# Experimental Study on Interface Frictional Characteristics between Sand and Steel Pipe Jacking
## 1 Introduction  
Steel pipe jacking construction has high precision, good safety and environmental friendliness, and it is commonly used for underground pipeline laying. The principle of steel pipe jacking is to jack the pipe jacking machine into the stratum through hydraulic jacks. During the tunnelling process, the pipe jacking machine cutterhead cuts the soil in front, and the soil cut down is discharged through the exhaust-earth device. The prefabricated steel pipe is jacked into the stratum section by section under the action of jacking force, so as to complete the pipeline laying [1]. In the process of steel pipe jacking construction, the pipe section in the jacking and the surrounding soil friction generate side friction, and the side friction will lead to insufficient jacking force; at the same time, the side friction resistance will disturb the soil. Serious cases induce soil-body collapsing, causing surface settlement, and the stability of the pipeline and the surrounding buildings and structures produce harm [2]. Therefore, reducing the side friction between the pipe and soil can effectively ensure the safety of construction at present, often through the injection of bentonite slurry between the pipe section and the surrounding strata in order to change the contact mode between the pipe and soil, reducing the sliding friction coefficient between the pipe and soil so as to reduce the side friction [3]. The study of the friction of the steel pipe jacking wall is often referred to as concrete pipe jacking, which is often studied by scholars at home and abroad through indoor model tests, direct shear tests and field data analysis. [PERSON] et al. [4] studied the frictional characteristics of bentonite slurry commonly used in pipe jacking construction in Taiwan by designing model tests, and the test results showed that bentonite slurry can reduce the friction coefficient of the interface of pipe and soil by 23%, and bentonite slurry withplasticizer can reduce the interfacial friction coefficient by 63%. [PERSON] and [PERSON] [5] studied the influence of slurry pressure size on the lubrication effect by changing the injection pressure. The test results showed that under the condition of very low slurry pressure continuous injection of bentonite slurry, the slurry and pipe can also form a lubrication interface with a friction coefficient of about 10% of the friction coefficient of the pipe and soil contact interface. [PERSON] [6] and [PERSON] [7] determined the friction coefficient of the interface between silt, sand and steel pipe jacking, with or without lubricant slurry and under different lubricant slurry formulation conditions. The friction coefficients of the silt, sand and steel plate under the conditions of different ratios of lubricant slurry were compared to obtain the optimal lubricant-slurry matching ratio. [PERSON] et al. [8] carried out a study on the mechanical properties of the coarse-grained soil-concrete interface under different slurry conditions. It was demonstrated that the stress-strain curve was hyperbolic when the bentonite slurry was present on the contact surface. When the mixed soil slurry was present on the contact surface, the stress-strain curve had an obvious strain-softening phase, and the higher the cement content, the higher the peak strength. [PERSON] et al. [9] found that the water content of the slurry changed the shear stress-shear displacement curve of the interface, and when the water content was low, the curve was elastic-plastic in character, while when the water content was high, the curve was rigid-plastic in character. [PERSON] et al. [10] used the DIC technique to study the mechanical properties and mesoscopic failure mechanism of the gravel-sand-concrete interface with different relative densities. [PERSON] et al. [11] used a ring shear apparatus to study the mechanical properties of the clay-concrete interface, with and without slurry lubrication.