锚杆挡土墙概述.doc

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Bolt is a new type of tension member, one end of which is connected with engineering structures, the other end is anchored in the stable formation, to inherit the earth pressure exerted on the structure of the thrust, thus the use of anchor bolt and formation to maintain structureAnchor retaining wall is a kind of retaining structure formed by bolt technique. Bolt is a new type of tension member, one end of which is connected with engineering structures, the other end is anchored in the stable formation, to inherit the earth pressure exerted on the structure of the thrust, thus the use of anchor bolt and formation to maintain the stability of structures.Before 50s, bolt technology was only a temporary measure of construction process. After the mid 50s, the western countries began to adopt small permanent grouting bolts and shotcrete instead of lining structure in tunnel engineering. The anchor retaining wall in China began in the Chengdu Kunming railway line in 1966, and then in many railway line construction, the use effect is good. Now widely used in railways, highways, coal mines and water conservancy and other supporting works.The anchor retaining wall can be divided into column, plate retaining wall and wallboard retaining wall according to the structure of the wall, as shown in figure 10-35. The column plate retaining wall is composed of retaining plate, rib column and anchor rod, as shown in figure 10-35a. The rib column is bearing retaining plate, bolt is a support rib column, the wall of the lateral earth pressure acting on the retaining plate, and the retaining plate is transferred to the ribs, the ribs to anchor, balance by anchoring force between the anchor and the surrounding strata that anchors. In order to maintain the body wall, and the stability of the soil behind the wall. The panel type anchor retaining wall consists of a wall panel and a bolt, as shown in figure 10-40b. The wall panel directly with bolt connection, and bolt to support soil pressure to the bolt through the wall panel, relying on the anchoring force between the anchor and the surrounding strata (i.e. pullout resistance) earth pressure, in order to maintain the balance and stability of retaining wall. At present, multipurpose column plate anchor retaining wall.(a) column plate B) panel typeFigure 10-40 types of anchor retaining wallsThe anchor retaining wall can be designed as single or multistage according to the topography, and the height of each wall shall be no more than 8 m. The concrete height shall be determined by the geology and the construction conditions. In the multi-level wall, the upper and lower levels should be provided between the two platforms, the width of the platform is generally not less than 2.0m. The platform shall be made of C15 concrete with a thickness of not less than 0.15 m, and shall be inclined to the slope outside the wall, with a slope of 2%. The total height of multi story wall shall not be greater than 18m.The characteristics of retaining bolt is: (1) the light structure, the structure of light retaining wall, compared with gravity retaining wall, can save a lot of masonry and save the project investment; (2) to the mechanization and construction of the retaining wall, can improve labor productivity; (3) without excavation a large number of foundation pit, can overcome the bad foundation excavation difficulties for construction safety. But the anchor retaining wall has some shortcomings, so that the design and construction are limited, such as higher construction process requirements,There must be drilling, grouting and other supporting special machinery and equipment, and the use of certain steel.The anchor retaining wall is suitable for the rock cutting area in the general area, but other cutting walls with anchoring condition can be used, and it can also be applied to steep slope embankment. In the use of bad geological areas, we must take corresponding measures.Another type of retaining bolt for vertical prestressed anchor retaining wall, it is the use of anchor technology, namely vertical anchor rock foundation, and prestressed, the vertical prestressed anchor part of masonry section instead of gravity retaining wall, reduce the number of masonry retaining wall and increase its stability. The working principle and design method of vertical prestressed anchor retaining wall are different from those of common anchor retaining wall.Two. Calculation of earth pressureBecause of the existence of bolts in the rock (soil) layer behind the wall, which leads to a complex state of force, the calculation of the earth pressure has not been well solved. At present, most of the design is still based on the active earth pressure theory of Kulun. However, the anchor retaining wall is generally rock mass, and the earth pressure generated by the rock mass is not appropriate to use the formula of Kulun. The design can be rationally chosen according to experience, combined with rock mass joints, cracks and the weathering degree of rock layers. Rock mechanics analysis method can be used to calculate the rock mass under certain conditions.For the multi stage retaining wall, the back earth pressure at each stage should be calculated by using the extended back wall method. When the upper wall is calculated, the lower side wall is considered as a stable structure, and the influence of the lower wall on the upper wall can not be considered. When calculating the lower wall, the influence of the upper wall should be considered.Three. Calculation of uplift force of anchorDetermination of bolt pullout force of the anchor rod is the foundation wall design, and its anchor form, formation properties, anchor hole diameter, the effective anchorage length and the construction method of filling materials, etc. Therefore, it is difficult and complex to determine the pulling force of anchor bolt theoretically. So far, there is no ideal method. At present, the commonly used method is based on the previous construction experience, theoretical calculation value and pull-out test results.(1) pulling resistance of friction grouting anchorFriction type grouting with cement mortar is a group of bars anchored in the drilling stratum, reinforced by the tension of the mortar bolt surrounding the gripping force transmitted to the mortar, and then through the friction anchorage section of surrounding strata transfer to the stability of anchorage zone layer, as shown in figure 10-41.Uplift force of 1. rock boltWhen the bolt is anchored in the more complete rock stratum, the frictional resistance of the mortar due to the rock layer and the hole wall is generally greater than the bond stress of the mortar on the anchor bolt. Therefore, the pullout capacity of the anchor rod is generally determined by the holding capacity of the mortar, and the ultimate pullout capacity of the anchor bolt is:(10-48)Type: - Ultimate Uplift Capacity of anchor (kN);D - diameter of anchor (m);Effective anchor length (m) of anchor rod;U - average bond stress (kPa) of mortar to steel bars.Uplift force of 2. soil anchorWhen the anchor rod is anchored in the weathered rock and soil, the frictional resistance of the anchor hole wall to the mortar is generally lower than that of the mortarFig. 10-41 stress state diagram of grouted anchor bolt sectionThe gripping force of the anchor bolt. Therefore, the ultimate uplift capacity of the anchor boltDepending on the maximum frictional resistance produced by the anchorage stratum in the anchorage section, the ultimate pullout capacity of the anchor rod is:(10-49)Type: D - bore diameter of bolt (m);R - anchoring mortar and around hole wall, the average shear strength (kPa). Shear strength not only depends on the formation characteristics, and construction method,As for grouting quality, it is better to do field pull-out test in order to take the tension deformation curve of 6-42 anchor rodDetermination of ultimate uplift force of anchor bolt.In the absence of test conditions, according to the statistical data obtained from the past pullout test (refer to table 10-9), the construction shall be done with pullout test.Table 9 ultimate shear strength of mortar with hole wall 10 - 3.When calculating the anchor length of the bolt, the key is to determine the pulling force of the anchor. Many data and practical experience show that there is considerable discreteness between the calculated and measured values or the measured values under the same conditions. Therefore, the calculated values can only be used as an estimate, and the specific values should be determined after field pull-out tests. In foreign countries, it is clearly stated in the bolt that in order to avoid excessive reliance on the calculation formula of anchor pulling capacity, the allowable uplift force of anchor bolt should be determined according to the results of in-situ pullout test and material strength.Anchor pullout test is used to verify the design scheme, should be carried out in the preliminary design before and after comprehensive operation, and should be in the project site at least three limit root anchor pullout force and tensile deformation (P) - (S) curve (Fig. 10-42). Taking the apparent turning point on the curve, the tensile force corresponding to the A is the ultimate pullout force.The pull-out test results to obtain the ultimate pullout force, it is important to choose a measure of ultimate pullout capacity of the standard, China Academy of Railway Sciences for anchor pullout force proposed three criteria, namely the stability limit standard, local deformation failure criterion and the limit standard, is the second criteria to determine the ultimate pullout force in the turning point of A. According to the ultimate pullout capacity of pullout test, certain safety reserve should be taken into account when the allowable bearing capacity of anchor is TR.The existing data show that the value will not increase proportionally with the length of the anchor section, and the formula (10-49) is only suitable for the anchorage section within 10m. In addition, the value of the utility model can not be increased proportionally with the increase of the diameter of the anchor bolt.(two) uplift resistance of expanded grouted anchor1. compression pile methodFor the bolt with reaming at the end of the bolt, the ultimate pullout force is different depending on the nature of the stratum. When the anchor in rock bolt, the ultimate pullout force depends on the compressive strength of mortar; when the anchor in soil, pullout capacity of anchor to anchor the side friction resistance and the anti pressure section protruding part and (Fig. 10-43), i.e.:(10-50)Formula: F, the circumferential friction resistance of the anchor;Q - anti stress on the compression surface of anchor.Fig. 10-43 compression pile method Tutu 10-44 column shearing method2. column shear methodThe soil reaming bolt, bolt in the drawing force that anchored soil above expand along the bolt axis direction of column shear failure, as shown in figure 10-44, the ultimate pullout force of anchor:(10-51)In the model, the shear strength (kPa) between the expanded soil and the outer soil surface is increased.The value is also determined according to statistical data or experience, or based on field pull-out test values.Four, component designThe anchor retaining wall comprises a wall panel, a reinforced concrete rib column and an anchor rod.1. wall panel designGenerally, the wall panels are made of reinforced concrete trough plates, rectangular plates and hollow slabs, and sometimes arch plates are used, mostly prefabricated ones. Concrete strength is not less than C20, wall panel thickness shall not be less than 0.2m, width depending on the capacity of lifting equipment, but not less than 0.3m, generally use 0.5 m. The length of the prefabricated wall panel takes into account the connection between the anchor rod and the rib column, usually 0.1 to 0.12 m shorter than the column spacing of the rib column, or the wall plate of the anchor rod is left with a gap. The lap length of wall panel and rib column is not less than 0.1 M.The wall panel with ribs as a fulcrum, when the trough plate, rectangular plate and hollow slab precast wall panel, calculation of internal forces by simply supported plate, the calculation of span span in both ends of the lap length; when the arch board prefabricated wall panel, according to the calculation of internal force of double hinged arch board. The wall panel is directly subjected to the earth pressure, and the load is trapezoidal uniform load for each wall panel, and the load on each plate is different. In the design, the wall panels are generally divided from top to bottom into several sections, the thickness of the wall panels in each section is the same, and the maximum load is calculated in the section, but the specifications of the wall panel should not be too much.In cast-in-situ concrete structure, wall panels and often make ribs even in continuous plate together, should according to the calculation of internal force of continuous beam.2. rib column designThe cross section of the rib column can be rectangular, T and square, and the width of the column should be less than 0.3m along the length of the wall. Spacing rib column determined by the topography, geology, geological high wall and construction conditions, considering the pullout force of site factors such as lifting capacity and anchor, the general use of 2 2.5 M. The rib column can be integrally prefabricated, or assembled in sections