C-C-S-S Composite Structure And Pressure Cast-situ-pile With Spray-Expanded Frustum Mechanism And Application Research

Long spiral multi-function auger drill rigs when drilling holes,high-pressure rotary spray expand the diameter of the end or part of pile’s body.The lifting drill compress and vibrate superfluid concrete.A composite structure of concrete,cement soil,reinforced soil and undisturbed soil is formed at pile end or part of pile’s body.The fixed spray cement slurry of the pile body and the concrete of the cast-in-place pile body are simultaneously pressed into the reinforcement cage,and form a pressure cast-situ-pile with spray-expanded frustum,pile body with wings,pile ends or part of the pile body with truncated cone,to greatly improves the bearing capacity of single pile.In this paper,two groups of field tests are carried out.By means of numerical simulation and theoretical analysis,the working mechanism of pressure cast-situ-pile with spray-expanded frustum is revealed,and the optimal structure of pile body and the theory of compressive bearing capacity is obtained.The conclusion is as follows:1 The pressure grouting effect of rotary jet reaming and fixed jet wing plate is clarifiedThe lateral resistance of the soil within a certain range on the upper part of the frustum and wing has an enhanced effect.The influence range of the soil around the grouting pile is 7-8m;with no wing plate,the increased lateral resistance can reach 1.5 to 3 times the survey recommended value;with a wing plate,the lateral resistance reaches by about 2 to 4 times;the upper part of the pile body is strenthend compared to the lower soil body.2 The optimal structure of a single pile is obtainedThe optimal structure of pressure cast-situ-pile with spray-expanded frustum is:cone-angle angle 50°-55°;diameter expansion ratio 2-2.75;truncated cone located 1D-2D(D is cone diameter)above the pile end;wing plate sprayed 7m～8m below the pile top(pressure grouting effect range).Compared with the test model,the bearing capacity of the optimal structural model is increased by 19%;if multiple diameter-expanding bodies is set for the pile body,the net spacing of the diameter-expanding bodies should be bigger than 3.75D;in the group pile system,the net distance between the truncated cones of adjacent single piles Should be bigger than 3D.3 the c-c-s-s composite construction size is obtainedUsing the free turbulent jet theory of circular cross-section,on the basis of field tests,the calculation method of the diameter of the truncated cone(concrete layer)in the CCSS composite structure is given.Through the grouting volume and grouting height,the thickness of the cement soil layer is obtained.With the circular hole expansion theory,the range of soil reinforcement is clearly defined,and give the displacement and stress fields of the surrounding soil.4 The recommended formula of compressive bearing capacity of pressure cast-situ-pile with spray-expanded frustumAccording to the pile foundation building code,and compared with the field test results,revises the theory of the compressive bearing capacity of the single pile of the pressure cast-situ-pile with spray-expanded frustum;through test case verification,the accuracy is 20%higher than that of the existing code calculation method5 The calculation method of the settlement of the pressure grouting pile with jet expanding truncated cone is clarifiedUsing load transfer method,calculates the Q-S curve of power function and hyperbolic displacement modes of cone platform,proves that the power function displacement mode is closer to the relationship between bearing capacity and displacement of test foundation pile,and gives a practical settlement calculation method for the design of pressure cast-situ-pile with spray-expanded frustum.