Investigation and disposal of hidden danger of open-pit mine slope and dump

(3) Hang protective nets

The protective network is divided into active network and passive network according to its structural form, protective function and mode of action. The protection of active net is used for slope enclosure, limiting rock fall and preventing the occurrence of collapse. The passive protective net is mainly used to intercept falling rocks under the sliding body.

The anchorage bar of active mesh should pass through the surface fracture zone and its anchorage force should be checked. The passive network should ensure the stability of the foundation, check the rockfall energy, and select the corresponding energy level specification.

(4) Mechanical reinforcement method

Mechanical reinforcement of slope is to improve the stability of slope by increasing the strength of rock. Mechanical reinforcement is considered only when other methods of stabilizing the slope, such as slowing down the slope Angle or draining the slope, are not feasible or more costly.

1. Shore up the slope with anchor rods (cables)

It is an ideal method to reinforce the slope with anchor rod (cable), which can be used to reinforce the slope with obvious weak surface. Anchor rod is a kind of high-strength steel rod, and anchor cable is a kind of high-strength steel cable or steel rope.

The anchor bolt (cable) is generally composed of three parts: anchor head, stretching section and anchoring section. The anchor head is outside the anchor rod (cable), and its function is to exert force on the anchor rod (cable). The tensile section is in the hole, and its function is to evenly transfer the prestress (tensile stress) obtained by the anchor rod (cable) to the surrounding rock of the anchor rod hole, and increase the normal stress (normal stress) on the weak surface, so as to improve the anti-sliding force.

For the hard and broken rock, the prestress of the bolt can produce compressive stress in the surrounding rock of the bolt hole, thus increasing the friction resistance between the broken rock blocks and improving the shear strength of the surrounding rock.

The length of the bolt should pass through the sliding surface, and the length of the prestressed bolt is generally 2.5~3m. The length of prestressed anchor cable can reach tens of meters or even nearly 100 meters, so it is suitable for strengthening large slopes.

In order to ensure the effect of the anchor rod (cable) strengthening the slope, the reinforced concrete beam is laid between each two anchor rods (cable), and the wire mesh is hung on the anchor head and beam, and then the cement slurry is sprayed on the wire mesh to prevent the slope rubble from tumbling and weathering, and the slope rock constitutes a complete system with the anchor rod (cable) reinforcement, which strengthens the stability of the slope.

2. Reinforcement of slopes with shotcrete

Shotcrete is used as slope surface treatment. It can seal the rock on the surface of the slope in time to avoid weathering, delixing and spalling, and at the same time can strengthen the rock and improve the strength of the rock.

Shotcrete can be used alone to strengthen the slope, or it can be used in combination with the anchor rod. The thickness of the spray layer is generally about 250px. In order to improve the strength of shotcrete, especially to improve the tensile strength and plasticity, reinforcement mesh can be added. Sometimes, steel wire or glass fiber can be added to the shotcrete dry material to improve its tensile strength, which is called steel wire fiber reinforced concrete.

3. Reinforce the slope with anti-slide piles

There are many kinds of anti-slide pile, generally use reinforced concrete pile to strengthen the slope, which is divided into large section of concrete pile and small section of concrete pile. The former is generally used for reinforcement of broken and scattered structure slopes, while the latter is generally used for reinforcement of massive and layered structure slopes.

There are many advantages of anti-slide pile to strengthen the slope, such as flexible layout, construction does not affect the stability of the slide body, simple construction technology, fast speed, high efficiency, can be combined with other strengthening measures, large bearing capacity and so on. Therefore, this method has been widely used in slope reinforcement projects of open pit mines at home and abroad.

4. Reinforce the slope with retaining walls

Retaining wall is a kind of artificial structure to prevent loose materials. It can be used not only as a small landslide barrier, but also as one of the comprehensive measures to control large-scale landslide.

The principle of retaining wall is to rely on its own weight and the strength of its structure to resist the sliding force and toppling of the slope. Therefore, in order to ensure its anti-sliding effect, attention should be paid to the location of the retaining wall. In general, the retaining wall is mostly located at the leading edge or foot of the unstable slope.

5. The slope is reinforced by grouting

It is through the grouting pipe under a certain pressure to make the slurry into the crack of the rock mass slope. On the one hand, the crack and the broken rock mass are consolidated by slurry, and the broken rock is bonded as a whole, which becomes a stable solid frame in the broken rock and improves the strength of the surrounding rock. On the other hand, the channel of groundwater is blocked to reduce the harm of water to the slope.