R&D And Application Of Field Test Equipment For Soil Continuous Dynamic Character

In the field of geotechnical investigation,the dynamic characteristics of the soil,the damping ratio,the dynamic stiffness and other dynamic characteristics are important parameters for evaluating the response of the soil and its superstructure under dynamic loading.Generally,the dynamic characteristics of the soil are measured by laboratory tests such as dynamic triaxial test and resonant columns test.The sample preparation process inevitably destroys the original structure of the soil and has a size effect.The dynamic characteristics of the soil can also be obtained through the field test.Domestic and foreign scholars have developed a variety of soil dynamic testing methods,but they are mostly used to test the response of soil under impact load or the macroscopic phenomenon of soil and structure interaction,which are not allowed to test the dynamic response of soil under continuous dynamic loading.In order to solve the problem that the existing in-situ dynamic test method can not apply continuous dynamic load to the soil,the research team has designed and manufactured a soil in-situ continuous dynamic test equipment.The equipment applies a vertical continuous sinusoidal load on the surface of the load,to get the dynamic hysteresis curve of soil.The vertical dynamic stiffness of the soil is calculated from the obtained long axis slope of the hysteresis curve.The soil damping ratio is calculated from the ratio of input energy to dissipated energy,and the dynamic modulus of the soil is calculated based on the elastic half space theory.On this basis,this thesis uses the prototype of the equipment to carry out the indoor calibration test and the Chengdu clay site field test.The results show that all parts of the prototype of the equipment run well and reach the expected design function.The excitation force of the output meets the design index.The developed equipment can completely measure the dynamic response of the soil under continuous dynamic load;The hysteresis curve of Chengdu clay is is full and nearly closed.The vertical dynamic stiffness and dynamic modulus of the soil decrease with theincrease of loading stress under the condition of in-situ test,and the damping ratio increases with the increase of loading stress.After the dynamic stress increases to a certain amplitude,the sudden increase of the cumulative deformation of the soil under the plate appears,indicating that the soil is damaged.During the failure process,the dynamic stiffness and dynamic modulus of the soil increase,while the damping ratio of soil decrease with the increase of the vibration times.It is considered that the soil has a vibration compaction,and the soil structure under the plate has been rearranged,and finally a dense soil with high modulus,high rigidity and small damping is formed.Moving the center of the hysteresis curves of the the first six load stages to the zero point of the coordinate axis and connecting the vertices of each hysteresis curve in order to get the backbone curve of the soil.From the backbone curve,it can be seen that the stress-deformation relationship of the in-situ soil under continuous dynamic load is obviously nonlinear,and its shape is similar to hyperbolic.