Application of cross hole seismic CT in karst exploration of urban rail transit
Cross hole seismic CT (also known as seismic tomography) is an underground geophysical exploration method that analyzes the changes in the duration, amplitude, energy, velocity, waveform, and other factors of seismic waves passing through the interior of the detection target, and performs velocity imaging on the detection target. It has many characteristics such as high detection accuracy, short detection period, and low cost, and is mainly used for high-precision detection of underground target. At present, the cross hole seismic CT method has been widely used in the comprehensive survey of urban rail transit in limestone areas. This method can effectively identify the location, depth, geometric distribution characteristics and scale of karst develop-ment within the line range, and can also distinguish the depth and undulation of bedrock, providing necessary geological basis for subsequent subway design and construction. Taking a karst exploration of a subway project in Guangzhou, Guangdong Province as the research object, a cross hole seismic CT was used to divide the detection area into soil rock interfaces in detail, delineate the locations of karst caves and dissolution development, select abnormal locations for drilling verification, and obtain cross hole seis-mic CT results that reveal a high degree of consistency between the rock surface and karst cave positions and the drilling results. The maximum error in the elevation of the rock surface and karst (soil) cave positions is within 1 meter. The results of drilling and geophysical exploration have played a complementary and mutually validating role.
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