Abstract: To study the dynamic response characteristics of soil under impact load, flat dynamic load tests (FDLT) with different load levels and loading rates were carried out on two typical soils (sand and clay) in Guangzhou University Town by using the self-developed additional excitation force-type FDLT system, obtaining three characteristic curves of load-time curve, displacement-time curve, and load-displacement curve, establishing the empirical formula of dynamic deformation modulus and loading rate, and comparing the effects of loading rate of the two soils under impact load. It shows that: (1) There is a threshold of charging voltage in the FDLT test of sand. During the impact test on this threshold, the loading rate has a great effect on the dynamic strength and deformation of sand, while it has no obvious effect on clay under the same conditions. (2) The same point of the loading rate on the displacement response of clay and sand is that the maximum load and maximum displacement of the two soils both increase with the increase of loading rate. The difference is that the time for clay to reach the peak displacement increases with the increase of loading rate while the time for sand to reach the peak displacement shows a pattern of increasing and then decreasing with the increase of loading rate. (3) The dynamic deformation modulus varies logarithmically with the loading rate. The results can provide a reference for soil dynamic characteristics study, dynamic and static parameter conversion and engineering design.

Key words: loading rates, flat dynamic load test, impact load, dynamic parameters