binding reinforcement mesh: the reinforcement mesh shall be constructed layer by layer with soil nails and set layer by layer.
The first grouting should be cement mortar, and the grouting volume should not be less than 1.2 times of the borehole volume.
(III) before the positioning drilling and hole cleaning of soil nails, the hole position shall be determined and marked and numbered according to the design requirements.
The grout outlet shall always be buried under the surface of the slurry in the hole to ensure that the gas in the hole can be completely discharged.
When the thickness of the surface layer exceeds 100mm, the concrete shall be sprayed in layers.
The reinforcement mesh shall be 6-10mm in diameter, and the spacing shall be 150-250mm, The reinforcing bar shall be micro pile composite soil nailing wall pile with diameter of 14 ~ 20mm.
After filling, the pressure shall be maintained for 1 ~ 2min.
During grouting, the tremie shall be pulled out slowly and evenly.
The soil nail shall be drilled slowly in alignment with the hole position, and the normal speed can be drilled only when a certain depth is reached and the soil layer is relatively stable.
The same section shall be from bottom to top.
(VII) install drain holes and insert horizontal (slightly downward) drain pipes with a length of 400 ~ 600mm and a diameter of no less than 40mm at the back of the support surface layer.
Vi.
The horizontal and vertical spacing of soil nails shall be 1-2m, the inclination angle shall be 5-20 °, and the hole forming diameter shall be 70-120mm.
The grouting pressure should be 0.4-0.6mpa; (6) The maximum particle size of aggregate for shotcrete shall not be greater than 15mm; The operation shall be carried out in sections and pieces at one time.
(II) the shotcreting sequence of the primary shotcreting bottom layer concrete shall be from top to bottom.
The structure of the support shall not hinder the free flow of grout during grouting.
The distance between the nozzle and the shotcreting surface shall be controlled within 0.8 ~ 1.5m.
The shotcreting direction shall be vertical to the shotcreting surface.
The thickness of one shot shall not be greater than 120mm.
(7) The thickness of protective layer of soil nail reinforcement shall not be less than 25mm…
The concrete shall be watered for curing within 2h after final setting to keep the concrete surface wet.
After each layer of soil is excavated, it shall be trimmed to remove the protruding soil and compact the loose soil on the surface to ensure the flatness of the shotcrete surface.
Single soil nailing wall is used for non soft soil foundation pit above groundwater level or for precipitation, with depth ≤ 12m; Prestressed anchor composite soil nailing wall is used for non soft soil foundation pit above groundwater level or for precipitation, with depth ≤ 15m; When the cement soil pile composite soil nailing wall is used for the foundation pit of muddy soil, the depth is ≤ 6m.
Shotcrete construction shall be started after the reinforcement mesh and soil nails are accepted.
The nozzle shall be vertical to the sprayed surface.
The overlapping width shall not be less than twice the thickness.
The thickness of concrete surface layer shall be 80-100mm, and the design strength grade shall not be less than C20.
Construction process flow 1: the earth on the trimming slope shall be excavated in layers and sections.
The joints shall be staggered.
The first applicable condition is that the safety grade of the side wall of the foundation pit is grade II and III.
VIII.
The outer end of the drain pipe extends out of the support surface layer, and the spacing of the drain pipes can be 1.5 ~ 2m, so as to drain the water in the soil layer behind the shotcrete surface layer.
Structural requirements: the slope ratio of soil nail wall shall not be greater than 1:0.2.
The second grouting can be carried out after the initial setting of the first grouting; For the second injection of pure water slurry, the grouting amount is 30% – 40% of the first grouting amount.
The grouting pipe is about 0.5m away from the bottom of the hole.
(4) After the grouting of the upper layer of soil nails is completed for 48h, the lower layer of earth can be excavated.
The excavation elevation shall be 200mm below the position of soil nails.
(IV) place the soil nail reinforcement.
(2) After the construction of each layer of soil nails, spot check the pull-out force of soil nails as required.
(5) The hole forming grouting type soil nail shall be constructed by twice grouting process.
V.
The drilling shall not disturb the surrounding strata, and high-pressure air or water shall be used for hole cleaning after drilling.
The thickness of one shotcreting shall not be less than 40mm.
HRB400 and HRB500 reinforcement shall be selected as the soil nail reinforcement, and the grouting material with diameter of 16-32mm can be cement slurry or cement mortar.
The thickness of the first layer shall not be less than 40mm.
grouting: pressure grouting shall be adopted for grouting.
The main reinforcement shall be cut according to the design length plus 20cm.
It is a slope reinforcement type support construction method that combines the foundation pit slope with soil nailing made of steel bars, laying a reinforcement mesh on the slope surface, spraying a layer of concrete surface and earth slope.
The conduit shall be inserted at 250 ~ 500mm from the hole bottom, and the grout stop plug shall be set at the orifice.
The thickness of the protective layer shall not be less than 20mm, the overlapping length shall not be less than 30d, and the single side welding length shall not be less than 10d.
The shotcreting concrete shall be properly added with accelerator to improve the setting speed of the concrete and prevent the concrete from collapsing.
When placing the main reinforcement, bind the grouting pipe with the main reinforcement.
II.
The strength shall not be less than 20MPa.
The end of the soil nail is connected with the reinforcement bar and the reinforcement mesh in the surface layer through the reinforcement bar.
(3) After excavation, the soil nail placement and shotcrete surface course shall be completed within 24h, and the soil nail placement and shotcrete surface course shall be completed within 12h for muddy soil.
The grout mix ratio and grouting pressure shall be controlled according to the design requirements.
The main reinforcement shall be welded with a centering support every 1-2m to prevent the main reinforcement from deviating from the center of the soil nail.
Soil nailing wall is a commonly used support method in foundation pit engineering.
The outer end shall be provided with a 90 degree 20cm hook.
After the final setting of the previous layer of concrete, the next layer of concrete can be sprayed.
The length of the pile extending into the pit bottom shall be greater than 5 times of the pile diameter and greater than 1m.
The excavation depth of each layer shall be consistent with the vertical spacing of soil nails.
The length of the cement soil composite soil nailing wall pile extending into the pit bottom shall be greater than 2 times of the pile diameter and greater than 1m; The 28d unconfined compressive strength of the pile body should not be less than 1MPa three construction requirements (1) the construction of the soil nailing wall must follow the principle of “advance support, layered and segmented construction, layer by layer construction, limited time closure, and no over excavation”.
The reinforcement mesh shall extend to the ground surface and extend 0.5m beyond the slope line.
Key points of construction technology: soil nailing wall can be divided into single soil nailing wall, prestressed anchor composite soil nailing wall, cement soil pile composite soil nailing wall, micro pile composite soil nailing wall and other types.
