Application Of High Density Resistivety Method To Karst Collapse Exploration In East Yanglou Of Tai'an City

Karst collapse is one of common geological disasters which greatly endangers peoples' life and property. In order to survey the exact location of karst collapse in the investigating area, we designed and placed twenty HDRM survey lines based on predecessors'researches to discuss the expressing forms of all kinds of geologic bodies such as quaternary system clay, sand layer, limestone, karst caves etc. in resistivity profiles. And then we will invert and deal with the collected data which has been systemized, rejected and smoothed into inverting profile map by means of relative software. By comparing the geological conditions reflected by all profile maps, we make sure the resistivity magnitude, expressing forms and depth of quaternary system, sand layer and limestone combining the definition of collapse and drill information, thus discuss the distribution of karst. The expressing forms of resistivity is uniform when HDRM is used to measure the resistivities of quaternary system, sand layer and limestone and can clearly reflect locations of karst caves and earth caves. By learning predecessors'data, we can infer the structure and distribution of this area according to abnormal density of resistivity distribution. Form the south to north, the middle area of the researched area is one where karst caves frequently develop. From the west to east, we can know these caves are relative to each other. By analyzing inverting profile map, we can find the relationship of construction and karst development, thus infer the forming theory of karst development and collapse factors.The location of Yanglou collapse of Tai'an city in May,2003 is the interchange of inferred construction F4 and ordovician limestone interface(the interface of ordovician limestone and tertiary system sandstone). The following are collapse factors:first, soluble underground limestone at construction location is corroded by circulating ground water and becomes hollow, thus forms the karst prerequisite. Soluble limestone is corroded by active ground water and flew away, then becomes hollow and form hollow holes or water tunnel, which directly changes the force equilibrium relation between former stratums and makes overlying bodies hang in the air; second, the floating change of ground water level is big which can be caused by many reasons(including local residents'exploiting ground water). This kind of area can directly cause limestone to form hollow holes, and these holes are sometimes under high pressure and sometimes low pressure(tested by nearby whistle sound when collapse takes place), which indirectly causes the disequilibrium between stratums and thus form collapse in the end.