Study On Bearing Capacity Of Strength Composite Pile Based On Typical Strata In Guangxi

The stiff body composite pile is a new type of pile with high bearing capacity and low cost in theory.However,there are still a lot of gaps in the research on mechanical properties,construction technology,engineering applicability and economy of rigid composite piles in China,which is almost blank in Guangxi.As a result,there are many unknowns and constraints in the engineering application of the rigid composite pile in Guangxi.Therefore,based on the typical mudstone strata(Nanning)and limestone strata(Guilin)in Guangxi,A series of multi-dimensional pile tests have been designed in marine sedimentary strata(Beihai).According to the three typical strata,three new pile-planting techniques are designed,which are rotary excavation method,down-hole hammer high-pressure rotary injection method and"high-pressure rotary jet mixing method",which take more than one year and are right.The mechanical properties,construction technology,economy,engineering practice and application of the composite pile in typical strata of Guangxi are studied in all directions.The main work and research results of this paper are as follows:1.Based on the analysis of the test and economic ratio of the test-pile ratio,three conclusions are drawn:(1)the strength of the pile and the static-pressure pipe pile,the bearing capacity of the pile and the relative displacement control of the pile-soil are of absolute superiority.And(2)the strength of the core pile is increased in a certain range,and the bearing capacity of the single pile of the composite pile of the stiff body can be improved in a whole.(3)The cost of the single pile of the rotary drilling and pile-in-place pile is 43%higher than that of the rotary-dug bored pile,and the bearing capacity of the cast-in-place pile is 318%higher than that of the rotary-digging pile,and the cost of the bearing capacity of the static-pressure pipe pile is lower than that of the energy-strength body.The height of the pile is 20%.The curing time of rigid composite pile is much shorter than that of bored cast-in-place pile,and its quality is more easily controlled,so it is a kind of pile type with high cost-performance and high bearing capacity.2.In Guilin limestone stratum of Guangxi,two conclusions are drawn:(1)the bearing capacity of precast concrete pipe pile is higher than that of single precast concrete pipe pile after the concrete precast pipe pile is formed with cement-soil pile,and its bearing capacity is higher than that of single concrete precast pipe pile.The control ability of pile-soil relative displacement has been greatly improved.(2)with the increase of pile length and ratio of length to diameter in a certain range,the pile-soil relative displacement control capacity and bearing capacity of the rigid composite pile with fixed pile diameter will be better as the pile length and the ratio of length to diameter increase.3.In limestone areas where karst phenomena such as karst ditch,trough and cave are developed in Guangxi,the technology of pile-planting by high-pressure rotary spraying with down-hole hammer is used to build piles,and the economic comparison is made between them and the pile-forming process by rotary-digging method.The results show that:(1)the pile-forming effect of high-pressure rotary spraying method with down-hole hammer is very good,stable and reliable,which can solve the difficulty of pile-forming inb ad limestone area,and the difficulty of bad pile-forming effect and instability;(2)the cost of hole-forming by high-pressure rotary jet method is 1.75 times as much as that by rotary-digging method,and the high-pressure rotary-jet method is more suitable for formation.4.In the marine sedimentary strata of Guangxi,a destructive static load test was carried out in the marine sedimentary area of complex geological conditions by applying the pile-planting technology of rigid composite pile combined with"high-pressure rotary jet mixing"method to super-high-rise buildings and difficult geological conditions.The experimental data show that this application is successful,which solves the difficult problem of retaining wall and easily collapsing hole when pile types such as bored grouting pile and prefabricated pile pass through thick and dense coarse sand and gravel sand layer.5.In the marine sedimentary strata of Guangxi,the characteristic value of bearing capacity of single pile is much higher than that of 3100KN calculated by the code formula,and the characteristic value of bearing capacity of the former is 1.6 times of that of the latter,and the characteristic value of bearing capacity of the measured single pile is much higher than that of the code formula.This shows that the values of relevant parameters and adjustment coefficients may be too conservative and not conducive to the economy of the project,and should be revised through further tests.6.The comprehensive and full-text analysis shows that the composite stressed structure,soil squeezing effect and cement penetration of the core concrete prefabricated pipe pile in the outer core cement-soil pile are the core factors which are excellent in the bearing performance of the rigid composite pile.