The key points of falling weight deflectometer in the test of subgrade surface deflection and elastic modulus

Relying on the subgrade engineering of an expressway in Guangdong Province, according to the compiled test scheme, six FWD survey lines were laid in the test area according to the load levels of 3t, 4t and 5t, and the subgrade surface deflection test under different FWD loads was carried out. The average value of the deflection data and load data of the last 4 hammers after 5 blows is used as the final deflection data and load data of this testing point, and the unstable first hammer data is discarded. Then, based on the obtained single-point data, the elastic modulus value of soil foundation at this test point is obtained by inverse calculation through the displacement formula of elastic half-space under single circular load. The abnormal test data is removed by using the 3-fold standard deviation method, and the representative values of deflection and soil foundation modulus of each survey line are calculated by the unilateral confidence level of 95%. The results show that the surface deflection value of single-point subgrade and the elastic modulus of soil foundation are fluctuating, and they are not proportional to FWD load, but the representative values obtained according to the survey line are linear with the load.