【作者】 李勇峰；

【导师】 徐光黎；

【作者基本信息】 中国地质大学 ， 地质工程， 2013， 博士

【摘要】 我国岩溶分布面积广,约占国土面积的1/3。岩溶地面塌陷可能是岩溶地区工程建设所面临的主要工程地质问题。近年来,随着社会经济的不断发展,岩溶地区人类工程活动导致的岩溶塌陷灾害日趋频繁,灾害后果越来越严重。受限于客观条件,许多重大工程只能布置在岩溶发育区,岩溶探测方法准确度不高、地面塌陷成因机制复杂、塌陷治理难度大。研究工程场地岩溶探测方法、岩溶地面塌陷成因机制及危险性评价预测,对于保证工程施工及运营安全、保证工期具有重要的工程意义,而且具有重要的学术价值。深圳大运中心是世界第第26届世界大学生夏季运动会的主场馆,已于2010年底完工并投入使用。其主体建筑物有主体育场、体育馆、游泳馆、热身赛场、地下停车场、人工湖和道路等,这些主体建筑物载荷大,对沉降、差异沉降敏感,安全等级为一级,是深圳市乃至世界瞩目的大型建设工程项目。其场地工程地质条件复杂,地层岩性多变,岩面起伏,埋藏型土洞、溶洞发育,是深圳市地质条件最复杂、岩溶最发育的场所。在桩基础施工过程中,出现了实际桩长与设计桩长相差较大、地表开裂、桩孔揭露土洞或溶洞,个别桩的承载力达不到设计要求等问题。其中,体育馆于2008年1月进行了大面积预应力管桩施工过程中出现2次地面塌陷。鉴于工程重要性及工期紧迫性,深入研究岩溶探测方法,准确查明场地岩溶发育规律、明确岩溶地面塌陷机制及危险性评价研究不仅具有重要的理论意义,而且具有重要的现实意义,显得十分必要和迫切。本论文依托中国地质大学科研项目“深圳大运中心场地土洞、溶洞物探工程”,以深圳大运中心溶洞、土洞为研究对象,以岩溶地面塌陷危险性评价为研究主线,运用地质学、地球物理学、工程地质学、数理统计、力学分析、计算机模拟等方法为研究手段,研究采取的主要研究方法是：大量文献阅读、资料收集、现场地质调查、岩溶探测的基础上,综合运用数理统计、地质分析等方法,系统分析研究深圳大运中心地质环境背景、岩溶探测方法、岩溶发育规律及分布特征的基础上,进一步研究岩溶地面塌陷形成机制,建立岩溶地面塌陷危险性评价体系并应用于工程实际中。研究内容及主要结论如下：(1)区域地质环境条件研究。大运中心场地可溶岩为石炭系下统大唐阶石磴子组(Cls)的微风化灰岩,热身赛场,体育场,游泳馆的东侧、西侧为岩溶浅埋区(<15m)其中,热身赛场和体育场的地下室附近,灰岩埋深很浅,大多<5m。场地属岩溶中、强发育带,龙岗城镇地面局部不稳定地基复杂段。场地地质构造复杂多变,处于官井复式背斜倾伏段的西北翼,东、西边界被NE向的红旗岭断裂、沙塘围断裂,南、北边界被NW向的油甘铺断裂、青塘断裂所围限。其中,NE向的红旗岭断裂对本区岩溶的影响最大。受裂断、褶皱地质构造的影响,场地测水组(C1c)碎屑岩、石磴子组(Cls)灰岩岩体破碎,裂隙发育,对岩溶的发育、演化起着重要作用。(2)场地土洞、溶洞探测及解释。充分分析和利用已有勘察资料的基础上,以土洞、溶洞为研究对象,以“宏观控制与重点勘察相结合”为指导思想,采用高密度电法、地质雷达、CT层析成像、验证性工程地质钻探4种综合勘察手段和方法,探测查明了土(溶)洞、位置、规模及其物质组构关系。共完成高密度电法测线84条,完成地质雷达探测33个剖面线,层析成像24对,验证性工程地质钻探50个,其中揭露到土洞堆积物的钻孔有20个,揭露溶洞的7个,松软土层(或破碎带)的钻孔8个,验证结果总有效率达70%。所采用的综合勘察手段和方法弥补了单-方法的缺陷和不足,提高了岩溶异常的识别和判断能力,具体工程中,各种探测方法资料解释过程应结合现场实际情况进行,并比较、验证各种手段所得成果。(3)岩溶发育分布规律研究。场地可溶岩分布全区,岩溶发育。岩溶深度从地表出露到埋深大于60m,高程在50-10m,基岩面起伏,溶槽、溶沟发育。场地见洞率为11～19%,平均14%,其中土洞约占5%。土洞或溶洞大多有洞穴堆积物充填,空洞占3%。岩溶发育分布不均,在场地不同部位表现出不同的特征。体育馆东、东南,体育场东、西和西北,游泳馆西南、北,地下停车场东等地为岩溶强发育区,局部见洞率超过50%。开口溶洞、充填溶洞呈单层或多层出现。土洞多发育于测水组风化砂页岩与灰岩接触面附近。(4)岩溶发育演化及溶洞、土洞发展趋势分析。在岩溶探测等资料的基础上,结合地质学、工程地质学等专业知识,对深圳大运中心岩溶发育过程进行综合分析并对土洞、溶洞的发展趋势进行分析。分析认为：岩溶发育、演化规律是古强今弱。近代,由于区内地下水循环交替微弱,岩溶几近停止发展,在自然条件下区内不易形成岩溶地面塌陷。但在人类活动影响下,如大量抽取岩溶地下水、建筑施工打桩振动、工程建筑加载等作用下,则存在诱发地面塌陷发生的可能。(5)岩溶塌陷机制研究。依据勘察资料及类似工程实例,概化出塌陷的静力学模型,选取合适的物理力学参数,对已发生塌陷进行静力学分析,分析认为施工振动等人类工程活动产生的外力是本次岩溶塌陷的直接诱因。在全区地质勘察及岩溶探测资料的基础上,按盖层结构概化出适用于研究区的两种岩溶塌陷模型,分别为“粉质粘土+灰岩”及“粉质粘土+强风化砂岩+灰岩”两种地质模型,选取“粉质粘土+灰岩”类型的模型,利用ANSYS软件分析了动荷载作用下覆盖层厚度对于岩溶塌陷的影响。(6)岩溶地面塌陷危险性评价研究。选取岩溶基础条件、覆盖层特征、建筑物属性、水文地质条件等4个一级指标,岩性、覆盖型岩溶存在情况、岩溶发育程度、距构造线距离、覆盖层结构、覆盖层厚度、建筑物重要程度、地下水位等8个二级指标,基于中国地质大学自主研发的MapGIS平台,分别采用层次分析法(AHP法)和PLS Path Model数学模型进行了岩溶地面塌陷综合评价分区,将地面塌陷危险性等级分为：高、较高、较低和低等4个等级。结果为：采用层次分析法所得危险性分区中,危险性高、较高、较低和低等4个等级分别总面积的1.33%、8.67%、23.83%和66.17%,由PLS Path Model数学模型评价所得对应结果为1.05%、10.71%、19.39%和68.85%,两种方法所得结果相近。说明预测结果具有一定可信任性,本文提出的两种预测方法在岩溶地面塌陷危险性预测方面具有一定的应用价值。总体上,危险性高区主要出现在体育馆东边、东南角,体育场的西北角、东边和游泳馆西南角等地,其危害大,应予充分的重视,并采取工程措施。岩溶地面塌陷危险性较高区主要出现在体育馆东边、东南角,体育场的西北角、东边,地下停车场东边和游泳馆西南角,以及2条推测断层的附近等地方。岩溶地面塌陷危险性较低和低区,只要地下水变化、人为振动力不大,一般不会出现地面塌陷,无需特别处理。综上所述,本研究遵循“地质环境条件-岩溶探测-岩溶发育规律-岩溶地面塌陷机制-危险性评价”的宏观研究思路,查明了深圳大运中心岩溶发育分布规律,探讨了岩溶发育过程及土洞、溶洞发展趋势,为地面塌陷危险评价提供了基础和依据。危险性评价结果基本能反应客观实际情况,部分溶洞在本研究开展的过程中已经得到处置。特别地,本研究引入的PLS Path Model数学模型,丰富了岩溶危险性评价模型。采用的岩溶综合探测方法较好地解决了实际问题,但鉴于岩溶探测是一个世界性难题,岩溶区溶洞、土洞的探测及各种方法的实用性需进一步研究。更多还原

【Abstract】 Karst area is widely distributed in China, which accounts for about a third of the total land area. The karst ground surface collapse is the main engineering geological problems in karst regions. In recent years, with the rapid development of social economic, karst collapse and the corresponding disasters caused by human engineering activities are becoming increasing frequently and serious in karst regions. Limited by objective conditions, many major projects can only be arranged in the karst area. Detection accuracy in karst area is low and the ground subsidence mechanism is complex. Therefore, it is difficult to conduct the control engineering project. Study of the karst detection methods, the formation mechanism of karst ground collapse and hazard assessment, have significant value to ensure the safety of construction and operation. Besides, the study also has important academic value.Shenzhen universiade center is the main stadium of the26th world summer universiade. It was completed and put into use at the end of2010. It has a main stadium, gymnasium, swimming pool, warm-up court, underground parking, man-made lake and roads, etc. Loads of these buildings are large. They are sensitive to settlement, and have an engineering category of I. The stadium is one of the large construction projects in Shenzhen, even among the world. Engineering geological condition of this site is complex. It is the most complicated karst cave area in Shenzhen city. During the construction of a pile foundation, the actual length of the pile has a large difference from the design length. Cracks can be observed at the ground surface, some piles are crossing the karst caves. For some piles, the bearing capacity cannot meet the design requirement. After the construction of prestressed pipe piles in January2008, the surface collapse occurred in two sites. As the importance and urgency of this engineering project, study on the karst detection method, fully understand the ground surface settlement mechanism and the hazard assessment of karst area not only have an important theoretical significance, but also have an important practical significance.This research is based the research project "Shenzhen universiade center site soil cave, karst cave exploration engineering" finished by China University of Geosciences. The cave soil and the caves are the main research object. The hazard assessment of the karst surface collapse is the main line. Geology, geophysics, engineering geology, mathematical statistics, mechanics analysis and computer simulation methods are employed in this study.Based on the system analysis and study of the geological environment background, karst detection method, the regular pattern of karst development and distribution characteristics of Shenzhen universiade center, karst ground collapse mechanism and risk evaluation system are constructed and applied to the engineering practice. The research contents and main conclusions are as follows:(1) The regional geological environmental condition.The field lithology consists of limestone of Datang step stone rung subgroups (Cls). The warm-up court, stadium and the swimming pool on the east side and west side are shallow buried karst area (<15m). In the warm up court and stadium near basement, the burial depth is very shallow (<5m).The site is located in the medium or strong karst development zone in Longgang town, Shenzhen city, where the local ground foundation is unstable. Field geological structure is complicated, and is located along the GuanJing duplex anticline plunging section of northwestern wing. The east and west boundaries are Hongqiling Fault and Shatang Fault. The south and north boundary are Yougangpu Fault and Qingtang Fault. Hongqiling Fault has the biggest influence on the regional stability. Because of the gological structure of fault and fold, the rock mass group of Clc and Cls are highly fractured plays an important role to the development and evolution of karst.(2) Soil and karst caves’ survey methods and results.Based on the existing investigation data, four investigation methods such as high-density electrical method, geologic radar, CT tomography and verification of engineering geology drilling method are utilized to investigate the soil hole, location, size and material composition.84high-density electrical lines,33geological radar detection section lines,24tomographic images,50engineering geological drilling verification are conducted for this project. Among these boreholes,20are crossing the karst cave. The verification effective rate is70%. Comprehensive investigation methods make up the defects and shortcomings of a single method, which significantly improves the recognition and judgment ability of karst anomaly.(3) Distribution characteristics of karst development.The karst lava is distributed all over this site. The buried depth is more than60m, and the elevation is about50m-10m. The bedrock surface is fluctuating. The hole rate of the field is about11%-19%, with an average of14%. Empty holes accounts for3%. The karst has different characteristics at different place. The east and southeast part of stadium, west and northwest part of swimming pool and the east part of the underground parking are the severe karst area, hole rate is about50%. Soil holes are usually observed along the boundary of shale and limestone.(4) Karst evolution and karst cave and analysis of soil cave development trend.On the basis of karst survey, together with the professional knowledge such as geology and engineering geology, the development trend of the soil hole and karst cave are analyzed. The development speed of karst in ancient time is much more rapid than nowadays. Currently, because the ground water cycling is very weak, the karst development is nearly stopped. But with the influence of human activities, such as ground water pumping, engineering construction and construction load, potential of ground surface collapse still exists.(5) Mechanism of karst collapse.According to the investigation data and similar engineering projects, the statics model of subsidence is proposed. The statics mechanics analysis show that the human engineering activities such as outside force are the direct reason of this karst collapse. Based on the geological investigation and karst detection, two geological models are proposed, they are "silty clay+limestone" and "silty clay+strong weathered sandstone+limestone", respectively. Utilizing the first model and ANSYS, the influence of layer thickness under dynamic loads to karst collapse are analyzed.(6) Hazard assessment methods of karst ground collapse.Based on the MapGIS platform developed by the China University of Geosciences, mathematical models such as analytic hierarchy process (AHP) and PLS Path Model are employed to evaluate the karst surface collapse. Four first-level indicators and eight secondary level indicators are selected. The four first-level indicators of this evaluation are karst foundation condition, cover layer characteristics, building attributes and hydrogeological condition. The eight secondary level indicators are lithology, covered karst existence condition, degree of karst development, and distance from the tectonic line, coating structure, coating thickness, structure important degree and underground water level. The ground subsidence hazard grades are divided into four levels, such as high, relatively high, relatively low and low. The calculation results indicate that when the AHP method is used, the four areas of these four levels are1.3%,8.7%,23.8%and66.2%, respectively. When PLS model is used, the corresponding results are1.3%,8.7%,23.8%and8.7%, respectively. The high risk area is in the east and southeast side of the stadium, northwest side of the swimming court. Special engineering protection measures should be conducted in these areas. The relative high area is located in the east and southeast part of the stadium, east part of the underground parking, the southwest part of the swimming pool and the place near the two speculated faults. However, for the relatively low and low area, as long as the ground water level change and artificial vibration is not very significant, the ground surface will not collapse. Therefore, special engineering treatment is not necessary for this situation.In conclusion, this research follows the thought of "geological environmental conditions-karst cave, karst development law-the karst surface collapse mechanism-hazard assessment". Through this, the karst distribution of Shenzhen universiade center is figured out. The karst cave, karst development trend is discussed. These all provide the foundation and basis for the ground subsidence hazard assessment. The assessment results could reflect the reality, and engineering measures are taken for some of the caves during this research. In particular, the PLS Path Model introduced in this research enriches the karst hazard assessment model. Since the karst survey method is still a challenge problem among the world, the practicability of karst survey methods in karst area still needs further research.更多还原