Study On Geometric Characteristics Of Slurry Diffusion And Interfacial Shear Characteristics Of Bored Piles

Bored pile is widely used in construction engineering,highway engineering,railway engineering and marine engineering.Due to the diversity of foundation soil and the complexity of construction technology and process,there are phenomena such as and slurry diffusion after pile pouring,so the shape of pile-soil interface is complex.At present,the design method of pile bearing capacity has not accurately and quantitatively considered the influence of pile-soil interface,so as to affect the safety and economy of pile.In order to explore the diffusion effect of concrete slurry in sand and the shear strength characteristics of pile-soil interface after diffusion,this paper will carry out the slurry diffusion test between concrete and sand,and the direct shear test of different geometric characteristics of concrete-sand interface.The main research work and results are as follows:(1)By comparing and analyzing the applicability of existing surface roughness evaluation methods,the roughness evaluation method of concealed pile-soil contact surface was studied.A roughness evaluation method of interface based on the principle of sand filling method and CT scanning technology was proposed.In this method,the average depth of concave convex of pile-soil interface was used to reflect the geometric characteristics of slurry diffusion.(2)The diffusion characteristics of concrete slurry under different sand compactness and concrete water-cement ratio were studied by CT scanning technology.The results show that the relative density of sand has a great influence on the diffusion degree of concrete slurry.With the increase of relative density of sand,the average depth of slurry diffusion decreases significantly.With the increase of water-cement ratio,the average depth of slurry diffusion also increases.(3)The concrete sample with the same average depth and different geometric features were designed and manufactured,and the shear tests of concrete-sand interface with different geometric features were carried out.to analyze the interface shear properties which were influenced by normal stress,sand compactness and geometric features of interface.The results indicate that the shear stress and shear displacement curve of the interface show different shear properties,such as ideal elastoplasticity,strain softening,strain hardening and so on.(4)By conducting the shear test of concrete-sand interface with the same average depth(the same roughness)and different geometric features,the influence of geometric features on the shear strength of contact surface was analyzed.The results indicate that the shear strength of concrete sand interface is obviously different.For the triangular shape,the interfacial shear strength increases with the increase of the slope in the shear direction(the single groove depth remains unchanged);For the groove shape,the interfacial shear strength increases with the increase of the number of grooves(the average depth remains unchanged,and the single groove depth decreases);When the shape of single groove is axisymmetric and the depth is the same,the interfacial shear strength of rectangular and trapezoidal grooves is the lowest.(5)By conducting the shear tests of concrete-sand interface under the conditions of pure sand,undisturbed(concrete test block obtained from intrusion test),with different geometric characteristics interface and smooth interface,the variation law of shear strength and the shear mechanism of interface were analyzed.The results indicate that the shear strength of pure sand is the largest and that of smooth interface is the smallest.The shear strength of undisturbed interface is between the shear strength of triangular interface with sawtooth angle of 90° and 70°,and also between the shear strength of the semicircular interface with 13 and 9 grooves.(6)By carrying out interface shear tests with different sand particle size range and different groove depth(the same roughness),the influence of particle size range and groove depth on the shear strength of concrete-sand interface were analyzed,and the shear mechanism of contact surface was studied.The results indicate that the larger the particle size,the shallower the depth of a single groove,and the greater the shear strength of the interface.Because the larger the sand particle size range,the greater the mechanical bite force between the sand particles in the groove and the upper sand particles,the greater the shear resistance between the sand particles and the edge of the groove,and the shear process is mainly shear dislocation,slope climbing and rolling.With the decrease of particle size and the increase of single groove depth,the contact surface is dominated by sliding friction and shear dislocation between sand and contact surface,and the mechanical bite force is relatively small.In short,this paper studied the diffusion effect of bored pile slurry in sandy soil foundation through indoor model test.The diffusion range and the geometric characteristics of cement slurry and sand mixture were described quantitatively.Based on this research result,the concrete sample interface was generalized to stereotyped interface shape,and the corresponding strength difference was studied by shear test.The research results have reference value for the design and construction of bored pile.