Accurate assessment and prediction of the pipe friction resistance are crucial for designing the jacking force, arranging intermediate jacking stations, and setting the sediment removal timing in long-distance rock pipe jacking (PJ) projects. However, the applicability of pipe friction resistance calculation models for PJ in stable and unstable rock strata was not verified in sufficient cases. Besides, research on the assessment of specific skin friction and the primary factors influencing pipe friction resistance in rock strata remains scarce. In this study, field monitoring was conducted to first assess specific skin friction in long-distance deep-buried rock PJ projects under different geological conditions. Then, the applicability of pipe friction resistance calculation models for PJ in stable and unstable rock strata was verified. Finally, the primary factors influencing the friction resistance of pipes in rock strata were analyzed, including formation stability, lubricating mud and sediment, groundwater, pipe misalignment, and tunnel burial depth. The main conclusions are as follows: (1) in unstable strata, specific skin friction (M) can be considered ’very poor’, with the jacking length owing to the primary jacking station (L) being just 0.21–0.48 times the value of M in stable strata. The value of M in stable strata can be considered at least ’very good’ in the initial jacking stage and ’good’ in the normal jacking stage. (2) In stable strata, the pipe-slurry contact model with a pipe-rock contact angle (2θ) of 0° reflects the measured value of M in the early jacking stage. The pipe friction resistance calculation model established by with 2θ = 75° can conservatively estimate the value of M during the normal jacking stage. In unstable strata, the pipe-rock full contact model (2θ = 360°) can predict the value of M with an error of just 8 %. (3) The dynamic change in the pipe-rock contact state is affected by the sediment at the pipe bottom and bentonite mud buoyancy. When the sediment causes 2θ to be smaller than 30°, the pipe floats; otherwise, the pipe sinks. (4) A highly confined groundwater inrush sharply increases the pipe friction resistance within a small jacking range and maintains constant friction resistance. The friction caused by pipe misalignment deviation increases instantaneously and quickly decreases to the normal level after rectification. (5) The influence of tunnel burial depth on the pipe friction resistance can be ignored for deeply buried rock PJ engineering in stable rock strata. The results of this study are expected to be useful for future rock PJ projects because such results are rarely reported.

中文翻译：

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岩石中管道摩阻现场监测评估及影响因素研究


管道摩阻力的准确评估和预测对于长距离岩石顶管工程的顶进力设计、中间顶进站的布置以及排泥时间的设定至关重要。然而，PJ管道摩擦阻力计算模型在稳定和不稳定岩层中的适用性尚未得到足够的案例验证。此外，关于比表摩擦力的评估以及影响管道在岩层中摩擦阻力的主要因素的研究仍然缺乏。在这项研究中，首先进行了现场监测，以评估不同地质条件下长距离深埋岩石 PJ 项目的比表摩擦力。然后验证了PJ管道摩阻力计算模型在稳定和不稳定岩层中的适用性。最后，分析了影响岩层中管道摩擦阻力的主要因素，包括地层稳定性、润滑泥浆和沉积物、地下水、管道错位和隧道埋深等。主要结论如下：（1）在不稳定地层中，比表摩阻力（M）可以认为“非常差”，主顶升站的顶升长度（L）仅为表摩阻值的0.21~0.48倍。 M 在稳定地层中。稳定地层中的M值至少可以认为在顶升初始阶段为“非常好”，在正常顶升阶段为“良好”。 (2) 在稳定地层中，管岩接触角(2θ)为0°的管浆接触模型反映了顶进初期M的实测值。 2θ=75°建立的管道摩阻力计算模型可以保守估计正常顶进阶段的M值。 在不稳定地层中，管岩全接触模型（2θ=360°）可以预测M值，误差仅为8%。 (3)管岩接触状态的动态变化受管底沉积物和膨润土泥浮力的影响。当沉积物导致2θ小于30°时，管道上浮；否则，管道会下沉。 (4)高度承压的地下水突水使管道摩阻在小顶进范围内急剧增加并保持恒定的摩阻。管道不对中偏差引起的摩擦力瞬间增大，矫正后很快减小到正常水平。 (5) 对于稳定岩层的深埋岩PJ工程，隧道埋深对管道摩阻力的影响可以忽略不计。这项研究的结果预计对未来的岩石 PJ 项目有用，因为此类结果很少被报道。