Research on Natural Foundation Bearing Capacity and Foundation Pit Settlement of Prefabricated Utility Tunnel

Prefabricated assembled integrated pipe corridor has the significant advantages of fast assembly, controlled quality of factory prefabricated forming, short construction period, energy saving and environmental protection compared with on-site casting. In this paper, a shallow plate load field test was carried out to test the bearing capacity of the natural foundation of the assembled pipe corridor and a numerical simulation analysis of the settlement of the substrate was carried out in combination with the typical local soft soil geological conditions, using the JXSG-6 beam making site in Gu'an South of the Beijing-Xiong Intercity Railway in Xiong’an New Area as the test site. The results of the study show that: during the vertical loading to 320 kPa, the overall displacement settlement of the foundation soil of each experimental group is small, mainly elastic deformation, and the final settlement of each test group is 6.68 mm, 10.89 mm and 5.38 mm respectively, with no cracks and no damage to the foundation soil. According to the calculation of the straight line section of the load settlement data, the average value of the foundation soil bearing capacity deformation modulus is 43.1 MPa, and the average value of the foundation stiffness of the 0.8 m diameter circular bearing plate is 78.2 MPa/m, which can provide a parameter basis for the structural design of the pipe corridor and the subsequent superstructure test calculation. However, due to the large stiffness difference between the structure of the pipe gallery and the soil, the soil settlement deformation process and the pipe gallery relative displacement, the shear effect on both sides of the pipe gallery; differential settlement under the influence of the local surface of the pipe gallery may occur tensile damage, the maximum displacement concentrated on both sides of the pit reached 0.6 mm, in the acceptable range. Therefore, the lower base of the pipe corridor has good bearing capacity and can meet the construction requirements of the installation stage of the integrated pipe corridor sections.

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