| The design of impact energy in the static-dynamic drainage consolidation method(SDDCM) are influenced by many complicated factors, so far there are no unified understanding in its theoretical calculation or no codes and standards. Engineering analogy method and empirical method are often utilized in the design; Trial ramming is necessary to verify the design parameters before the formal construction. When the SDDCM is applied for ultra-soft soil foundation consolidation, a too small impact energy cannot meet the reinforced depth request, a over large energy may cause a hammer buried or or "rubber soil" phenomenon, so the choice of the impact energy relates to the success or failure of foundation treatment. Therefore, the determination of impact energy is a burning research subject of important research significance.According to the basic principle of the SDDCM, the theoretical model of impact energy in which several affecting factors are taken consideration is built, the results of in-situ test of the soft soil foundation treatment engineering in refined oil reservoir of Taishan petrochemical in Guangzhou, Nansha are applied to Verify the correctness of the model. To explore the microscopic mechanism of reinforcing soft soil using impact energy and to design the best impact energy scientifically, and to seek the corresponding load level and rate, the nuclear magnetic resonance(NMR) method is utilized in this paper to solve the following two questions:The first is water phase variation of the ultra-soft soil under different load level and rate; The second is pore size distribution and its change of ultra-soft soil under different impact load level and rate, to explore the internal structure and its distribution law under the corresponding conditions.Research results in this paper include the following aspects:1. The best impact energy in the aspect of macroscopic mechanical(1) The max allowable stress ratio of soft soil R is defined, and the main parameters in the model is discussed, finally get calculation formula of the best impact energy: (2) Field measured data is used to calculated the max allowable stress ratio, and R is among2-3.The value increases with tamping times and impact energy, which means that the maximal allowable pressure at the top of the soft soil is improved, which can be explained on microscopic by gradual adjustment of the soft soil microstructure and the full use of the micro pore and micro cracks in the drainage consolidation of soft soil.2. The best impact energy from the microscopic view:(3) Under the usual engineering load, dynamic triaxial test with low load level and rate (100kPa and1.6MPa/s respectively, and below), the bound water in the ultra-soft soil cannot be converted to free water; Under the load conditions used in the static and dynamic drainage consolidation method, high-speed impact load (load level of3787kPa per blow, load rate of631.2MPa/s), bound water can be converted into free water; and the greater total impact energy (increase with impact hits) was more easily to produce free water;(4) Pore radius of muck from the Pearl River Delta area is mainly in the range1～20μm. When the impact load reaches a certain impact level, the proportion of both max-pore and small-pore will decrease, thus the pore size tends to be more uniform. Under a relatively low load(680kPa), load rate is the key factors to determine the proportion of relative large pore:decrease in rate will make a bigger proportion, while a bigger rate makes a smaller proportion. The threshold value is between>0.8MPa/s and≤1.6MPa/s;(5) Under a certain impact load level and rate, the large-pore and max-pore in muck decreased obviously with the increase in impact hits, and/or the increase of impact energy; however, this effect is reduced with a shorter interval time and more impact hits. In other words, for an efficient decrease in large-pore, there existed a suitable value of impact hits for muck. |
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