CN117960773A - A method for remediation and loss prevention of heavy metal soil on slopes in karst areas - Google Patents

Abstract

The invention discloses a method for restoring and preventing and controlling loss of heavy metal soil on a slope surface of a karst area, which relates to the field of soil management and control restoration and specifically comprises the following steps: s1, cleaning polluted waste residues on a steep slope, and sampling and detecting on-site polluted soil; s2, deep excavation is carried out according to the depth result of the heavy metal soil detection; s3, then throwing the deeply excavated polluted soil into soil restoration equipment; s4, constructing a barrier layer at the bottom of the deep digging area; s5, backfilling, solidifying and repairing the soil above the barrier layer; s6, finally, performing surface soil conservation measures on the backfilled solidified and repaired soil; according to the method for restoring and preventing and controlling the heavy metal soil on the slope of the karst area, soil moisture regulation and control and water and soil conservation can be performed through the measures of soil conservation on the surface layer, so that the excessive water flow speed caused by heavy rain or surface water in the later period can be slowed down, and the excessive speed can be realized; while the surface water flow can be collected and directed.

Description

A method for remediation and loss prevention of heavy metal soil on slopes in karst areas

Zhou Zhongfa, Li Dandan

Karst Research Institute of Guizhou Normal University

Technical Field

The present invention relates to soil restoration and control technology, and in particular to a method for restoration and loss control of heavy metal soil on slopes in karst areas.

Background technique

The secondary enrichment of heavy metal elements in the process of carbonate rock weathering and soil formation in the karst area makes the formed soil have a significant high content of heavy metals. In addition, the region is rich in lead and zinc mineral resources, and its mining and smelting process causes heavy metal pollution. Coupled with the high background characteristics of heavy metals, the regional environmental heavy metal geochemistry is abnormal. Under the special geological background of the karst area, heavy metal elements are easily migrated and diffused with soil loss under the action of rainwater erosion, aggravating soil heavy metal pollution. Therefore, the construction of soil heavy metal remediation methods and the prevention and control of heavy metal elements migration and changes with soil loss have become hot topics.

At present, the methods for remediating heavy metal contaminated soil are divided into: physical remediation, chemical remediation and biological remediation. Physical remediation methods include soil import, soil replacement, electric remediation, heat treatment and vitrification; chemical remediation methods include soil leaching, solidification and stabilization; biological remediation methods include microbial remediation, plant remediation, microbial assisted remediation. The effect of a single soil remediation method is poor, and heavy metal elements migrate and diffuse with soil loss, which can easily cause secondary pollution. Therefore, physical remediation + chemical remediation + biological remediation are necessary measures to fix and remove heavy metals in the soil. At the same time, combined with soil loss cultivation and engineering prevention and control measures, heavy metal soil remediation can be achieved, and the problem of heavy metal soil loss can be effectively prevented and controlled.

Summary of the invention

The purpose of the present invention is to provide a method for repairing and preventing heavy metal soil loss on slopes in karst areas to solve the above-mentioned deficiencies in the prior art.

In order to achieve the above-mentioned object, the present invention provides the following technical solution: a method for remediation and loss prevention of heavy metal soil on slopes in karst areas, specifically comprising the following steps:

S1. Determination of heavy metal content in soil: First, before excavation, the surrounding environment of the contaminated soil on the slope of the karst area is cleaned and the site is leveled; second, the contaminated soil is sampled and tested;

After sampling and testing, spread lime powder on the contaminated soil and leave it for 5 to 10 days to neutralize the contaminated soil;

S2. Deep soil excavation: After the neutralization treatment is completed, deep soil excavation is carried out according to the depth results of the heavy metal soil detection;

S3. Solidification and remediation of heavy metal soil: The excavated contaminated soil is then put into soil remediation equipment to remove stones, crush the soil, and spray it with chemicals to complete the solidification of the heavy metal content in the soil;

S4. Constructing a barrier layer: laying a barrier layer of mixed materials with a thickness of 10 to 30 cm at the bottom of the deep excavation area;

S5. Backfill soil: After the barrier layer is filled, the solidified and repaired soil is backfilled on top of the barrier layer;

S6. Prevention and control of surface soil restoration: Finally, soil conservation engineering measures such as cross-slope throttling ditches and longitudinal slope ridges are laid on the surface of the backfilled soil;

At the same time, horizontal and vertical cooperative farming measures are adopted on the soil surface to plant herbaceous plants and trees to repair soil heavy metals. The spacing between trees is greater than or equal to 2mx2m.

The grass seeds are sown in a mixed manner, with the sowing amount being greater than or equal to 30 g m ^-2 .

Furthermore, the soil in S1 was selected from 3 to 4 locations in a 10mx10m plot, and a mixed sample was collected every 10cm from the surface to 50cm below the soil. The mixed sample was air-dried and then put into a plastic ziplock bag;

Furthermore, the mass ratio of lime powder to contaminated soil in S1 is controlled between 1% and 5%.

Furthermore, the soil remediation equipment in S3 includes: a crushing system, a stirring system and a solid-liquid mixing system;

The pulverizing system includes a vibrating screening plate capable of screening the input soil and a compound pulverizer installed below the vibrating screening plate;

The solid-liquid mixing system includes a reagent tank, a mixing device installed in the reagent tank, and a spray washing system;

The mixing system is used to mix the sprayed agent and the crushed soil.

Furthermore, the agent tank is filled with a spray agent and an improvement agent;

The spraying agent is a passivating agent, and the raw materials of the improved agent include, by weight: 3 parts of manure, 1 part of plant litter and 1 part of moss.

Furthermore, the barrier layer in S3 comprises, by mass percentage, 65% to 70% of mineral clay material, 21.5% to 23.5% of cement and 5% to 8% of rock powder, with the remainder being adhesive.

Furthermore, the surface soil loss prevention and control measures in S6 adopt horizontal and vertical coordinated farming measures and engineering measures; at the same time, sensors are set at soil sampling and detection points to monitor and collect data, and a data model is obtained through the monitored collected data to complete the verification of the soil loss prevention and control effects of horizontal and vertical coordinated farming measures and engineering measures;

First define:

Definition 1: When the soil layer load conditions and the shear parameters of the steep slope soil surface are consistent with the actual situation of the steep slope, the theoretical minimum safety factor of the slope is close to 1 and slightly less than 1;

Definition 2: When the soil layer load conditions and the shear parameters of the steep slope soil surface are consistent with the actual situation of the steep slope, the theoretical minimum safety factor of the slope is close to 1 and slightly less than 1, and the corresponding most dangerous steep slope soil surface must be consistent with the actual sliding surface of the steep slope;

When a steep slope that has slid is about to slide but has not yet slid at the place where it last slid or slid recently, it is in a state of limit equilibrium.

The section taken on it belongs to the section of limit equilibrium state. The residual sliding force of the last soil strip in the thrust calculation formula established based on this section is equal to zero, that is:

_Bn = _{Bn -1fn} + _{FsVn sinɑn -Vn cosɑn tanfn -cnln = 0} ; (1)

Where: _Fs is the sliding safety factor, _Vn is the deadweight of the nth soil strip, _ɑn is the inclination angle of the sliding surface of the nth soil strip, _cn is the cohesion of the nth soil strip of the steep slope, _fn is the internal friction angle of the nth soil strip of the steep slope, _ln is the arc length of the sliding surface of the nth soil strip, and _fn is the transfer coefficient, that is:

f _n =cos(ɑ _n-1 -ɑ _n )-tanf _n sin(ɑ _n-1 -ɑ _n );

Let F _s = 1, and assume c or f;

And from formula (1) we can get:

Bi _-1 = _{Bi -Fs} Vi _sinɑi + Vi _{cosɑi tanf} + cl _i / _fi ; (i = 1 _, 2, ..., n) (2)

Assuming the thrust of the last soil strip _Bn = 0, we can calculate by recursive step by step from formula (2):

B ₁ =B ₂ -F _s V ₂ sinɑ ₂ +V ₂ cosɑ ₂ tanf+cl ₂ /f ₂ ; (3)

At the same time, from formula (1), we can also get:

B' ₁ =F _s V ₁ sinɑ ₁ -V ₁ cosɑ ₁ tanf-cl ₁ +B ₀ f ₁ ; (4)

Where: B ₀ = 0;

Let G = B ₁ -B'₁; (5)

When the steep slope is in the limit equilibrium state (i.e., F _s = 1.0), given any c or f value, a corresponding f or c value can be obtained from equation (5) so that G = B ₁ -B' ₁ , which is equal to or approximately equal to zero;

The values of c and f of each section in the limit equilibrium state can be solved respectively;

By plotting the pairs of c and f values of two different sections on the plane with safety factor _Fs = 1.0, two intersecting cf value curves can be obtained. The set of c and f values at the intersection is the unique solution, which is also the shear strength index value that conforms to the actual state of steep slope sliding.

Compared with the prior art, the method for remediation and loss prevention of heavy metal soil on karst slopes provided by the present invention first neutralizes the contaminated soil and then crushes and solidifies it for remediation, so that the harmful substances in the contaminated heavy metal soil are more effectively removed, the removal efficiency is higher, and the overall safety, environmental protection and practicality are higher;

Through surface soil loss prevention and control measures, soil moisture control and soil and water conservation can be carried out, which can not only slow down the excessive and fast water flow caused by heavy rain or surface water in the later period; at the same time, surface water flow can be collected and guided, and soil moisture can be adjusted, vegetation can be protected, and soil erosion can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

FIG1 is a flow chart of a repair and prevention method provided by an embodiment of the present invention;

FIG2 is a structural perspective view of a soil remediation device provided by an embodiment of the present invention;

FIG3 is a three-dimensional diagram of the structure of the horizontal and vertical coordinated farming measures and engineering measures provided by an embodiment of the present invention.

Description of reference numerals:

1. Side ditch; 2. Cross slope interception ditch; 3. Back ditch; 4. Ridge; 5. Ridge ditch along the slope; 6. Vibrating screening plate; 7. Compound crusher; 8. Solid-liquid mixing system; 9. Chemical tank; 10. Mixing device; 11. Spray washing system; 12. Stirring system.

Detailed ways

In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

Embodiment 1:

Please refer to Figures 1 to 3, a method for heavy metal soil restoration and loss prevention and control on slope surfaces in karst areas, specifically comprising the following steps:

S1. Determination of heavy metal content in soil: First, before excavation, clean up the waste residue on the steep slope of the karst lead-zinc mining area and level the site; second, take samples of the contaminated soil for testing;

After sampling and testing, spread lime powder on the contaminated soil and leave it for 5 to 10 days to neutralize the contaminated soil;

S2. Deep soil excavation: After the neutralization treatment is completed, deep soil excavation is carried out according to the depth results of the heavy metal soil detection;

S3. Solidification and remediation of heavy metal soil: The excavated contaminated soil is then put into soil remediation equipment to remove stones, crush the soil, and spray it with chemicals to complete the solidification of the heavy metal content in the soil;

S4. Constructing a barrier layer: laying a barrier layer of mixed materials with a thickness of 10 to 30 cm at the bottom of the deep excavation area;

S5. Backfill soil: After the barrier layer is filled, the solidified and repaired soil is backfilled on top of the barrier layer;

S6. Prevention and control of surface soil restoration: Finally, soil conservation engineering measures such as cross-slope throttling ditches and longitudinal slope ridges are laid on the surface of the backfilled soil;

At the same time, horizontal and vertical cooperative farming measures are adopted on the soil surface to plant herbaceous plants and trees to repair soil heavy metals. The spacing between trees is greater than or equal to 2mx2m.

The grass seeds are sown in a mixed manner, with the sowing amount being greater than or equal to 30 g m ^-2 .

In S1, 3 to 4 locations were selected in a 10mx10m plot, and a mixed sample was collected every 10cm from the surface to 50cm below the soil. After air drying, the mixed sample was placed in a plastic ziplock bag;

The mass ratio of lime powder to contaminated soil in S1 is controlled between 1% and 5%. Lime powder is a commonly used alkaline substance that can increase the pH value of the soil, according to the soil analysis results and the required pH value adjustment range.

Please refer to FIG. 2 , the soil remediation equipment in S3 includes: a crushing system, a stirring system 12 and a solid-liquid mixing system 8;

The crushing system includes a vibrating screening plate 6 for screening the input soil and a compound crusher 7 installed below the vibrating screening plate 6. The vibrating screening plate 6 and the compound crusher 7 are both common knowledge in the art. They only need to have the properties of vibrating screening and crushing the soil, and will not be described in detail here.

The solid-liquid mixing system 8 includes a reagent tank 9, a mixing device 10 installed in the reagent tank 9, and a spray washing system 11. The user fills the reagent into the reagent tank 9, and mixes the filled multiple reagents through the mixing device 10. The spray washing system 11 then extracts the mixed reagent and sprays it into the crushed soil. An infusion tube is connected between the reagent tank 9 and the spray washing system 11, and the reagent in the reagent tank 9 is extracted by a liquid pump in cooperation with the infusion tube and then sprayed out by the atomizing nozzle at the end.

The stirring system 12 is used to mix and stir the sprayed agent and the crushed soil.

The stirring system 12 is common knowledge in the art, and it only needs to have the property of mixing solid and liquid, and will not be described in detail here;

The reagent tank 9 is filled with spray reagent and improvement reagent;

The spraying agent is a passivator, and the best choice of the passivator is a silicon-calcium heavy metal passivator, which contains 23% calcium and 17% silicon;

The raw materials of the improved agent include, by weight: 3 parts of manure, 1 part of plant litter and 1 part of moss.

The barrier layer in S3 includes, by mass percentage, 65% to 70% of mineral clay material, 21.5% to 23.5% of cement and 5% to 8% of rock powder, with the remainder being adhesive.

The surface soil loss prevention and control measures in S6 adopt horizontal and vertical coordinated farming measures and engineering measures; please refer to Figure 3, that is, from the bottom to the top of the steep slope, a side ditch 1, a cross slope interception ditch 2 and a back ditch 3 are opened in sequence perpendicular to the slope direction, and at the same time, a ridge 4 is built under the steep slope of the side ditch 1, and then several slope ridges 5 are opened parallel to the slope direction. The slope ridges 5 are also perpendicular to the side ditch 1, the cross slope interception ditch 2 and the back ditch 3. In this way, soil loss can be prevented to the greatest extent. The side ditch 1, the cross slope interception ditch 2 and the back ditch 3 can intercept the soil sliding from top to bottom laterally to reduce the entrainment caused by its rolling. At the same time, soil moisture regulation and soil and water conservation can be carried out, which can not only (a) slow down the water flow speed: the water flow speed on the steep slope is fast, which is easy to cause soil loss on the slope. By opening horizontal and vertical ditches, the water flow path can be cut off and the water flow energy can be dispersed, thereby slowing down the water flow speed and reducing the scouring effect of the water flow on the slope. (ii) Collect and guide water flow: Horizontal and vertical ditches can collect runoff water from steep slopes and guide it to appropriate locations for treatment or discharge, avoiding large-scale scouring and erosion on steep slopes. (iii) Regulate soil moisture: Opening horizontal and vertical ditches on steep slopes can help regulate soil moisture distribution. They can collect and store rainfall water, increase soil moisture content, and supply water to the slope when needed, providing better growth conditions. Also: (iv) Protect vegetation: The construction of horizontal and vertical ditches can reduce the speed and impact of water flow on steep slopes, which is conducive to the growth of vegetation. By controlling the water flow path and dispersing water flow energy, the damage to vegetation by water flow can be reduced, providing a better protective environment. (v) Prevent soil loss: By opening horizontal and vertical ditches, the water flow and speed can be effectively controlled to reduce soil loss.

At the same time, sensors are set up at the soil sampling and detection points on the steep slope to monitor and collect data. The sensors include but are not limited to weight sensors, angle measuring instruments and length sensors. The monitor can set the sensors at the side ditch 1, the cross slope interception ditch 2 and the back ditch 3 or the cross section of the steep slope soil layer, and obtain a data model through monitoring the collected data; if the steep slope body is likely to slide along many sliding surfaces, it will be destroyed along the sliding surface with the least resistance when it loses stability; when the sliding surface of the steep slope body is determined, the reaction force on the sliding surface and the internal force in the steep slope body can be adjusted automatically to exert the maximum anti-sliding ability;

First define:

Definition 1: When the soil layer load conditions and the shear parameters of the steep slope soil surface are consistent with the actual situation of the steep slope, the theoretical minimum safety factor of the slope is close to 1 and slightly less than 1;

Definition 2: When the soil layer load conditions and the shear parameters of the steep slope soil surface are consistent with the actual situation of the steep slope, the theoretical minimum safety factor of the slope is close to 1 and slightly less than 1, and the corresponding most dangerous steep slope soil surface must be consistent with the actual sliding surface of the steep slope;

It is suitable for sliding surfaces of any shape. It assumes that the resultant force between strips is parallel to the bottom surface of the previous strip. According to the force balance condition, it is pushed down one by one until the thrust of the last strip is zero.

When a steep slope that has slid is about to slide but has not yet slid at the place where it last slid or slid recently, it is in a state of limit equilibrium.

The section taken on it belongs to the section of limit equilibrium state. The residual sliding force of the last soil strip in the thrust calculation formula established based on this section is equal to zero, that is:

_Bn = _{Bn -1fn} + _{FsVn sinɑn -Vn cosɑn tanfn -cnln = 0} ; (1)

Where: _Fs is the sliding safety factor, _Vn is the deadweight of the nth soil strip, _ɑn is the inclination angle of the sliding surface of the nth soil strip, _cn is the cohesion of the nth soil strip of the steep slope, _fn is the internal friction angle of the nth soil strip of the steep slope, _ln is the arc length of the sliding surface of the nth soil strip, and _fn is the transfer coefficient, that is:

f _n =cos(ɑ _n-1 -ɑ _n )-tanf _n sin(ɑ _n-1 -ɑ _n );

Let F _s = 1, and assume c or f;

The establishment of the following equation model must meet one of the following conditions:

(1) For the same steep slope, the corresponding equations established for two sections with equal distances on both sides of the main axis can be combined.

(2) If two sliding events occur on the same steep slope and the position of the sliding surface remains basically unchanged, the two equations established for the main axis sections of the two sliding events can be combined; the equations established for other sections corresponding to the two sliding events can also be combined.

(3) For two steep slopes, if the properties of the steep slope soils are similar and the factors affecting their strength changes are also the same (generally, two steep slopes within a short distance in the same area), the equations established for the main axis sections or other two corresponding sections of the two steep slopes can be combined.

The conditions for establishing the equation model are generally easy to find in the process of the formation and development of steep slopes. They are not limited to the above-mentioned situations. It is sufficient to follow this basic principle. However, the unknowns c and f in any two equations must be equal in these two sections, which means that the strength of the steep slope soil in these two sections is the same.

And from formula (1) we can get:

Bi _-1 = _{Bi -Fs} Vi _sinɑi + Vi _{cosɑi tanf} + cl _i / _fi ; (i = 1 _, 2, ..., n) (2)

Assuming the thrust of the last soil strip _Bn = 0, we can calculate step by step by step recursion from formula (2):

B ₁ =B ₂ -F _s V ₂ sinɑ ₂ +V ₂ cosɑ ₂ tanf+cl ₂ /f ₂ ; (3)

At the same time, from formula (1), we can also get:

B' ₁ =F _s V ₁ sinɑ ₁ -V ₁ cosɑ ₁ tanf-cl ₁ +B ₀ f ₁ ; (4)

Where: B ₀ = 0;

Let G = B ₁ -B'₁; (5)

When the steep slope is in the limit equilibrium state (i.e., F _s = 1.0), given any c or f value, a corresponding f or c value can be obtained from equation (5) so that G = B ₁ -B' ₁ , which is equal to or approximately equal to zero;

The values of c and f of each section in the limit equilibrium state can be solved respectively;

Plotting the pairs of c and f values of two different sections on the plane with safety factor _Fs = 1.0, we can get two intersecting cf value curves. The set of c and f values at the intersection is the only solution, which is also the shear strength index value that meets the actual state of steep slope sliding.

The monitor can reproduce the accurate soil shear strength index value obtained and put it into formula (1) to monitor in real time whether the value of _Fs is close to 1 but slightly less than 1, so as to verify the effectiveness of surface soil loss prevention and control measures.

The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that, for those skilled in the art, the described embodiments can be modified in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims (7)

1. A method for remediation and loss prevention of heavy metal soil on slopes in karst areas, characterized in that it specifically comprises the following steps: S1. Determination of heavy metal content in soil: First, before excavation, the surrounding environment of the contaminated soil on the slope of the karst area is cleaned and the site is leveled; second, the contaminated soil is sampled and tested; After sampling and testing, spread lime powder on the contaminated soil and let it stand for 5 to 10 days to complete the neutralization of the contaminated soil; S2. Deep soil excavation: After the neutralization treatment is completed, deep soil excavation is carried out according to the depth results of the heavy metal soil detection; S3. Solidification and remediation of heavy metal soil: The excavated contaminated soil is then put into soil remediation equipment to remove stones, crush the soil, and spray it with chemicals to complete the solidification of the heavy metal content in the soil; S4. Constructing a barrier layer: laying a barrier layer of mixed materials with a thickness of 10 to 30 cm at the bottom of the deep excavation area; S5. Backfill soil: After the barrier layer is filled, the solidified and repaired soil is backfilled on top of the barrier layer; S6. Repair and control heavy metals in the surface soil: Finally, lay out soil conservation engineering measures such as cross-slope throttling ditches and longitudinal slope ridge ditches on the surface of the backfilled soil; At the same time, horizontal and vertical cooperative farming measures are adopted on the soil surface to plant herbaceous plants and trees to repair soil heavy metals. The spacing between trees is greater than or equal to 2mx2m. The grass seeds are sown in a mixed manner, with the sowing amount being greater than or equal to 30 g m ^-2 . 2. A method for remediation and loss control of heavy metal soil on slopes in karst areas according to claim 1, characterized in that 3 to 4 places of the soil in S1 are selected in a sample plot of 10mx10m, 50cm is taken from the surface to the bottom of the soil, a mixed sample is collected every 10cm, and the mixed sample is air-dried and packed into a plastic ziplock bag. 3. A method for remediation and loss control of heavy metal soil on slopes in karst areas according to claim 1, characterized in that the mass ratio of lime powder to contaminated soil in S1 is controlled between 1% and 5%. 4. A method for heavy metal soil remediation and loss prevention and control on slope surfaces in karst areas according to claim 1, characterized in that the soil remediation equipment in S3 comprises: a crushing system, a stirring system and a solid-liquid mixing system; The pulverizing system includes a vibrating screening plate for screening the input soil and a compound pulverizer installed below the vibrating screening plate; The solid-liquid mixing system includes a reagent tank, a mixing device installed in the reagent tank, and a spray washing system; The mixing system is used to mix the sprayed agent and the crushed soil. 5. A method for heavy metal soil restoration and loss prevention and control on slope surfaces in karst areas according to claim 4, characterized in that the agent tank contains a spraying agent and an improving agent; The spraying agent is a passivating agent, and the raw materials of the improved agent include, by weight: 3 parts of manure, 1 part of plant litter and 1 part of moss. 6. A method for remediation and loss control of heavy metal soil on slopes in karst areas according to claim 1, characterized in that the barrier layer in S3 comprises, by mass percentage, 65% to 70% of mineral clay material, 21.5% to 23.5% of cement and 5% to 8% of rock powder, with the remainder being adhesive. 7. A method for remediation and loss control of heavy metal soil on slopes in karst areas according to claim 1, characterized in that the surface soil heavy metal loss control measures in S6 adopt horizontal and vertical coordinated farming measures and engineering measures; at the same time, sensors are set at soil sampling and detection points to monitor and collect data, and a data model is obtained through the monitored collected data to complete the verification of the soil loss control effect of horizontal and vertical coordinated farming measures and engineering measures; First define: Definition 1: When the soil layer load conditions and the shear parameters of the steep slope soil surface are consistent with the actual situation of the steep slope, the theoretical minimum safety factor of the slope is close to 1 and slightly less than 1; Definition 2: When the soil layer load conditions and the shear parameters of the steep slope soil surface are consistent with the actual situation of the steep slope, the theoretical minimum safety factor of the slope is close to 1 and slightly less than 1, and the corresponding most dangerous steep slope soil surface must be consistent with the actual sliding surface of the steep slope; When a steep slope that has slid is about to slide but has not yet slid at the place where it last slid or slid recently, it is in a state of limit equilibrium. The section taken on it belongs to the section of limit equilibrium state. The residual sliding force of the last soil strip in the thrust calculation formula established based on this section is equal to zero, that is: _Bn = _{Bn -1fn} + _{FsVn sinɑn -Vn cosɑn tanfn -cnln = 0} ; (1) Where: _Fs is the sliding safety factor, _Vn is the deadweight of the nth soil strip, _ɑn is the inclination angle of the sliding surface of the nth soil strip, _cn is the cohesion of the nth soil strip of the steep slope, _fn is the internal friction angle of the nth soil strip of the steep slope, _ln is the arc length of the sliding surface of the nth soil strip, and _fn is the transfer coefficient, that is: f _n =cos(ɑ _n-1 -ɑ _n )-tanf _n sin(ɑ _n-1 -ɑ _n ); Let F _s = 1, and assume c or f; And from formula (1) we can get: Bi _-1 = _{Bi -Fs} Vi _sinɑi + Vi _{cosɑi tanf} + cl _i / _fi ; (i = 1 _, 2, ..., n) (2) Assuming the thrust of the last soil strip _Bn = 0, we can calculate by recursive step by step from formula (2): B ₁ =B ₂ -F _s V ₂ sinɑ ₂ +V ₂ cosɑ ₂ tanf+cl ₂ /f ₂ ; (3) At the same time, from formula (1), we can also get: B' ₁ ＝F _s V ₁ sinɑ ₁ -V ₁ cosɑ ₁ tanf-cl ₁ +B ₀ f ₁ ； (4) Where: B ₀ = 0; Let G = B ₁ -B'₁; (5) When the steep slope is in the limit equilibrium state (i.e., F _s = 1.0), given any c or f value, a corresponding f or c value can be obtained from formula (5) so that G = B ₁ -B' ₁ , which is equal to or approximately equal to zero; The values of c and f of each section in the limit equilibrium state can be solved respectively; By plotting the pairs of c and f values of two different sections on the plane with safety factor _Fs = 1.0, two intersecting cf value curves can be obtained. The set of c and f values at the intersection is the unique solution, which is also the shear strength index value that conforms to the actual state of steep slope sliding.