Must be engaged in disaster prevention and control personnel: analysis and prevention of landslides!

Landslide accident 1: At about 6 o'clock on June 24, 2017, a high mountain collapse occurred in Xinmo Village, Diexi Town, Mao County, Aba Prefecture, Sichuan Province, causing more than 40 farm houses and more than 100 people to be buried. The river channel was blocked for 2 kilometers.

Landslide Accident 3: At 10 o'clock on the evening of June 24, 2017, a large area of ​​landslides and mudslides suddenly occurred in a place called “Water Hole” in Sanhe Village, Persimmon Town, Yanjin County, Zhaotong City. The Difeng Feng Road was buried. A section of nearly 200 meters long caused a two-way interruption of traffic on the road.

Landslide accident three: At 10:40 am on August 28, 2017, a geological disaster of landslide occurred in Zhangjiawan Town, Nayong County, Bijie City, Guizhou Province. Up to now, the accident has caused 2 deaths, 4 people were injured, 25 people lost contact, and the loss of joint personnel is being searched and rescued.

The landslide accident is shocking. People are concerned about the casualties and losses caused by landslides. At the same time, they may pay more attention to why there are many landslides. Is it a natural disaster or a man-made disaster? How to prevent such accidents from happening again?

Xiaotang has compiled some information about landslides. The purpose is to introduce some domestic and foreign research results and practical experience to engineers and technicians engaged in the prevention and control of landslide hazards, so as to draw lessons from future work. At the same time, I hope to attract geoscientists. Pay attention to and discuss and jointly promote the development of our national defense disaster reduction and disaster reduction cause.

1

Introduction to landslide hazards

Section 1 Geological Hazards and Slope Disasters

I. Geological disasters

Geological disasters are geological phenomena in which the geological body deforms, destroys, and moves under the influence of many factors, causing damage to human living environment and loss of life and property. Such as earthquakes caused by deep crustal movement, volcanic eruptions, ground fissures, landslides (collapse) formed by the movement of slope blocks, landslides, patchwork, dumping, collapse and deep creep of rock masses; debris flows and debris formed by surface water Flow, soil erosion; karst collapse caused by groundwater, land subsidence, collapsibility, water inrush, etc.; desertification, salinization, weathering, spalling, expansion, shrinkage, etc. caused by epigenetic geological processes. Here we mainly discuss the various types of slope block motion.

Second, slope disaster

Regarding the deformation and type of movement of the slope, the Americans Varnes proposed the types of collapse, dumping, landslide, lateral expansion, and flow in 1978, as shown in Table 1-1. Early China is also referred to as their "collapse", "collapse landslide", "collapse mud flow", rail and highway departments called: "roadbed disease." Later, as the research progressed, they gradually distinguished them from the deformation mechanism and prevention. According to the depth (scale), motion characteristics and material categories of deformation, we divided it into slope deformation, slope deformation and slope deformation, as shown in Table 1-2.

Figure 1-1 Schematic diagram of the main types of slope block motion

a. landslide (collapse); b. landslide; c. staggered; d. dumping; e. collapse; f. deep creep of rock mass

Table 1-2 Classification of slope deformation

Table 1-3 Examples of major landslide disasters in the world

Section 2 Definitions, elements and terminology of landslides

First, the definition of landslide

Part of the soil or rock mass on the slope slides down along a certain surface or belt.

Second, the elements and terminology of the landslide

Table 1-6 Comprehensive classification of landslides

Section III Types and Characteristics of Landslides

First, the type of landslide

Table 1-5 Classification of single indicators of landslides

Table 1-6 Comprehensive classification of landslides

Second, the characteristics of the landslide

(1) Plane features

Figure 1-5 Plane shape of the landslide

1. 簸箕 shape; 2. tongue shape; 3. elliptical shape; 4. bench shape; 5. inverted pear shape; 6. horn shape; 7. parallelogram; 8. diamond shape; 9. leaf shape; Shape; 11. composite shape

(ii) Profile characteristics

Figure 1-6 Schematic diagram of a typical landslide profile

a. arc shape; b. plane shape; c. line shape; e. soft rock extrusion

Figure 1-7 Composite profile shape

Morphology of the back and front of the landslide

Figure 1-8 The depression in the back of the landslide

a. crack dense zone; b. depression depression; c. trailing edge cracking groove

Figure 1-9 Characteristics of the front of the landslide

a. braided shear outlet; b. drum dome and bulging crack; c. landslide flexion

Figure 1-10 Cross-sectional characteristics of the landslide

The conditions and causes of the fourth section of landslide

First, the topographical geological conditions

(1) Terrain conditions

(2) Geological conditions

Stratum, lithology

Slope structure and slip zone

Geological structure

Hydrogeological conditions

Table 1-7 Summary of China's Easy Landslide Formation

Table 1-8 Types of slope structure and failure mode of landslide

Figure 1-11 Slope structure and failure mode of landslide

a. cohesive soil arc-shaped rotary sliding; b. loess arc-shaped rotary sliding; c. filling soil arc-shaped sliding; d. soil layer-by-layer sliding; e. semi-diagenetic stratum layer-by-layer sliding; f. rock layer bedding-cutting Sliding; g. soft rock extrusion type (staggered type) sliding; h. extrusion type translational sliding; I. accumulation layer smoothing sliding; j. rock layer bedding plane sliding; k. rock layer sliding along the surface; Tidal layer bedding layer-slice layer sliding; m. anti-dip rock layer cutting layer sliding; n. anti-dip rock layer dumping-sliding layer sliding; o. fractured rock layer rotating sliding; p. broken rock layer sliding along structural plane; q. The rock mass slides along the structural plane (like the plane); r. the structural core slides along the structural fracture zone

Second, the role of landslide

The landslide is the result of the combination of various factors in the slope with sliding conditions, but there is always one or two factors controlling the occurrence of landslide for a particular landslide. We call it the main control factor, which should be used in the prevention and control of landslides. Efforts should be made to find out the mechanism and range of changes of the main control factor and its effects, and take major engineering measures to eliminate or control its role to stabilize the landslide. For other factors, take general measures to achieve the purpose of comprehensive management, such as those caused by groundwater The underground interception and drainage project is the main one, and those who are weakened by the supporting force of the slope are mainly responsible for the restoration and strengthening of the supporting works.

The factors affecting the landslide are summarized in Table 1-10, which can be divided into natural factors and human factors, and can also be divided into long-term action factors, short-term action factors and periodic action factors, but in terms of their effects on the formation of landslides, It is a factor that changes the stress state of the slope, increases the stress of the slope and the shear stress (ie, the sliding force) of the slip zone soil, such as the factors of changing the slope shape such as river erosion, excavation slope, and slope loading; The properties of the slip zone soil reduce the factors of anti-sliding resistance, such as surface underwater seepage, groundwater level change, reservoir water level rise and fall, irrigation water and production domestic water infiltration, sloping erosion and dissolution, etc. The third is the factors that increase the sliding force and reduce the anti-sliding force and even cause the structural damage of the slip zone (such as liquefaction), such as earthquake and blasting vibration. In short, its role is not only mechanical, but also physical and chemical, as well as the time course of action, comprehensive dynamic analysis is necessary.

Table 1-10 Factors affecting landslides

Section 5 Research Contents of Landslide Prevention

First, the basic properties of landslide

Second, landslide prevention and control technology research

2

Landslide mechanism

Plane stress field of the first section of landslide

Figure 2-1 Landslide plane stress field

Section should stand

Figure 2-2 Three-stage sliding mode and its stress field

1. traction section; 2. main sliding section; 3. anti-slip section

The development process and stage of the second section of landslide

First, the creep properties of the soil

Second, the development stage of the landslide

Locally unstable creep compression stage (K>1)

Uniform sliding stage of overall instability (K=1)

Sliding sharply to the destruction stage (K<1)

Post-slip consolidation compaction stage (K>1)

Figure 2-4 Schematic diagram of landslide development

Section 3 Deformation and Failure Law of Slide Soil

I. Factors affecting the shear strength of soil

Stress state and stress path

2. Strain

3. Pore water pressure

4. Loading rate and stress time

5. Soil inhomogeneity and anisotropy

Second, the stress and strain characteristics of the slip zone soil

in conclusion:

The residual strength of the viscous slip zone soil decreases with the increase of clay content in the soil;

The residual strength is independent of the original stress state and the original density of the soil; therefore, the residual strength can be obtained by remolding the soil;

Determination of the difference in residual strength at home and abroad;

The difference in residual strength measured by different instruments and methods;

The effect of coarse particle content on residual strength.

The fourth section of the landslide mechanism

First, the basic theory

1. The change of pore water pressure in the slip zone soil;

2. Change of slope stress state

3. Progressive destruction

4. Residual strength

5. Shock liquefaction

Second, from the analysis of geological conditions

1. Rotational sliding of homogeneous soil

2. Sliding layer

3. Slice sliding

4.Bedding layer - slice sliding

5. Soft rock extrusion sliding

Third, analysis from the main factors

1. Sliding caused by heavy rain

2. Sliding caused by vibration

3. Sliding caused by the rise and fall of the reservoir water level

4. Sliding caused by goaf collapse

5. Irrigation caused by irrigation

6. Sliding caused by excavation

7. Sliding caused by stacking

Section 5 Movement Characteristics of Landslides

First, the type of sliding

Slow creep type

2. Uniform sliding type

3. Intermittent sliding type

4. High speed sliding type

Figure 2-6 Schematic diagram of the sliding type

1- slow creep type; 2- uniform sliding type; 3-intermittent sliding; 4-high speed sliding type

Second, the formation conditions of high-speed landslide

1. Has a considerable height difference (>100m)

2. Has a considerable volume (> 1 million m3)

3. Has a steep slope (>200)

4. Has a large difference in peak residual strength (ratio greater than 2)

5. Has a high landslide cut exit

6. Open terrain in front of the landslide

7. Landslide prevention and control technology

The first section of the landslide prevention principles and planning

First, the principle of prevention and control of landslides

(1) Correct understanding of the principle of landslide

(2) Principles of prevention

(3) The principle of not eradicating the problem

(4) Principles for comprehensive planning of phased governance

(5) Principles of comprehensive governance

(6) The principle of treating early treatment

(7) The principle of technical feasibility and economic rationality

(8) Principles of scientific construction

(9) Principles of dynamic design and dynamic construction

(10) Strengthening the principle of maintenance and repair of anti-skid engineering

Second, the prevention and control planning of landslides

(1) Investigation stage

(2) Design stage

(3) Construction stage

(4) Operation stage

The second section of landslide prevention

1. Avoid existing old and new landslides

Second, to prevent the resurrection of ancient landslides

1. Do not fill the top of the landslide, do not cut the support force in the anti-slide section

2. Do not set up water-permeable buildings on the landslide body

3. Strict management of production and domestic water does not allow it to penetrate into the sliding body

4. Set the necessary anti-slip measures

5. Change the paddy field to dry field when conditions permit

Third, to prevent the deformation of the landslide caused by large sliding

1. Stop construction, strengthen monitoring, prevent disasters

2. Strengthen surface drainage and fill ground cracks

3. Upper weight reduction, leading edge back pressure and drainage of groundwater are often effective measures

Fourth, to prevent landslides in landslides

1. Survey and analysis of high slope geological data;

(1) lithology of the formation, slope structure;

(2) Easy landslide stratum and its distribution location and traits;

(3) Groundwater distribution and exposure location.

2. Analysis of possible types and laws of deformation;

3. Reasonable slope shape, slope rate, slope height and reinforcement measures design;

4. Scientific construction methods and sequences.

Section III Engineering Measures for Landslide Prevention

Table 3-1 Classification of landslide control projects in the United States

Figure 3-1 Classification of Landslide Control Engineering of the Japanese Landslide Society

Table 3-2 Summary of landslide control measures of the International Geotechnical Society

Table 3-3 Summary of China's landslide control measures

Figure 3-2 Schematic diagram of the ground drain

Figure 3-7 Schematic diagram of hole-hole joint drainage

The difference between the anti-slip retaining wall and the general retaining wall is as follows:

(1) It is not subject to general earth pressure, but landslide thrust, which is much larger than the former.

(2) The chest slope is slow, the center of gravity is low, and the chest slope is 1:0.4~1:1.

(3) The foundation depth is large, 0.5~1.0m in the bedrock, 1.5~2.0m or more in the soil layer, and it must be placed in the stable stratum below the slip surface.

(4) Try to use the backfill weight of the wall.

(5) The longitudinal blind ditch behind the wall is required to be high.

(6) In addition to anti-sliding, anti-overturning and section strength check, the wall stability check should also check the possibility of sliding from the bottom of the wall and sliding out from the top of the wall to determine the depth and wall height of the wall.

(7) The position of the thrust point is generally not at the height of one third of the wall, but at the height of one-half or two-fifth of the wall.

(8) The construction must be excavated in sections and pushed from the sides to the middle to avoid the sliding of the landslide caused by the digging.

Section 4 Landslide thrust calculation

The landslide thrust calculation is a necessary work content for the anti-skid engineering design. The technicians who are involved in the landslide prevention work often find it difficult to grasp.

The calculation of landslide thrust mainly involves the following:

The calculation range of the landslide thrust;

The choice of calculation formula;

Selection of the strength index (c, φ) of each segment of the sliding belt;

Additional strength considerations and determinations;

Determination of the safety factor;

Calculate the check of the thrust.

First, the determination of the calculation range of landslide thrust

1. First, divide each sliding block from the geological analysis, and calculate each one separately.

2. Whether the same landslide is graded and the relationship between the front and rear stages. Generally, only one level of the through crack is calculated, and if it is stable in the front, it will naturally be stable.

3. The multi-layer sliding surface should be layered to calculate its landslide thrust.

Second, the choice of calculation formula

There are many calculation methods, which should be selected according to different sliding conditions. Generally, the block thrust transfer coefficient method is used.

The remaining sliding force of the i-th block is: Ei = KWisinαi - Wi cosαitgφi – CiLi+Ei-1Φi

Where: K - safety factor, generally take K = 1.10 ~ 1.25;

Wi — the weight of the i-th block, KN;

Αi — the slip angle of the sliding surface of the i-th block;

Ci — the cohesion of the slip zone of the i-th block, Kpa;

Φi — the internal friction angle of the slip zone of the i-th block;

Li — the length of the slip surface of the i-th block slide, m;

Ei-1—the remaining sliding force of the sliding block of the I-1 block to the sliding block of the i-th block;

Φi - transfer coefficient.

Φi = cos(αi –αi-1 )– sin(αi –αi-1 )tgφi

Third, the selection of the shear strength index (c, φ) of each section of the sliding belt

1. Due to the great difference between geological conditions and soil properties, the values ​​of c and φ of different landslides are quite different. The sampling test results in numerical dispersion due to sampling representativeness and test methods. Therefore, the reference test values ​​are combined with the empirical values ​​at home and abroad, and the inverse sliding section c and φ values ​​are obtained by the inverse algorithm.

2. Test method. It is necessary to make the undisturbed soil, and it is necessary to reshape the peak strength and residual strength of the natural water content (natural, plastic, soft plastic state) under the different water content of the sliding belt.

3. Comparison of empirical data refers to the analogy of the same type of landslide slip zone soil under the same geological conditions. The change of lithology and the change of c and φ values ​​of the traction section and the anti-slide section are small and can be selected according to experience.

4, the inverse algorithm, mainly to inversely calculate the main slip segment c, φ value.

(1) First determine the current stability of the landslide, such as 1.0, 0.98, 1.02, etc.;

(2) An equilibrium section equation is used to find an index. Two equilibrium section equations are combined to obtain two values ​​of c and φ, which can also be obtained by graphic method.

(3) When conditionally restoring the limit equilibrium state before sliding, use the limit equilibrium section to reverse; if the original section cannot be restored (such as the ancient landslide), only the existing stable section can be reversed.

Fourth, the consideration of additional strength

1. Consideration of seismic forces (consideration of seismic zones above 7 degrees);

2. Consideration of static and dynamic water pressure;

3. Consideration of the buoyancy of the sliding body into the water;

4. Other additional strength considerations.

V. Determination of safety factor

1. The degree of understanding of the nature of the landslide is clear to those who are small and unclear;

2, the importance of protecting objects, important people take large values;

3, the landslide's harmfulness, the big ones take a large value;

4. The temporary project takes a large value, and the permanent project takes a large plant.

Sixth, calculate the thrust check

1. Determine the lower limit of the strength of the damaged building in the local area;

2. Defining the lower limit of landslide thrust (such as passive earth pressure) from the local landslide shear outlet and the anti-slip segment slide thickness;

3. Compare the thrust value of the landslide from the nature and scale of the landslide.

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