A landslide emergency disposal method based on failure of existing retaining structure

Abstract

The application discloses a landslide emergency disposal method based on existing retaining structure failure, which comprises the following steps: arranging two drainage ditches outside the landslide area by 5m to cut off the supply path of external water body to the slope body; arranging two drainage blind trenches transversely on the slope surface of the landslide area, compacting clay at the trench bottom, pouring reinforced mesh concrete at the trench bottom and the water side, with a thickness of 15cm, backfilling the trench with broken stones and pebbles, and covering the upper part with soil; setting horizontal drainage holes every 5m apart from the trench bottom by 50cm on the water side of the blind trench to the slope body direction to uncover the potential sliding surface, inserting a flower tube in the horizontal drainage hole, inserting a hard water-permeable tube in the flower tube, and filling fine sand in the pore part; arranging two rows of horizontal drainage holes at the anti-slide pile inter-pile plate part of the non-failed area of the anti-slide pile; the application has small disturbance to the slope body, small construction safety risk, and does not occupy farmland, is suitable for landslide treatment in the deformation stage, and can restore the original landform after construction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of landslide emergency treatment, and particularly relates to a landslide emergency treatment method based on failure of an existing retaining structure. BACKGROUND

[0002] In recent years, due to the enhancement of climate variability, internal dynamic action such as earthquakes, the scale, quantity and frequency of geological disasters are also increasing, especially the occurrence of landslide disasters, which has seriously threatened the survival and life of human beings. Among the numerous landslide disasters, the proportion of accumulation layer landslide is important, and the accumulation layer landslide refers to the landslide in the Quaternary loose accumulation layer except loess and cohesive soil. Due to its special engineering geological characteristics, it is widely distributed in most parts of China.

[0003] After the occurrence of the accumulation layer landslide, the support mode of the cantilever pile is generally adopted for disposal, but due to the complex geological conditions and large changes in stratum lithology, the market may occur due to the reasons such as survey design and construction quality, so that part of the anti-slide pile fails, thereby making the landslide in an unstable state. SUMMARY

[0004] In order to solve the above problems, the present application provides a landslide emergency treatment method based on failure of an existing retaining structure.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] A landslide emergency treatment method based on failure of an existing retaining structure, comprising the following steps:

[0007] S1, respectively calculating the stability of the anti-slide pile failure area and the anti-slide pile non-failure area and the residual sliding force of the landslide, and determining the reinforcement measures to be taken in the two areas;

[0008] S2, arranging two drainage ditches outside the landslide area 5m apart to cut off the supply path of the external water body to the slope body;

[0009] S3, arranging two drainage blind trenches transversely on the slope surface of the landslide area, compacting the clay at the bottom of the trench, pouring the reinforced concrete at the bottom of the trench and the water side, the thickness is 15cm, the particle size of the gravel and pebble in the trench is 10cm, and the upper part is covered with 1.0m of soil;

[0010] S4, setting horizontal drainage holes every 5m towards the slope body at 50cm from the bottom of the blind trench on the water side of the blind trench, and exposing the potential sliding surface, the horizontal drainage hole has a diameter of 170mm, an 168mm steel pipe with a wall thickness of 8mm is inserted into the pipe, 2-3 layers of hard water permeable pipes with different diameters are inserted into the pipe, and fine sand is poured into the pores;

[0011] S5, arranging 2 rows of horizontal drainage holes at the inter-pile plate part of the anti-slide pile in the non-failure area of the anti-slide pile, with a spacing of 8 m, a row spacing of 1.5 m, a length of the horizontal drainage hole of 20 m, and a hole diameter of 170 mm, and pressing in a 168 mm steel pipe (flower pipe) with a wall thickness of 8 mm in the drilling construction process, and inserting 2-3 layers of hard permeable pipes with different diameters into the pipe, and filling fine sand into the pore part;

[0012] S6, collecting the water in the drainage hole to the blind ditch and then discharging it to the two side water intercepting ditches.

[0013] Further, in the step S3, 2 drainage blind ditches MG3 and MG4 are arranged along the transverse direction of the landslide, and two slope drainage blind ditches MG1 and MG2 are arranged along the longitudinal direction of the slope surface, the cross sections of the drainage blind ditches MG1 and MG2 are all inverted trapezoids, the bottom width is 2.0 m, the opening width is 7.03 m, the depth is 3.0 m, and the slope of the ditch wall is 50°; the cross sections of the drainage blind ditches MG3 and MG4 are all inverted trapezoids, the bottom width is 2.0 m, the opening width is 7.16 m, the depth is 3.0-3.4 m, the slope of the water-facing side ditch wall is 45°, and the slope of the backwater side ditch wall is 60°.

[0014] Further, in the step S3, the bottom of the drainage blind ditch is backfilled with gravel and pebbles, and the void ratio is not less than 10%, the upper 1 m of the blind ditch is naturally backfilled with soil, the bottom and the backwater side ditch wall are poured with 15 cm reinforced concrete, and the water-facing side ditch wall is paved with single seepage geotextile, so that the underground water in the slope body can only enter the blind ditch.

[0015] Further, in the steps S4 and S5, 2-3 layers of hard permeable pipes with the upper half being 2 / 3 with small holes and the lower half being 1 / 3 without holes are filled in the drainage flower pipe, and the outer diameter of the hard permeable pipe is 150 mm.

[0016] Further, the step further comprises arranging 1 observation well at the middle and the water outlet part of each drainage blind ditch, the depth is consistent with that of the blind ditch, and the step is used for observing the drainage condition in the blind ditch.

[0017] Further, the step further comprises the measures of filling soil in the failure area, setting a gravity type retaining wall for support, and using a grouting steel pipe pile for reinforcement in the non-failure area.

[0018] The present application has the following beneficial effects:

[0019] 1) The drainage blind ditch and the drainage hole are both buried underground, the original topography can be restored after the construction is completed, and no farmland is occupied.

[0020] 2) There is no large amount of earthwork, the disturbance to the slope body is small, the construction safety risk is small, and the landslide treatment in the deformation stage is more suitable.

[0021] 3) The effect of large-area arrangement of horizontal drainage holes is better than that of single drainage gallery (adit).

[0022] 4) Steel pipe, hard drain pipe are high strength material, which intersect with slide surface at large angle, have certain anti-sliding capacity, landslide treatment effect is more obvious. BRIEF DESCRIPTION OF DRAWINGS

[0023] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, when read in conjunction with the accompanying drawings:

[0024] Figure 1 is the landslide treatment engineering profile in the embodiment of the application.

[0025] Figure 2 is the structural schematic view of the horizontal drainage hole in the embodiment of the application.

[0026] Figure 3 is the blind ditch and ditch bottom drainage hole construction schematic view in the embodiment of the application.

[0027] Figure 4 is the steel pipe pile construction process flow chart in the embodiment of the application.

[0028] In the figure: 1-ground line; 2-drainage ditch; 3-existing cantilever pile; 4-blind ditch; 5-horizontal drainage hole; 6-ground line; 7-sliding surface; 8-drainage open ditch; 9-drainage flower pipe; 10-hard permeable pipe; 11-original topographic line. DETAILED DESCRIPTION

[0029] The application will be described in detail below with specific embodiments. The following embodiments will help the person skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that, for those skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made. These all belong to the protection scope of the application.

[0030] As Figure 1As shown, the embodiment of the present application provides a landslide emergency disposal method based on failure of existing retaining structure, comprising the following steps: arranging two drainage ditches outside the landslide area outside 5m to cut off the supply path of external water body to the slope body; and arranging two drainage blind trenches transversely on the slope surface of the landslide area, using clay compaction on the trench bottom, and using 10cm particle size broken stone and pebble backfill in the trench, and covering the upper part with 1.0m soil; specifically, arranging two drainage blind trenches MG3 and MG4 along the transverse direction of the landslide, and arranging two slope surface drainage blind trenches MG1 and MG2 along the longitudinal direction of the slope surface, the cross sections of the drainage blind trenches MG1 and MG2 are all inverted trapezoids, the bottom width is 2.0m, the opening width is 7.03m, the depth is 3.0m, and the slope of the trench wall is 50°; the cross sections of the drainage blind trenches MG3 and MG4 are all inverted trapezoids, the bottom width is 2.0m, the opening width is 7.16m, the depth is 3.0-3.4m, the slope of the water-facing side of the trench wall is 45°, and the slope of the backwater side of the trench wall is 60°; the broken stone and pebble are backfilled on the bottom of the drainage blind trench, the void ratio is not less than 10%, the upper part of 1m of the blind trench is naturally backfilled with soil layer, the bottom and the backwater side are poured with reinforced mesh sheet concrete with a thickness of 15cm, and the underground water in the slope body can only penetrate into the blind trench;

[0031] Then, horizontal drainage holes are arranged every 5m towards the slope body at a distance of 50cm from the bottom of the blind trench on the water-facing side of the blind trench, and the potential sliding surface is exposed, such as Figure 2 As shown, the horizontal drainage hole has a diameter of 170mm, and a 168mm steel pipe (flower pipe) with a wall thickness of 8mm is inserted in the horizontal drainage hole, 2-3 layers of hard permeable pipes with the upper half of 2 / 3 with small holes and the lower half of 1 / 3 without holes are filled in the drainage flower pipe, the hard permeable pipe has an outer diameter of 150mm, and fine sand is filled in the pore part;

[0032] Two rows of horizontal drainage holes are arranged at the inter-pile plate part of the anti-slide pile in the non-failure area of the anti-slide pile, the interval is 8m, the row interval is 1.5m, the length of the horizontal drainage hole is 20m, the diameter is 170mm, a 168mm steel pipe (flower pipe) with a wall thickness of 8mm is pressed into the horizontal drainage hole in the drilling construction process, 2-3 layers of hard permeable pipes with the upper half of 2 / 3 with small holes and the lower half of 1 / 3 without holes are filled in the drainage flower pipe, the hard permeable pipe has an outer diameter of 150mm, and fine sand is filled in the pore part;

[0033] The water body in the drainage hole is collected to the blind trench and then discharged to the two side water intercepting ditches, and one observation well is arranged at the middle and water outlet part of each drainage blind trench, the depth is consistent with that of the blind trench, and the drainage condition in the blind trench is observed.

[0034] Application example

[0035] 1. Landslide hazard situation

[0036] According to the "Guizhou Provincial Building Science Research and Testing Center Judicial Authentication Opinion" (Guizhou Provincial Building Science Research and Testing Center from February 25, 2022 to July 18, 2022), in the Shashipu landslide treatment area, the 1-19th anti-slide piles encountered pile bodies at positions of 2.8-8.6m, cracks existed in the borehole walls of the 2nd, 4th, 20th-22nd anti-slide piles, and suspected cracks or construction joints existed on the borehole walls of the 38th anti-slide pile. Combined with the landslide slope sliding condition, the 1st-22nd anti-slide piles have been damaged by the deformation of the slope. Based on the above, the Shashipu landslide area is divided into two regions: anti-slide pile failure area and anti-slide pile non-failure area.

[0037] Anti-slide pile failure area: including the area where the 1st-22nd anti-slide piles are located, most of the pile bodies in this area have been broken, and the pile body integrity is class IV, which is a severely defective pile. The maximum concrete strength detection value of the 22nd anti-slide pile in this area is 40.0Mpa, and the minimum concrete strength detection value of the 16th anti-slide pile is 15.1Mpa.

[0038] Anti-slide pile non-failure area: including the area where the 23rd-54th anti-slide piles are located, the pile body integrity of the anti-slide piles in this area is basically class II-III, among which the 26th, 35th, 38th and 41st anti-slide piles have class IV pile body integrity and serious pile body defects. The maximum concrete strength detection value of the 25th anti-slide pile in this area is 41.9Mpa, and the minimum concrete strength detection value of the 26th anti-slide pile is 20.4Mpa.

[0039] Due to the long-term creep deformation of the Shashipu landslide, some anti-slide piles have failed. In order to ensure the stability of the slope, the soil backfilling measure has been taken at the slope toe position in the anti-slide pile failure area. According to the latest monitoring report (Guizhou Geological Engineering Investigation and Design Research Institute Co., Ltd. prepared in July 2022), the anti-slide pile failure area is still deforming, and the landslide has the possibility of continuing to slide and damage. The landslide instability and damage will threaten the life and property safety of the residents in the slope, the vehicles and pedestrians on Longquan Avenue, and the construction of the resettlement housing project below the slope, with more than 400 households and more than 1900 people threatened, potential economic losses of more than 50 million yuan, and great harm. According to Table 3 of the "Geological Disaster Risk Assessment Specification" (GB / T 40112-2021), the risk of this landslide disaster is great.

[0040] 2. Geographical and geological environmental conditions

[0041] 2.1 Topography and geomorphology

[0042] Xifeng County is a low mountain-peak cluster karst gully landform of erosion. The landslide area is a low mountain landform of denudation and shallow cutting, and is located in the high southwest and low northeast slope section. The landslide area is located in the lower slope section of the northeast side of the Tuan Yuan Mountain, a famous scenic spot in Xifeng County. The overall trend of the mountain range is northeast-southwest.

[0043] 2.2 Hydrogeological conditions

[0044] (I) Groundwater type

[0045] The landslide area has a double-layer structure of overlying loose soil layer and underlying bedrock. Groundwater is divided into two types according to its occurrence characteristics and water properties: bedrock fissure water and Quaternary loose layer pore water.

[0046] Quaternary loose layer pore water: mainly distributed in the clay and gravel stratum of Quaternary residual slope deposition in the landslide slope body. This layer is a strong water-rich layer. It mainly receives lateral recharge of atmospheric precipitation and bedrock fissure water, and flows through the interconnected pores of loose soil layer. The surface water is discharged to low-lying areas, and a small amount of pore water seeps out at the front of the landslide. The soil permeability coefficient K value is between 10 -5 -10 - 4 cm / s, which is weakly permeable.

[0047] Bedrock fissure water: the bedrock fissure water in the landslide area occurs in the fissures of the Jurassic middle and lower Ziliujing group (J 1-2 zl 1+2 ) gray black, gray brown and brown mudstone interbedded with limestone, and is poor in water abundance.

[0048] (II) Recharge, runoff and discharge conditions of groundwater

[0049] The groundwater level in the site changes greatly due to seasonal precipitation. Groundwater is mainly recharged by atmospheric precipitation, and runs off to low-lying areas. The main discharge modes are evaporation and downward seepage.

[0050] (III) Corrosive characteristics of groundwater

[0051] According to the "Investigation Report", the pH value of groundwater in the landslide area is 7.49, the free CO2 value is 8.35, and there is no erosive CO2, which has a slight corrosive effect on concrete and steel structures.

[0052] 2.3 Engineering geological conditions

[0053] Supplement the description of the stratum lithology revealed by drilling in the "Investigation Report". According to different rock and soil characteristics, the engineering geological rock group classification is carried out.

[0054] According to the "exploration report", the rock-soil composition in the landslide area is relatively complex, the slope body is composed of plain fill, quaternary clay with gravel, and the underlying bedrock is Jurassic lower self-flowing well group (J 1-2 zl 1+2 ) strong-medium weathered mudstone, mudstone.

[0055] ① Plain fill: loose structure, brownish yellow, mainly for landslide fill, clay, and broken stone, backfill time more than 2 years, thickness about 6.4-9.2m.

[0056] ② Quaternary residual slope accumulation clay with gravel (Q4 el+dl ): brownish yellow, yellowish brown, purplish red, mainly composed of clay with gravel, thickness about 8.4-24.4m, average thickness about 15m. The gravel particle size is 2-5cm, the structure is loose, the shape is rhombus, and the gravel is mainly mudstone and mudstone in the strong weathering layer. This layer is saturated with water and has poor stability. According to the comprehensive analysis of drilling results, the clay with gravel in the whole site is mainly divided into two regions: high gravel content and relatively low gravel content.

[0057] ③ Strong weathering broken layer mudstone with mudstone (J 1-2 zl 1+2 ): gray black, gray brown, the whole site drilling is exposed, the core recovery rate is poor, the structure is blocky, thin-medium bedded, the mudstone is strongly weathered, the mudstone is relatively weak, the soft rock is easy to soften after soaking.

[0058] ④ Medium weathered mudstone with mudstone (J 1-2 zl 1+2 ): gray black, gray brown, brown, the whole site drilling is exposed, the core is broken, short columnar, the core recovery rate is higher, the structure is thin-medium bedded, the structure is mud-crystal, the joint fissure is well developed, the core at the top of the slope is better, the stratum occurrence is 240°∠36°.

[0059] According to the mechanical properties, lithology and combination relationship of rock and soil body in the landslide area, the rock-soil layers in the area are divided into two types: loose rock engineering geological rock group and soft rock engineering geological rock group.

[0060] (1) Loose rock engineering geological rock group

[0061] composed of quaternary (Q4 el+dl ) residual slope accumulation layer and plain fill, brownish yellow, yellowish brown, purplish red, mainly composed of clay with gravel, with loose structure and large porosity.

[0062] (2) Soft rock engineering geological rock group

[0063] composed of Jurassic lower self-flowing well group (J 1-2 zl 1+2), which is composed of gray-black, gray-brown, brown mudstone with limestone. Thin to medium thick structure, argillaceous-microcrystalline structure, poor rock integrity, core is mostly broken, short column, weathering layer is thick, low mechanical strength, easy weathering and erosion.

[0064] 3. Basic characteristics and stability analysis of landslide

[0065] 3.1 Basic characteristics of landslide

[0066] 3.1.1 Range and scale of landslide

[0067] According to the "exploration report", the rear edge of Shashipos landslide is determined by tension cracks, and the two sides are bounded by damaged drainage ditches, and the plane is tongue-shaped. The main sliding direction of the landslide is 63°, the average length of the sliding body is about 200m, the slope width is about 150m, the average thickness of the sliding body is about 12m, and the volume is about 36x10 4 m 3 , which belongs to medium-sized middle-layer traction soil landslide.

[0068] 3.1.2 Material composition of landslide

[0069] The material composition of the sliding body is mainly clay with gravel, generally plastic, locally soft plastic, and low shear strength. The specific gravity of clay with gravel is γ = 19.2KN / m 3 , and the saturated state is γ sat = 20.4KN / m 3 .

[0070] The material composition of the sliding zone is that the upper part of the sliding surface of Shashipos landslide is the contact surface between the Quaternary clay with gravel layer and the adjacent underlying bedrock, and the lower part of the sliding surface is the yellow clay layer with relatively low gravel content in the clay with gravel. The underlying bedrock is mainly strongly weathered mudstone, which has poor permeability. After precipitation, water is easy to accumulate at the rock-soil interface and is not easy to drain. After being soaked by water, the strength of the bottom of the clay with gravel in the sliding zone decreases, and the properties deteriorate. The sliding surface is generally 10°-40°. Under natural conditions, the standard value of cohesion in the sliding zone is C = 16.9kpa, and the standard value of internal friction angle is φ = 10.2°; under saturated conditions, the standard value of cohesion is c = 15.2Kpa, and the standard value of internal friction angle is φ = 9.2°.

[0071] The material composition of the sliding bed is mainly the mudstone layer of Jurassic middle and lower Ziliujing group (J 1-2 zl 1+2 ) and the Quaternary residual slope clay with gravel (Q4 el+dl ) layer; Jurassic middle and lower Ziliujing group (J 1-2 zl1+2 ) The lithology is gray-black, gray-brown, brown mudstone with limestone, the occurrence of the strata is 240°∠36°, thin to medium bedded structure, argillaceous-microcrystalline structure, poor rock integrity, most of the core is in the form of soil with rock and short column, the weathering layer is thick, the mechanical strength is low, and it is easy to weather and erode. The Quaternary residual deposit clay with gravel (Q4 el+dl ) Brownish yellow, yellowish brown, purplish red, according to the site drilling, it is mainly composed of clay with gravel, and the slide bed is mainly at the boundary between high gravel content and low gravel content.

[0072] 3.2 Landslide deformation characteristics

[0073] 3.2.1 Recent deformation and damage of the landslide

[0074] The Shashipu landslide treatment project began to deform in 2013, and in 2018, anti-slide piles were used for support, but the anti-slide piles were locally failed, the slope body continued to deform and destabilize, most of the drainage ditches built in the middle of the slope body were damaged, and three cracks (LF1-LF3) of different sizes appeared on the surface of the slide body along the drainage ditches. At present, it is in a stable to basically stable state. According to the latest "Xifeng County Yongyang Street Office Shashipu resettlement plot landslide front, anti-slide pile and slope top ground deformation monitoring report" in July 2022, there are obvious displacement signs in the anti-slide pile failure area.

[0075] 3.2.2 Development trend of landslide deformation

[0076] The landslide has partially slid, and the anti-slide pile has partially failed due to shear failure of the sliding mass, resulting in structural damage and failure. To prevent further sliding of the sliding mass, relevant units have taken counter-pressure measures at the toe of the slope. According to the latest monitoring report in July 2022, the anti-slide pile failure zone is still deforming, and the anti-slide pile non-failure zone is not deforming. According to the field investigation, cracks are well developed, and local surface cracks form depressions. Rainwater accumulates in the depressions after rainfall, and the counter-pressure soil in the anti-slide pile failure zone plays a role in resisting sliding. However, considering the continuous effect of heavy rainfall, the landslide has the potential to continue to slide and cause damage. According to the latest monitoring report and field investigation, the horizontal displacement cumulative increment of the anti-slide pile non-failure zone from July 1, 2022 to July 31, 2022 is 0.17mm, and the average daily displacement rate is 0.01mm / d. The vertical displacement cumulative increment is 1.95mm, and the average daily displacement rate is 0.06mm / d. The slope deformation is not obvious, and no sliding phenomenon is observed. The maximum settlement deformation of the anti-slide pile failure zone from July 15, 2019 to September 29, 2019 is 299.1mm, and the maximum horizontal displacement is 808mm. The maximum horizontal displacement rate is 10.8mm / d. Part of the pile body and the crown beam deformation and failure have occurred, which threatens the safety of the construction of the residential area at the toe of the slope, the construction safety of the Heilongquan Road (more than 400 households and 1900 people, threatening property of more than 50 million yuan), and the safety of life and property of local people on the slope.

[0077] 3.3 Landslide stability analysis and evaluation

[0078] According to the "Investigation Report", the stability calculation of the sandstone slope landslide in Yonghong Village, Yongjing Town, Xifeng County is shown in Table 1.

[0079] Table 1 Stability calculation results of sandstone slope landslide in Yonghong Village, Yongjing Town, Xifeng County

[0080]

[0081] The stability coefficient of the anti-slide pile failure zone (profile 1-1') is 1.046 before the toe counter-pressure and 1.117 after the toe counter-pressure under the condition of heavy rain according to the broken line sliding method. The stability coefficient of the anti-slide pile non-failure zone (profile 2-2') is 0.989 without considering the effect of the anti-slide pile and 1.110 considering the effect of the anti-slide pile under the condition of heavy rain. It does not meet the design safety factor requirement and needs to take support measures.

[0082] Through stability analysis and calculation of the anti-slide pile failure zone and the anti-slide pile non-failure zone, in order to protect the safety of life and property of residents around the slope, and considering the field situation and the requirements of the owner, effective prevention and control engineering measures need to be taken for the sandstone slope landslide.

[0083] 3.3 Inducing factors of landslide

[0084] According to the Survey Report, the inducing factors of the landslide are mainly as follows:

[0085] (1) Topographic and geomorphic conditions: The landslide area is a sloping section with the southwest side higher and the northeast side lower, with a natural slope of 15° to 35°. The rear and front edges of the landslide are steep, the middle part is relatively flat, and the overall terrain is ladder-shaped.

[0086] (2) Stratum and lithology factors: The main composition of the sliding body is clay with gravel, with uneven properties, from plastic to hard plastic. According to the Survey Report, the gravel content is lower in the soil layer above the sliding surface and higher in the lower part. The surface soil is relatively loose, and the soil strength increases with depth, with relatively good engineering properties. The surface drainage ditch in the landslide area has been damaged, and the slope drainage condition is poor. After rainfall, rainwater infiltrates into the landslide slope, and the underlying bedrock is mainly mudstone with mudstone, which is weakly permeable. The accumulated water cannot be easily discharged, and the soil body is immersed for a long time, increasing the self-weight and reducing the shear strength.

[0087] (3) Rainfall factor: The landslide area is rich in rainwater, and under the action of heavy rainfall, the infiltration of rainwater increases the self-weight of the potential sliding body. The accumulated water cannot be discharged in time, which softens the contact surface between the potential sliding body and the rock-soil body, reduces the physical and mechanical indicators of the potential sliding surface, and becomes one of the main inducing factors of landslide formation.

[0088] (4) Influence of human engineering activities

[0089] Human engineering activities such as soil and stone excavation at the slope toe caused the slope body to creep and crack. The sandstone slope at the slope toe was excavated for the housing project site leveling construction, forming a free surface under the natural slope of the mountain, leading to cracks on the slope surface, and then instability and deformation. After the construction of the anti-slide pile support at the landslide toe was completed, due to the complex geological conditions, some of the anti-slide piles south of No. 22 anti-slide pile failed, and the sliding body continued to deform along the original sliding surface in the anti-slide pile failure area.

[0090] 4 Calculation of landslide thrust

[0091] The landslide is a Quaternary accumulation landslide, and the slope body mainly occurs as a broken line along the potential sliding surface. This time, profile 1-1' and 2-2' are selected to calculate the residual sliding force in the anti-slide pile failure area and the anti-slide pile non-failure area, respectively. According to Table 1 and Table 5 of the "Landslide Prevention and Design Specification" GB / T38509-2020, the importance level of landslide prevention engineering is grade I. The design safety factor under natural conditions is 1.30, and the design safety factor under heavy rain conditions is 1.25. According to the "Landslide Prevention and Design Specification" (GB / T38509-2020), the formula for calculating the residual sliding force of the landslide is as follows:

[0092]

[0093] Wherein:

[0094] T i = (W i + V i ) sin α i + Q i cos α i - P i cos (α i + β i )

[0095]

[0096] E i = T i - R i / F s + ψ i E i-1

[0097] Wherein: F s - landslide safety factor;

[0098] R i - the i-th sliding block resistance to sliding force, unit kN, the n-th sliding block resistance to sliding force R n ;

[0099] ψ i - the i-1-th sliding block to the i-th sliding block transmission coefficient;

[0100] T i - the i-th sliding block under the sliding force, unit kN, the n-th sliding block under the sliding force T n ;

[0101] W i - the i-th sliding block weight, unit kN;

[0102] V i - the i-th sliding block vertical seismic inertia force (V direction to " - ", down to " + "), unit kN;

[0103] Q i - the i-th sliding block horizontal seismic inertia force (Q i direction consistent with the sliding direction to " + ", otherwise to " - "), kN;

[0104] U bi - the i-th sliding block bottom hole pressure, unit kN;

[0105] P i-- The external force acting on the i-th sliding block (excluding the slope external water pressure), in units of kN;

[0106] α i -- The angle between the bottom surface of the i-th sliding block and the horizontal line (with the horizontal line as the starting line, counterclockwise positive angle, clockwise negative angle), in units of degrees (°);

[0107] β i -- The angle between the external force P of the i-th sliding block and the horizontal line (with the horizontal line as the starting line, clockwise positive angle, counterclockwise negative angle), in units of degrees (°); i

[0108] c′ i 、 -- The effective cohesion (kPa) and internal friction angle (°) of the bottom surface of the i-th sliding block;

[0109] b i -- The length of the i-th sliding block along the sliding surface, in units of meters (m);

[0110] E i-1 -- The thrust of the i-1-th sliding block acting on the i-th sliding block, in units of kN, i = 2, 3, 4,..., n;

[0111] E i -- The reaction force of the i+1-th sliding block on the side surface of the i-th sliding block, in units of kN, equal in size and opposite in direction to the thrust of the i-th sliding block.

[0112] After calculation, the residual sliding force calculation results of the anti-slide pile failure zone (cross section 1-1') and the anti-slide pile non-failure zone (cross section 2-2') are shown in the following table, and the calculation process is detailed in the calculation book.

[0113] Table 2 Residual sliding force calculation results of anti-slide pile failure zone (cross section 1-1') and anti-slide pile non-failure zone (cross section 2-2')

[0114]

[0115]

[0116] ​In summary, according to the actual situation on site, the failure zone of anti-slide pile (profile 1-1') has taken soil counter-pressure measures at the toe position, and the slope body is in a basically stable-stable state under natural and storm conditions, and the stability coefficient does not meet the design safety factor requirement, so support measures need to be taken. According to the residual sliding force of 325.69 kN / m (12th sliding block) under storm conditions according to the broken line sliding method, the support structure taken is checked. If the construction quality of the anti-slide pile in the non-failure zone of the anti-slide pile (profile 2-2') is considered to meet the design requirements, the stability coefficient of the slope under storm conditions is 1.110, which does not meet the design safety factor requirement, and according to the "Guizhou Provincial Building Science Research and Testing Center Judicial Expert Opinion" (Guizhou Provincial Building Science Research and Testing Center from February 25, 2022 to July 18, 2022), there are serious defect piles of type IV in this area, therefore, appropriate disposal measures need to be taken in this area.

[0117] 5 Landslide treatment engineering design

[0118] 5.1 Basic parameters

[0119] (1) Meteorology

[0120] The storm intensity is designed for a 50-year return period and checked for a 100-year period.

[0121] (2) Earthquake

[0122] This design does not consider earthquake prevention.

[0123] (3) Treatment engineering load

[0124] ① Self-weight + groundwater: above the groundwater, take the natural unit weight of the soil, and below the saturated unit weight.

[0125] ② External load: the main external load on the slope surface is the local residential building. Since there are currently no high-rise buildings, the slope load is not considered in the calculation.

[0126] (4) Grade of landslide prevention and control engineering

[0127] According to Table 3 of "Specification for Landslide Prevention and Control Engineering" (GB / T 32864-2016), the grade of this landslide geological disaster prevention and control engineering is level I.

[0128] (5) Geotechnical physical and mechanical parameters

[0129] According to the "Investigation Report", the values of various geotechnical parameters in the landslide area are as follows:

[0130] 1) Landslide soil: clay with gravel, unit weight γ = 19.2 KN / m 3 , saturated state γ sat = 20.4 KN / m 3 .

[0131] 2) Slip zone soil: Under natural conditions, the standard value of cohesion is C = 16.9 kPa, and the standard value of internal friction angle is φ = 10.2°; under saturated conditions, the standard value of cohesion is c = 15.2 KPa, and the standard value of internal friction angle is φ = 9.2°.

[0132] 5.2 Overall layout of treatment project

[0133] 5.2.1 Treatment project zoning

[0134] According to the "Guizhou Provincial Building Science Research and Testing Center Judicial Expert Opinion" (Guizhou Provincial Building Science Research and Testing Center from February 25, 2022 to July 18, 2022), in the Shashipu landslide treatment area, No. 1-19 anti-slide piles meet the pile body at 2.8-8.6 m, No. 2, No. 4, No. 20-22 anti-slide piles have cracks on the borehole wall, and No. 38 anti-slide pile has suspected cracks or construction joints on the borehole wall. Combined with the landslide slope slip condition, comprehensive analysis shows that No. 1-22 anti-slide piles have been damaged by the deformation of the slope. Therefore, the Shashipu landslide treatment area is divided into two areas: anti-slide pile failure area and anti-slide pile non-failure area.

[0135] Anti-slide pile failure area: including the area where No. 1-22 anti-slide piles are located, most of the pile bodies in this area have been broken, and the pile body integrity is class IV, which is a severely defective pile. The maximum concrete strength detection value of No. 22 anti-slide pile is 40.0 Mpa; the minimum concrete strength detection value of No. 16 anti-slide pile is 15.1 Mpa.

[0136] Anti-slide pile non-failure area: including the area where No. 23-54 anti-slide piles are located, the anti-slide pile body integrity in this area is basically class II-III, and the anti-slide pile body integrity of No. 26, No. 35, No. 38 and No. 41 is class IV, with serious defects in the pile body. The maximum concrete strength detection value of No. 25 anti-slide pile is 41.9 Mpa; the minimum concrete strength detection value of No. 26 anti-slide pile is 20.4 Mpa.

[0137] 5.2.2 Design idea of treatment project

[0138] The anti-slide pile failure area (cross section 1-1') has taken soil counterpressure measures at the slope toe position. Under condition I, considering the action force of the counterpressure soil, the slope is in a stable state, meeting the specification requirements; under condition II, considering the action force of the counterpressure soil, the slope is in a stable state, but the slope stability coefficient does not meet the design safety factor requirements. The soil structure of the counterpressure soil is relatively loose, and the monitoring data shows that the slope still has a certain displacement. In order to ensure the safety of the resettlement land, a gravity retaining wall is set up at the slope toe position.

[0139] In the unfailed area of ​​the anti-slide piles (section 2-2'), if the construction quality of the anti-slide piles meets the design requirements, the slope stability coefficient under working condition II is 1.15, which does not meet the design safety factor requirements. In addition, there are piles with serious quality defects of Class IV in this area. In order to ensure the safety of the resettlement site, steel pipe piles are used to reinforce the slope behind the anti-slide piles, and drainage holes are set at the pile joints of the anti-slide piles to lower the groundwater level at the location of the anti-slide piles and reduce the thrust of the landslide soil on the anti-slide piles.

[0140] Based on on-site investigation and borehole water level monitoring during the exploration period, the upper layer of the middle and lower parts of the gravel slope landslide area is rich in perched water, and the surface clay layer of the slope is thick with poor permeability, remaining saturated for a long time. Even after the main support structure was completed in October 2018, the slope continued to deform, causing the rear edge of the landslide to move backward by 80 meters. In the middle and upper parts of the gravel slope landslide area, the groundwater level is relatively deep, and the surface clay layer is relatively thin with good permeability. Through comprehensive analysis, the influence of groundwater is the main factor contributing to the continuous deformation of the gravel slope landslide. Its hazards are mainly manifested in increasing the weight of the soil and rock, increasing the sliding force, reducing the shear strength of the soil, increasing the dynamic water pressure of groundwater, increasing the buoyancy force, and reducing the effective stress on the sliding surface. If a reasonable interception and drainage system is installed in the landslide area to drain the groundwater (surface water), allowing the landslide body to operate under its own weight for a long time, the long-term stability of the landslide area can be guaranteed. Therefore, comprehensive landslide control is implemented by setting up drainage ditches around the perimeter of the landslide area and blind ditches in the middle and lower parts.

[0141] 5.3 Sub-item Engineering Design

[0142] 5.3.1 Interception and Drainage Works

[0143] (1) Interception drainage ditch

[0144] To prevent surface water from replenishing the landslide slope, four new intercepting and drainage ditches were added around the landslide area and connected to the existing undamaged drainage ditches (e.g., Figure 1 (As shown).

[0145] The total length of the intercepting drainage ditch designed in this project is 692.6m, with sections A-A' measuring 398.4m, B-B' 82.9m, C-C' 109.5m, and D-D' 101.8m. The drainage ditch has a trapezoidal cross-section, with net dimensions of 0.65m × 0.40m × 0.65m (net width × net width × net height), consistent with the dimensions of the existing intercepting drainage ditch on the site. C25 cast-in-place concrete is used, with reinforcing mesh at the bottom and along the sides, using φ8@HPB300 steel bars. Settlement joints are installed every 10-15m and filled with asphalt-impregnated hemp or other waterproofing materials.

[0146] Design standards: The most important design standard for surface drainage engineering is the rainfall standard, followed by the superelevation standard of the drainage ditch and the flow velocity standard.

[0147] 1) Rainfall criteria: The design rainfall intensity of the landslide area is 50 years. The drainage ditch is designed based on this standard.

[0148] 2) Ultra-high standard: Not less than 0.3m under design conditions.

[0149] 3) Water flow velocity standard: Not more than 4m / s under design conditions.

[0150] Drainage engineering layout principles:

[0151] 1) The rainfall in the landslide area is guided into the peripheral drainage ditch through two drainage ditches to the maximum extent.

[0152] 2) The water interception ditch is arranged along the contour line as much as possible, so that the ditch can maximize water interception and be easy to drain.

[0153] 3) The ditch bottom of the drainage ditch should ensure that the ditch does not wash and does not silt, that is, a certain water speed is ensured, so that it neither washes the ditch structure nor appears silt accumulation.

[0154] 4) Try to avoid crossing with other structures, reduce bends, and try to be arranged within the scope of land acquisition, occupy less or no farmland.

[0155] According to "Landslide Prevention Design Specification" (GB / T38509-2020) 9.2.3, when the catchment area is less than 3km 2 (0.08km 2 of catchment area outside the treatment area according to topographic conditions), the design frequency of surface water runoff Q p is calculated as follows:

[0156] Q p = φS p F

[0157] Where: Q p — Design frequency of surface water runoff, unit: cubic meters per second (m 3 / h);

[0158] S p — Design rainfall intensity, unit: millimeters per hour (mm / h), according to the maximum daily rainfall of Xifeng County for many years, 138.7mm, take 10mm / h when calculating; (Verify rainfall data)

[0159] Φ— runoff coefficient, φ = 0.7 for hilly land in landslide area;

[0160] F— catchment area, km 2 ;

[0161] The design runoff of the drainage ditch Q is calculated as follows:

[0162] Q = VA g

[0163] where: Q = design flow rate, in cubic meters per second (m 3 / s);

[0164] V = average flow velocity in the ditch, in meters per second (m / s);

[0165] A g = design cross-sectional area, in square meters (m 2 ) ;

[0166] The average flow velocity in the drainage ditch can be calculated as follows:

[0167] V = R2 / 3i1 / 2 / n s

[0168] where: V = average flow velocity in the ditch, in meters per second (m / s);

[0169] R = hydraulic radius, in meters (m);

[0170] i = hydraulic slope, which can be taken as the bottom slope of the ditch or pipe, and the minimum value is 0.02.

[0171] n s = roughness coefficient of the ditch wall or pipe wall, which is 0.014 for a cement mortar coated channel.

[0172] A g = design cross-sectional area, in square meters (m 2 ) ;

[0173] After calculation, the flow parameters of each drainage open ditch are shown in Table 3.

[0174] Table 3 Flow parameters of each drainage open ditch

[0175] Drainage ditch F(km 2 )]]> Q p (m 3 / s)]]> A g (m 2 )]]> R(m) Q(m 3 / s)]]> v(m / s) PS1-PS4 0.08 0.56 0.34 0.17 1.05 3.10

[0176] According to 9.2.7 of the “Landslide Prevention Design Specification” (GB / T 38509-2020), the maximum allowable flow rate of the concrete open ditch is 10.0 m 3 / s, and the design flow rate of the drainage ditch is 1.05 m 3 / s, which is greater than the design frequency of the site surface water flow rate of 0.56 m 3 / s, and the drainage ditch design meets the requirements.

[0177] (2) Underground drainage blind ditch

[0178] The groundwater of Shashipo landslide is mainly the upper layer of stagnant water in the clay layer with gravel, so the underground drainage system is mainly arranged for the clay layer with gravel. Two drainage blind trenches (MG3, MG4) are arranged along the transverse direction of the landslide, and the horizontal drainage holes are set every 5m towards the slope body. In order to guide the surface water to MG3 and MG4, two slope surface drainage blind trenches (MG1, MG2) are arranged along the longitudinal direction of the slope. The groundwater in the blind trenches is drained to the peripheral drainage ditch of the landslide, and finally drained out of the landslide along the drainage ditch.

[0179] The drainage blind trenches MG1 and MG2 are arranged along the longitudinal direction of the landslide, with lengths of 183.2m and 180.4m respectively. The cross section of each is inverted trapezoidal, with a bottom width of 2.0m, an opening width of 7.03m, a depth of 3.0m, and a slope of 50°. The drainage blind trenches MG3 and MG4 are arranged along the transverse direction of the landslide, with lengths of 176.8m and 205.8m respectively. The cross section of each is inverted trapezoidal, with a bottom width of 2.0m, an opening width of 7.16m, a depth of 3.0-3.4m, a slope of 45° on the water-facing side, and a slope of 60° on the backwater side.

[0180] The bottom of the drainage blind trench is backfilled with gravel and pebbles, with a void ratio not less than 10%. The upper 1m of the blind trench is naturally backfilled with soil. The bottom and walls of the trench are paved with single-ply water-permeable geotextile, and the groundwater in the slope body can only penetrate into the blind trench. Horizontal drainage holes are set every 5m towards the slope body, with a diameter of 170mm. A 168mm outer diameter drainage flower pipe is pressed into the hole during drilling. The upper 2 / 3 of the drainage flower pipe is filled with small holes, and the lower 1 / 3 is not filled with holes. A hard permeable pipe with a diameter of 150mm is used to quickly drain the groundwater and prevent secondary seepage of groundwater.

[0181] (3) Horizontal drainage holes

[0182] Drainage holes are set at the inter-pile plate part of the anti-slide pile in the non-failed area, with a spacing of 4m and a length of 20m. The drainage holes have a diameter of 170mm, and a 168mm outer diameter drainage flower pipe is pressed into the hole during drilling. The upper 2 / 3 of the drainage flower pipe is filled with small holes, and the lower 1 / 3 is not filled with holes. A hard permeable pipe with a diameter of 150mm is used to quickly drain the groundwater and prevent secondary seepage of groundwater.

[0183] (4) Backfilling of drainage ditch

[0184] According to the site investigation and design scheme, part of the drainage ditch in the landslide area has been damaged. This scheme designs to add 4 sections of interception and drainage open ditches to connect with the original undamaged drainage open ditches, and to backfill the damaged and unused drainage ditches with clay.

[0185] 5.3.2 Retaining wall engineering

[0186] The gravity retaining wall is arranged at the position of the anti-slide pile failure zone (the 12th slide block) and the counter-pressure slope toe. The retaining wall is divided into five sections, i.e. AB, BC, CD, DE and EF, with a total length of 118 m, wherein the length of AB section is 54 m, the length of BC section is 8 m, the length of CD section is 6 m, the length of DE section is 8 m, and the length of EF section is 42 m. The wall height is 8.0 m, the wall top is 1.5 m, the wall bottom width is 4.6 m, the wall body is made of C25 cast-in-situ concrete, and the foundation is buried 1.5 m deep and filled with graded gravel.

[0187] 5.3.3 Steel pipe pile project

[0188] Four rows of steel pipe piles are arranged at the position of the 5th slide block in the anti-slide pile non-failure zone, with a treatment width of 76 m. The steel pipe piles are arranged in a plum blossom shape with a hole spacing of 2 m and a row spacing of 1 m, and the hole diameter is 250 mm. The 20# seamless steel pipe with an outer diameter of 194 mm and a wall thickness of 10 mm is used, and 1 piece of 12# I-shaped steel is inserted into the pipe, which is filled with C25 concrete. The pipe is externally injected with M30 cement slurry, the top of the pile is firmly welded with a Φ25 tie rod to increase the integrity, and a C25 concrete slab with a thickness of 20 cm is poured to seal the top.

[0189] 6 Project monitoring design

[0190] 6.1 Monitoring work scheme

[0191] 6.1.1 Monitoring method

[0192] (1) Deep displacement

[0193] The reading changes and the cumulative changes with depth of the corresponding positions in the inclinometer tube at different times are observed by the borehole inclinometer. The horizontal displacement amounts of the inclinometer tube mouth and different depths are obtained, the size, direction and rate of the displacement of the slope are determined, and the full-depth and full-direction deformation observation purposes are achieved.

[0194] (2) Absolute displacement monitoring of landslide surface

[0195] The conventional geodetic deformation measurement is used to realize the monitoring of the size, direction and rate changes of the horizontal displacement and vertical displacement of the crack segmented slide body.

[0196] (3) Relative displacement monitoring of cracks

[0197] The relative displacement monitoring of cracks on the slope body is arranged along the slope body development, and the purpose is to intuitively understand the deformation development condition of the slope surface layer, and guide the disaster prevention and mitigation work with other monitoring means.

[0198] (4) Visual observation

[0199] The designated personnel are arranged to check the ground deformation signs of each section and whether the protection project is failed at irregular intervals, find out the problems, and timely report to the relevant departments so as to timely and properly handle the problems.

[0200] 6.1.2 Monitoring arrangement

[0201] According to the geological and topographic features of Shashiposlope, surface displacement and groundwater level monitoring are arranged in the landslide section. A total of 6 surface absolute displacement monitoring points and 4 groundwater level monitoring points are newly arranged on the landslide body, and the existing monitoring points (2 monitoring reference points, 5 surface absolute displacement monitoring points) are used to form a monitoring network. The coordinates of the monitoring points are as follows:

[0202] Table 4 Coordinates of monitoring points in Shashipo landslide area (independent coordinate system of Guiyang City)

[0203] No. X coordinate Y coordinate Monitoring point type Remark GSJ1 98292.418 74271.973 Monitoring reference point Built GSJ2 98011.063 74329.340 Monitoring reference point Built GS1 98011.063 74260.430 Displacement monitoring point Built GS2 98116.697 74270.306 Displacement monitoring point Built GS3 98084.561 74288.316 Displacement monitoring point Built GS4 98047.637 74297.247 Displacement monitoring point Built GS5 98066.441 74236.995 Displacement monitoring point Built GSSW1 98145.308 74233.362 Water level monitoring point Newly added GSSW2 98094.176 74242.474 Water level monitoring point Newly added GSSW3 98103.498 98103.498 Water level monitoring point Newly added GSSW4 98052.577 74198.928 Water level monitoring point Newly added GSWY1 98217.904 74237.215 Displacement monitoring point Newly added GSWY2 98185.546 74251.103 Displacement monitoring point Newly added GSWY3 98158.167 74185.927 Displacement monitoring point Newly added GSWY4 98021.341 74213.913 Displacement monitoring point Newly added GSWY5 97988.058 97988.058 Displacement monitoring point Newly added GSWY6 97922.216 73998.919 Displacement monitoring point Newly added

[0204] 6.2 Technical requirements for monitoring work

[0205] 6.2.1 Monitoring level

[0206] According to the "Code for Monitoring of Collapse, Landslide and Debris Flow" (DZ / T 0221-2006), general landslide observation in the field should be observed according to the deformation measurement level three, and the coordinate error of displacement observation point should be less than or equal to 10 mm.

[0207] 6.2.2 Determination of monitoring period

[0208] The deformation observation period should be able to systematically reflect the change process of the monitored deformation and not miss its major changes. According to the size of deformation per unit time and the influence of external factors, the observation period should be shortened and the number of observations should be increased when heavy rain, rapid deformation speed or the possibility of sudden disasters are found during observation.

[0209] In the rainy season, observation is carried out every 10 days, and in the dry season, observation is carried out every half month; during construction, the horizontal and vertical displacement changes of the slope body, the horizontal and vertical changes of the landslide rear edge crack are continued to be monitored to achieve the purpose of safety monitoring. After the completion of the treatment engineering construction, long-term monitoring should be converted, which can be monitored once every 15-30 days, and the displacement (deformation) of the pile top of the treatment engineering should be monitored, and the monitoring time is 2-3 hydrological years. Long-term monitoring should be designed and managed by units with corresponding qualifications.

[0210] 7 Construction technical requirements and matters needing attention

[0211] 7.1 Drainage works

[0212] (1) Drainage open ditch

[0213] ① Construction preparation

[0214] The construction site three pass one flat work to complete, into the working face and other construction auxiliary road has been built; all steel, concrete raw materials have been tested and qualified; all construction machinery has been in place and meet the construction production requirements; all workers have been in place and technical briefing training; according to the engineering needs and engineering division, technical personnel, management personnel and other personnel have been in place.

[0215] ②Measurement and sampling

[0216] The retest work of each excavation section has been completed, and the excavation slope is manually trimmed to meet the requirements, and then the range of the drainage ditch is measured and sampled. The blocked water ditch section should be adjusted according to the site, and the slope should be ensured to be no water accumulation.

[0217] ③ Foundation excavation

[0218] According to the design drawings, the foundation excavation is carried out, and the manual and mechanical excavation is adopted, and the construction is carried out strictly according to the relevant specifications. If the construction conditions are poor, manual excavation is adopted.

[0219] ④ Steel mesh

[0220] After the foundation excavation is leveled, a 50mm thick C25 cushion is laid on the ditch bottom and wall. After the bottom cushion is initially cured, the steel mesh is laid, and then the 50mm thick C25 concrete cushion is poured again. Before the cushion construction, the surrounding soil should be rammed to prevent the surrounding soil from rolling into the cushion and collapsing.

[0221] ⑤ Formwork

[0222] The formwork is assembled according to the design size using wood or bridge board. The formwork line type is hung in line with the construction requirements, and the quality of the ditch axis and slope is checked before the formwork is erected. The formwork surface is brushed with release agent, and the formwork joint is flat, tight, and accurate in clear size, and is designed to be beautiful.

[0223] ⑥ Pouring

[0224] The frame section size should be checked before pouring. The frame concrete must be continuously poured and vibrated. If there are signs of concrete sliding during pouring, quick-setting or early-strength concrete or cover mold pressing can be used. The concrete of each vertical beam should be continuously poured, and if the pouring is interrupted for any reason, the joint should be treated in the usual way. C25 concrete is used for pouring, and the top surface is smooth and pressed. Expansion joints are made every 20m or at geological changes, and filled with asphalt and burlap.

[0225] (2) Underground drainage blind ditch

[0226] The bottom of the blind drainage ditch is backfilled with gravel and pebbles, and the void ratio is not less than 10%. The upper part of the blind drainage ditch is naturally backfilled with soil, and the bottom and wall of the ditch are paved with single-ply water-permeable geotextile. The underground water in the slope body can only flow into the blind drainage ditch. A horizontal drainage hole is arranged every 5m towards the slope body at the bottom of the blind drainage ditch. The diameter of the horizontal drainage hole is 170mm. A drainage flower pipe with an outer diameter of 168mm is pressed into the hole during drilling. The drainage flower pipe is filled with a hard type water-permeable pipe which is capable of quickly draining underground water and preventing secondary seepage of underground water. The outer diameter of the hard type water-permeable pipe is 150mm. The horizontal drainage hole is constructed during construction, and then the blind drainage ditch is excavated and other construction work is carried out after the construction of the horizontal drainage hole is completed. The specific construction is shown in the following figure Figure 3 .

[0227] 7.2 Retaining wall engineering

[0228] (1) General requirements

[0229] The foundation of the retaining wall should be excavated in sections. The bottom should be cleaned to meet the requirements. The foundation pit should be well protected during the wall building process. The quality and specifications of the stone should meet the requirements. The quality of all the cement, sand and water used in the mortar should meet the requirements.

[0230] (2) Construction procedures: site leveling → measurement and positioning → foundation excavation → mortar mixing → wall building → pointing → wall maintenance.

[0231] (3) Material requirements

[0232] Cement: ① 32.5 Portland cement should be used; ② The cement should have a product certificate and a factory inspection report. Different types of cement should not be mixed.

[0233] Sand: Medium sand or coarse sand should be used and should be sieved. When medium or coarse sand is not available, fine sand can also be used. The quality of the sand should meet the quality standards for the corresponding materials in concrete engineering.

[0234] Water: The water from the south side of the project area can be used to meet the requirements of mortar mixing and water use. When other water sources are used, they should be tested according to the relevant standards to confirm their eligibility.

[0235] Stone: The strength of the stone should not be less than MU30. The shape should be roughly square, the thickness should not be less than 200mm, the width should not be less than or equal to the thickness, and the top and bottom surfaces should be flat. When used as a facing, the stone should be slightly chiseled, the edges and corners should be removed, and the surface concave part should not be greater than 20mm.

[0236] (4) Construction during the rainy season

[0237] ① Rainy season construction should have rain protection measures to prevent rainwater from eroding the masonry. When it rains, construction should be stopped immediately, and the completed wall should be covered and protected from the rain.

[0238] ② When building retaining walls in deep trenches, necessary drainage measures should be taken to prevent water from soaking the walls.

[0239] 7.3 Steel Pipe Pile Engineering

[0240] 1. The construction process of grouting micro steel pipe pile reinforcement is as follows: Figure 4 :

[0241] 2. Steel pipe piles shall be drilled mechanically, with the thickness of sediment at the bottom of the hole not exceeding 50mm, the rock embedment depth of the pile body not less than 1 / 3 of the pile length, and adjacent holes shall not be drilled simultaneously.

[0242] 3. The bottom of the steel pipe should be at least 10cm above the bottom of the hole, and the top tie bar should be firmly welded to the steel pipe.

[0243] 4. The concrete inside the steel pipe must be poured densely and segregation is strictly prohibited. Grouting can only be carried out on the outside of the pipe after the concrete has initially set.

[0244] 5. The grout used outside the pipe shall be prepared with ordinary Portland cement of grade P042.5, with a water-cement ratio of 2.0 to 5.0, and the grouting volume shall not exceed 50 L / min;

[0245] 6. For external grouting, it is recommended to start from the outermost row and grout in sections, with a section height of 2.0–3.0 m. The grouting pressure should not exceed 1.0 MPa. During the grouting process, the relationship between the grouting volume and the grouting pressure should be measured to determine the grouting pressure control value adapted to the soil properties. Grouting can be terminated when the injection rate is less than 0.4 L / min under this control value and remains stable for 30 minutes.

[0246] 7. The steel pipe must be accurately positioned, with a top-to-bottom deviation not exceeding 1 / 3 of the pipe diameter, and the grout between the pipe and the soil must be densely filled. The grouting radius outside the pipe is 50cm.

[0247] 8. During the grouting process, the grouting pump shall be operated by a designated person, the grouting volume shall be controlled by a designated person, the pressure gauge shall be observed by a designated person, and records shall be made in a timely manner. Excessive pressure shall be strictly prohibited to prevent the pile body from floating.

[0248] governance effect

[0249] After treatment, the soil moisture content was reduced, and the landslide stability coefficient was greater than 1.3 under natural conditions and greater than 1.25 under saturated conditions, meeting the specifications.

[0250] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A landslide emergency disposal method based on failure of an existing retaining structure, characterized in that: It comprises the following steps: S1, respectively calculate the stability of the failure area and the non-failure area of the anti-slide pile and the residual sliding force of the landslide, and determine the reinforcement measures to be taken in the two areas; S2, arrange two drainage ditches outside the landslide area 5m apart to cut off the supply path of external water to the slope body; S3, arrange two drainage blind trenches transversely on the slope surface of the landslide area, compact the clay at the bottom of the trench, and pour reinforced concrete at the bottom and the water side, with a thickness of 15cm, and backfill the trench with 10cm diameter gravel and pebbles, and cover the upper part with 1.0m of soil; S4, set horizontal drainage holes every 5m towards the slope at 50cm from the bottom of the blind trench on the water side, all embedded in the sliding surface, with a hole diameter of 170mm, an inner wall thickness of 8mm, and a 168mm steel pipe inserted, with 2-3 layers of hard permeable pipes of different diameters inserted into the pipe, and fine sand poured into the pores; S5, arrange two rows of horizontal drainage holes at the anti-slide pile inter-pile plate part in the non-failure area of the anti-slide pile, with a spacing of 8m and a row spacing of 1.5m, a length of 20m, and a hole diameter of 170mm, and a 168mm steel pipe with a wall thickness of 8mm is pressed into the hole during drilling, and 2-3 layers of hard permeable pipes of different diameters are inserted into the pipe, and fine sand is poured into the pores; S6, collect the water in the drainage holes to the blind trench and then discharge it to the two side water intercepting ditches.

2. The landslide emergency disposal method based on failure of an existing retaining structure according to claim 1, characterized in that: In step S3, two drainage blind trenches MG3 and MG4 are arranged along the transverse direction of the landslide, and two slope drainage blind trenches MG1 and MG2 are arranged along the longitudinal direction of the slope surface, the cross sections of the drainage blind trenches MG1 and MG2 are all inverted trapezoidal, with a bottom width of 2.0m, an opening width of 7.03m, and a depth of 3.0m, and the slope of the trench wall is 50°; the cross sections of the drainage blind trenches MG3 and MG4 are all inverted trapezoidal, with a bottom width of 2.0m, an opening width of 7.16m, and a depth of 3.0-3.4m, and the slope of the water side trench wall is 45°, and the slope of the water side trench wall is 60°.

3. The landslide emergency disposal method based on failure of an existing retaining structure of claim 1, characterized in that: In step S3, the bottom of the drainage blind trench is backfilled with gravel and pebbles, with a void ratio of not less than 10%, the upper 1m of the blind trench is naturally backfilled with soil, the bottom and the water side of the trench wall are poured with 15cm reinforced concrete, and the water side trench wall is paved with one-way water permeable geotextile, and the underground water in the slope body can only seep into the blind trench.

4. The landslide emergency treatment method based on failure of an existing retaining structure of claim 1, wherein: In steps S4 and S5, the outer diameter of the hard permeable pipe is 150mm.

5. The landslide emergency disposal method based on failure of an existing retaining structure according to claim 1, characterized in that: It further comprises the steps of arranging an observation well in the middle and outlet part of each drainage blind trench, with a depth consistent with the blind trench, for observing the drainage condition in the blind trench.

6. The landslide emergency treatment method based on failure of an existing retaining structure of claim 1, wherein: It further comprises the measures of filling the failure area with soil, setting a gravity retaining wall for support, and reinforcing the non-failure area with grouting steel pipe piles.

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