When constructing pipe roof drilling rigs in soft soil layers, surface settlement is a particularly prominent issue, primarily due to the high compressibility, low strength, and high water content of soft soil. Soft soil is prone to creep under the disturbance of pipe roof drilling rig construction, leading to loosening of the soil structure and subsequent ground settlement. To effectively control this problem, a comprehensive approach is needed, encompassing multiple dimensions such as construction parameter control, soil improvement, real-time monitoring, grouting reinforcement, equipment selection, deviation correction strategies, and auxiliary measures.
Precise control of construction parameters is paramount. The jacking speed of the pipe roof drilling rig needs to be dynamically adjusted according to the characteristics of the soft soil, avoiding excessive speed leading to excessive soil disturbance, or excessive slowness causing cumulative soil deformation. Simultaneously, the slurry pressure or soil chamber pressure must be balanced with the water and soil pressure at the excavation face to prevent pressure imbalance from causing soil instability. For example, in soft soil layers, the slurry pressure can be appropriately increased to enhance the support of the soil and reduce the risk of settlement.
Soil improvement technology is key to enhancing the stability of soft soil. Injecting modifiers such as bentonite slurry into the soil can improve its physical and mechanical properties, increasing its resistance to deformation. The modified soil particles are more tightly connected, effectively resisting construction disturbance and reducing settlement. Furthermore, the modifier can reduce friction between the soil and the pipe wall, lowering jacking resistance and indirectly reducing soil disturbance.
Real-time monitoring and information-based construction are the "eyes" of settlement control. Using equipment such as levels and total stations, ground settlement data can be acquired in real time. Once settlement exceeds the warning value, construction parameters can be adjusted immediately or emergency measures can be taken. For example, if monitoring data shows significant settlement in a certain area, the slurry pressure or jacking speed can be quickly adjusted to prevent further settlement.
Grouting reinforcement is an effective means of filling the voids between the pipe section and the soil, enhancing soil stability. Simultaneous grouting technology allows for the simultaneous injection of cement grout or chemical grout during jacking, filling the annular gap around the pipe section and reducing ground loss. Grouting pressure needs to be precisely set according to the stratum depth and soil conditions to ensure effective grout filling without excessive soil compression. After pipe jacking is completed, secondary grouting is required to fill the gap between the pipe wall and the soil in a timely manner to further consolidate the settlement control effect.
The selection of the pipe roof drilling rig must fully consider the characteristics of soft soil. In soft soil strata, earth pressure balance or slurry balance pipe jacking machines are recommended. These types of machines can better control the stability of the excavation face and reduce soil disturbance. At the same time, the cutter design must be adapted to the cutting requirements of soft soil to avoid clay adhering to the cutter, which could lead to reduced cutting efficiency or equipment damage.
Correction operations must follow the principle of "frequent measurement and correction, small-angle correction." When the pipe roof drilling rig is advancing underground, deviations are prone to occur due to uneven geological conditions or improper operation. Once a deviation is detected, it should be adjusted immediately using hydraulic correction cylinders. However, the single correction angle should not be too large to avoid excessive correction causing pipe section twisting or damage, which could lead to wider soil disturbance and settlement. Auxiliary measures such as reinforcing the working and receiving shafts and protecting the surrounding environment are equally important. The working and receiving shafts must withstand the reaction force of the pipe jacking machine and construction loads; their structural strength and stability must meet requirements to prevent ground subsidence caused by shaft settlement. For existing buildings and underground pipelines within the construction impact area, targeted protective measures must be taken based on their importance and sensitivity, such as grouting reinforcement within the pipe gallery and installing protective sleeves, to reduce the impact of construction.
