## 1 Introduction  
Pipe jacking is widely used in long-distance natural resource transportation projects because of its high construction accuracy, good safety, and little impact on the surrounding environment [1, 2]. During pipe jacking construction, the pipe is continuously pushed into the stratum under the action of jacking force. There is sliding friction between the pipe and the surrounding soil, and the resulting friction resistance of the pipe soil increases with the increase in the jacking distance, which may lead to the problem of insufficient jacking force. However, blindly increasing the jacking force causes structural damage to the working shaft and endangers the construction safety. In addition, the friction resistance has a disturbing effect on the soil, and the increase in the friction resistance results in an enhanced disturbance action on the soil. This may lead to the soil body collapsing, resulting in land subsidence, which seriously endangers the structural stability of surrounding buildings and the safety of pipe jacking construction. Therefore, reducing the friction resistance of pipe soil has become an important link to ensure the smooth construction and construction safety of pipe jacking engineering. After injecting bentonite slurry into the annular space between the pipe and the surrounding soil, the dry sliding friction between the pipe and the surrounding soil can be transformed into wet sliding friction, which can effectively reduce the friction coefficient of pipe soil to reduce the friction resistance of pipe soil and act as a lubricant. In addition, under the action of grouting pressure, the slurry penetrates and diffuses into the stratum, and combines with the surrounding soil to form a relatively dense mud cake. The mud cake transfers the grouting pressure, which exceeds the formation water pressure, to the soil particles, resulting in soil compaction and support of the stratum [3, 4, 5]. Traditional bentonite slurry is generally composed of bentonite, water, soda ash, and CMC according to a certain mass ratio, in which the mass of bentonite usually does not exceed 10% of the mass of water. Many scholars have carried out a series of research work on pipe jacking slurry. [PERSON] (1989) summarized the friction coefficient between the pipe and the soil in pipe jacking engineering under different stratum conditions, and believed that under the condition of grouting, the friction coefficient between the pipe and soil was in the range of 0.1-0.3 [6], [PERSON] and [PERSON] (1992) believed that the ideal drag reduction effect can be achieved only when the slurry is wrapped on the outer pipe wall and the pipe is under the action of buoyancy [7]. [PERSON] et al. (2009) studied the influence of slurry injection on the jacking force and land subsidence during jacking in the silt stratum through a model test. The test showed that traditional thixotropic slurry has a better drag reduction effect and HL compound slurry is better suited to controlling subsidence [8]. [PERSON] et al. (2016) optimized lubrication slurry with PAC-HV (polyanionic cellulose high viscosity) as a treatment agent using the orthogonal test for the curved pipe jacking pipe roof project in the Gongbei tunnel [9]. [PERSON] et al. (2018) found that highly viscous bentonite slurry mixed with polymer is more suitable for the lubrication of long-distance steel jacking by comparing the drag reduction effect and grouting amount with traditional bentonite slurry [10]. [PERSON] et al. (2019) studied the influence of bentonite, caustic soda, sodium carboxymethyl cellulose, and hydrolyzed polyacrylamide on the performance parameters of drag reduction slurry, and proposed a formula for drag reduction slurry that is suitable for large-section rectangular pipe jacking [11]. Laboratory tests are a common method used to study the friction characteristics of the pipe-soil interface and calculate the friction coefficient of the interface. [PERSON] et al.