Research,Development And Engineering Application About BMT-? Microtremor Testing Equipment

Bore-hole microtremor testing is a new in-situ testing method which directly measures deep soil microtremor signal by inserting sensors into boreholes.It can acquire the dynamic parameters of deep soil layer to provide for major engineering with deep foundation,such as bridges,subway,ports,nuclear power plants and high-rise buildings.At present,the research of bore-hole microtremor testing is in the preliminary exploratory stage,and there is no suitable equipment and testing method for bore-hole microtremor testing.Based on the research of BMT-I bore-hole microtremor testing equipment,BMT-II bore-hole microtremor testing equipment has been developed and applied to engineering practice and the corresponding test methods and standards have been compiled,the test data has been processed and analyzed,including the following contents:(1)BMT-II bore-hole microtremor testing equipment has been developed,which is a new type equipment for bore-hole microtremor testing.The equipment retains the functions and characteristics of BMT-I bore-hole microtremor testing equipment,and it improves and innovates in some aspects.First,the equipment has two three-component sensors with a distance of 1 meter,which can complete the test of two different depth points at the same time,so it saves testing time and improves testing efficiency.Because the test signals of the two sensors have good correlation,which can improve the test precision.Second,some improvements have been made on the adherent system: canceling the reset counterweight in the original design,resetting the device by the self-weight of the rod,and adding a rotating limit device,which ensured good adherence effect and made the operation easier and faster.Three,its sensors have good low frequency characteristics,which can be used not only for bore-hole microtremor test,but also for wave speed test.Four,the equipment is easy to assemble.(2)A method of bore-hole microtremor and shear wave velocity test which is suitable for BMT-II bore-hole microtremor testing equipment is proposed.The feasibility of the method is verified by engineering measurement.The test standard of BMT-II bore-hole microtremor testing equipment is compiled.In addition,the matters needing attention in testing are put forward,and the corresponding solutions to the common problems encountered in the testing process are presented.(3)A method for calculating shear wave velocity of soil layer by using bore-hole microtremor signals is presented.Based on the correlation between the horizontal signals of the upper and lower sensors,the shear wave velocity of the soil layer between the two measuring points is calculated by cross-correlation analysis.Compared with the traditional shear wave velocity measurement method,this method does not need man-made vibration source and oblique distance correction is not necessary in the calculation process.