Karst Collapse Mechanism and Criterion for Its Stability

Karst collapse, caused by natural or artificial abstraction of groundwater, has been a focus of environmentalgeological problems for its ever-increasing hazardousness. The potential erosion theory and vacuum suction erosion theory, which reveal the origin of karst collapse macroscopically, are popularly accepted. However, a mathematic prediction criterion for karst collapse cannot be established only by these two theories. From a new perspective, this paper attempts to explain the microcosmic mechanism of karst collapse on the basis of these two theories. When the shear stress surpasses the shear strength of soil, a certain point or a certain plane in the unconsolidated soil covering karst caves will fail under the mechanical effects of water and air as well as its load-pressure, and with the increase of damaged points, a breaking plane appears and the soil on karst caves is completely damaged; as a result, the karst ground collapses. On the basis of the Mohr-Coulomb failure theory and previous studies,     

鄂尔多斯盆地奥陶系热水岩溶特征

鄂尔多斯盆地奥陶系深部白云岩中的溶蚀孔洞,其成因属于热水岩溶作用的结果。本文通过成因矿物学及Fe2+ 、Mn微量元素分析和气液包裹体测定,结合岩溶发育的构造背景,深入揭示了本区热水的来源主要为深部循环热水,局部尚有深部上升的热液加入 ;其热能除地温梯度加热、构造运动加热外,在盆地基底古断裂附近可能还有深部热源的影响而形成的中低焓地热流体。充填矿物包裹体均一温度为 15 0～ 34 9℃,气相成分中CO₂ 摩尔浓度达到44.3%～ 5 6.98%。Fe2+ 、Mn微量元素在鄂 6、定探 1、李华 1井、芦参 1井、陕 8井和旬探 1井白云岩中的富集,指示了这些井区是热水运移的主要近源区。认为热水岩溶的发育,对奥陶系内幕储层的形成具有重要意义     

滨海岩溶区过渡带碳酸盐岩溶浊作用的试验研究

滨海岩溶具有内陆一般岩溶区不同的发育机理，其过渡带混合溶蚀作用是控制滨海岩溶发育的最主要因素之一。通过七组不同淡水与海水配比的混合溶蚀实验（封闭CO2－H2O系统），初步得出了过渡带混合溶蚀作用的基本结论：（1）滨海岩溶区过渡带岩溶发育的基本规律与内陆一般岩溶区岩溶发育规律的基本一致，即岩性，结构是控制滨海岩溶发育的最主要因素；（2）滨海岩溶区混合过渡带内碳酸盐岩的混合溶蚀速率大于纯淡水或纯海水中同种岩石的溶蚀速率；（3）在不同的CO2分压条件下，滨海岩溶区混合过渡带内碳酸盐岩的混合溶蚀机理不同。     

Results from the Big Spring basin water quality monitoring and demonstration projects,Iowa, USA

Agricultural practices, hydrology, and water quality of the 267-km² Big Spring groundwater drainage basin in Clayton County, Iowa, have been monitored since 1981. Land use is agricultural; nitrate-nitrogen (-N) and herbicides are the resulting contaminants in groundwater and surface water. Ordovician Galena Group carbonate rocks comprise the main aquifer in the basin. Recharge to this karstic aquifer is by infiltration, augmented by sinkhole-captured runoff. Groundwater is discharged at Big Spring, where quantity and quality of the discharge are monitored. Monitoring has shown a threefold increase in groundwater nitrate-N concentrations from the 1960s to the early 1980s. The nitrate-N discharged from the basin typically is equivalent to over one-third of the nitrogen fertilizer applied, with larger losses during wetter years. Atrazine is present in groundwater all year; however, contaminant concentrations in the groundwater respond directly to recharge events, and unique chemical signatures of infiltration versus runoff recharge are detectable in the discharge from Big Spring. Education and demonstration efforts have reduced nitrogen fertilizer application rates by one-third since 1981. Relating declines in nitrate and pesticide concentrations to inputs of nitrogen fertilizer and pesticides at Big Spring is problematic. Annual recharge has varied five-fold during monitoring, overshadowing any water-quality improvements resulting from incrementally decreased inputs. Electronic Publication     

Induced seismicity at wujiangdu reservoir,China: a case induced in the karst area

To date 19 cases of reservoir-induced seismicity have been acknowledged in China and 15 of them are associated with karst. The Wujiangdu case is a typical one induced in the karst area. The dam with a height of 165 m is the highest built in a karst area in China. Seismic activity has been successively induced in five reservoir segments seven months after the impoundment in 1979. A temporary seismic network consisting of 8 stations was set up in one of the segments some 40 km upstream from the dam. The results indicate that epicenters were distributed along the immediate banks, composed of karstified carbonate, and focal depths were only several hundred meters. Most of the focal mechanisms were of thrust and normal faulting. It is suggested that karst may be an important factor in inducing seismicity. It can provide an hydraulic connection to change the saturation and pressure and also weak planes for dislocation to induce seismicity.     

天津岩溶地热田热储特征研究

从天津大地构造特征和地层分布入手，综合分析了岩溶热储特征.认为天津地区主要大地构造格局从西北向东南依次为冀中拗陷、沧县隆起和黄骅拗陷，主要断裂有北东向的沧东断裂、天津断裂以及北西向的宁河-宝坻断裂.岩溶地热田主要分布在沧县隆起上，发育了王草庄、大城、潘庄、双窑和小韩庄凸起等地热田.研究认为蓟县系雾迷山组在天津全境普遍分布，岩性为深灰色粗晶白云岩、隧石条带状白云岩，裂缝岩溶发育，孔渗性较好，是主要热储层.寒武系、奥陶系热储在沧县隆起核部大面积缺失，在其他地区广泛分布，是主要热储层之一.沧县隆起的热流值较周围地区高，地热水的来源主要为北部蓟县山区，热水运移的最重要通道是大断裂以及不整合面.     

彭县塘坝子—葛仙山景点石灰岩溶洞景观及旅游资源开发前景

塘坝子-葛仙山景点,地处举世瞩目的龙门山推覆-滑覆构造带上,已成为拟建中的“龙门山地质公园”的重要组成部分。其独特的石灰岩岩溶地貌和溶洞景观,是成都旅游区和彭县景区内宝贵的旅游景观配套资源,除旅游开发价值较高外,亦是离成都市区较近较理想的人防各战疏散基地,因而具有一定的资源综合开发潜力。对该景点的尽早开发,还可缓解邻区旅游热点的人满之患。     

塔里木与扬子新元古代热-构造事件特征、序列和时代——扬子与塔里木连接(YZ-TAR)假设

淄博市大武水源地是中国北方罕见的特大型岩溶-裂隙地下水水源地,地下水开采量为52×10~4m~3/d。为了对岩溶地下水进行有效监测,需要建立最优的地下水监测网。文中在对岩溶地下水流系统分析的基础上,建立了地下水流系统确定性-随机性数学模型,运用有限元与卡尔曼滤波耦合的模拟递推算法,对大武水源地地下水监测网进行了优化设计,结果显示:现有地下水位动态监测网难以达到监测目标,最优地下水位监测网由14个监测井,每月监测一次的监测频率组成,比现有地下水位监测网减少了2个监测井。     

塔河油田奥陶系碳酸盐岩岩溶发育模式的测井分析

构造运动控制着岩溶发育的期次。塔河油田奥陶系主要发育了加里东中期岩溶和海西早期的两期岩溶。加里东中期岩溶保留于本区南部下奥陶统,岩溶较弱,以发育小的溶孔为特征;海西早期的两期岩溶发育于北部下奥陶统,岩溶较强,以大型溶洞、地下暗河为特征。各期岩溶在纵向上可分为三个带：地表岩溶带、垂直渗沈岩溶带和水平潜流岩溶带。利用各岩溶带自然伽玛测井、井径测井、双侧向电阻率、密度测井、中子孔隙度测井、声波副井和地层檄电阻率成傈测井的响应特征,对两口典型井岩溶带进行划分。以“双峰灰岩”为标准,对两口井的岩海带进行横向对比,建立加里东中期和海西早期岩溶空间分布与发育强度的模式。     

Manifestation and measurement of the fractal characteristics of karst hydrogeological formations

A new method of estimating the fractal dimension of the percolation backbone of karst systems, which are discharged through karst springs, is presented. This method is based on the simulation of the spring by the MODKARST deterministic mathematical model. Application has been made to the Psiloritis karst formation in Crete, which feeds the periodically brackish karst spring “Almiros” in Crete. Furthermore, the estimated dimension justifies an independently determined power law that quantifies the sea intrusion into the karst system.