Acoustic Cross-well Tomography and the Seismic Wave Attenuation to Explore the Mechanism of Land Subsidence,Taking Chengdu Metro South Railway Station as an Example
By using 4 exploration holes in the site,cross-well seismic tomography method and cross-well seismic wave attenuation analysis are used to find out the subsidence reason of Chengdu Metro Line 18 South Railway station.The acoustic velocity of mudstone on the east side of foundation pit of Chengdu Metro South Railway Station is lower than that on the west side,and the seismic wave penetrating mudstone has strong low frequency energy,weak high frequency,and large attenuation of high frequency components.On the west side,the seismic wave penetrating mudstone has strong high-frequency energy and small attenuation of high-frequency components.It shows that the mudstone fracture is more developed and the mudstone strength is lower on the east side of the foundation pit,while the mudstone layer is more complete on the west side.There are many abandoned ground source heat pump deep Wells on the east side,mudstone physical weathering occurs under the action of long-term heat exchange.At the same time,groundwater moves along the mudstone joints and fissures,further softening the mudstone,reducing the bearing capacity of the rock mass and leading to ground subsidence.The introduction of seismic wave attenuation analysis into traditional seismic wave tomography is more conducive to identifying the properties of rock mass,thus identifying the cause of ground subsidence and taking targeted engineering treatment measures
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