This paper studies the influence law of existing tunnels on the construction of intersecting new tunnels in a shallow slope burial context through 3D numerical analysis. The emphasis is on exploring the effect of new tunnels constructed in 54 conditions, including three ratios of overburden to tunnel height (C/H), three ratios of slope distance to tunnel span (D/W), two backfilling conditions of the existing tunnel (“hty” and “htn” conditions), and three magnitudes of surface loads (10 kPa, 20 kPa, and 30 kPa), on the deformation of lateral slopes and the overlying road. As the results show, the rigidly separated area between the existing and newly built tunnels in parallel to the excavation direction was precisely the sensitive area affected by the existing tunnel backfilling condition. The road settlement simulations perpendicular to the excavation direction revealed that various C/H and D/W ratio combinations controlled the shape and size differences of the settlement trough curve. This was because the C/H ratio primarily controlled the effective span and height transition of the newly built tunnel, whereas the D/W ratio mainly controlled the intersection position of the tunnels. Next, model A-A (“hty” condition) was identified as the only feasible construction model among all models in accordance with the engineering safety control criteria. Lastly, comparison of monitoring data with simulations found a slight difference in the distribution pattern between the two. Nevertheless, the final maximum settlement fully satisfied the construction control requirements overall. Aside from proving the correctness of simulation results, the present study also sets an excellent referential example for similar projects.

Line 2 of the Guanjingkou Pipe Jacking Project in Chongqing encountered a pipe sticking problem, whose occurrence was inevitably attributed to the higher total frictional resistance of pipe strings rather than the maximum jacking force. Line 1, which is about to start construction, has basically the same construction environment as Line 2 using the same microshield and pipe string sizes. To avoid repeating the pipe sticking problem of Line 2, the mutual friction characteristics between the surrounding rocks and jacked pipe strings are studied for Line 1 by adopting the same test method under seven complex contact conditions (the presence or various combinations of three substances, i.e., extrapipe string field debris, bentonite slurry, and sand-laden waste slurry, on the jacked pipe string-surrounding rock contact surface are mainly considered). The results show that sufficient bentonite slurry can effectively reduce the frictional resistance, and when the amount of bentonite is insufficient, the average friction coefficient (AFC) of the later contact surface increases by 50%∼70%. The comparison of the monitored versus predicted jacking forces indicates that the value predicted by the test is slightly higher than the monitored force and the variation trends of the two match well, thus proving the correctness of the test results. It is possible to continue predicting the variation trends of the jacking force and frictional resistance based on the contact situation outside the pipe string wall, which greatly lowers the probability of re-encountering pipe sticking. The test results not only explain the important role of bentonite slurry in reducing the pipe string wall frictional resistance but also suggest that an increase in the pipe string wall frictional resistance resulting from the complex contact inflow into the overexcavation gap is the root cause of pipe sticking; moreover, the number of jacked pipe strings matching a single IJS is the second cause of pipe string sticking. The methodology of this study can provide a reference for other studies concerning the jacking force of long-distance rock microshield tunnelling.