Multichannel Method Of Transient Rayleigh Wave Detecting In Consideration Of Arrival Time Difference Phase Between Channels

The detection method of Rayleigh has been gradually accepting and applying in engineering since the early 1970 s.At present,transient Rayleigh wave exploration technique has become a popular geophysical method in engineering.Limited by the concept of spatial sampling rate in wave problems,the existing multichannel transient Rayleigh wave exploration technique observes the transient Rayleigh wave excited at a single blow with an array of multichannel geophones of small channel spacing.The method does realize the observing and recording of the waves with multiple frequency components simultaneously,but it can only get one curve of phase velocity vs.depth with an array of multichannel geophones,therefore,its work efficiency and lateral resolution power are greatly limited.In addition,the classification of Rayleigh wave phase velocity imaging has not formed a fixed reference standard,which makes the interpretation of the Rayleigh wave detection results having much subjective and limitations.Nowadays,the imaging of the Rayleigh wave detection results mainly expressed in two dimensions,it’s very difficult to directly and accurately reveal the scale and distribution that karsts of unfavorable geological body in space.In order to overcome the defects,this paper obtained three views and innovation for the method of extraction the transient Rayleigh wave velocity and it’s imaging results:(1)Proposing the method of transient Rayleigh wave phase velocity extraction which considering the arrival time difference phase between channels and forming a new technology to calculate phase velocity.This approach breaks through the traditional sampling theorem and gets rid of the shackles of the existing method which limited by the spacing channels and it can extract phase velocity of different frequency components with only two geophones record wave,completed a whole array detection task in existing method.And the lateral resolution and the efficiency of operation in situ are highly improved.(2)Proposing classification scheme of Rayleigh wave phase velocity,through testing the wave velocity of rock and soil specimen on the site,and establishing the corresponding relationship with phase velocity and the karst fracture characters.It laid the physical foundation for engineering rock Rayleigh wave phase velocity imaging.(3)Using the spatial distribution of measure rock data,relying on the Guiyang metro project of karst cave exploration established corresponding relationship scheme with phase velocity and the karst fracture characters,applying the imaging profile of the Rayleigh wave phase velocity and the horizontal slice composed the Rayleigh wave phase velocity 3D visualization.From the 3D map of the Rayleigh wave phase velocity,we can directly see the scale,position and connection of karst caves.The approach is no precedent in engineering.This detection method applied in Guiyang metro where karats development is intense.And the detection results is good agreement with the actual situation which verified the rationality and correctness of the approach while provided the powerful technical support for the karst disease management in Guiyang metro engineering.