Types and prevention of landslides in open pit mining.

In the recent rainy season, landslides occurred in some open-pit quarries, causing a lot of losses. Here, I want to tell you about the types and prevention of slope landslide accidents in open pit mines, hoping that people in the industry will pay attention to them.

A, open pit slope components

Open-pit mining is to divide ore and rock into horizontal layers with a certain thickness, and mine them layer by layer from top to bottom, forming stepped steps around the open-pit mine. A slope composed of multiple steps is an open-pit slope.

The slope of open pit mine is composed of steps, upper flat plate of steps, lower flat plate of steps, slope surface of steps, slope angle of steps, height of steps, top line and bottom line of steps.

Steps can be divided into working platform, safety platform, cleaning platform and transportation platform according to their uses. The final slope refers to the slope composed of steps mined to the final interface. Final slope angle refers to the angle between the final slope surface and the horizontal plane.

With the gradual increase of mining depth, the height, area and maintenance time of open pit slope should also be greatly increased accordingly, otherwise the slope sliding disaster will become increasingly prominent. Therefore, the stability of slope has increasingly become one of the key points of mine disaster prevention in China.

Second, the types of landslides

There are generally five types of slope landslides: plane landslide, wedge landslide, circular landslide, toppling landslide and compound landslide, among which plane landslide is the most common type of landslide.

Third, the cause of the landslide.

Slope landslide activity is a phenomenon that rock mass finally evolves from deformation to caving under various stresses. The whole process can be divided into three stages:

Slope landslide is affected by many factors, mainly divided into the following six aspects.

(1) The determination of slope angle is unreasonable: the design of slope angle is too slow and the slope stability is high, which increases the stripping workload and cost, but reduces the slope maintenance cost. Increasing the slope angle leads to poor stability, reducing the stripping workload and stripping cost, but it brings personal and equipment insecurity.

(2) Influence of geological factors on slope: Rock mass is composed of many kinds of rocks, and there are many structural planes in the rock mass. The distribution of structural planes in rock mass affects the stability of slope rock mass. A large number of landslide examples show that the sliding surface and edge contour of landslide are controlled by the structural plane of rock mass.

(3) Groundwater in rock mass: Groundwater can change the physical and mechanical properties of rock mass and generate static pressure and buoyancy in the cracks of rock mass. When groundwater flows in the cracks of broken rocks, these broken rocks will be subjected to the dynamic pressure of water, thus reducing the stability of slopes.

(4) Blasting: The earthquake caused by blasting can open the joints of rock mass and even break the rock, which will affect the slope stability.

(5) Slope geometry: In open-pit mining, when the slope angle is constant, the higher the slope, the more unstable it is. When the slope height is constant, the greater the slope angle, the more unstable it is. Seen from the horizontal section, the more slopes there are, the more unstable they are. This is because the slope protruding to the stope is easy to be damaged by tension, which is not conducive to the stability of the slope.

(6) Other factors affecting the slope: there are management factors, such as overbreak at the foot of the slope, waste rock and equipment piled up on the upper part of the slope, buildings and houses, etc. The influence of weathering and seismic activity will reduce the stability of slope.

Fourth, the prevention and control of landslides

1, reasonably determine the slope angle of the working stage.

Open-pit mining and stripping are the first steps before mining, and it is forbidden to dig the bottom and caving to cause landslides. In the working stage, drilling, blasting, shipment and geological survey are needed, which move constantly with the advancement of mining. The rocks near the slope are affected by blasting vibration, and accidents often occur because the slope angle is too large at this stage, resulting in rock collapse or platform width narrowing. Therefore, in the design and production of open pit mines, it is necessary to determine the appropriate slope angle and specify the minimum working platform width according to the geological conditions, rock mechanics properties and performance specifications of various equipment used, and set up stripping transportation equipment, power supply and communication lines within the stable slope of the working platform.

2. Slope maintenance

Open pit slope must be inspected and maintained regularly to ensure slope stability and prevent disasters. Establish a professional team for slope maintenance, strengthen inspection and maintenance, and if necessary, manually put slopes, spread turf, plant shrubs, build local retaining walls or embed anti-slide piles.

It is necessary to set up a drainage pipe network to prevent surface rainwater from flowing into the mine to scour the slope and lubricate the cushion; Deep open pit mines should set up facilities around the pit to prevent mountain torrents and mudslides. The drainage pipe network includes the following three parts: surface drainage, underground drainage and three-dimensional drainage system. When blasting near the slope, pre-splitting and damping blasting methods should be adopted to reduce the charge in a single hole, increase the number of blastholes, and reduce the number of blastholes in each delayed blasting to prevent open-pit blasting from damaging the stability of the slope.

3. Anti-slide engineering and reinforcement methods

Anti-slide engineering is an indispensable part of landslide prevention, especially for mining slopes, which is related to the safety of life and property.

Anti-slide engineering includes: anti-slide retaining wall, reinforced retaining wall, anchor plate retaining wall, prestressed anchor cable retaining wall and anchor rod retaining wall.

Anti-slide piles: large-section row anti-slide single piles, anti-slide chains, steel pipe piles, platform anti-slide piles, flood-resistant piles, pile foundation retaining walls, seat retaining walls, row anti-slide piles, anti-slide rigid frame piles, sheet pile anti-slide piles and anchor piles.

Soil improvement: grouting, micropiles.

4. Landslide monitoring

By monitoring the displacement of rocks, we can find the precursors of landslides. Hydrometers should also be used to observe groundwater activities under the slope; The influence of blasting vibration is observed by seismometer, and the slope dynamics are obtained.

5, landslide prevention and control

The government restricts unlicensed mining and prohibits illegal mining; Remediation of mines occupying mountains and slopes; Prohibit predatory mining without starting, stripping or stripping while mining; It is forbidden to destroy the vegetation on the hillside. The edge of open pit mine must be equipped with flood control facilities to divert water flow. The slope should be mechanically reinforced, and anchor rods and piles should be set up.

In the process of open-pit mining, slope stability directly restricts the safety of the mine and is one of the most critical factors affecting the economic benefits of the mine. Generally, the influence of landslide runs through the mine production to the end of mining, so the treatment of open-pit slope will last until the end of mining, and its investment is huge.