What is the traditional construction scheme of mining tunnel?

With the rapid development of China's economic construction, China's comprehensive national strength has been continuously enhanced. In order to solve the urban traffic problem, many big cities in China are speeding up the planning, design and construction of urban rail transit, such as Beijing, Shanghai, Tianjin, Chongqing, Shenzhen, Guangzhou, Nanjing and Xi 'an. In hilly and mountainous areas with complex geological strata, the bedrock burial fluctuates greatly, so the application of simple shield construction technology and simple mining construction technology has become more and more limited to adapt to the strata, which can not meet the current requirements of subway tunnel construction. In this paper, the combination of shield method and mining method is used flexibly to solve the construction problem of the tunnel between Donggang Road Station and China Merchants East Road Station of Shenzhen Metro Line 2 in soft and hard rock alternating strata. General situation 2. 1. Overview of the project: The mileage of the tunnel between Donggang Road Station and China Merchants East Road Station of Shenzhen Metro Line 2 ranges from Y (z) ck5+435.6 to YCK6+345.95 (ZK6+350.1), and the lengths of the left and right shield tunnels are 887.428m and 909.303m respectively. In the mileage section of this section, the strata in the tunnel crossing section are mainly gravelly clay, gravelly sand layer, muddy clay and fully ~ slightly weathered rock, with large fluctuation, soft upper part and hard lower part, alternating with soft and hard ground water, and the engineering geological conditions are quite complicated, especially in the left line: ZC5+942.8 ~ ZC6+090.3 and the right line: YCK. Even most of the tunnel body is located in weathered rock, and the stratum where the tunnel is located is uneven in hardness and the strength of weathered rock is very high (143.5mpa). Therefore, when shield tunneling enters this stratum, it will cause many unpredictable problems, such as tunnel segment damage, tunnel centerline deviation, shield machine damage and so on, which will bring very unfavorable factors to shield construction. See attached figure 1 for the geological conditions between Donggang Road Station and China Merchants East Road Station. 2.2. Selection of tunnel construction method According to the geological exploration data, the left line of the interval tunnel is ZK5+942.8 ~ ZK6+090.3 (length 147.5m), and the right line is YCK5+904 ~ YCK6+191(length 287m. Weathered rocks have high strength (143.5mpa). Therefore, when shield tunneling enters this stratum, it will cause many unpredictable problems, such as tunnel segment damage, tunnel centerline deviation, shield machine damage and so on, which will bring very unfavorable factors to shield construction. At the same time, there are high-rise buildings such as Aocheng Garden on the surface of this section, so it is impossible to implement open excavation and concealed cover. Therefore, this section of tunnel is constructed by mining method, but both sides of this section are constructed by shield method, and the shield should be able to pass through this section of tunnel smoothly, so the combination of shield method and mining method is considered in this section. So as to reduce or even avoid the construction risk caused by a single construction method. The construction scheme planning adopts the combination of shield method and mining method, that is, the initial support of the tunnel is constructed by mining method first, and then the tunnel is pushed through by shield. At the same time, the shield is used to assemble segments to form the secondary lining of the mine tunnel, and gravel (fine stone) with the particle size less than 10mm is used to fill the gap between the secondary lining and the primary support, and then grouting is used to fill the gap between the gravel. Finally, the mine tunnel is composed of fine stone concrete and segments. Mining method construction technology The mining method tunnel is designed according to the principle of NATM. The tunnel lining and supporting parameters are compared with similar projects mainly according to structural section, surrounding rock grade, hydrogeological conditions, structural stress characteristics and other factors, and are comprehensively determined through calculation, analysis and optimization. The primary support is mainly composed of advanced small conduit, mortar anchor pipe, steel mesh, shotcrete and steel frame, and the secondary lining is formed by assembling segments by shield machine. Fill the pores between the secondary lining and the primary branch pipe with crushed stones (fine stones) with the particle size less than 10mm, and then fill the gaps between the crushed stones with grouting. Finally, the secondary lining of mine tunnel is composed of fine stone concrete and segment. In this section of the tunnel, there are two main differences between detailed exploration geology and preliminary exploration geology, one is the compressive strength index of weathered rock, and the other is the classification of tunnel surrounding rock. According to the preliminary geological report, the saturated uniaxial compressive strength of rock mass is 29.2 ~ 73. 1 MPa, with an average value of 50mpa. The detailed geological survey report shows that the saturated uniaxial compressive strength of rock blocks is 58.8 ~ 143.5 MPa, with an average of 85.6mpa. In the preliminary geological survey report, YCK 5+904 ~ YCK 5+907, the tunnel comprehensive surrounding rock is classified as Class V, YCK 5+907 ~ YCK 5+976, and the tunnel comprehensive surrounding rock is classified as Class IV. YCK5+976 ~ YCK6+191,the comprehensive surrounding rock of the tunnel is classified as YCK5+904 ~ YCK6+191in the geological report of Hunan, and the comprehensive surrounding rock of the tunnel is classified as Grade VI. According to the difference of geology and surrounding rock, this section is divided into single-line A-type lining and single-line B-type lining. The specific structure is shown in Figure 2 and Figure 3. 65438+ After the grouting construction is completed, the grouting conduit is removed, and 600-thick c25 plain concrete is poured at the interface as a temporary retaining wall. When the shield passes through, the plain concrete retaining wall is directly cut. See attached figure 4 for interface reinforcement between underground mining tunnel and shield tunnel. 2. Shield transit (second lining) 2. 1. As the guiding foundation of shield transit, the guide platform is set at the bottom of horseshoe-shaped mining tunnel, which is made of c25 reinforced concrete and has a thickness of150 mm. The elevation of the guide platform axis and cambered surface must be rechecked, and it must be strictly consistent with the tunnel design axis. 2.2. When the guide rail is installed in the shield section, in order to control the axis of the shield conveniently, 43kg/m guide rail is set on the guide platform, and the central angle of the two guide rails is 50o. The elevation of the guide rail surface and the central axes of the two guide rails must meet the requirements that the central axis of the shield is consistent with the design axis during shield propulsion. The guide rail must be installed firmly to meet the stability of shield propulsion. After the installation of the guide rail is completed, it must be re-inspected and measured, and adjusted if necessary. The shield can only be advanced after it is qualified, and the guide rail is firmly fixed. When the shield passes, it can be buttered to reduce friction. See attached figure 5 for the layout of shield transport guide rail in mine+shield construction. 2.3. Temporary support of segments Because there is a gap of about 30cm between segments and the initial lining of mining method construction, in order to prevent segments from sinking after leaving the shield tail and the whole circle is not round, φ50 thread support holes are embedded in the back cover block and standard block during segment fabrication, and φ50×6mm× 1.0m long spiral pipes are used to support the initial lining structure immediately after segments leave the shield tail, and the segments are supported through the embedded holes. After the segment is backfilled and grouted, remove the temporary support and make waterproof seal. See attached figure 6 for temporary support during segment assembly. 2.4. Connection between segments: After the mining method is completed, the segments are assembled in the empty push state, and there is no earth pressure in front of the shield, which easily leads to a large gap between segments, and the waterproof strips attached to the segments cannot reach a certain compression amount, thus failing to achieve the waterproof effect of the tunnel. Every five rings are a group, which are led out from the circumferential bolts by pad joints and welded on the section steel, and each section has four fixed section steel. Immediately after the segment leaves the shield tail, tighten the circumferential and inter-ring bolts, and connect the segment in time through the inter-ring steel connection measures to ensure the segment assembly quality. After the backfilling and grouting of segments are completed, the connecting section steel shall be removed. See attached figure 7 for the connection between shield segments driven by underground mining roadway. 2.5. When the concrete curing strength of the shield transit guide platform reaches 100% and the track axis is qualified, the shield can be pushed through on the track. In order to reduce the friction resistance during shield propulsion, a layer of butter can be coated on the track. When the shield passes through, the segment is assembled by the shield to form the second lining of the mine tunnel, and the assembled segment must be fastened with horizontal and vertical bolts in time. 2.6. Backfilling after segment includes pebble spraying, tail grouting and backfill grouting. When the segment leaves the tail of the shield, small gravel is sprayed to support the segment to prevent the segment from sinking and causing dislocation. The synchronous grouting system of shield machine is used to inject cement mortar, so that the segment is in close contact with the initial support and stratum, and the support effect is improved. According to the inspection results after grouting, the segment is reinforced by grouting from the segment grouting hole. After the segment is assembled, the gap between the segment periphery and the stratum should be backfilled with small gravel in time. The backfill material is small gravel with a particle size of 5 ~ 10 mm, which is used to support the segment and increase the friction of the shield. After the segment is backfilled with small gravel, grouting is carried out through the synchronous grouting system of the shield machine itself. Cement mortar is used for grouting. Controlling the grouting pressure should not only ensure the effective filling of the circumferential joint, but also ensure that the segment structure will not be displaced, deformed and damaged due to grouting, and at the same time prevent mortar from escaping to the front of the shield cutter head. When the segment of shield machine is installed with 10 ring, check the grouting effect in the segment grouting hole every 6 rings. According to the grouting effect inspection, determine whether secondary supplementary grouting is needed. Conclusion (1) The combination of shield method and mining method can reduce or even avoid the construction risk caused by a single method in the complex foundation with both soft and hard application. (2) The shield method+mining method is combined with the construction method, and the mining method is used to construct the initial support of the tunnel, and then the shield is pushed through the interval tunnel, thus avoiding many unpredictable problems such as tunnel segment damage, tunnel centerline deviation and shield machine damage caused by direct shield construction; (3) The combined construction method of shield method and mining method is to support the tunnel at the initial stage by mining method, and then push the shield through the interval tunnel. After the interface is properly handled, the two technologies can be constructed at the same time, which greatly saves the construction period of the whole project; (4) In the downtown area with complex soft and hard rock and soil, the combination of shield method and mining method can avoid occupying a lot of land resources due to open excavation.