Analysis Of Influence Of Dynamic Compaction Construction Onhuangcaoba Diversion Tunnel

The dynamic compaction method is to use the free fall of the tamper to generate huge slamming energy,so that the shock wave and the large impact stress appear in the soil,which can significantly reduce the compressibility of the soil,improve the strength and uniformity of the soil,improve the liquefaction resistance of sand and eliminate the collapsibility of the collapsible loess,it is one of the most commonly used and most economical deep ground treatment methods in China.In this paper,a large-scale public infrastructure is proposed above the Huangcaoba diversion tunnel section of the Central Yunnan diversion project,and the foundation consolidation treatment is adopted as the background.the large impulsive dynamic stress under the dynamic compaction effect may lead the crack to appear in the diversion tunnel structure,which affects the normal operation.By using the finite element basic analysis method,the two-dimensional and three-dimensional numerical models of the site and the tunnel are established,the vibration velocity,maximum principal stress and minimum principal stress time history curve and stress cloud diagram of the Huangcaoba diversion tunnel under various conditions are discussed in detail.It is judged from the calculation results whether the treatment of dynamic compaction is feasible,and provide a certain reference for the dynamic compaction construction.The main contents and conclusions are as follows:(1)In the simulation analysis,firstly analyze the steady state action of groundwater in the soil and its influence on the soil,and couple the self-heavy stress field with the steady flow field of the groundwater to analyze the shaped area of the soil,the physical and mechanical parameters of the shaped area are reduced in strength,and then the impact analysis of the slamming effect is performed.(2)Under the premise of clicking sniping energy of 3000kN·m and filling the soil layer according to 4m each layer,the vertical influence depth range of three typical sections under dynamic compaction effect is analyzed,combining with geological exploration report,the geological condition of the 3-3 section is relatively poor,so that the deep research and discussion are needed.(3)Analyzing the elevation of different fills for the 3-3 profile,and obtain the safety distance between the tamping point and the tunnel axis in the horizontal direction under the dynamic compaction effect: the safety distance gradually decreases with the increase of the elevation,and the applicable range is getting bigger.On the basis of the above analysis,the vibration effect under the double slamming effect is studied.It is concluded that when the fill height exceeds 1870 meter and the safety distance is satisfied,it is recommended that the distance between the two points is not less than 20 meters.There is no superposition effect in the stress-affected area underneath,and the impact stress effects of the two tamping points have no effect on each other.In addition,the slamming action of 4000kN·m is clicked.When the fill height is set above 1862 meter,the horizontal distance between the tamping point and the tunnel axis should be not less than 100 meters.(4)The division of the stratum in the three-dimensional numerical simulation analysis is slightly different from the two-dimensional model.Combined with the complexity of the modeling and the difficulty of the calculation process,the stratification of the foundation soil of the proposed site is relatively simple,so the analytical results are slightly different,but the overall trend is consistent: when the fill height is 1878 meters,the maximum tensile stress and vibration velocity at the three typical sections of the diversion tunnel under dynamic compaction effect are smaller than the standard requirement,and the dynamic compaction construction can’t cause damage to the tunnel lining structure.(5)In the process of compacting the fill soil layer by mechanical rolling method,the stress change of the soil is very small,so it is recommended to carry out the mechanical rolling method in the area where the dynamic compaction construction is not suitable.