Study On Theory And Application Of Light-penetration Test Technique For Relative Density In Abutment Back Sand Filling

With the rapid development of highway construction in China, vehicle bouncing at bridge approach has become a very important influencing factor and has been paid much attention in domestic and overseas transportation study. Strict quality control in bridge-culvert back sand filling and construction process is of vital importance to prevent the differential settlement of bridge approach. However, the objective and effective test of sand relative density in bridge-culvert backfilling has been a hot yet difficult problem. In this study, based on model and on-site test under a scientific research program of the Guangdong Transportation Group—Sand Relative Density Test on Bridge-Culvert Backfilling(2008-13), the mechanism and the feasibility of light penetration test have been systematically studied. The following contents are investigated:1. Based on the abutment back sand filling, three available light penetration tests and possible program are proposed for the relative density of sand:(1) heavy dynamic penetration,(2) light penetration,(3) standard penetration.2. Fuzzy mathematic model is proposed to evaluate Light-Penetration test technique for Relative Density in Abutment Back Sand Filling, according to which three proposed scenario are compared to determine the best one.3.The optimal one is applied in model test. The relationship between model test result and on-site test result is determined by combining the mathematical statistics and the analogue simulation. Therefore, empirical relationship Dr～N10is established (N10—blow counts in light penetration, Dr—coarse sand relative density in bridge-culvert backfilling).4. Based on discrete element methods, numerical analysis is carried out to figure out the interaction between the light penetration and sand. The sand contact, separation, collision and mechanical injury are also analyzed to test the feasibility of light penetration theoretically. Static penetration test is also used to test the feasibility of light penetration with middle-sized sand, coarse sand and gravelly sand.5. According to the loading experiment result, the settlement rules are analyzed, and the quality standard of relative density for the filling sand is obtained.6. With the comparison of model test results and on-site test results, the test technique of sand relative density is obtained for the test and evaluation of bridge-culvert back-filling based on light penetration.