Study Of Soil Compaction Effect By Blast Loading

With the rapid development of the high-rise buildings, underground space and high-speed traffic, the application of the traditional methods of ground treatment, to some extent, is limited. For its shorter duration, lower cost and simpler equipment, the treatment foundation by explosive compaction is more and more valued in geotechnical engineering field and it has wide application in the deep foundation treatment and the underwater foundation treatment far away from cities. However, as the researches on its compaction principles are not in-depth and the explosion parameters are mainly based on engineering experience, theories on the treatment foundation by explosive compaction have lagged behind the engineering practice, with a result that the treatment foundation by explosive compaction has not been widely used in the actual projects.Through the combination of theoretical analysis, numerical simulation, and field test, explosive compaction principles and compaction effects are explored in this thesis. First, based on the relevant knowledge of explosion dynamics and soil plasticity, explosive compaction model is established. In addition, explosive compaction range, compaction degree and the formulas of different blasting-center density distance are derived theoretically. Second, by using software ANSYS/LS-DYNA, the finite element models are built. Then the compaction process of soil blast is numerically simulated and the relative phenomena and influencing laws of the effect of blasting on the blasting cavity dimension, the blasting stress, vibration velocity as well as compaction effect are calculated and analyzed. Finally, seven field tests with decoupling coefficient of 2.000,1.741,1.500,1.333,1.200,1.091 and 1.000 are conducted in the blasting hole whose pore diameter is 48mm and two contrastive analyses are carried out in each group of the test. After blasting, two sections are dug at the angle of 90 degrees to the direction of the center of the blasting hole. Three layers of symmetric sampling points are laid out in each section and the density value is tested. After two groups of data at the angle of 90 degrees in each test are averaged,42 density curves are drawn. Meanwhile, the curves of intensity parameter are also drawn. Therefore, numerical values of compaction range and compaction degree are obtained, and the correctness of theoretical formula and the feasibility of numerical simulation are verified. The main conclusions can be obtained as follows:(1) The soil explosion density formulas given in the thesis are more accurate, in which the theoretical value is close to the experimental value, and the calculation error is less than 6.03%. Therefore, these formulas can be applied to engineering practice so as to build communication between explosive compaction effect and explosive parameters and determine the blast parameters to guide the engineering practice. Meanwhile, the correctness of explosion compaction model is confirmed, that is, the soil after blasting is divided into three regions:explosion cavity area, compaction zones and areas of undisturbed soil. And the application of yield criterion of Mohr-Coulomb is better than that of the former yield criterion of Mises.(2) The blasting phenomena and the variation laws obtained from the numerical simulation and the results of the field test are similar, which confirms the feasibility of the application of numerical analysis to practical engineering. Numerical simulation analysis, to a certain extent, provides a better guiding practice, and more importantly, the variation laws and phenomena hardly observed are gained through its features of low cost and the repeat-able adjustment of parameter to simulate.(3) Soil density and strength parameter values first increase and then decrease to the initial soil parameter with the increase of distance to explosive's center. In the meantime, curve numerical values of the ascending portion are all larger than the initial soil numerical value.(4) When the experimental conditions are identical and the dimensions of the blasting hole are fixed, the compaction range and compaction degree first increase and then decrease with no-coupling coefficient decreasing. When decoupling coefficient is of about 1.200, compaction effect is effective. Meanwhile, the maximum range mounts up to 73 and compaction degree up to about 1.06.(5) When the experimental conditions are identical and the dimensions of the blasting hole are fixed, explosion chamber radius mainly depends on the peak pressure, while the compaction effect is the comprehensive result of peak pressure and action time.(6) The variation laws of each density curve and intensity parameter curve are almost the same, therefore, the compaction effect in silty clay is stable and test repetitiveness is also better.