杂,第四系覆盖土层厚度大,底部粉质黏土层土洞发育、隐伏基岩为壶天群灰岩,溶洞及断层破碎带发育,单个溶洞、土洞规模较大,溶洞与溶洞、土洞与溶洞之间连通性能较好。岩溶地面塌陷是以覆盖层粉质黏土层或砂类土层的扰动和土洞的形成为起点的,根据勘查区上覆盖层二元结构的特征,区内地面塌陷及土洞的发育过程可分为"下黏上砂"二元结构塌陷模式和"下黏上砂、软土"多元结构塌陷模式,塌陷区的岩溶塌陷致塌机制主要为机械贯穿作用,塌陷发育大约经历了四个阶段,建议今后不宜在勘查区及其周边一定范围进行地下工程建设活动及抽、排岩溶地下水行为,避免地下水动力条件发生改变,再次发生岩溶地面塌陷。     

山东省泰莱盆地岩溶塌陷发育特征及形成机理

泰莱盆地位于山东省中部,截止2013年底,盆地内共发生有记录岩溶塌陷97处,161点次,严重威胁人民生命财产安全。文章在总结前人研究基础上,结合最新调查、监测成果,研究了泰莱盆地岩溶塌陷的分布特征、地质结构模式及其形成机理。结果表明:盆地内岩溶塌陷点多集中分布于岩溶地下水降落漏斗及其影响范围内;塌陷点分布受构造控制明显;塌陷区第四系厚度一般小于30 m,下伏基岩主要为奥陶纪灰岩;80%以上的塌陷集中发生于汛期。根据岩溶塌陷点土层结构、地下水动力条件的不同,建立了3种岩溶塌陷的基本地质模式:单层、双层和多层结构土层岩溶塌陷,其中单层结构土层岩溶塌陷的形成历经“真空吸蚀-崩解剥落-塌陷”3个阶段;双层土层结构岩溶塌陷形成演化过程可概括为“渗透变形-崩解垮塌-塌陷”或“真空吸蚀-渗透变形-塌陷”3个阶段;多层结构土层岩溶塌陷历经“真空吸蚀-渗透变形-崩解垮塌-塌陷”4个阶段。      

湖北武汉白沙洲隐伏岩溶区地质结构与岩溶塌陷分类

武汉市可溶岩大多隐伏于第四系土层及白垩—古近系红层下部,可溶岩分布地区地质结构与岩溶地面塌陷关系密切,已发生的岩溶地面塌陷中上黏下砂地质结构占绝大部分。以白沙洲岩溶条带长江两岸为研究区,根据盖层黏性土、砂性土、软弱土、非可溶岩（红层）的上下叠置关系及地面塌陷特征,将可溶岩分布区地质结构划分为3类、5型;岩溶塌陷的实质是土体塌陷,在岩溶区地质结构研究的基础上,根据土体物理力学特征差异,受力后塌陷过程中土颗粒的运移方式,即黏土块体塌落、砂颗粒漏失、软弱土流失,系统将研究区岩溶塌陷机理分为土洞型、沙漏型、泥流型3类,同时也存在多种类型复合型岩溶塌陷。     

重庆市中梁山地区隐伏塌陷特征及物探勘测的思路

为查明隐伏塌陷区域,分析重庆市中梁山地区岩溶塌陷的特征,发现塌陷主要发生在以岩溶裂隙发育为主的松散粉质黏土区域;地震映像法能方便、快速地查清土层的松散状态,而高密度电阻率法通过正演模拟发现只能探测出2～3倍电极距的异常范围,但能反映出岩溶裂隙发育的漏斗形态,即只要能找出岩溶裂隙的大致位置和浅表松散土层的范围就能圈定隐伏塌陷的区域。对中梁山地区某居民点进行野外勘测,综合以上两种方法圈定隐伏塌陷区域,其推断结果与钻探资料十分吻合,说明这种隐伏岩溶探测思路是可行的。      

基于AHP和GIS技术的湖南怀化地区岩溶塌陷易发性评价

湖南省怀化市为新兴区域交通枢纽城市,在近年来的大量工程活动影响下,城区发生多起岩溶塌陷灾害,对当地人民群众生命财产安全和城市发展造成较大威胁。依托岩溶塌陷专项地质调查成果,选择岩溶发育程度、到断层的距离、土层结构、土层厚度、岩溶水位波动幅度、岩溶水位与基岩面关系、地下水开采强度、岩溶塌陷密度8个因素作为评价因子,运用层次分析法建立岩溶塌陷易发性多因素判别模型,并系统研究各因素对岩溶塌陷形成的影响作用,确定各因素权重赋值。在此基础上,运用地理信息系统（GIS）技术,对怀化地区进行岩溶塌陷易发性评价,结果显示:怀化地区岩溶塌陷高、中易发区面积分别为107.48 km2、157.13 km2,分别占易发区总面积的34.7%、50.7%;区内穿越岩溶塌陷高易发区、中易发区的各类交通线路长度分别为16.4 km、88.9 km,占穿越易发区总线路长度的12.9%和69.9%,受岩溶塌陷地质灾害威胁较大。      

广州市白云区夏茅村岩溶地面塌陷特征及致灾因素和风险分析

广州市白云区夏茅村岩溶塌陷地质灾害严重,塌陷区内地质环境条件极其复杂,隐伏灰岩岩溶土洞发育强烈,溶洞、土洞规模较大,且发育多层溶洞,溶洞间相互连通,岩溶塌陷区基岩面起伏较大,高程变化剧烈,第四系覆盖层厚度较大,底部粉质黏土层土洞发育,土体中规模巨大的土洞是产生岩溶地面塌陷的基础条件。基岩断裂构造带及其影响带范围内,岩石破碎,形成导水断层,存在地下水迳流通道,沿断裂带地下水循环活跃,溶蚀强烈,形成岩溶强发育带,为岩溶塌陷的发生提供了良好的动力条件。区内楼房基础施工扰动了地下水和土洞间的平衡状态从而成为了地面塌陷发生的诱发因素。运用7项地质环境条件指标和5项经济人口指标分别定性评估岩溶地面塌陷的易发度和易损度,并将二者叠加进行地质灾害风险评估。研究结果表明,夏茅村潜在地质灾害风险大,只有严格控制地下水动力条件,才能避免再次发生岩溶地面塌陷。     

武汉市江夏区大桥新区红旗村黏土盖层岩溶塌陷致塌模式分析

武汉市江夏区大桥新区红旗村文化大道附近发生岩溶塌陷,其上覆盖层为黏土。文章针对该类型岩溶塌陷,结合岩溶发育特征、土体物理力学性质、水文地质条件和人类工程活动等影响因素,对致塌模式进行了综合分析,得出在溶沟底部分布有软塑至流塑状的力学性质较差的红黏土,溶沟底部发育的溶蚀裂隙与下部的溶洞或通道相联通;流塑状红黏土流失至下部岩溶通道中,形成土洞;钻探施工、楼房载荷、振动作用加速黏土体的软化、崩解和溶蚀作用,进而加速土洞向上发展。此外,地基开挖减少上覆黏土厚度,降低了土体抗剪强度,最终在上覆土体自身重力和附加荷载作用下发生塌陷。根据土体受力情况,得出塌陷力学模型,并利用数据进行验证,其验证结果与实际相符合,并结合致塌模式和力学分析提出应增强土体抗塌性能、增加建筑物地基稳定性和减缓岩溶系统水动力因素变化的防治措施。      

泰安市城区—旧县水源地岩溶地面塌陷历程及影响因素分析

文章总结泰安市城区—旧县水源地内岩溶塌陷的发生发展历程，综合前人研究成果及最新的野外调查统计结果，对影响研究区岩溶塌陷的分布及影响因素进行了剖析，探明了岩溶塌陷的发育条件及诱发因素。结果表明:(1)研究区内岩溶塌陷主要发生在岩溶发育较强、断裂带附近、土层厚度小于30 m的区域；发生塌陷区域的土层结构以二元结构为主，其次是多元结构；塌陷大多发生在汛期，尤其是在大型降雨之后；(2)强烈的地下水开采活动引发的岩溶水大幅度波动是塌陷发生的最主要诱发因素，且岩溶地下水位在基岩面附近波动时最易引发塌陷；外界对土体的扰动也对塌陷有一定的影响，泰安城区旧镇铁路交汇处的塌陷与列车行车震动有密不可分的联系。综合分析以往岩溶塌陷的研究方向和程度，建议今后的研究重点应为塌陷过程演化监测与模拟、塌陷预警预报方法探索及数据库建设。      

黔中高原台面浅覆盖型岩溶塌陷分布及影响因素浅析

黔中高原台面处于贵州省第二阶梯,平均海拔800～1 600 m。具有可溶岩分布面积广,岩溶极其发育,第四系土层覆盖薄,地下水埋深浅、地下水动力条件强等特点,岩溶塌陷是该区主要地质灾害之一。文章以黔中地区岩溶塌陷调查项目统计资料为依据,对岩溶塌陷分布及影响因素进行分析,结果为83.8%的岩溶塌陷分布在的峰丛谷地和溶丘谷地中、97.5%的岩溶塌陷分布于土层厚度1～10 m黏土中、83.7% 的岩溶塌陷分布于三叠系中统关岭组和中下统安顺组白云岩地层中、73.3%的岩溶塌陷沿活动断裂及褶皱地带分布、地下水是区内最主要的触发因素;在人为因素方面与地下水开采强度、城镇化进程等因素密切相关,且随城镇化进程及抽水活动的增加而增多。      

Sinkhole subsidence due to mining

This paper reviews the modes of formation of sinkhole subsidence associated with mining activities, drawing on examples in India. Sinkhole (pot-hole) subsidence is an abrupt local depression at the surface which can be hazardous to life and property due to its tendency to occur without warning. Shallow extraction, weak overburden and geological discontinuities are the main factors which cause them. Sinkholes occur due to the failure of a mine roof which migrates through the overlying strata until the failure zone intercepts the unconsolidated overburden. Alternatively they may occur by the creation of cavities in the overburden following the inflow of sand and soil from the overlying weathered and friable strata through faults. Overburden cavities eventually cave in and sinkholes appear at the surface. Sinkholing phenomena can be controlled to some extent by proper design of mining supports and construction of walls to create a barrier around an area prone to sinkholes in bord and pillar workings. Backfilling and grouting can be used to stabilize abandoned underground workings.     

Application of seismic velocity tomography in investigation of karst collapse hazards,Guangzhou, China

This paper describes seismic velocity tomography applied to the investigation and assessment of karst collapse hazards to facilitate accurate characterization of geological conditions of karst sinkhole formation. In the survey areas of Xiamao, Guangzhou, China, and Huangchi, Foshan, China, seismic velocity tomography was used to explore the structures of rock and soil associated with karst collapse. The results show that sand intercalated with clay or clay intercalated with soft soil dominates the cover of these two areas. The overburden is 20–33 m thick and underlain by Carboniferous limestone. In the limestone, there are well-developed karst caves and cracks as well as highly fluctuating bedrock surfaces. The seismic velocities are less than 2500 m/s in the cover, 2500–4500 m/s in the karst fracture zones and caves of Xiamao, and 1500–2000 m/s in the Huangchi collapse area. The karst fracture zones, relief of bedrock surfaces, and variations of soil thicknesses revealed by seismic velocity tomography are well constrained and in agreement with those in the drilling borehole profiles. This paper demonstrates that seismic velocity tomography can delineate anomalies of rock and soil with the advantages of speed, intuitive images, and high resolution.     

Formation mechanism of large sinkhole collapses in Laibin,Guangxi, China

On June 3, 2010, a series of karst sinkholes occurred at Jili village surrounded by Gui-Bei highway, Wu-Ping highway and Nan-Liu High-Speed Railway in Laibin, Guangxi, China. The straight-line distances from an large sinkhole pit, 85 m in diameter and 38 m in depth, to the above mainlines are 200, 600 and 500 m, respectively. Several investigation methods including geophysical technology, borehole and well drilling, groundwater elevation survey and hydrochemistry analysis of groundwater were used to study the formation mechanisms of these sinkholes. Based on the results, the spatial distribution of the Jili underground river was confirmed with a strike of SN along the middle Carboniferous limestone bedrock and the Quaternary deposits controlled the sinkhole formation. In addition, both historical sinkhole events and analysis of the groundwater–air pressure monitoring data installed in the underlying karst conduit system indicate that sinkholes in this area are more likely induced by extreme weather conditions within typical karst geological settings. Extreme weather conditions in the study area before the sinkhole collapses consisted of a year-long drought followed by continuous precipitation with a daily maximum precipitation of 442 mm between May 31 and June 1, 2010. Typical geological conditions include the Jili underground river overlain by the Quaternary overburden with thick clayey rubble. Especially in the recharge zone of the underground river, a stabilized shallow water table was formed in response to the extreme rainstorm because of the presence of the thick clayey rubble. When the underground conduit was flooded through the cave entrance on the surface, air blasting may have caused the cave roof collapse followed by formation of soil cavities and surface collapses. Borehole monitoring results of the groundwater–air pressure monitoring show that the potential karst sinkhole can pose threats to Shanbei village, the High-Speed Railway and the Wu-Ping highway. Local government needs to be aware of any early indicators of this geohazard so that devastating sinkholes can be prevented in the future. The results also suggest that groundwater–air pressure monitoring data collected both the Quaternary deposits and the bedrock karst system provide useful indicators for potential sinkhole collapses in similar karst areas where sinkholes usually occur during rainy season or karst groundwater level is always under the rockhead.     

青藏高原南缘某机场场区深厚覆盖层工程地质特征

青藏高原南缘某拟建机场场区发育第四系深厚覆盖层,对该工程建设具有较大的制约作用。钻孔资料显示,该深厚覆盖层普遍分布于整个场区,厚度均在30m以上,最大孔深105m仍未揭穿。纵向上深厚覆盖层由上而下可划分为4层:全新世泥石流堆积层(Q₄sef)、全新世冲洪积堆积层(Q₄al+pl)、全新世湖相堆积层(Q₄l)和晚更新世冲洪积堆积层(Q₃al+pl)。其中:泥石流主要由角砾和碎石组成,最大厚度约13m,分布于研究场区西侧;全新世冲洪积层组成物质复杂,以粉细砂和圆砾居多,无明显分层规律,最大厚度约7m;湖相沉积粉质黏土呈可塑-流塑状,局部夹含砂,最大厚度约43m;晚更新世冲洪积层以细砂和中粗砂为主,局部夹有卵砾石,厚度大于42m。分析表明,深层覆盖层成因与晚更新世以来喜马拉雅快速隆升及间冰期气候密切相关,而表层覆盖层与全新世以来青藏高原气候回暖及短期冷暖交替气候密切相关。试验揭示深厚覆盖层物理力学性质差异明显,研究场区存在不均匀沉降、渗漏破坏、边坡稳定性及冻融诱发地基破坏等主要工程地质问题。     

Geophysical response of filled sinkholes,soil pipes and associated bedrock fractures in thinly mantled karst,east-central Illinois

Karst aquifers are often protected by a thin mantle of unconsolidated sediment. Soil pipes and sinkholes may breach this natural protective barrier and open pathways for contaminants to quickly reach bedrock aquifers. Geophysical surveys offer a quick and noninvasive way to identify these features; such surveys may also be sequenced to reveal increasing detail in critical areas. At a study site in east-central Illinois, electromagnetic (EM) surveys mapped high conductivity anomalies over filled sinkholes and soil pipes that penetrated the unconsolidated cover. Two-dimensional inverted resistivity sections, made over these anomalies, depict filled sinkholes and soil pipes as conductive zones above deeply weathered bedrock fractures. Borings verified the geophysical models and suggest high conductivities associated with the filled sinkholes are the result of enhanced moisture near active soil pipes. EM surveys also identified conductive zones in the overburden above a probable bedrock fracture linking sinkhole areas 0.5 km apart. Resistivity and EM methods, used in a phased and sequential manner, thus proved useful in mapping filled sinkholes and in delineating the vertical and lateral connections between soil pipes and hydraulically active bedrock fractures.     

某岩溶矿山电耙机基座塌陷形成条件及治理技术

某电耙机基座位于南方某岩溶矿山,地基由粉质黏土、卵石及壶天群灰岩组成。2009年6月发生塌陷,平面上塌陷坑长约3 m,短约2 m,造成电耙机大部被埋入溶洞内,严重威胁到周边尾砂堆场及水泥罐的安全。调查分析及土洞塌陷过程模拟表明,该电耙机基座塌陷主要由于壶天群灰岩溶蚀裂隙发育强烈,地下水位在岩土界面附近上下波动,以及日常生产中电耙机基础旁长期受冲水综合作用,致使基岩面上的土层颗粒被潜蚀带出进而形成土洞坍塌。针对以往塌陷治理多以回填为主,复塌比较频繁,本电耙机基座塌陷采用孔内旋喷造浆注浆方法处理,即先根据孔深的不同向水泥浆中添加不同比例的速凝剂,然后将添加速凝剂的水泥浆液快速送入孔内,并利用高压和高转速切割周边土层,使得单纯的水泥浆成为水泥黏土浆液,在高压下浆液劈裂土层,从而达到快速封堵溶洞口和加固土层的目的。检测结果显示,该方法不仅能有效快速地封堵基岩面溶蚀裂隙或溶洞口并加固土层,消除塌陷的基本条件,而且工艺成熟,成本远小于注浆加固,适合在岩溶矿区推广应用。