Experimental Study On Improvement Depth Of Dynamic Compaction Considering The Difference Of Hammer Weight And Drop Distance

The depth of improvement is the basic parameter for the design of dynamic compaction(DC)construction,and it is also an important parameter to evaluate the reinforcement efficiency of DC.Nowadays tamping energy or tamping momentum has been adopted to estimate the depth of improvement.However,it suffers obvious drawbacks that the reinforcement efficiency varies with the same tamping energy or tamping momentum.In this paper,the DC model tests were carried out with different combinations of hammer weights and drop distances.This paper explored the differences in crater depth caused by different tamping methods.The impact of the tamper and the internal response of the soil was analyzed.The different roles of tamper weight and drop distance in DC were revealed.Based on the principle of uniqueness,a new index for the reinforcement efficiency of DC was proposed.Furthermore,a new method for estimating the depth of improvement is proposed.The main conclusions are as follows:(1)A set of indoor model test systems has been developed independently,which can simulate the DC process.The system can collect the impact characteristics of the tamper.It also can get information on the dynamic stress and displacement field of the soil.The operation process and steps of the DC model test are described in detail.The applicability of the DC model test system is verified.(2)MHα is used to represent the different combinations of tamper weight M and drop distance H.The DC model tests with different values of a were carried out.The results show that when the tamping energy(α=1.0)and the tamping momentum(α=0.5)are constant,a"heavy tamper with low drop distance" tends to obtain a deeper crater depth than a "light hammer with high drop".When α=0.3,the cater depth obtained by different tamping methods is the same,and the soil type has little effect on the values of α.A new index of MH0.3 is recommended to evaluate the reinforcement efficiency in DC.The value of α in MHα reveals the role of tamper weight and drop distance on reinforcement efficiency.The smaller value of a means the drop distance H plays a minor role in the reinforcement efficiency,and the tamper weight M plays a major role in the reinforcement efficiency.(3)The impact characteristics of the tamper and the internal response law of the soil were analyzed.The results show that the impact of different tampers makes the propagation characteristics of stress waves in the soil different,resulting in different response laws inside the soil,which are reflected in the macroscopic results of different crater depths.(4)The data of the improvement depth in the other literature are summarized.It is found that taking MH0.3 as the calculation index can predict the depth of improvement more accurately.A new method for estimating the depth of improvement is proposed based on the new index.The purpose of this research is to provide a reference for DC engineering practice and provide a basis for further research on the mechanism of DC.