In this paper, a static load test and a multiparameter statistical analysis method are used to study the value of pile side friction in different soil layers in a loess region. Currently, static load testing is the most commonly used method to determine the bearing capacity of pile foundation. During the test, a vertical load is applied at the top of the pile, the data under each load level are recorded, and a Q-S curve is drawn to obtain the ultimate bearing capacity of a single pile. Reinforcement stress gauges are installed at different sections of the pile body, and then the axial force and the pile side friction of each section are calculated. Few studies have investigated the calculation of pile side friction in different soil layers using the multiparameter statistical analysis method. Obtaining accurate results using this method will provide an important supplement to the calculation of pile side friction and will also be conducive to the development of theoretical calculation of pile side friction. Therefore, taking Wuding Expressway project in loess region as an example, the lateral friction resistance of six test piles is studied through static load testing and multiparameter statistical analysis. The multiparameter statistical analysis method is compared with the static load test results, and the error is controlled within 20%. The results show that the calculation results of multiparameter statistical analysis essentially fulfill engineering requirements.

The shear strength of soil-rock mixtures (S-RM) is an important parameter affecting the stability of engineering. Therefore, taking the S-RM along Shiyan-Tianshui Expressway (G7011) in Qinba Mountains as the research object, large-scale direct shear tests on S-RM with different rock content and water content were conducted in this paper. The test results show that the shear deformation curves of S-RM samples are basically the same, which can be divided into four stages: elastic deformation, initial yield, strain hardening and shear failure stages. The cohesion of S-RM decreases with the increase of rock content, and the internal friction angle increases linearly with the increase of rock content. The cohesion increases first and then decrease with the increase of water content, while the internal friction angle and shear strength decrease with the increase of rock content. Then, according to the large-scale direct shear test results, the fitting equations of shear strength and shear strength index of S-RM were obtained, and the fitting equations were verified by an engineering example. The results show that the fitting equations were suitable for loess and gravel mixtures with similar properties, and have important guiding significance for the calculation of shear strength of similar engineering materials.

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