Study On High Energy Dynamic Replacement Method For Shenzhen Soft Soil Improvement

Since dynamic replacement(DR) method successfully used for the soft ground improvement in 1980s, it's get wide range of applications in coastal areas. However, due to the poor study on its mechanism and the relations between the design parameters and replacement effects, it always depend on designer's experience and field test in practical applications, yet no mature theory and design method for DR already. This paper avoids complex derivation of theoretical analysis, basing on the test, aiming to reveal the law. In view of the soft soil in Shenzhen, a systematic study was conducted from indoor model testing, field tests and simulation analysis on the radical mechanism of dynamic replacement and the relationship between replacement effect and pounding energy, blanket thickness, hammer diameter, have made some great practical significance conclusions in several areas:By 1# model box 31 points of test results, visually shows replacement body forms with the development of the tamping times. Mastering the law of replacement body development, and provides reliable parameters and checking data for a large strain dynamic finite-element program to simulate dynamic replacement process at the same time. Through the numerical simulation of the model testing and inversion of soft soil damage parameters, summing up the variation law of damage parameters and its value ranges, and provides a reliable basis of parameters for subsequent site condition numerical analysis.According to 24 replacement body forms measured from 2# model box, summarizes the relations between replacement body form and parameters of tamping energy, hammer diameter and blanket thickness systematically, and revealing the law of pore pressure changes with development process of replacement body, which help us have a deeper understanding on the mechanism of dynamic replacement method.Through field tests of high energy dynamic replacement, the paper compares the parameters of different drop energy, hammer diameter, blanket thickness on the extent to which the replacement depth, further validating the laws concluded by model tests. Based on the field tests study, a special construction technology of which adjusts energy dynamically by one-blow hammer penetration has advanced, which can get a better replacement effect.A large dynamic finite-element program Abaqus has been used to simulate the field working conditions, the program analyzed the relations of dynamic replacement effect and parameters of pounding energy, blanket thickness, hammer diameter, based on the quantitative relationship between them, a replacement depth prediction formula has been summarizes, and be proved have very good consistent with in-site measurements.On the basis of above results, related design parameters including blanket filling technology and thickness, replacement depth, pounding spacing, feeding patterns, pounding energy, construction sequence and duration of pounding has been analyzed and researched, create favorable conditions for the quantitative design method of dynamic replacement method to deal with the Shenzhen soft soil.