What are the tunnel excavation methods?

1. Full-face excavation method \x0d\ Full-face excavation method is a construction method of blasting once according to the design outline and then laying the lining. \x0d\ Applicable conditions: \ x0d \ (1) Class I ~ IV surrounding rock, when used for Class IV surrounding rock, the surrounding rock should have the conditions to maintain its own stability from full-face excavation to initial support. \x0d\ (2) It has drilling trolley or self-made workbench and efficient shipping machinery and equipment. \x0d\ (3) The length of tunnel or construction section should not be too short, and generally not less than lkm according to experience, otherwise large-scale mechanized construction will be adopted, and its economy will be poor. \x0d\ Construction characteristics of full-face method \x0d\ (1) The excavation section and working space are large and the interference is small; \x0d\ (2) Make full use of machinery and reduce manpower; \x0d\ (3) Less working procedures, which is convenient for construction organization and management and improves working conditions; \x0d\ (4) One-time excavation has little disturbance to surrounding rock, which is beneficial to the stability of surrounding rock. \x0d\x0d\ 2。 Step method construction \ x0d \ Step method is a construction method in which the upper section is excavated first, and the lower section is excavated at the same time after a certain length, and the upper and lower sections go hand in hand \ x0d \ According to the step size, there are three types: long step, short step and ultra-short step. In recent years, due to the design of large-section tunnels, three-step temporary inverted arch method and even multi-step method have appeared. As for what kind of bench construction method is adopted, it should be decided according to the following two conditions: \ x0d \ (1) The time requirement for the initial support to form the closed section, the worse the surrounding rock, the shorter the closed time requirement; \ x0d \ 2 Requirements on the construction site size of mechanical equipment such as excavation, support and slag discharge used in the construction of the upper section. \x0d\ In weak surrounding rock, the former should be given priority to, while the latter should be taken into account to ensure construction safety. When the surrounding rock conditions are good, it is mainly to consider how to give full play to mechanical efficiency and ensure the economy of construction, so only the latter condition is considered. \x0d\ Advantages and disadvantages of bench excavation method: Bench excavation method can have enough working space and considerable construction speed. But there is interference in the up-and-down operation; Although bench excavation increases the number of disturbances to surrounding rock, it is beneficial to the stability of excavation face. Especially after the upper excavation and support, the lower operation is safer, but attention should be paid to the influence of the lower operation on the upper stability. \x0d\ The following points should be paid attention to during excavation steps: \x0d\ (1) Solve the problem of mutual interference between upper and lower sections. Micro steps are basically combined into a working face for synchronous excavation; Long steps are basically turned on, with little interference; However, the short steps are disturbing, so we should pay attention to the operation organization. For short tunnels, the upper section can be connected before the lower section is built. \x0d\ (2) When excavating the lower part, attention should be paid to the stability of the upper part. If the stability of surrounding rock is good, it can be excavated in stages. If the stability of surrounding rock is poor, the circulating footage of lower excavation should be shortened; If the stability is poor, it can be staggered left and right, or the middle groove can be pulled first and then the side wall can be dug. \x0d\ (3) The lower side wall must be sprayed with concrete immediately after excavation, and the initial support shall be done as required. \x0d\ (4) The measurement work must be carried out in time to observe the displacement values of the vault, arch foot and the middle part of the side wall. When the speed increases, the inverted arch should be closed immediately. \ x0d \ x0d \ 3。 Method of retaining core soil in circular excavation \x0d\ (1)0 The footage of circular excavation should be 0.5- 1.0m, and the area of core soil should not be less than 50% of the total cross-section area \ x0d \ (2) After excavation, shotcrete and anchor support should be carried out in time, and steel frame support should be installed. \x0d\ (3) When the geological conditions of surrounding rock are poor and the self-stabilization time is short, advance support shall be carried out according to the design requirements before excavation. \x0d\ (4) The core soil and the lower steps shall be excavated after the step support is completed and the shotcrete reaches 70% of the design strength. \ x0d \ \ x0d \ 4。 The middle wall method (CD method) \x0d\ CD method is a construction method of excavating one side of the tunnel first and then the other side, which is mainly adopted. \x0d\ x0d \ 5。 Crossed partition method (CRD method) \ x0d \ means that in a long-span tunnel with weak surrounding rock, one or two parts on one side of the tunnel are excavated as local partition walls and underground continuous walls, and then one or two parts on the other side of the tunnel are excavated to complete the construction of underground continuous walls; Then excavate the last part of the first construction side, extend the middle partition wall, and finally excavate the remaining part. When the short step method is difficult to ensure the stability of the working face, CRD method with small frame size should be adopted, which is beneficial to control the deformation. \x0d\ CD method is the abbreviation of "central aperture", while CRD law is the abbreviation of "cross aperture". There are both connections and differences between them. Both are used in weak strata and large-section tunnels. The former is the excavation method of separating the lower wall with steel support and shotcrete; The latter is the excavation method of dividing the section up and down, left and right by partition wall and inverted arch when the geological conditions require timely closure of the section. Therefore, the only difference between CRD method and CD method is that every step in the construction process needs temporary inverted arch to close the section. \x0d\ In CRD method or CD method, a key problem is to remove the intermediate wall. Generally speaking, the middle wall can only be removed after the whole section is closed and the displacement of each section is completely stable. \x0d\\x0d\ 6。 Double-side heading method \x0d\ (1) The next excavation can only be carried out after the completion of the side heading excavation. When the geological conditions are poor, temporary steel frame or temporary inverted arch should be set at the bottom of each step according to the design requirements. \x0d\ (2) When excavating various parts, the peripheral contour should be as round as possible. \x0d\ (3) The excavation on the other side shall be carried out after the strength of sprayed concrete on the excavation surface on the first side meets the design requirements. \x0d\ (4) The longitudinal spacing between the left and right tunneling faces should not be less than 15m. \x0d\ (5) When the whole section is formed by excavation, the initial support closure of the whole section shall be completed in time. \x0d\ (6) When pouring the secondary lining, the partition wall and temporary support shall be removed in sections.