2. Supporting mechanism of bolt and anchor combined support The difficulty of composite roof support lies in the existence of geological weak surface of soft interlayer (coal line, mudstone), resulting in low bonding force between upper and lower layers, ordinary anchor It is impossible to include the package in the anchorage range, and the bearing capacity is limited, and the loose expansion of the weak interlayer itself will also form a large vertical load on the lower rock layer, which may easily cause the roof to collapse. In particular, the 3401W transport lane is located below the 3202W surface being mined. Under the dual effects of ground pressure and mining pressure, certain reinforcement measures must be taken to ensure construction safety. The application of "anchor net + anchor cable" combined support can overcome the shortcomings of simple anchor (anchor net) support. The â€œanchor netâ€ can exert the effect of extrusion reinforcement, which promotes the formation of rock within the anchorage range to withstand a certain load of the overall structure, maintains the roof in the range of the length of the bolt, maintains the integrity, and prevents the looseness of the upper surrounding rock to some extent. With deformation. Taking into account the characteristics of medium stable roof, using W metal strip with diamond mesh to maintain the roof. Anchor anchored in the upper portion of the roof rock stable, suspension play its role, the layer of roof collapse within the scope of the potential on an intact solid suspended roof rock, borne by the anchor The vertical load on the rock formation within the fall range prevents the roof rock from separating.
3, support parameter design 3.1 anchor belt network support parameters design The role of the anchor belt network is to maintain the integrity of the roof of the roadway and the two coal walls. Therefore, according to the reinforcement arch principle and the loose circle theory, the calculation of each parameter is carried out. The final design of the anchor belt net support parameters is: the top anchor rod is 1.8m long, Ð¤18 full threaded anchor rod, the spacing is 0.85m, the row spacing is 0.7m. 2m, using 1 Z2835 resin coil: The steel strip is BHWZ50â€”800Ã—2Ã—3200. 3.2 Anchor cable parameter design According to the actual situation of the top and bottom of the coal seam, in order to ensure sufficient suspension capacity of the anchor cable, the anchor cable is anchored in the old roof of the sandstone, and the anchoring length of the anchor cable in the old roof is 1.0m, so the anchor will be anchored. The total length of the cable is set to 6m. The self-heavy load of the direct top rock stratum in the area of â€‹â€‹potential overburden of the overlying strata is: W=Sâ€¢Î³â€¢D in the row Sâ€”the area of â€‹â€‹the potential damage range, hâ€²â€”potentially high, hâ€²=1. 5B=4. 8ç±³ã€‚ B, the width of the roadway, taking 3. 2m; Î³-rock mass density, take 24kN / m3; D row of a cable, the row of anchors, according to the 2 rows of anchors, 1 anchor cable design, take 1. 4m. Therefore, the suspension capacity P of W= 241.9kN anchor cable is: P=P1>W P1 is the breaking load of the anchor cable, P1=260kN 3401 West transportation lane anchor rod + anchor cable support overall arrangement see Figure 2.
4. Research on mine rock pressure observation In order to verify the reliability of bolting and anchor cable combined support for the maintenance of composite roof coal roadway, comprehensive mine pressure observations such as surface displacement and roof separation are carried out on the roadway. It provides a basis for adjusting and optimizing the supporting parameters. 4.1 Mine pressure observation results (1) Surface displacement observation. See Figure 3 for the relationship between the deformation of the top plate and the two sets of II, III and IV stations.
(2) The anchor is subjected to force observation. See Figure 4 for the force versus time curve for the top and gang bolts.
(3) The cable is subjected to force observation. The relationship between the force and time of the anchor cable is shown in Fig. 5.
4.2 Analysis of observation results (1) Bolt support effect The result of surface displacement observation is that the II station is affected by mining, so the deformation is large, in which the roof subsides 175mm, the two gangs move closer to 218mm and 102mm, in the roadway After about 15 days of excavation, it basically stabilized, indicating that the support is basically reasonable. From the observation of the force of the bolt, it has played an active role. The artificial setting improves the overall performance of the surrounding rock and promotes the surrounding rock. The composite beam and the reinforcement arch are formed to withstand the ground pressure by the stability of the surrounding rock itself. This is a proactive approach and the fundamental difference between it and the shed. It is also better than the shed in terms of effect. With the advancement of the mining face, the No. I station in the shed section was observed. Although the shed was added on the basis of the 800mm shed, the shed distance reached 400mm, but the sinking amount of the roof still reached 372mm. The gang has moved nearly 459mm, and some of the sheds have been slammed down. The sill beam is bent, the shacks are deformed and smashed out, and the gangs are intensified. Bolt support is used, even when subjected to mining pressure and lateral bearing pressure. Under the combined action, the top and the gang still have higher strength to resist external forces and maintain self-stability. When affected by mining, the top anchor rods withstand a force of about 100kN, and the anchor bolts withstand forces of about 80kN. The roof separation layer and the coal wall slab are effectively prevented from anchoring the anchor. Through the force-measuring anchor, the radial force and axial force of the bolt are also obtained respectively. The axial force provided by the bolt increases the friction between the rock layers of the roof and prevents the layer-to-layer anchoring between the layers. The radial force of the anchor indicates that the anchor itself has a certain anti-shearing ability, which improves the ability of the top plate to maintain stability against external forces. (2) Anchor cable support effect Anchor cable also plays an important role in the entire support system. The anchor cable force of the II station is up to 160kN, which indicates that the anchor cable has assumed the load from the overburden. The double height separation indicator near the anchor cable reads 18mm and has entered the warning range. It is indicated that due to the existence of geological weak surface such as stratification on the coal, the rock layer in the anchorage range of the anchor has been separated from the upper stable rock layer. If the subsurface subsidence cannot be effectively controlled, it must develop into a caving and anchoring cable. The role is to establish a connection between the layered rock formation and the upper old roof, preventing direct roof sinking and maintaining the overall structure of the overlying rock stratum. Before this test, the anchor net support test was carried out in this roadway. With the extension of time and the advancement of the mining face, the amount of roof subsidence is up to 300mm or more, in order to ensure safety and part of it. Even if the roof is shed, the roof will continue to sink. In this test, anchor cable support was adopted as the reinforcement measure. The anchor cables of the III and IV stations were stable and fluctuated only within a small range; the top plate is not too large, and is controlled within the safe range. The anchor cable is used as an active support to balance the load on the rock formation within the potential slump and prevent it from falling, further increasing the bearing capacity of the surrounding rock.
5 The evaluation test is successful. The outstanding advantages of the combined support are reduced in labor intensity and improved efficiency; the roadway maintenance effect is good, the subsequent engineering quantity is reduced; the saving of a large amount of materials, the effect of saving and reducing consumption is remarkable, and the safety and reliability are large.
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