武汉市工程施工引发岩溶塌陷机理分析

Mechanism of karst collapse caused by engineering construction in Wuhan City

文章对武汉市岩溶塌陷进行了全面梳理,主要对由工程施工引发的岩溶塌陷进行了归纳总结,按施工类型将其分为4大类,对其在不同地质条件下引发岩溶塌陷的成因机理、致塌模型进行举例分析,得出结论:钻探施工诱发的岩溶塌陷以岩层顶板破坏—垂直渗压致塌模式及崩解—土洞顶部破坏—加载致塌模式为主;桩基础施工以岩层顶板破坏—渗流液化致塌模式为主;抽排地下水诱发的岩溶塌陷为潜蚀-吸蚀致塌模式,荷载振动诱发的岩溶塌陷为潜蚀—振动—加载致塌模式。武汉市岩溶塌陷以钻探、桩基施工诱发为主,因其容易破坏岩土体结构、水动力条件,具有猛烈而快速的特点;抽取地下水影响范围较广,隐蔽、不易察觉;振动荷载只能作用于土洞形成后。

Wuhan City is situated in a karst collapse-prone region where karst collapses frequently occur and have caused serious losses of life and property in the past. In recent years, due to extensive infrastructure and construction projects along with its rapid urbanization taking place in the city, problems associated with the engineering construction induced karst collapse in the karst areas have been becoming increasingly prominent, which seriously affects the urban planning and construction process. There are in total 36 karst collap- ses occurred 36 in the city, of which 28 events were caused by engineering construction, and 8 cases by natu- ral factors. It is noted that the collapses occurred after 2001 are all induced by the engineering construction. They collapses can be divided into 4 categories according to construction types, i. e. twenty one collapse in- duced by the drilling, pile foundation construction, five events by draining underground water and two by heavy vehicle load. Geomorphologically, the Wuhan City is located in the transition zone between Jianghan plain and the mountainous region of eastern Hubei. Twenty five out of the 28 karst collapses caused by engineering construction occurred at the first terrace of Yangtze River （alluvial plain area）, where the overlying quaternary soil layer has the dualistic structure characteristics of ＂clay in upper layer and sandy soil in lower layer＂ ; the rest 3 collapses occurred at the ridge hill areas, where the overlying quaternary soil layer has the single clay structure. Based on the previous research and through the comprehensive analysis of the collected data, this paper studied typical characteristics of karst collapse caused by engineering construction, in order to reveal its geological background conditions and control factors. Some examples are also presented to ana- lyze the formation mechanism and collapse mode in different geological conditions. Research findings and an- alytical results collectively show that, （1） the karst collapse caused by drilling was mostly ＂Destroy of Strat- fled Roof-Vertical Seepage Pressure＂ collapse mode or ＂Disintegration-Damage at The Top of Soil Cave-In- ：reasing Loading ＂collapse mode; （2） the karst collapse caused by pile foundation construction was mostly ＂ ）estroy of Stratified Roof-Seepage Liquefaction＂ collapse mode; （3） the karst collapse caused by draining un- terground water was ＂Suffosion-Suction Erosion＂ collapse mode; （4） the karst collapse caused by load vibra- ion was ＂Suffosion-Vibration-Inereasing Loads＂ collapse mode. In addition, this paper demonstrated that he karst collapse in Wuhan was mainly caused by drilling or pile foundation construction, because it not only iestroyed the geotechnical structure and hydrodynamic conditions, but also happened rapidly and violently. 7he affected area of draining underground water was so wide, and could not be easily detected due to its concalment. Load vibration could only take effect after the formation of soil cave. It is expected to provide useful information for the prevention and control of karst collapse in Wuhan.