An example of mine geological disaster restoration and management-Jinan Yanchi Mountain restoration and management demonstration project

Yanchi Mountain is located in the southwest of Yaojia Village, Yaojia Town, Lixia District, Jinan City, with the main peak at an altitude of 188.67m and geographical coordinates of1kloc-0/704'15 "~1704' 29. Yanchi Mountain is distributed in northeast-southwest direction, with a length of about 650 meters, a width of about 430 meters and an area of about 0.28 square kilometers. The working area has convenient transportation, connecting Yaotou Road and Shi Jing East Road in the south, Jiefang East Road in the north, Jiangshuiquan Road in the east and Erhuan East Road in the west.

The main type of geological disasters is the mountain cracks formed by the collapse of iron ore mined-out, which are generally distributed linearly on the mountain, and the main crack I # runs through the whole mountain (photo 9- 1). The formation of mountain cracks is due to external force-mine goaf collapse. The main forms of movement are vertical lifting and horizontal stretching.

Photo 9- 1 Overlooking Yanchi Mountain (before treatment)

Yanchishan Iron Mine started from 1956, was mined by Jianshe Iron Mine 100, and then gradually turned to underground mining. During the period from1957 to1960, other units participated in open-pit mining, and after many subcontracts, the mining mode and horizon were chaotic, and the distribution of mines (holes) was irregular. 1996 due to pit mining, the surface rock and soil are stripped during mining, resulting in high and steep slope free surface. With the continuous advancement of the working face, the free face is getting bigger and bigger. After entering the roadway for mining, with the increasing of the goaf, the regional stress field changes, and the rock mass loses its lower support, resulting in unloading instability and deformation, which leads to the cracking of Yanchishan mountain, resulting in 16 cracks, including 3 main cracks, numbered ⅰ # and ⅱ #. The strike, scale and spatial distribution of secondary cracks are controlled by main cracks. Affected by the slit, the mountain collapsed locally. At present, the cliff height on the north side of the mountain is 16 ~ 85m.

1998, the maximum vertical drop and width of main cracks in I # Mountain were 1.00 m respectively. By July 2003, the maximum drop and width were 1.50 m and 2. 10 m respectively. 1996 to July 2003 is the development period of mountain cracks, and both horizontal displacement and vertical displacement of cracks have changed greatly (photos 9-2 and 9-3).

Figure 9-2 Local Cracks

Figure 9-3 Crack Covered Area

Second, the stability and harm

Mountain cracks have experienced gestation period, development period and basic stability period. From the mining of Yanchishan iron mine to the pit closure of 1996 iron mine, the incubation period of mountain cracks appeared. During this period, the unloading of the rock mass above the goaf is unstable, and the mountain cracks gradually form along the original joints and cracks of the mountain. The scale of cracks in this period is small, which is reflected in the intermittent cracks on the surface, and the horizontal and vertical distances are basically unchanged. 1996 to 2003 was the development period of mountain cracks, during which ground cracks gradually formed. During this period, the scale of mountain cracks developed rapidly, and the length, width and vertical drop of cracks expanded rapidly. At the end of the period, the vertical drop of cracks reaches 120cm, and the maximum horizontal width reaches 2 10cm.

Yanchi Mountain is located in the densely populated area in the east of Jinan, surrounded by government agencies, enterprises and institutions such as Jinan Urban Construction Administration, Jinan Police Academy, Shandong the Supreme People's Procuratorate, China Railway 14th Bureau, office buildings and dormitory areas, as well as local primary schools, kindergartens and residential areas. According to the investigation, there are 16 houses and 56/kloc-0 houses threatened by geological disasters around Yanchi Mountain.

Although the activity of the cracks in Yanchi Mountain is weak and basically stable in a short time, we should consider the basic characteristics of the ground cracks, that is, their development is irreversible and their stability is only relative. If the induced conditions are met, they will move and develop rapidly, which will cause great damage in a short time. Considering the geological background and environmental conditions of the occurrence and development of mountain cracks in Yanchi Mountain, the development and destruction of cracks may lead to many secondary geological disasters. If ground fissures encounter inducing factors and cause substantial development, it may lead to secondary geological disasters such as landslides, and multiple disasters will occur together, with disastrous consequences.

Third, comprehensive management.

(A) the principle of governance objectives

1. Governance objectives

Through reasonable engineering treatment measures, the threat of main crack 1 to tourists is eliminated, the landform of Yanchi Mountain is restored, the bad visual effect of Yanchi Mountain is beautified, and the overall image of Yanchi Mountain is improved.

2. Governance principles

Safety principle: firstly, we must ensure the overall stability of Yanchi Mountain, and we cannot eliminate existing geological disasters and form new geological disasters at the same time; Secondly, construction safety. In the process of construction, construction measures that are beneficial to or do not affect the stability of the mountain should be taken as far as possible to prevent the instability or collapse of the mountain. Safety protection measures for construction personnel should be put in place to prevent construction safety accidents.

Principle of environmental protection: this treatment project must ensure the harmony between the treatment area and the surrounding environment after the completion of the project, and achieve a seamless natural effect with the overall landscape effect of Yanchi Mountain. In the process of construction, attention must be paid to protecting the existing landform and geological environment of the mountain. It is forbidden to use local materials and dig in the mountains to protect the landscape. At the same time, it is necessary to clean up the site after the completion of the project, and clean up all kinds of building materials, equipment and facilities and construction waste.

Principle of natural restoration: after the completion of the treatment project, the effect of natural restoration of the ecological environment should be achieved, and the treatment and maintenance costs should be saved. In the process of vegetation breeding, plant varieties with strong vitality can survive independently and develop healthily depending on natural conditions.

(2) Construction specifications and procedures

1. Basis of specifications and standards

1) Code for Design of Building Foundation (GB 50007—2002);

2) Technical Specification for Building Foundation Treatment (JGJ 79—2002);

3) Code for Acceptance of Construction Quality of Building Foundation Engineering (GB 50202—2002);

4) Code for Acceptance of Construction Quality of Concrete Structure Engineering (GB 50204—2002);

5) Code for Quality Acceptance of Masonry Engineering (GB 50203—2002);

6) Technical Code for Building Slope Engineering (GB 50330—2002);

7) Technical Code for Safety of Working at Height in Building Construction (JGJ80-91);

8) Safety Code for Power Supply and Utilization in Construction Sites (GB 50194—93-93);

9) Regulations on the Prevention and Control of Geological Disasters (March 2004);

Regulations of Shandong Province on Geological Environment Protection (March 2003).

2. Geological foundation

1) geological environment control plan of Yanchishan mine in Jinan (Shandong Geological Environment Monitoring Station, August 2005);

2) Geological Environment Treatment of Yanchishan Mine in Jinan I # Main Crack Treatment Project Construction Scheme (Shandong Geology and Mineral Group Co., Ltd., July 2007).

(3) treatment engineering methods and key points of construction technology

According to the development characteristics of mountain cracks and the conditions of construction site, this project mainly adopts the methods of unloading dangerous rock mass, backfilling ground cracks, intercepting and draining water on slope surface, landscaping engineering and engineering maintenance. Its technical requirements are as follows:

1. Unloading of dangerous rock mass

Before the project starts, according to the site survey, the dangerous rock blocks in the crack construction area are mainly distributed on both sides of the crack and inside the crack. According to different situations, take corresponding construction measures to dismantle or reinforce. The dangerous rock deformation bodies located at the edge and inside of the cracks are hammered and pried, and large single movable rocks standing or isolated around the cracks are hammered and crushed, and filled into the cracks to prevent the injury to tourists and eliminate the potential safety hazards to tourists. Remove about 50m3 of dangerous rocks.

2. Slope interception and drainage

The west side of the ground fissure is located in the surface runoff gathering area, and the surface runoff formed in the process of heavy rainfall enters the ground fissure along the slope, which objectively reduces the residual bond strength of the ground fissure and promotes the development of the ground fissure. During the construction, a simple retaining wall was built above the main crack I # along the direction perpendicular to the surface runoff, which prevented the surface runoff from flowing to the ground fissure along the slope, changed the direction of the surface runoff, made the surface runoff flow down the ridge, and prevented a large amount of surface runoff from entering the ground fissure under bad weather conditions, which adversely affected its stability. The retaining wall played a great role in the construction and experienced the baptism of "718" rainstorm. After the rain, it was found that the surface runoff did not affect the crack filling material, but really changed the direction of the surface runoff and effectively protected the crack filling material.

3. Ground fissure backfill

In order to ensure the construction efficiency and reduce the safety risks in engineering construction, the ground cracks are mainly filled by machinery, supplemented by manual assistance. After mixing all kinds of raw materials according to the design requirements, the construction personnel will transport the materials to the starting point of the material handling equipment with a large forklift, and then transport the materials to the upper part of the mountain crack through the material handling equipment. The material will pass through the guide chute and enter the crack along the guide chute with manual assistance. The filling material will fall into the cracks under its own weight, and the material will be compacted by the impact of the free fall of the material. Before the construction in the second area, firstly, the material handling equipment and transfer track on the slope are set up, which are basically laid along the crack direction. The material handling equipment will transport the filling materials to the top of the crack in the first area for transfer, and then the filling construction will be carried out in the second area along the crack direction, and the materials will directly enter the crack through the guide chute. The slope of the crack section in the third construction area is large, so it is impossible to lay the track. The method of lengthening the guide groove is used to fill the cracks. The height of the top surface of the filling material should be 70cm away from the crack footwall. In the process of construction, the specifications and design requirements were strictly implemented and the operation was carried out according to the regulations, which ensured the smooth progress of the project construction.

4. Concrete engineering

In the FG section of the ground fissure, because the width and depth of the fissure are relatively large, in order to ensure the construction quality of the project, it is determined through consultation with the supervision unit before construction that steel mesh is laid at the bottom and middle of the fissure, and concrete is poured separately to reinforce the fissure filling material.

5. Landscape greening project

According to the requirements of the treatment scheme, firstly, a red clay cover plate with a thickness of about 20cm is covered on the top of the filler as a waterproof bottom plate to prevent surface water from entering the cracks and adversely affect the stability of the cracks; The second is to conserve topsoil and promote the growth of topsoil plants. The top of the clay cover plate is paved with 50 cm thick cultivated soil (exotic soil) as the greening soil layer. The greening and beautification project is carried out in a multi-angle three-dimensional way. First, the seeds of Festuca arundinacea are planted on the surface of backfilled cultivation soil for ground greening. Secondly, climbing plants such as Fructus Forsythiae and Bauhinia are planted at irregular intervals in the crack construction area to cover the crack, cover the crack area, and carry out multi-level and multi-angle three-dimensional greening on the crack construction area in order to achieve the best construction effect.

6. Maintenance

During and after the construction, the vegetation and other projects in the crack area should be maintained by special personnel, and the vegetation should be covered and watered with grass curtains in time to ensure the survival rate of the vegetation. Determine the full-time maintenance personnel in time after the project is completed, and sign the project maintenance target contract with them to ensure that the governance project can be effectively maintained within 2 years after the project is completed.

(4) Construction technology and process

1. Construction process flow

The construction process of this project includes site reconnaissance, project construction preparation, project commencement, unloading of dangerous rock mass, slope drainage, crack filling, concrete engineering, landscaping engineering, maintenance and completion cleaning (Figure 9-7).

2. Construction process

(1) field survey

Organize technicians and engineering construction management personnel to climb Yanchi Mountain, conduct on-site reconnaissance on the mountain crack construction site, check various engineering data, grasp the actual situation of the project, analyze and formulate the construction plan on the spot, and determine the main construction management personnel. After careful analysis of the site conditions, according to the site conditions such as the strike, slope and crack scale of different sections of cracks, it is determined to carry out the construction of cracks in different zones, which reduces the construction difficulty and improves the construction efficiency. AB and BC are the first construction areas, the second construction areas are CD, DE and EF, and the third construction areas are FG and GH. See Figure 9-8 for details.

Figure 9-7 Engineering Construction Process Flow Chart

Figure 9-8 Construction zoning map

(2) Engineering construction preparation

According to the site survey and zoning, organize the project construction management personnel to go deep into the project construction site, investigate and analyze the site environment and construction conditions, study and determine the project construction measures, as well as the transportation route, stacking position and transshipment route of the equipment, machines, materials and engineering materials. , and a detailed comparative study of the materials used.

Site cleaning: firstly, the material storage site is cleaned and renovated to ensure that the site meets the construction requirements, and the material transfer route is widened and renovated in time to ensure the safety and smoothness of the route and the timely and safe transportation of building materials; Secondly, actively negotiate with local village committees and residents to get their support, and rent about 50m2 houses and temporary water and electricity near the site; The third is to set up the construction site headquarters to guide and solve the difficulties and problems encountered in the construction process in time.

Manufacture and installation of material transportation equipment: in order to improve the construction efficiency, considering that the construction site is located on a hillside with large slope and high height, it is difficult to transport, which is the focus of this treatment project. Therefore, the materials, machinery, equipment and waste materials required for the construction of this project are removed by the way of "step track project" (Figure 9-4), which combines transportation with manual assistance. The concrete method is: the engineering materials are stacked on the south side of the Shanxi slope of Yanchi, and the materials are transported by ZL-50 forklift, and the transportation route is along the original gravel road. In the middle of the western slope of the mountain, the starting point station of the material transportation track is placed, and electric equipment such as generators and electric control equipment are placed on site. From this starting point, the track is basically laid along the ridge to the top of the mountain, and the track support is built by the pipe rack of the construction project. The track laying process shall be carried out in strict accordance with the construction and relevant specifications to ensure the track is safe, qualified and smooth.

Figure 9-4 Material Transportation Trajectory

Figure 9-5 Material Transfer

The material transportation track is divided into two sections, the 1 section is the feeding track, and the second section is the transfer track. Building materials are transferred at the top of the hillside to facilitate the construction of the second and third areas. The transit track is about 80m away from the foot of the mountain, basically laid along the crack direction, and located in the second construction area.

Safety protection facilities: In the construction process, in order to prevent falling rocks, construction workers slipping and mechanical slipping of material transportation equipment, protective nets are installed in the direction of cracks in front of the construction, safety fences are erected with construction scaffolding pipes, protective fences and protective nets are installed under the material transportation route, and anti-skid devices are installed above the side of the track winch to prevent the winch from slipping down the slope and causing safety accidents. Safety warning signs have been placed around the construction site, and residents around Yanchi Mountain are advised to climb mountains to remind climbers to pay attention to safety. Organize personnel to build safety fences and safety nets along the bottom of cracks to prevent fillers from falling off and construction personnel from falling down during construction, so as to ensure the safety of engineering construction. Install a protective fence (net) along the lower part of the material transportation route to prevent people from falling during the material transportation.

After the project construction preparation is completed, all the project preparation materials will be submitted to the supervision unit immediately and the project preparation will be reported to the supervision unit, and the supervision unit will agree to start construction after on-site inspection.

(3) Construction process

Unloading of dangerous rock mass: According to the on-site investigation, the on-site construction technicians delineated the cracks and the dangerous rock blocks around them, and determined the treatment scheme. The dangerous rock mass inside the crack is chiseled, and the dangerous rock mass on both sides of the crack is broken, backfilled or reinforced, and more than ten dangerous rock masses are treated, which ensures the safety of the next construction process and eliminates the potential threat to tourists.

Slope interception: the construction area of ground fissure control is located on the north slope of Yanchi Mountain, which is in the convergence area of mountain surface runoff. The construction period is in the flood season, and rainfall may cause surface runoff on the slope, which poses a potential threat to the construction of crack treatment projects and the stability of crack filling materials. Therefore, during the construction period, the site construction personnel built a water retaining wall with a length of about 35m and a height of about 30cm along the upper direction of the crack, so as to change the flow direction of surface runoff, prevent the surface runoff from gathering in the direction of the ground crack, and prevent the surface water from flowing to the crack, which adversely affected the engineering construction and the stability of the crack. After the crack construction is completed, it will be removed and the original landform will be restored.

Backfilling of mountain cracks: according to the technical requirements of the treatment scheme and the requirements of the construction scheme, the ground cracks are backfilled, and the backfill material is graded macadam. The material is transported by the winch through the transportation track (Figure 9-5), and freely falls into the ground fissure through the guide chute, and the material is compacted by its own weight.

Concrete engineering: it is the key working procedure of this project. Its core is to ensure the connection strength of cracks. The concrete engineering of this project is mainly in the process of crack construction in FG section, which has a large width and depth, the maximum width is about 2. 10m, and the maximum depth is about 12. 10m. In order to ensure the construction quality of the project and eliminate the potential threat of the main crack I # to tourists, after consultation with the supervision unit, it is decided to lay two layers of reinforced concrete at the bottom and middle of the crack to strengthen the structural strength of the crack filling material, and to lay two layers of concrete respectively? 16@250×250 steel mesh. The thickness of the concrete layer is 50cm, and the number is C25.

During construction, the bottom of the crack is preliminarily filled, the filling height is about 1.0m, and the top surface of the filling material is flat. After the preparatory work is completed, measure the width and depth of the crack, and determine the specifications of the reinforcing cage according to the measurement results. After on-site consultation, it was decided to make the reinforcing cage into an isosceles trapezoid, and put the processed reinforcing cage on the top of the filler in the crack. The distance between the bottom of the reinforcing cage and the top surface of the material is about 10cm. The main reinforcement of reinforcing cage is 7 ~ 9? 18 @ 250 ~ 400, annular reinforcement? 8.5@250。 After the reinforcement cage is placed stably, check its distance from both sides of the crack and the distance from the top surface of the filler to ensure that it meets the requirements of construction specifications and the thickness of the protective layer of reinforcement meets the construction requirements. The concrete is cast-in-situ C25 concrete. The concrete is evenly mixed at the foot of the mountain, transported to the construction site through the material conveying track, and enters the cracks along the guide chute. During the pouring process, a vibrating rod is used for vibration compaction. Reinforced concrete is not less than 60cm. See the sketch map of concrete engineering construction section (Figure 9-9) for details.

Figure 9-9 Schematic Diagram of Concrete Engineering Construction Section

Landscaping project: it is the key process of this project construction. Its core is to ensure the stable combination of overburden and rock mass and prevent new soil erosion. The key point of construction is to ensure the close contact between red clay and the two walls of cracks. The adopted construction technology is "Thumbnail Bed Soil Consolidation Technology", and the specific methods are as follows:

According to the design requirements, a red clay cover plate with a thickness of 20cm is laid on the top of the joint sealant, and the red clay of piedmont residual soil is selected. The construction shall be carried out in strict accordance with the technical requirements, and the red clay shall be in close contact with the two walls of the crack and compacted manually. Farming soil layer is laid on the upper part of clay cover plate for greening and maintenance in ground fissure control area. The cultivated soil layer is 50cm thick, and cultivated soil is used. During construction, the plough layer shall be tamped manually. In order that the compaction measures will not affect the stability of ground fissures, a hammer weighing 16 pound is used for compaction (Figures 9-6 and 9-7).

Figure 9-6 Ploughing and Planting Soil Filling Construction

Figure 9-7 Manual tamping

In order to restore the landscape of Yanchi Mountain to the maximum extent, engineers and technicians have determined a multi-angle and three-dimensional landscaping and greening scheme after many discussions: firstly, seeds of Festuca arundinacea are planted on the surface of cultivated soil, which is cold-resistant and drought-resistant, and can grow independently in the field, and the ground is afforested; Secondly, plants such as bauhinia and forsythia are planted irregularly in the crack treatment area to block the vertical crack surface of the crack to achieve the best visual effect.

In order to ensure that the surface backfill soil layer will not be lost with surface runoff or atmospheric precipitation, a nail bed (photo 9-8) is buried in the topsoil of the fractured FG section to fix the topsoil layer. The slope of the crack in this section is large, and the width and depth of the crack are larger than those in other parts. In order to ensure the construction quality of cracks in this section and prevent topsoil from losing with surface runoff, nail beds are buried in FG section, with a width of 50cm, a length of 250cm and a nail length of about 20cm. The principle of fixing the surface vegetation by nail bed is that the roots of the surface vegetation are connected with the nail bed after going deep underground, which effectively increases the surface adhesion of the surface vegetation and prevents the surface vegetation from sliding as a whole due to excessive slope.

Maintenance: During the construction process, the construction shall be carried out in sections, and the maintenance personnel of the greening project shall be determined in time to maintain the greening area. After sowing grass seeds on the surface, cover it with a straw curtain for protection (Figure 9-9), and water it in time for maintenance. Sign an agreement with the on-site maintenance personnel to be responsible for the regular maintenance of the ground fissure construction area within 2 years after the completion of the project.

Photo 9-8 Photo of nail bed

Figure 9-9 Ground Greening

Cleaning after completion: carpet cleaning shall be carried out on the construction site in time after the completion of the project. Be sure to clean up all kinds of construction tools and construction waste, clean up the site in time and dispose of it properly, so as to clean up the site after work. Vegetation damaged by construction will be restored in time to protect the environment.

Fourth, the governance effect.

1) Unloading of dangerous rock mass: according to the field investigation, determine the position and scale of dangerous rock mass on both sides of the crack, and take unloading measures or reinforcement measures in time. After the completion of the construction around the crack, there is no dangerous rock mass that poses a potential threat to tourists.

2) Slope cutting and drainage: Slope cutting and drainage retaining wall played a role in the construction process. The heavy rain on July 18 did not adversely affect the cracks. The green vegetation in the cracks is well preserved, and the retaining wall effectively blocks the surface runoff, preventing most of the surface runoff from entering the cracks and destroying the stability of the cracks and filling materials. After the completion of the treatment project, it will be demolished to protect the geological environment of the mine to the maximum extent.

3) Backfilling of cracks: Construction shall be carried out in strict accordance with the design requirements and construction scheme requirements. The fillings in the cracks are dense and the settlement deformation is very small. After the baptism of heavy rain on July 18, no settlement and deformation occurred. At the same time, the reinforced concrete layer is added at the crack of FG section, which enhances the overall structural strength of crack filling material and ensures the construction quality of the project.

4) Landscaping: The clay cover plate and cultivated soil shall be backfilled in strict accordance with the design requirements, and the red clay is in close contact with both sides of the crack, which can effectively prevent water. Mature soil is adopted in the cultivated soil layer, which is beneficial to the planting and survival of green vegetation. Manual tamping is adopted in the construction, the thickness meets the design requirements, and the construction quality is good.

The greening and beautification project adopts a multi-angle and three-dimensional way, planting cold-resistant and drought-tolerant tall fescue grass seeds on the surface for greening, supplemented by climbing plants such as forsythia and bauhinia, so as to restore the geological landscape of Yanchi Mountain to the maximum extent and ensure its good visual effect.

See Figure 9- 10 for the specific treatment effect.

Figure 9- 10 Simulation Effect Diagram of West Side after Processing