Landslides do great harm to engineering construction, often disrupting traffic and affecting the normal transportation of highways. This paper mainly introduces the construction measures of mountain roads to deal with landslides.

Keywords: landslide; Expressway; measure

1 landslide overview

Under the influence of natural or man-made factors, some rock and soil on the slope move downward along a certain sliding surface, which is called landslide. The sliding surface can be a penetrating shear failure surface or area with maximum shear stress, or it can be an existing weak structural surface in rock mass. Large-scale landslides generally slide slowly and for a long time, and some landslides slide quickly. The process is divided into two stages: creep deformation and sliding failure, but some landslides show sharp sliding, and the sliding speed ranges from several meters to tens of meters per second. Landslides often occur on slopes, slopes, river banks, embankments or foundation pits in hilly areas. Landslide is very harmful to engineering construction, which may affect construction or damage buildings. Due to landslides, traffic is often interrupted, which affects the normal transportation of expressways; Large-scale landslides can block rivers, destroy roads, destroy factories and mines, bury villages, and do great harm to mountain construction and traffic facilities.

The purpose of landslide classification is to summarize the geological environment, morphological characteristics and various factors that cause landslides, so as to reflect the engineering geological characteristics of various landslides and the laws of their occurrence and development, so as to effectively predict and prevent the occurrence of landslides, or to effectively control them after they occur. According to different principles and indicators, scholars and engineering departments in various countries put forward different landslide classification schemes. For a landslide, there are different classifications from different angles, but in practice, we should grasp the main contradiction of the problem and classify the landslide according to the prominent factors. The principle of classification is to see if it helps us to understand, prevent and deal with this landslide.

2 landslide mechanism analysis

2. 1 Geologically, the surface of the slope is completely weathered and strongly weathered rock, with weak lithology, broken rocks and developed joints and cracks;

2.2 After the cutting slope is excavated, the rock stratum on the slope faces the air, which makes the rock and soil on the slope out of balance;

2.3 The excavation and slope cutting of road cutting destroyed the original balance of the slope, and at the same time, the unloading of the slope opened the joints and cracks of the slope, which provided a channel for water infiltration on the slope, and the existence of irrigation ditches provided water for the slope sliding;

2.4 Infiltration water softened the strongly weathered slate and mud, which provided favorable conditions for the final formation of landslide.

3 parameter selection of sliding surface

According to the geological data obtained in landslide survey and the current sliding state of the landslide, the mechanical parameters of the sliding surface are calculated by the inversion analysis method, and the inversion value is taken as the parameter value in the landslide control design. Groundwater is one of the factors inducing landslides, and the geostress of groundwater should be considered in the stability analysis of landslides.

4 Design scheme of landslide treatment for mountain roads

According to the principle of "safety, environmental protection, comfort and beauty", on the premise of meeting the requirements of safety and codes, considering the feasibility and economic rationality of construction technology, the landslide is treated according to the site topography, engineering geological conditions and actual situation of this contract section.

In the construction of a mountain highway, due to the large landslide thrust, a row of prestressed anchor anti-slide piles were laid on the upper part of the west section of No.2 landslide to resist the sliding force of the landslide, and the center of the piles was about 18m away from the center line of the left line. Because the anchor hole intersects with the pier, some anti-slide piles are changed into ordinary anti-slide piles because they cannot avoid the anchor cable and pier. * * * Anti-slide pile 15, including anchor anti-slide pile 12 and common anti-slide pile 3.

4. 1 Main construction process

Anti-slide piles shall be constructed first, and piers and abutments shall be constructed after the landslide is stabilized.

The construction sequence of anchor cable anti-slide pile is as follows: measuring pile position → cleaning and stabilizing the slope near the pile hole → constructing anti-slide pile lock → excavation → node hole → binding retaining steel bar → formwork support → pouring retaining concrete → excavating the next pile hole node → repeating the above four procedures until the design elevation → sealing bottom → binding pile steel bar → pouring pile concrete to a distance of 2m from the pile head, reserving anchor cable hole position → pouring residual concrete. Drilling anchor hole → lowering steel strand → grouting → tensioning → locking.

Anchor cable and pile engineering can be carried out separately, and the order can be determined according to the actual situation, but attention should be paid to mutual cooperation and connection.

4.2 Anti-slide Pile Construction

6.5438+0 survey piling

Anti-slide piles should be accurately laid out and positioned according to the direction of pile row and the mileage and coordinate position of control piles.

4.2.2 Pile foundation excavation under general geological conditions

A before the anti-slide pile construction, the slope near the pile location or the part of the surface that is easy to slide should be removed, and the surface water near the pile location should be intercepted.

B. Excavate anti-slide piles by jumping piles, and do a good job of locking plate and retaining wall in each section. The excavation depth of each section shall not exceed1m. When excavating a section, do a good job of wall protection. The next section can only be excavated after the concrete for retaining wall has a certain strength. The longitudinal reinforcement of each retaining wall must be welded, and simple binding is prohibited.

C. When pouring concrete for retaining wall, it is necessary to ensure that the retaining wall does not invade the gap between piles. During the excavation of the pile pit, the verticality and clearance size shall be corrected at any time. ? 4.2.3 Pile Foundation Excavation under Special Geological Conditions

6 # ~ 15 # in the western section of 2# landslide is brownish yellow, brownish gray and brownish black loam with loose top. The landslide area is rich in surface water and groundwater. In the process of pile excavation, there is a lot of water seepage, and the soil is in a flow plastic state. The wall around the pile collapsed seriously, making it difficult to form holes. The back of the retaining wall is seriously depressed, and the completed retaining wall bears great earth pressure, which leads to the deformation and cracking of the retaining wall and brings great hidden dangers to the safety of engineering construction.

Construction treatment scheme of anti-slide pile retaining wall in special geology;

(1) The deformation and cracking of the completed retaining wall are serious. φ 108*6 steel pipe is used as temporary support to control the deformation of the retaining wall.

(2) Open a hole in the completed retaining wall, and fill C25 concrete into the back cavity of the retaining wall from the hole until the back cavity of the retaining wall is completely dense. The opening of the retaining wall is from top to bottom, with a size of 30×30cm square holes, arranged in a quincunx pattern with a spacing of 2m, and φ 25 Ⅱ steel bars are appropriately added at the opening, so that the retaining wall, the filled concrete and the soil around the pile are integrated.

(3) The concrete thickness of the breast wall is adjusted from the original design of 20cm to 40cm, and the reinforcement of the breast wall is adjusted from the original single-layer steel mesh to double-layer steel mesh. The length of each anti-slide pile retaining wall is controlled at 60cm.

(4) In order to ensure the smooth construction of the anti-slide pile, advance small conduits are arranged in the sliding surface area, with L = 2mφ42 * 4 flower tubes, the spacing is 50×50cm, the extrapolation angle is 30 degrees, and the effective length of the advance small conduits is 1.73m, and the excavation is divided into 2-3 cycles. The small conduit is injected with double liquid slurry by a double liquid grouting machine, the ratio of double liquid slurry is C:S= 1:0.5, the water cement ratio is 0.7:0.9, and the grouting pressure is 2.5MPa. The small conduit not only strengthens the loose body around the retaining wall in the excavation section, but also plays the role of advanced support.

(5) The excavation of retaining wall cannot be carried out seriously. In the next excavation, the gravel soil shall be backfilled with permeable materials to the crack for secondary excavation.

4.2.4 Anti-slide pile anchor cable construction

A. The measurement and setting of anchor hole position shall be accurate, with the deviation less than 3, and the allowable deviation of inclination angle less than 3% of the length of anchor cable; Considering the influence of ballast, in order to ensure the depth of anchor cable, the actual drilling depth is greater than the design depth1.0m.

B, it is forbidden to use boiling water when drilling anchor cable, so as to ensure that the deep construction of anchor cable will not worsen the engineering geological conditions of landslide. During the construction of 2# landslide anchor cable, the anchor cable hole often collapses, which makes it impossible to construct normally. The treatment method is to inject double liquid slurry to reinforce loose body and drill holes twice with drilling machine.

C. The tension of anchor cable is divided into five stages, and the load of each stage is 0.25, 0.5, 0.75, 1.0, 1. 1 times of the design tension. The last stage needs to be stabilized for 10 ~ 20 minutes, and the remaining stages need to be stabilized for 5 minutes, and the elongation of each stage is recorded separately. The displacement of the anchor head must be measured and read three times in each level of stabilization time. In addition to the pre-tensioning, the tension of the anchor cable should be graded alternately, so as to ensure the uniform stress of the anchor cable in each hole. If there is obvious prestress loss after tensioning, make up tensioning in time.

D, after tensioning to the last level of load and stable deformation, unloading to the locking anchor cable. After the anchor cable is locked, the redundant steel strand shall be removed as required. After the grouting of the anchor head and the anchor hole of the pile body is completed, the anchor head shall be sealed with C25 concrete in time.

5 conclusion

The above briefly introduces the morphological characteristics of landslide, factors affecting slope stability, landslide formation conditions and landslide prevention measures. Slope formed by natural or artificial excavation can be seen everywhere, which leads to slope instability for various reasons and landslides of various scales from time to time, bringing great disasters to people's production and life. Therefore, as civil engineering technicians, we have the responsibility and obligation to study and control landslides, so as to reduce the occurrence of landslides and reduce the losses caused by landslides. I believe that with the deepening of our research, the landslide phenomenon will be controlled to a certain extent, and our highway construction will be safer.

refer to

[1] Rowen, Hao Yu. Cause analysis and treatment measures of a highway landslide.

[2] Shi Fengbin. Construction technology of anti-slide pile in landslide group.

Xiao Qingfeng, Sun Lianjun, Wang Huoming. On the Causes of Landslides and Preventive Measures [J]. China Waterway (Academic Edition), 2006,9.

;