Study On Bearing Behavior Of Composite Foundation With Nail Shaped Cement Mixing Pile In Deep Soft Soil Foundation

Soft soil foundation treatment technology has always been a hot issue in geotechnical engineering.As a new technology based on cement mixing stake,nail shape cement mixing stake has been widely used in China's coastal areas in recent years.Combining with Ningbo rail transportation foundation processing project,the paper conducted indoor cement soil mixing proportion test and nail shape cement mixing stake drilling core test and static load test of single stake and single stake composite foundation to the nail shape cement mixing stake;The bearing characters of the composite foundation of nail shape cement mixing stake were studied by the reactive sensor set on the stake.The main research contents include:(1)The relationship between cement soil strength and the amount of cement and age of silt in Ningbo area was obtained through indoor test of cement soil.Through orthogonal experimental,the optimum ratio of cement soil composite admixture was3.0% of calcium chloride,3.0% of aluminum hydroxide and 0.03% of DEIPA.(2)The law of the strength of the nail pile gradually attenuated with the change of depth,and the strength of the pile had quite high level of discreteness through the field coring test.The strength of the cement soil in the clay was high,and the cement soil strength in the silt was low.Compared with the indoor test results,the reduction coefficient of pile strength was 0.21~0.63s(3)Through the sensor embedded in the pile,the transmission law of pile load of single pile and single pile composite foundation to the nail shape cement mixing pile under load is obtained.With the increase of depth,the axial force of the nail shape cement soil mixing single pile and the composite foundation were attenuated gradually,and the axial force attenuation of the head was faster than that of the lower part of the pile.The axial force diffusion of the pile was mainly concentrated on the expansion head.The lateral friction resistance of pile was mainly located in the expansion head part of the pile body.Under the variable section,the friction resistance of pile side decreased rapidly with the increase of depth.(4)It analyzed soil reduction factor ? between piles research according to the bearing capacity of single pile and single pile composite foundation bearing capacity of the field test results.The value range of the soil bearing capacity reduction factor of the pile composite foundation of the test section is 0.7~0.85,which is lower than that in thestandard of Jiangsu.(5)FLAC3D finite element software was used to study the stress characteristics of bearing capacity of the composite foundation of nail shape cement mixing pile.Considering the influence of bearing and sinking of single pile composite foundation by different expansion head height/pile length(H/L),the ratio of up and low pile(D/d),Pile length L and pile spacing S.the optimum design is 6 m of expansion head height,1.0 m in diameter of expanding head,15 m of pile length,1.8 m of pile distance.It also studied the failure mode of composite foundation of nail shape cement soil mixing single pile under different working conditions.The research results of this paper have important theoretical guiding significance and engineering application value for the nail shape cement soil mixing pile in deep soft soil area.