The slope protection in deep cutting section generally adopts prestressed frame anchor cable to plant grass. The height of each slope is 10m and the slope is 1: 1. Generally, the first stage is to thicken the retaining wall, the second stage is to anchor the beam, and the third stage is to spread the net to plant grass. When the slope is the fourth grade, another net is set between the retaining wall and the beam anchor cable.
The construction sequence of frame anchor cable is: construction preparation, anchor hole drilling, anchor rod preparation, anchor hole grouting, concrete structure reinforcement preparation, concrete pouring, anchor hole tension locking and anchor sealing.
(1) construction preparation
Before construction, do a good job in construction organization design, calibrate tensioning equipment and related machines and tools, and conduct pull-out failure test of anchor cable (rod) according to design requirements.
⑵ Anchor cable construction
The platform is built with steel pipe scaffolding, and the platform is fixed on the slope with anchor rods. The drilling rig is accurately positioned in strict accordance with the designed hole position, inclination and orientation. Anchor cable drilling adopts dry drilling, and the drilling will be stable for 3 ~ 5 minutes after reaching the design depth. When the rock stratum is broken, the drilling speed should be slowed down appropriately, and casing drilling should be used when necessary.
(3) Anchor reinforcement system
After drilling, remove the cuttings and water in the hole with high-pressure air duct, and then install the anchor rod. The anchor rod shall be made in the corresponding production bench and simple shed, mechanically cut, cut, assembled and transported to the hole for installation. During installation, it should be pushed smoothly according to the designed inclination angle and orientation to prevent beam scattering and blockage.
(4) Grouting of anchor holes
The strength of grouting slurry is not less than 40MPa, and the grouting pressure is about 2MPa. Grouting at the bottom of the hole shall be carried out in time after drilling the anchor hole, and the time interval shall not exceed 24 hours.
5] Anchor bar tension locking
Before the anchor cable is formally tensioned, it shall be tensioned according to the design tension load 10 ~ 20% to make all parts closely contact, and then tensioned in stages according to the design load of 25%, 50%, 75%, 100%, 10%, and finally10%. The tensioning sequence adopts cyclic tensioning, which is carried out according to the operating principles of first left and then right, first middle, first up and down and then middle, and first diagonal and then middle.
[6] Anchor hole sealing anchor
After the anchor bar is locked, the anchor bar in Yu Lu will be cut off mechanically, the gap between the anchor pad and the anchor head will be filled with cement slurry, and the anchor will be sealed as designed.
2. Planting grass with anchor frame
Slope excavation in mudstone, shale and other soft rocks adopts anchor frame to plant grass. The frame is composed of C25 concrete and steel skeleton, with a width of 30cm and a thickness of 30cm. The steel skeleton joints are fixed with φ25 threaded steel bars, and the exposed end of the anchor rod is welded with the stirrup of the steel skeleton, and a hook is set for connection.
(1) anchor construction
During construction, the slope should be cleaned first, and the support should be set up as the construction platform. Then drill holes according to the diameter and depth required by the design, and put in anchor rods. Finally, grouting should be closed.
2 steel skeleton binding
The steel skeleton is loaded and unloaded on the ground, and is bound and shaped in pieces. After driving the anchor rod and grouting, hang the steel skeleton on the anchor rod in blocks and connect it with the anchor rod by welding. The installation of steel skeleton should be close to the slope, and fixed anchor piles should be set to anchor on the slope.
(3) formwork erection and concrete pouring.
Concrete pouring formwork adopts composite steel formwork, which is reinforced with steel pipes and log bolts. Concrete is produced centrally by the mixing station, transported by the mixer truck, manually put into the formwork, and vibrated by the internal vibrator.
(4) Pulling nets and planting grass
Planting soil in the frame, and then spreading nets to plant grass, usually in spring and autumn, to avoid construction in the rainstorm season and ensure the survival rate.
3. Planting grass with three-dimensional net
Three-dimensional net planting grass is suitable for slope protection when the height of fill slope is more than 4m, and its construction sequence is: leveling slope surface → watering slope surface → hanging net to fix → spraying grass → plastic film maintenance.
First, level the slope surface according to the designed slope ratio, then sprinkle water for wetting, then hang a three-dimensional net and fix it with U-shaped nails. The stereoscopic net is a three-layer stereoscopic net, the bottom layer is one layer, and the net wraps two layers. The raw material is polyethylene, the thickness is 12 mm, and it is stitched and lapped with geotextile rope in zigzag, and the lap width is 15cm. Every 1 1.25M of suspended three-dimensional net grass is a settlement section, which does not overlap, and only two sides are fixed with encrypted U-shaped nails.
Grass planting is completed by hydraulic sprayer. After spraying, cover plastic film or geotextile in time for maintenance, and replenish enough water in time until it germinates and survives.
4. Retaining wall and facing wall
The retaining wall designed in this section is mortar rubble (or concrete structure, according to bridge and culvert construction), and its construction points are as follows:
(1) Retaining wall adopts artificial excavator to excavate foundation trench; The foundation trench should be constructed without water, and the accumulated water in the foundation pit should be drained by digging a water pit.
(2) Mortar masonry is constructed by hanging line squeezing method, and the process is the same as that of drainage engineering. Before foundation laying, the base should be leveled and compacted manually, and the bearing capacity of the base should meet the design requirements. The flaky concrete is poured in layers, vibrated by internal vibrator and dumped manually.
(3) The retaining wall shall be built in sections according to the setting positions of expansion joints and settlement joints, and the drainage holes and gravel filter layer shall be built synchronously with the masonry. After a period of masonry is completed, cover it with straw bags and sacks in time, and spray water for maintenance.
(4) Shoulder retaining wall and embankment toe retaining wall shall be constructed synchronously and coordinately with subgrade filling, the retaining wall shall be filled once every 1m, and the backfill behind the wall shall be tamped by hand-held vibration impact rammer.
5. Arch or herringbone skeleton slope protection
The construction sequence is: leveling the slope → construction of mortar rubble skeleton → backfilling cultivated soil → planting grass → covering non-woven fabric → early maintenance.
According to the design skeleton size of 1: 1, pay out the hanging line, excavate the trench, select the high-quality stone with hard texture, no cracks and no weathering from bottom to top, and use the squeezing method for masonry; The joint mode is flat groove joint (concave joint). After the initial setting of mortar, the mortar shall be cured with water for 7 ~ 14 days.