The Analysis Of Dynamic Characteristics Of Backfilled Foundation After Dynamic Compaction With Different Diametral Hammer

Dynamic compaction is one of the economical and efficient methods of foundation treatment in the current. Dynamic compaction can improve the strength of the foundation soil, ameliorate liquefaction of sandy soil, eliminate the collapsibility of the Collapsible loess and reduce the compressibility of soil and so on. Dynamic compaction method has the advantages of simple construction, fast rate of reinforcement, good reinforcement effect and low cost, and it has been widely used in large area backfilled foundation treatment engineering, but theory is far behind the engineering practice for the research of dynamic characteristics of backfilled foundation after dynamic compaction with different diametral hammer. This thesis was based on numerical analysis method of soil elastoplastic large deformation theory, by using explicit dynamic finite element analysis software ANSYS/LS-DYNA, three-dimensional finite element models for dynamic compaction of backfilled foundation with different diametral (1.2m,2.0m,2.5m) hammer were established, and variety laws of stress, displacement, surface vibration velocity and acceleration in the process of dynamic compaction with different diametral hammer were analyzed. The main conclusions of this paper:(1) Different diametral hammers tamping under the same energy level, hammer’s diameter has great influence on soil dynamic stress and surface vibration near the tamping point, and the soil dynamic stress and ground vibration increase with hammer’s diameter increasing. Hammer’s diameter has relatively small influence on dynamic stress and surface vibration of soil away from the tamping point. So in the precondition of satisfying the reinforcement depth, dynamic compaction ground where near the buildings should use small diametral hammer.(2) Reinforcement effect of shallow soil with small diametral hammer is better than it with large diametral hammer, and small diameter can be well focused shock force and it is conducive to the deformation of shallow soil layer, but the horizontal reinforcement range is small, it needs smaller distance between compaction points to achieve the requirement of reinforcement.(3) Dynamic compaction under the different energy level, dynamic stress and surface vibration of soil near the tamping point increase with energy level increasing, and energy level has relatively small influence on dynamic stress and surface vibration of soil away from the tamping point.(4) With the increase of number of dynamic compaction, dynamic stress increases at the same depth, and the strengthening depth increases gradually, and the surface vibration increases. In practice, we should pay attention to several continuous tamping reinforcing effects on the ground surface vibration.(5) The vibration isolation effect of surface behind the vibration-isolation trench is significant. To make the vibration isolation effect of vibration-isolation trench best, we should increase the distance between tamping point and the vibration-isolation trench as far as possible and reduce the distance between protected objects and the vibration-isolation trench. To a certain extent, isolation trench is deeper, and reduced vibration effect is better, but the existence of a critical depth, vibration isolation effect will not increase significantly when the vibration-isolation trench depth than this value. Isolation trench width on the vibration isolation effect is not obvious.