Landslide sliding is mostly related to surface water or groundwater activities. Therefore, in landslide prevention and control, it is often necessary to try to remove surface water and groundwater, so as to prevent surface water from infiltrating into landslide, reduce the erosion of surface water on landslide rock and soil and the floating support of groundwater on landslide, and improve the shear strength of sliding soil and the overall stability of landslide.
The purpose of surface drainage is to prevent the surface water outside the landslide from flowing into the landslide, and at the same time make the surface water inside the landslide flow out of the landslide.
The method of removing groundwater is to intercept and discharge groundwater through underground buildings, so as to reduce the groundwater level. According to the types of groundwater, burial conditions and construction conditions of this project, underground drainage works include intercepting blind ditch, supporting blind ditch, slope seepage ditch, drainage tunnel, vertical seepage well with horizontal pipeline, horizontal drilling group and seepage pipe drainage, etc.
When there are waterlogged wetlands and spring outcrops on the surface of the landslide, the upper end of the drainage ditch can be made into a water seepage blind ditch, which extends into the wetland to achieve the purpose of draining the water in the upper layer of dry and wet land. Seepage blind ditch shall be filled with no mud and gravel, with filter layers on both sides and at the top (Figure 4-29).
Figure 4-29 Schematic diagram of blind ditch section of underground drainage support for landslide (according to Technical Code for Design and Construction of Landslide Prevention and Control Engineering (DZ/T02 19—2006))
In order to intercept the deep groundwater behind the landslide and reduce the groundwater level in the landslide, a transverse interception drainage tunnel should be built below the sliding surface at the rear edge of the landslide, which is basically perpendicular to the direction of groundwater flow. The longitudinal drainage tunnel can be built in the landslide (or old landslide), and the two sides are provided with branch interception drainage tunnels and inclined drainage holes which are basically perpendicular to the groundwater flow direction.
2. Weight reduction and loading
By loading the anti-slide section of the landslide and reducing the weight in the main slide section or traction section, the landslide can be controlled.
(1) The weight of the rear main sliding part and the traction part is reduced.
If the sliding mode of landslide is push type, and the sliding surface is steep and gentle, the control method of weight reduction of main sliding section and rear traction section can play a role in controlling landslide. In order to reduce the weight, it is necessary to calculate the landslide thrust and find the thrust along each sliding surface, so as to judge the stability of each landslide. Improper weight loss can not only stabilize the landslide, but also aggravate its development.
(2) the front load of landslide
Loading, that is, filling in front of the landslide or near the landslide shear outlet, to increase the anti-sliding ability of the anti-sliding section of the landslide. The premise of taking this measure is that there must be an anti-sliding section at the front of the landslide. Like weight reduction, the front load of landslide must be accurately calculated to achieve the goal of stabilizing landslide.
3. Anti-sliding retaining wall
Anti-slide retaining wall engineering is an effective measure commonly used in landslide control because of its small balance of mountain damage and quick effect of stabilizing landslide. Small and medium-sized landslides can be used alone, and anti-slide retaining walls can be used as part of comprehensive measures for large and complex landslides. When setting anti-slide retaining wall, it is necessary to find out the sliding range of landslide, the number and position of sliding surfaces, the direction and magnitude of thrust, etc. , and find out the situation of the retaining wall base, otherwise it will cause the deformation of the retaining wall, and even the retaining wall will slide with the landslide, resulting in the failure of the project.
Anti-slide retaining walls can be divided into masonry anti-slide retaining walls, concrete anti-slide retaining walls, solid anti-slide retaining walls, assembled anti-slide retaining walls and pile-plate anti-slide retaining walls according to their stress conditions, wall materials and structures.
The selection of retaining wall type should be determined according to landslide stability, construction conditions, land use and economy. Inclined retaining wall should be adopted if the topographic and geological conditions permit; When the stability of landslide is good and the land price is low during construction, vertical retaining wall should be adopted; When the landslide stability is good and the land value is high during the construction period, the inclined retaining wall should be adopted (Figure 4-30).
Figure 4-30 General Type Diagram of Retaining Wall Section (according to Technical Specification for Design and Construction of Landslide Prevention Engineering (DZ/T02 19—2006))
Special retaining walls can be used in the design according to the geological conditions, such as pressure relief platform retaining wall, anchor plate retaining wall and reinforced soil retaining wall (Figure 43 1).
4. Anti-slide pile
Anti-slide pile is a kind of engineering which uses piles as anti-slide engineering. Anti-slide pile is also called anchor pile (Figure 432), because it drives a number of large-size anchor piles between the sliding body and the sliding bed to make them become a whole, thus playing the role of anti-slide. The materials of piles include wooden stakes, steel sheet piles and reinforced concrete piles. The arrangement of anti-slide piles depends on the shape and scale of sliding body, especially the position of sliding surface and the magnitude of landslide thrust. Usually arranged in one or several rows as required. In China, reinforced concrete digging piles are mostly used in railway departments, and their cross sections are mostly square or rectangular, and their size depends on landslide thrust and construction conditions.
5. Slope protection works
Slope protection project mainly refers to the reinforcement of landslide slope, with the purpose of preventing surface water from scouring and infiltrating the slope. For loess and expansive soil landslides, slope reinforcement nursing is more effective. Specific methods include concrete grid frame slope protection and mortar rubble slope protection, and planting grass in the grid of concrete grid frame slope protection, or spraying seeds with SNS technology to increase vegetation and strengthen the slope (Figure 433).
Figure 4-3 1 Anchor plate, reinforced soil and retaining wall of pressure relief platform (according to Technical Code for Design and Construction of Landslide Prevention Engineering (DZ/T02 19—2006))
Figure 4-32 Anchoring
Figure 4-33 Using SNS technology to increase vegetation
Avoid it
Avoidance is a preventive measure, not a control measure. For the prevention and control of large-scale landslides or landslide groups, it is sometimes necessary to take avoidance measures to prevent landslide disasters because of the great difficulty, high cost and long construction period. For line avoidance, it is sometimes necessary to build a project to let the line pass through, or through the tunnel under the sliding bed, or through the dry bridge outside the front edge of the landslide, or to move the line across the river to a more stable section on the other side.
Fig. 4-34 Schematic diagram of borehole layout for landslide reinforcement grouting test (according to Technical Specification for Design and Construction of Landslide Prevention and Control Engineering (DZ/T02 19—2006))
7. Grouting reinforcement
Grouting reinforcement is a technology to improve the sliding zone. By pressure grouting the sliding zone, the shear strength of the sliding zone and the stability of the landslide are improved. After the improvement of sliding zone, the safety factor of landslide should be evaluated by shear standard. Grouting test and effect evaluation should be carried out before grouting, and excavation or drilling sampling inspection should be carried out after grouting.
The depth of grouting hole depends on the thickness of landslide and the required foundation bearing capacity. The grouting depth to improve the foundation bearing capacity can be less than 15m, and the grouting to improve the shear strength of the slip zone should pass through the slip zone at least 3m. Boreholes shall be distributed in plum blossom shape, and the spacing between holes shall be 2/3 of the grouting radius. The grouting radius should be determined by field test, and it should be 1.0~3.0m ~ 3.0m (Figure 4-34). The design hole diameter of drilling should be 9 1 ~ 130mm, and the hole should be 130mm. Use mechanical rotation or DTH hammer to drill holes, and do not use mud to protect the wall. Dry drilling is suitable for soil, and clear water or air drilling can be used for rock mass.
8. Other measures
The methods to prevent landslide sliding by improving the strength of sliding soil include drilling blasting, roasting, chemical reinforcement and electroosmosis drainage. These methods are feasible in theory, but they are rarely used in practice for technical and economic reasons.
summary
This chapter focuses on landslide types, landslide identification characteristics, landslide exploration points and methods, and landslide prevention measures. Landslide Classification focuses on Landslide Engineering Investigation Classification (DZ/T 0218—2006). The recognition characteristics of landslides should master the recognition characteristics of new landslides or active landslides and inactive landslides; The key points of landslide exploration should be landslide survey and the key points of landslide exploration in the feasibility demonstration stage; Landslide exploration methods should master the methods of landslide engineering geological mapping, exploration and testing-residual shear strength test of sliding surface (belt) and landslide monitoring; Landslide prevention measures should grasp the meaning of "blocking, discharging, stabilizing and consolidating" and the construction method of prevention measures.
Review thinking questions
1. What is the classification of landslides in Landslide Engineering Investigation (DZ/T02 18—2006)?
2. What are the identification features of landslides?
3. What are the general provisions in landslide survey?
4. What are the key points of landslide ground investigation?
5. What are the general provisions for landslide exploration in the feasibility study stage?
6. What are the key points of landslide exploration in the feasibility demonstration stage?
7. What is the classification of landslide disaster objects in Landslide Engineering Investigation (DZ/T02 18-2006)?
8. What is the key point of landslide environmental geological investigation in the feasibility demonstration stage?
9. What is the content and scale of landslide engineering geological mapping in the feasibility demonstration stage?
10. How to arrange exploration points and exploration lines for landslide exploration in the feasibility demonstration stage? What are the drilling methods and requirements?
1 1. How to identify the sliding surface (belt) in drilling and trial pit?
12. What are the requirements for landslide monitoring?
13. What are the contents of landslide prevention measures?
14. What are the construction methods of landslide prevention measures?
15. How to divide the development stages of landslides?
16. How to judge the stability of landslide?