Whether soil nailing wall slope protection is required when the slope stability is satisfied

JGJ 120-2012 Technical specification for building foundation pit support: It is mainly to ensure the safety of the slope under various limit states.

The following limit states should be adopted in the design of the supporting structure:

1. Ultimate limit state of bearing capacity.

1. The supporting structural components or connections are damaged due to exceeding the strength of the material, or are not suitable for continuing to bear the load due to excessive deformation, or there is compression and buckling and local instability;

2) the overall sliding of the supporting structure and the soil;

3) the soil at the bottom of the pit is uplifted and loses stability;

4) to the supporting structure, the soil at the bottom of the pit loses the embedding ability and makes the supporting structure push or overturn;

5) to the anchor pull retaining structure or soil nailing wall, the soil body loses the anchoring ability of the anchor rod or the soil nail;

6) Gravity cement soil wall overall overturning or sliding;

7) Gravity cement soil wall and retaining structure are damaged due to the loss of bearing capacity of the bearing soil layer;

8) Soil seepage damage caused by groundwater seepage.

2. Normal service limit state.

1) Cause damage to the buildings (structures) around the foundation pit, underground pipelines, roads, etc., or affect the supporting structure of its normal use.

Displacement; 2) Due to the decline of groundwater level, groundwater seepage or construction factors, the buildings (structures) around the foundation pit, underground pipelines, etc

deformation of the soil that damages or affects the normal use of roads;

3) the displacement of the supporting structure that affects the normal construction of the main underground structure;

4) Groundwater seepage that affects the normal construction of the main underground structure.

Supporting structures, buildings around the foundation pit and ground settlement

The following design expressions should be used for the calculation and verification of groundwater control:

1. Ultimate limit state of bearing capacity.

1) The design of the ultimate state of the bearing capacity of the supporting structural components or connections due to exceeding the material strength or excessive deformation shall comply with the following.

Requirements:

Mechanism of action of soil nailing wall The concrete surface layer works together to strengthen the in-situ soil. Soil nailing walls are not only applied.

It is also used for temporary supporting structures and for permanent structures. At present, the shear strength of the soil is low, and the tensile strength is almost negligible, but the soil has been widely used in many countries and has received great attention from the civil engineering community, and the soil has a certain structural integrity. During foundation pit excavation, the slope can maintain an upright nail wall in more and more foundation pit excavation support and excavation slope stabilization and other projects such as critical height, but in excess of this depth or when there is ground overload, it will suddenly be applied as a whole.

Therefore, the stability analysis of soil nailing wall support engineering is particularly damaged. The general slope protection measures are based on the passive restraint mechanism of supporting the slope protection, which is important. The retaining structure withstands the subsequent lateral pressure of the soil to prevent the overall stability of the soil from breaking.

The stability of the slope meets the requirements, which usually means that the stability of the slope has reached a certain safety level, and it is not easy to cause disasters such as landslides and collapses. However, this does not mean that support is not necessary. Supporting measures can help to further improve the stability of the slope and reduce the risk of geological disasters.

The selection and implementation of support measures should be determined according to the specific slope conditions and engineering needs. Some common support measures include:1

Retaining wall: Prevent soil landslides by setting up retaining walls to support the slope. 2.

Anchor: Push the anchor into the slope to make the slope and the anchor form a whole to improve the stability of the slope. 3.

Soil nailing wall: Inserting soil nails into the slope to form a soil nailing wall to improve the stability of the slope. 4.

Vegetation: By planting vegetation, the slope can be more resistant to erosion and reduce the risk of soil erosion. 5.

Drainage system: Set up a drainage stool system to ensure that the water in the slope soil is discharged in time and reduce the risk of slope instability. In short, although the stability of the slope meets the requirements, the support measures still help to further improve the stability and safety of the slope.

In the actual project, the selection and implementation of support measures should be comprehensively considered according to the specific situation.

1. Excavate and sort out the slope.

Soil nail support is carried out in layers, so the excavation depth can not exceed the design depth, and at the same time to ensure that the slope angle reaches the design requirements of 78 ° 80 °, the slope surface is smooth and smooth, and the slope angle does not meet the design requirements to be specially trimmed.

2. Initial spray. In order to prevent the excavated slope from collapsing, the excavated slope needs to be sprayed with concrete immediately to consolidate the surface layer. The mix ratio of its concrete material is cement: stone =, water-cement ratio =. Orange morning shirt.

3. Drilling. Using the method of artificial machinery acting together, the downward inclination angle of the borehole is 15 ° 25 °, and the method of air drilling is carried out, and the manual digger uses the Luoyang shovel, a group of two.

4. Insert rod and grout.

After the hole is formed, it is inserted into the 22mm fiber bar with a diameter according to the design requirements, and the straightening ring with a diameter of 110mm is welded into the reinforcement rod to play a guiding role. At the same time of inserting the reinforcement, the grouting pipe is brought into the place from the bottom of the hole with a reinforcement rod, and then the pouring is carried out, and the mix ratio of the grouting material is cement: sand = 1:

2。Water-cement ratio =. The hole must be filled to the fullest, and no cavities and pores can be formed.

5. Hang the net. After the completion of the previous process, according to the design requirements, the steel bar with a diameter of 6mm is welded according to the network spacing of 30cm and 30cm, and fixed on the slope; At the same time, the soil nails on the dangerous slope are connected together with metal pieces to further strengthen the support strength.

6. Re-spraying. After hanging the net, the entire slope surface is sprayed concrete, and its spraying thickness meets the design requirements. Generally, the length of the bolt is between 15 and 45m in the circular cavity, the diameter is larger, and the load borne by the bolt can reach more than 400kn; The insertion depth of the steel bar shall not be less than 90% of the design requirements, and it shall not be knocked or collided after installation.

The mortar used for grouting should be mixed evenly, mixed with use, the hole should be blown clean with wind before grouting, and the grouting should start from the bottom of the hole and be carried out continuously and evenly.

Answer: A, B, C

The soil nail support process can be anchored first and then sprayed, or sprayed first and then anchored. The slope structure system reinforced by soil nail support includes lifting: soil nail, shotcrete, steel bar and net, and soil nail anchor head.

The natural slope of the mountainous area, the bank slope of the river and the artificial slope formed by leveling the site and excavating the foundation pit in the construction project, due to the influence of some external unfavorable factors, cause the local soil of the slope to slide and lose stability, and the collapse of the slope often causes serious engineering accidents and endangers personal safety.

Therefore, the appropriate slope section should be selected, reasonable construction methods should be adopted, and the stability of the slope should be checked and appropriate engineering measures should be taken if necessary, so as to ensure the stability of the slope. The purpose of reducing the amount of earthwork filled, shortening the construction period and saving safety and saving.

The factors that affect the stability of the slope are generally as follows:

1) The soil slope force changes. For example, due to the stacking of materials on the top of the slope or the construction of buildings to load the top of the slope, or due to the vibration caused by piling, vehicle driving, blasting, etc., the original equilibrium state has been changed.

2) The reduction of the shear strength of the soil. For example, an increase in the water content or pore water pressure in the soil.

3) The role of hydrostatic pressure. For example, rainwater or surface water flows into vertical cracks in the soil slope, which creates lateral pressure on the soil slope and thus promotes the slippery front movement of the puncture.

4) The seepage of groundwater in the slope such as earth dam or foundation pit is often an important factor of slope instability, because the seepage will cause hydrodynamics, and the fine particles in the soil will pass through the pores between the coarse particles and be carried away by the seepage, so that the compactness of the soil will decrease.

5) The height of the soil slope or the foot of the slope increases due to the excavation of the foot of the slope.