Research And Analysis Of Dynamic Compaction And Reinforcement Treatment Of Deep And Thick Backfilled Soil

In recent years,with the rapid development of the country,the construction land in the city has been declining,and land use conflicts have increased sharply.The foundations formed by "opening mountains and filling valleys" and "reclamation of seas" have been gradually selected,but such backfilled foundations often cannot meet deformation.It is necessary to deal with the construction requirements such as,stability and bearing capacity.The dynamic compaction method is simple,economical and environmentally friendly.The treatment of this kind of backfill has huge advantages,so it is widely used.However,the mechanism of dynamic compaction and the complexity of the backfill soil quality have caused the theory of dynamic compaction to lag far behind engineering practice.Therefore,it is necessary to conduct related research on backfill soil,especially deep backfill cohesive soil foundation,to provide a certain theoretical basis for subsequent similar projects and experience.Based on a project in Yunnan,this paper analyzes the mechanism of dynamic compaction and the factors that affect the effect of dynamic compaction combined with previous dynamic compaction data and literature,and draws the following conclusions:(1)When the rammer rammed the soil,uplift occurred around the ram pit,and the soil also showed a large amount of settlement.The single-click settlement showed an "S"-shaped change with the contact time during ramming.The surface soil(within 2m)has the best reinforcement effect,and the soil settlement varies linearly with the depth;in the range of 2m-4m,the soil settlement decreases slowly with the increase of depth,and after 4m,the soil settlement that amount decreases rapidly as the depth increases.After ramming,the compressive modulus of the soil increased from 5.3 MPa to more than 20 MPa.(2)When the ramming energy is constant,as the number of ramming increases,the amount of soil settlement also increases,but the increase slows down.The best number of ramming in this paper is the 7th stroke;and the weight is low(30t*20m)under the distance of the ramming combination reinforcement effect is better,the use of small diameter(1.4m)rammer to strengthen the depth of the soil is greater,suitable for shallow backfilling.(3)The other parameters are the same,only the ramming energy level is changed,and it is found that the soil settlement and stress increase with the increase of ramming energy.When the ramming energy level increases from 4000 k N·m to 6000 k N·m,the vertical displacement of the soil increases by 44.2%,and when the ramming energy increases from 6000 k N·m to 8000 k N·m,the increase in ramming settlement is only 8.1 %,indicating that there is the best ramming energy in the project.The study found that under the energy level of 6000 k N·m,the effective reinforcement depth of dynamic compaction is in the range of 8m-9m,and the plastic deformation of the soil resembles a "pear shape";when the ramming energy increases from6000 k N·m to 8000 k N·m,the soil The effective reinforcement depth has not increased much,and it is also in the range of 8m-9m.(4)Change the internal friction angle,cohesive force,compression modulus and Poisson’s ratio of the soil in turn.It is found that the internal friction angle has the greatest influence on the deformation of the soil,followed by cohesion,while the compression modulus and Poisson’s ratio have Its impact is small.The larger the internal friction angle,cohesion,compression modulus and Poisson’s ratio,the smaller the soil deformation.When the cohesive force increased from 15 k Pa to 45 k Pa,the single settlement of the soil mass decreased by 56%.