Experimental Research Of Impact Roller Compaction Of Shallow Foundation And Its Numerical Simulation By PFC～(3D)

Traditional vibratory roller using working wheels' vibrator transmits vibrations of high frequency and small amplitude to soil. Then the density of the soil is increased while the particles of the soil vibrate with their natural frequency. Differently, impact roller using working wheels directly produce impulsive compaction of low frequency and big amplitude to the soil. How does the action affect the soil structure and the displacement of the particles? At present, the mechanism of impact roller compaction is understood purely based on the macroscopical hypothesis and it is still unclear concerning the relationship between soils compaction and change of meso-fabric of grains. The state of practice for impact compaction is only grounded on experience and in-situ test, and lack of suitable numerical modeling tool. In this dissertation, impact roller compaction of silty and fine sands is studied in details from macroscopical point and mesoscopical point by way of in-situ tests and Particle Flow Code in 3 dimensions numerical simulation.Based on the in-situ tests of Shanghai Pudong International Airport Project, the main works in this paper are the researches on the applicability of impact roller compaction of silty and fine sands and the influential factors, such as the depth of cushion, dewatering methods, number of impact roller passes and so on.. The data measured from standard penetration test, static cone penetration test and surface wave test are used to evaluate the effective influence depth, the strength of soils, the increase of foundation modulus and the influence to surroundings. The research indicates that dewatering does good to improve the strength of the soil, but different dewatering methods do the same. Cushion and increase of the cushion's depth make for the increase of foundation modulus. Impact roller compaction method affects the soil within the range of 6m of depth and 30m of length.Particle Flow Code in 3 dimensions, as a advanced numerical modeling code, provides a powerful and flexible tool for understanding and simulating liquefaction and compaction of sands for its suitability of modeling wave transmit and energy dissipation thanks to the ever increasing power of modern computers. In the thesis, PFC^3D is used to model impact roller compaction by additional programming using FISH language. In order to simulate impact compaction process, several models have been built: sand grains, impact roller compaction unit and sand box. By comparing with the in-situ test results, the efficacy of the model is proved. Based on the relationship of the meso-behavior of the investigated soil and the macro-response, the mechanism of impact roller compaction is investigated using the impact roller compaction model built by PFC^3D. The research indicates that the impact compaction destroys the contact structure of the soil particles in the range of 1.0m of depth, and the displacement of the particles is distinct in the range of 6.0m of depth. These results are consistent with the conclusions of the in-situ tests.