Accurate Recognition of Underwater Riprap of Rivers and Lakes Based on the Seismic Imaging

During the operation of rivers and lakes dam, due to the reasons for engineering measures, deposition or geological disaster, bank collapse and the river changes still occur. To enhance slope stability and anti-erosion ability, reducing the incidence of bank collapse, the riprap method is widely used in revetment dam engineering. In general, such as riprap stacked body is stable when dry, but with the water level rise and changes in natural conditions, loosely stacked body will slip to the bottom of collapse, leading to reservoir sedimentation, even a threat to the dam safety. Therefore, we should track and monitor the range, chemical speciation of these stacked body periodically, on the one hand is the need for the project to evaluate the quality of underwater riprap, the other is an indispensable work for the management to ensure the flood discharge section and the capacity of the reservoir. However enrockment has loose characteristics, the body full of water and sediment, it can no longer be regarded as a single block. Furthermore earthquake method is limited by the epicenter equipment frequency band, energy size and bubble effect, it is difficult to achieve seismic wave signal by artificial excitation penetrating the underwater gravel, riprap and other discrete body, so it is difficult to collect enough seismic wave that has high signal to noise ratio to reflect the occurrence status of enrockment. Combined with the exploration of Longhekou serveroir, using a new type of source equipment called ‘a light pressure type automatic trigger device which could be used in shallow water’. The practice results showed that the distribution and thickness of riprap which seismic imaging identified was coincided to the physical truth. This provided important theories and practical basis for accurate identification of underwater target in shallow water by using the seismic imaging method.