Impact Stress And 10000kN.m Series Of Experimental Investigations Of High Energy Level Dynamic Compaction

Dynamic Compaction(DC in short)has become a generally accepted ground improvement technique for its simplicity and cost-effectiveness.And High Energy Level Dynamic Compaction(HELDC in short) has been especially effective for compaction of rubble fills underlying deep mud,miscellaneous fills in mountain area,discard quarry(contains big boulder)and waste material with large effective depth of improvement(EDI in short).HELDC has been used for increase in load supporting capacity and homogeneous,reduction in compressibility of various types of soil deposits and liquefaction potential of sand or silty sand deposits,and densification of collapsible soils.The main subject investigated in this paper is granular materials,i.e.rubble fills in coastal areas and mountain areas,collapsible loess with big thickness,silty and sandy soil in North China and North-east, and muddy soil suitable for DC after pre-treatment and formation of drainage way.The Non-perfect Elastic Collision(NEC in short)DC model in half space is presented,considering the influence of participating soil mass and the interaction of tamper and ground during De.Series solutions of displacement,velocity,acceleration and impact stress are obtained.The NEC model is verified correct through the Boundary Element Method,Laplace-Hankel Mixed Inversion Transform Method and measured values from projects in Nanjing and Shanxi,China.It can be used to analyses the rules of DC,calculated the impact stress and explain the mechanism and phenomena during DC.And it is very simpler than other models.The simplified formulas of peak impact stress and dynamic superimposed stress at z depth are gained from the NEC model under different energy level.The academic concepts of effective depth of improvement and depth of influence are clarified from the point of engineering utility view.It is suggested that the Technical Code For Ground Treatment should define the profound meaning and quantized indexes of EDI in order to avoiding the economic dispute in construction contract.And the principles,methods and judge standards of determining EDI for different soils and aims are put forward. The experimental scheme of 10000kN.m HELDC is brought forward and series energy levels of experiment(3000kN.m,6000kN.m,8000kN.m,10000kN.m)are successfully put in practice on a rubble fills site in coastal area in Huizhou,Guangdong Province,for the first time in China.Mass data acquired from the experiment had gotten detailed analysis and provided the parameters for the design, construction and detection of 10000kN.m DC.As a result of our experiment,we conclude that the coefficient of Menard formula is 0.45 and the EDI for rubble fills and sand is 13～16m,if used in Code table.At the same time,10000kN.m DC is applied in a practical project for compaction of rubble fills underlying weak subjacent bed in Zhuhai,Guangdong Province.Our goal is to provide the parameters for the Code's revision and development.This paper summarized some results of the projects in Zhuhai and Pudong Airport where delayed improvement,that is Time Effect,is measured following dynamic compaction.The results and reasons for the time effect as suggested by other investigators are also presented.From the research work,we realize that the time effect on bearing capacity,especially on compressibility,should be taken into consideration when designing,constructing and detecting the DC subgrade.And the conclusion has provided a possible approach for dynamic evaluation.