The jack sets a partition wall in front of the tool pipe of the full cutting tunneling machine to form a sealed cabin. The sealed chamber is often filled with mud, and the Puyi mud keeps its fluidity. The cutting disc rotates and cuts in the mud, and strong stirring is applied. The cut soil and mud water are mixed into a new mud, which is discharged by a mud pump or a hydraulic lift; On the other hand, constantly replenish the pressure water. In the sealed cabin, the mud pressure is balanced with the vertical upward pressure and water pressure on the upper working surface to maintain the stability of the working surface. This method is called mud water pressurization method.
The mud water pressurization method has a wide range of soil ventilation, and can be jacked in multi water, fluid state and liquefied soil. The mechanized pollution degree is relatively high, the space in the pipe is large, and the operation is convenient. The front correction jack can also be used for jacking, overcoming the head-on resistance, relatively extending the jacking distance, safe operation, and no "air collapse" phenomenon. However, when mud water cannot be directly discharged, mud water separation treatment is required, which increases the cost; Poor sealing will lead to water leakage. For example, if the length of the pipe section is short, the water supply and drainage pipes must be disassembled every time the pipe is laid.
The construction cost of Jack freezing method is high. Generally, it is only used when the drainage or grouting method is not effective. When the permeability coefficient of the soil reaches 1-5 M / day, it is not suitable to adopt the Sichuan aging method. If the soil moisture content is less than 1065, the freezing strength is not easy to meet the requirements. On the contrary, the upper layer freezes up during the freezing process. When thawing, the ice melts and the volume shrinks, resulting in ground subsidence. Due to the high cost of the freezing method, it is rarely used in the general pipe jacking construction. Even if it is used, it is only used as a temporary emergency measure.
