How to construct soil nails in soil nail support

According to the construction plan, the anchor rod is made, and then according to the dug working face, the machine (with the air compressor) is used to drive into the layer (generally obliquely, according to the design angle).

Soil nail wall construction 1, soil nail wall construction process.

The construction of soil nailing wall is mainly divided into four steps, specifically:

1) The first step is to dig the soil and repair the slope. Excavation should pay attention to the grading coefficient of the earthwork, and the grading coefficient of the general soil nailing wall is; The main purpose of slope repair is to smooth the slope surface and correct the grading coefficient according to the design.

2) The second step is hole formation, reinforcement and grouting The hole is made of artificial Luoyang shovel, the hole diameter is 100mm, the water-cement ratio is filled into the hole, and the cement is made of cement; The reinforcement is put into the hole, and the HRB335 diameter 18mm steel bar is generally selected, and the length of the steel bar is selected according to the design.

3) The third step is to hang the reinforcement mesh and spray concrete. The steel bar is made of diameter steel bar, the grid spacing of the steel bar is 15 30cm, and the general spacing is 20cm; The concrete is made of C20 strength shotcrete, and the spraying thickness is 100mm.

4) the fourth step is to carry out the next step of excavation, slope repair, repeat the above actions, until the bottom of the foundation pit.

2. Requirements for the construction process of soil nailing wall.

The construction process of the soil nailing wall shall comply with the following provisions:

1) excavation working face, trimming the slope installation of soil nails (including holes, insertion of steel bars, grouting) binding reinforcement mesh, stiffeners, soil nails and stiffeners welding, adding cushion blocks Spraying the first layer of concrete, with a thickness of 50mm Spraying the second layer of concrete to the design thickness Set up the top of the slope, the slope surface and the drainage measures at the foot of the slope.

2) the foundation pit slope should be excavated in sections, each over-excavation depth shall not exceed, while excavation, while manually trimming the slope, while spraying concrete, when manually trimming the slope, the slope unevenness is not greater than 20mm.

3) spraying concrete should be carried out in sections, the spraying sequence in the same segment should be from bottom to top, a spraying thickness of 50mm, when spraying, the nozzle and the sprayed surface should be perpendicular, should keep the distance, the spraying hand should control the water-cement ratio, keep the concrete surface flat, moist and shiny, no dry spots or flowing phenomenon.

4) After the final setting of the sprayed concrete for 2h, it should be cured, and it can be appropriately adjusted according to the actual situation of the site. The strength grade of panel concrete is not less than C20, the maximum aggregate of concrete is not greater than, and the thickness of the spray layer is 8 10cm. At the same time, the soil nail wall panel should be flanged outward at the upper mouth of the foundation groove.

5) each locator is provided on the reinforcement to ensure that the reinforcement is centered in the hole, and the end of the soil nail is reserved for the slope surface of 15cm; Atmospheric gravity grouting, the strength of the grout is not less than 20MPa, and the grouting material is cement slurry; The steel mesh in the sprayed concrete should be straightened and rusted, the gap between the steel bar and the slope should be greater than 20mm, the steel mesh should be firmly connected with the soil nail and the reinforcing rib, and the steel bar will not shake when spraying concrete.

6) Before the use of soil nail steel bar, it should be straightened, rust removed, and the grouting material should be used: 1 cement slurry.

What is Soil Nailing Wall Support? Combined with the specific situation of soil nailing wall support in China, what are the specific applications of conventional soil nailing wall support? The following is a basic introduction to the construction terminology of soil nailing wall support compiled by Zhongda Consulting:

The soil nailing wall is reinforced by the natural soil body through the soil nailing wall in situ and combined with the sprayed concrete panel to form a similar gravity retaining wall to resist the earth pressure behind the wall; In order to maintain the stability of the excavation face, this soil retaining wall is called the soil nail wall.

Specific applications of soil nailing wall support:

Soil nailing wall is not only applied to temporary support structure, but also applied to permanent structures, when applied to permanent structures, it is advisable to increase the thickness of the sprayed concrete surface layer and give due consideration to its beauty, and the application fields of soil nailing wall mainly include:

1) Underpinning the wide positive foundation.

2) Foundation pit support or shaft.

3) Retaining walls on the slope surface.

4) Stability of the slope surface.

5) The protection of the inclined plane with the bolt retaining wall.

Borehole grouting type soil nail wall is layer by layer downward excavation mode, each step height is 1 2 meters, during the construction of soil nail rod, surface layer spraying concrete, the slope section needs to be able to maintain self-standing stability without support, so it is mainly suitable for:

1) Miscellaneous fill, cohesive soil, silt, loess and weakly cemented sand slope with certain cohesiveness.

2) It is suitable for the situation that the groundwater level is lower than the excavation layer or the groundwater level is lower than the excavation elevation after precipitation.

3) It is generally uneconomical to use the soil nailing method for the sandy slope where the standard penetration number (n) is less than 10 strokes.

4) For the soil with the sakuness index IP>20, it is necessary to pay attention to the creep characteristics of the soil before it can be used.

5) For the water-rich silt and fine sand layer, the soil nailing method of the sand and pebble layer is not possible.

6) It is not suitable for the silt soil layer without temporary self-stabilizing ability, and it is difficult to maintain the stability of the hole wall when the soft clay in the state of flow is formed, and the interfacial friction resistance is very low, and the technical and economic benefits are not ideal, so it is not suitable to be used.

7) Soil nails are not suitable for permanent retaining structures in corrosive soils such as cinder, coal ash, slag, acid mineral waste, etc.

The construction process of soil nail support is:

1. Anchor first and then eliminate difficulties. Dig the soil to the soil nail position, after driving the soil nail, dig the second step of soil, and then hit the second layer of soil nail, so that the cycle to the last layer of soil nail construction is completed. The first shotcrete was 50 mm thick, followed by anchoring, followed by a second shotcrete, 50 mm thick.

2. Spray first and then anchor. Excavate the soil to a certain distance below the position of the soil nail, lay the reinforcement mesh, and reserve the lap length, spray the concrete to a certain strength, and then drive the soil nail. Dig the second layer of earthwork to the second layer of soil nails under the position of a certain distance, pave the reinforcement mesh, and the last reinforcement mesh up and down lap joint, also reserve the lap length of the reinforcement mesh, spray concrete, hit the second layer of soil nails.

This is done until the pit is fully deep.