Composite treatment structure for surface collapse of karst area

Abstract

The utility model belongs to the technical field of karst surface collapse treatment, and discloses a composite treatment structure for karst area surface collapse. Comprising a foundation pit which surrounds a karst gap and is of an inverted trapezoidal structure, gabions which are transversely arranged in a front-back clinging mode in the direction of the karst gap, composite inverted filtering structures arranged on the other outer side faces, except the bottom side, of the gabions, and a plurality of ventilation pipes which are arranged in a bilateral symmetry mode and vertically inserted into the gabions. The foundation pit is filled with the cohesive soil layer, the planting soil layer is located over the cohesive soil layer, the bottom of the foundation pit is the upper surface of the bedrock layer, and the composite inverted filter structure comprises a geogrid, geotechnical cloth and a gravel inverted filter layer located over the gabion which are sequentially laid from inside to outside along the other outer side faces, except the bottom side, of the gabion. The three-dimensional ecological planting device has the advantages that composite treatment is achieved, rigidity and softness are combined, the overall stability is achieved, the three-dimensional ecological planting device is all-dimensional, three-dimensional and free of dead corners, and the attractiveness is high.

Description

Technical Field

[0001] This utility model belongs to the field of karst ground subsidence treatment technology, specifically relating to a composite treatment structure for ground subsidence in karst areas. Background Technology

[0002] Karst surface subsidence is a common geological hazard in karst areas. The fundamental cause of subsidence caused by engineering construction lies in changes in hydrogeological conditions: on the one hand, groundwater is rapidly lost along favorable drainage points created by underground engineering construction; on the other hand, due to surface soil erosion, precipitation and surface water can directly replenish groundwater. The contrasting strengths of replenishment and discharge over time lead to frequent and dramatic rises and falls in groundwater levels. The seepage and vacuum erosion caused by the drop in water level continuously erode the overburden layer, while the high-pressure expansibility caused by the rise in water level destroys the originally stable soil arch structure, leading to continuous loss of the overburden soil and ultimately, surface subsidence.

[0003] Currently, the commonly used measures for treating karst area collapses are: beam-slab crossing method, grouting sealing method, backfilling method, and pressure relief method.

[0004] The beam-slab crossing method uses a beam-slab structure to cross the opening of karst cavities, protecting the superstructure from the impact of collapse. It is an engineering measure aimed at avoiding disasters and does not interfere with the occurrence and development of collapse. Collapse will continue to evolve until it stabilizes naturally, resulting in permanent soil erosion and damage to the natural landscape.

[0005] Grouting sealing, which involves injecting grout to seal the openings of karst caves, offers good short-term treatment results. However, it neglects the condition of bedrock fissures, making it a short-sighted approach. The essential characteristic of rock masses is fissures; there are no fissure-free rock masses. Karst phenomena occur alongside fissures; isolated karst caves do not exist. While sealing the original caves, this method also diverts water and gas to surrounding karst caves or fissures, accelerating their development and inducing new collapses in the surrounding area.

[0006] Backfilling primarily uses sand and gravel or geotextiles to construct a filter layer to prevent seepage damage, thus conserving soil while also providing some aeration. This method involves filling the collapsed area in layers from bottom to top with sand and gravel of decreasing particle size. While vertical seepage damage is less likely, the bottom layer of larger-sized stones has greater porosity, making it prone to contact soil flow around the edges. Over time, this still carries the risk of re-collapse and subsequent settlement.

[0007] The pressure relief method uses pipes to connect karst caves to the outside atmosphere. Its main function is to allow air to pass through, solve the problem of internal and external air pressure balance, and effectively relieve vacuum erosion and high pressure expansion, thus preventing soil erosion. This method has a single function, mainly to prevent collapse, and is not a treatment structure for existing collapses.

[0008] Currently, the methods for treating karst ground subsidence generally lack the concept and measures for water blocking, ignoring the fundamental reason of changes in groundwater recharge conditions. This results in various types of surface water still being able to freely infiltrate and replenish the groundwater, and the frequent rise and fall of groundwater cannot be fundamentally alleviated, leading to subsidence treatment often being much more difficult than effective. Utility Model Content

[0009] This utility model aims to provide a composite treatment structure for ground subsidence in karst areas, which combines air permeability, soil retention, and water blocking to solve the problem that current karst area subsidence treatment measures cannot completely eliminate soil erosion.

[0010] Therefore, the technical solution adopted by this utility model is as follows: a composite treatment structure for ground subsidence in karst areas, including a foundation pit with an inverted trapezoidal structure around karst cavities, gabions arranged horizontally and closely attached to each other along the direction of the karst cavities, a composite filter structure set along the outer surfaces of the gabions except for the bottom side, several ventilation pipes symmetrically arranged on the left and right and vertically inserted into the gabions, a cohesive soil layer filling the foundation pit, and a planting soil layer located directly above the cohesive soil layer. The bottom of the foundation pit is the upper surface of the bedrock layer. The composite filter structure includes a geogrid, geotextile, and a sand and gravel filter layer laid sequentially from the inside to the outside along the outer surfaces of the gabions except for the bottom side. The top of the ventilation pipe extends vertically out of the planting soil layer and then bends horizontally. The planting soil layer is planted with green plants.

[0011] As a preferred embodiment of the above scheme, the foundation pit is excavated to the bedrock surface using the slope method to ensure the stability of the foundation pit slope; the center of the gabion is aligned with the center of the karst cavity, and the support lengths on both sides are the same and sufficient, so that the stress state of the gabion structure is reasonable and the overall structure is stable.

[0012] More preferably, the gabion includes a gabion frame made of horizontal, vertical and horizontal steel bars, and a gabion mesh installed on the gabion frame, thereby forming two symmetrical stone placement cells. The stone placement cells are filled with stones, and the gabion mesh is a double-twisted hexagonal mesh made of steel wire coated with polyvinyl chloride organic coating.

[0013] Further preferably, the stone is filled by manual layering and stacking, and the lower layer of stone has a larger particle size than the upper layer of stone. The stone is weather-resistant hard rock with an average particle size between 12cm and 16cm, and more than 85% of the stone has a particle size >12cm, which is a reasonable material selection.

[0014] Preferably, the geogrid is installed securely on the outer side of the gabion by binding. The geotextile is applied to the entire geogrid from top to bottom, and the bottom is fixed to the bottom of the foundation pit with U-shaped steel nails. The geotextile is made of polyester filament spunbond needle-punched nonwoven geotextile with an equivalent pore size of 0.05 mm and a permeability coefficient of 1×10⁻⁶. -3cm / s, reasonable material selection, seamless, stable installation, good integrity, and strong reverse filtration capacity.

[0015] More preferably, the cohesive soil layer is compacted to a thickness of 150mm to 250mm to ensure that the permeability coefficient of the compacted cohesive soil layer is less than 0.01m / d, thus ensuring the effect of mitigating surface water infiltration.

[0016] More preferably, the top of the vent pipe is provided with a right-angle bend with the outlet facing the horizontal direction, and the length of the horizontal section is 20cm to 24cm. The vent pipe is a rigid UPVC pipe with a diameter of 5cm to 10cm.

[0017] More preferably, the sand and gravel filter layer includes a medium-fine sand and gravel layer and a fine sand and gravel layer laid horizontally from bottom to top, forming a step-by-step filter to ensure the filter effect.

[0018] Further preferably, the planting soil layer is thicker than 30cm and has a reasonable size, and the greening plants are local dominant species and low shrubs with root systems shorter than 30cm, ensuring the survival rate of plant planting.

[0019] The beneficial effects of this utility model are:

[0020] (1) Currently, no karst area subsidence control measures can completely eliminate soil erosion. Conventional backfilling methods with filter layers only focus on soil conservation, neglecting water blocking and aeration, and cannot alleviate the frequent rise and fall of groundwater and changes in air pressure. This scheme adopts a composite treatment structure to construct a comprehensive three-dimensional filter barrier, which alleviates changes in air pressure within karst conduits, slows down the source of groundwater recharge, and integrates aeration, soil conservation, water blocking, load bearing, and greening functions to comprehensively control karst area subsidence, thereby inhibiting soil erosion and ground subsidence from the root. The concept is novel and the design is ingenious.

[0021] (2) Gabions are constructed across karst cavities on the leveled bedrock surface. Due to the high compressive strength of the bedrock and the reasonable stress state of the spanning structure, the overall structure has high stability. The steel reinforcement frame gives the gabions rigidity to support the loads of the overlying structural layers, preventing excessive deformation that could damage the overlying sand and gravel filter layer and cause significant ground subsidence. The gabion structure itself is flexible; when karst cavities expand, it can deform to adapt to and block new openings, preventing brittle failure. At the same time, the numerous interconnected pores between the stones placed inside the gabions ensure smooth airflow.

[0022] (3) Compared with the existing filter layer laid layer by layer from bottom to top, this scheme forms a three-dimensional filter by covering the gabion with geotextile and laying a sand and gravel filter layer directly above the gabion. This not only prevents water and soil loss from above, but also prevents lateral seepage damage to cohesive soil. The geotextile has a good soil retention effect, and the gabion also provides support for the geotextile, effectively preventing the geotextile from deforming and breaking due to excessive load. The layout is reasonable.

[0023] (4) Use cohesive soil to fill the remaining space of the foundation pit. Utilize the strong water-locking capacity of the cohesive soil to effectively reduce the permeability coefficient of the composite structure, prevent surface water loss and replenishment of the ground, and slow down or eliminate the frequent rise and fall of groundwater.

[0024] (5) A ventilation pipe is used to connect the karst caves with the atmosphere, maintain air circulation in the karst caves, balance the internal and external air pressure, effectively reduce the air pressure load on the gabion structure, and slow down or eliminate the vacuum erosion and high pressure expansion effects.

[0025] (6) Planting plants in the soil layer for greening, further blocking water through plant roots, maintaining the consistency of the ground environment landscape, restoring the living environment and natural landscape damaged by soil erosion, and improving the overall aesthetics.

[0026] In summary, this treatment structure takes comprehensive measures such as soil conservation, water blocking, and aeration to address the causes of collapse, including changes in groundwater recharge conditions, frequent rises and falls in groundwater levels, and changes in air pressure within the cavities. It has the advantages of composite treatment, a combination of rigidity and flexibility, overall stability, comprehensive three-dimensional design without blind spots, and strong aesthetics. It can effectively prevent the risk of re-collapse after treatment and subsequent settlement. Attached Figure Description

[0027] Figure 1 This is a front view of the composite governance structure constructed according to this utility model.

[0028] Figure 2 This is a schematic diagram of a gabion structure (the gabion mesh is not fully shown, and the top gabion mesh is not installed).

[0029] Figure 3 This is a diagram illustrating the composite governance structure constructed according to this utility model. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments and accompanying drawings:

[0031] Combination Figure 1 — Figure 3As shown, a composite treatment structure for ground subsidence in karst areas consists of a foundation pit 3 in the shape of an inverted trapezoid surrounding a karst cave 1, gabions 4 arranged horizontally and closely attached to each other along the direction of the karst cave 1, a composite filter structure set along the outer sides of the gabions 4 except for the bottom side, several ventilation pipes 8 symmetrically arranged on the left and right and vertically inserted into the gabions 4, a cohesive soil layer filling the foundation pit 3, and a planting soil layer 10 located directly above the cohesive soil layer.

[0032] The bottom of the foundation pit 3 is the upper surface of the bedrock layer 2.

[0033] The composite filter structure consists of geogrid 6, geotextile 7, and sand and gravel filter layer 9 laid sequentially from the inside to the outside along the outer sides of the gabion 4, except for the bottom side.

[0034] The top of the ventilation pipe 8 extends vertically out of the planting soil layer 10 and then bends horizontally.

[0035] The top 10 of the soil layer is planted with green plants.

[0036] The foundation pit 3 is preferably excavated by slope method to the surface of bedrock layer 2.

[0037] The center of gabion 4 is aligned with the center of karst cave 1, and the supports on both sides are of equal and sufficient length.

[0038] The gabion 4 consists of a gabion frame 41 made of horizontal, vertical and longitudinal steel bars and a gabion mesh 42 installed on the gabion frame 41, thus forming two symmetrical stone placement cells.

[0039] The stone placement cell is filled with 5 stones.

[0040] The preferred material for the gabion mesh 42 is a double-twisted hexagonal mesh made of steel wire coated with PVC organic coating.

[0041] Stone 5 is filled by manual layering and stacking, and the lower layer of stone 5 has a larger particle size than the upper layer of stone 5. Stone 5 is made of weather-resistant hard rock.

[0042] The geotextile 7 is made of a single piece that is attached to all the geogrids 6 from top to bottom, and the bottom is fixed to the bottom of the foundation pit 3 with U-shaped steel nails.

[0043] Geotextile 7 is preferably made of polyester filament spunbond needle-punched nonwoven geotextile.

[0044] The geogrid 6 is installed on the outer side of the gabion 4 by binding.

[0045] The cohesive soil layer is compacted in layers with a thickness of 150mm to 250mm.

[0046] The top of the ventilation pipe 8 is provided with a right-angle bend with the outlet facing the horizontal direction. The top horizontal section is more than 20cm higher than the top of the green plants, and the length of the horizontal section is preferably 20cm to 24cm. The ventilation pipe 8 is preferably made of rigid UPVC pipe with a diameter of 10cm to 12cm.

[0047] The sand and gravel filter layer 9 consists of a medium-fine sand and gravel layer 91 and a fine sand and gravel layer 92 laid horizontally from bottom to top.

[0048] The thickness of the planting soil layer 10 is preferably greater than 30cm.

[0049] When the thickness of the overburden layer in a karst landslide is between 2.5m and 5m, and the diameter of the vertical karst cavities is less than 30cm, a composite treatment method for landslides in karst areas is proposed, with the following specific implementation steps:

[0050] Step S1: Excavate around the karst cave 1 with a slope to the upper surface of the bedrock layer 2 to form a foundation pit 3. Then, level and clean the bottom surface of the foundation pit 3, and measure and mark the opening of the karst cave 1.

[0051] In step S1, based on geological survey data and actual site conditions, the excavation area is determined according to the working surface range at the bottom of the pit and the stable slope of the overburden layer. The slope method is used to excavate to the upper surface of the bedrock layer 2.

[0052] Step S2: Place gabions 4 symmetrically and closely along the direction of the karst cave 1, fill the gabions 4 with stones 5, and lay geogrid 6 and geotextile 7 along the other sides of the gabions 4 except the bottom side.

[0053] In step S2, the gabion 4 is mainly composed of a gabion frame 41 made of horizontal, vertical and longitudinal steel bars and a gabion mesh 42 installed on the gabion frame 41, thus forming two symmetrical stone placement cells. The center of the gabion 4 is aligned with the center of the karst cave 1 opening.

[0054] In step S2, the geotextile 7 is applied to all the geogrids 6 from top to bottom, and the bottom is fixed to the bottom of the foundation pit 3 with U-shaped steel nails.

[0055] The geotextile 7 has a minimum width of 10cm at the bottom, and its edges are laid flush with the bedrock at the bottom of the pit. The excess portion at the four corners is folded and attached to the respective surfaces, and the edges are fixed to the bedrock at the bottom of the pit with U-shaped steel nails. The geogrid 6 and geotextile 7 on the upper surface of the gabion 4 have perforations for ventilation pipes 8.

[0056] Step S3: Use cohesive soil to backfill the foundation pit 3 in layers and compact it initially. Reserve a space for a sand and gravel filter layer directly above the gabion 4. Then, ventilator pipes 8 are installed symmetrically on the left and right. The bottom end of the ventilator pipe 8 extends into the gabion 4, and the top end extends vertically out of the original ground. Then, it is bent horizontally at a position 20cm or more above the maximum height of the green vegetation.

[0057] In step S3, the initial backfill height of the cohesive soil is preferably no less than 60cm above the gabion 4.

[0058] Step S4: Lay a sand and gravel filter layer 9 in the reserved space, then backfill the remaining area of ​​the foundation pit 3 with cohesive soil, and finally lay a planting soil layer 10 and plant plants for greening.

[0059] In step S4, the thickness of the backfilled cohesive soil shall not be less than 50cm.

Claims

1. A composite treatment structure for ground subsidence in karst areas, characterized in that: The foundation pit (3) is shaped like an inverted trapezoid around the karst cave (1), gabions (4) are arranged horizontally and closely along the direction of the karst cave (1), a composite filter structure is set along the outer side of the gabions (4) except for the bottom side, several ventilation pipes (8) are symmetrically arranged and vertically inserted into the gabions (4), a cohesive soil layer filling the foundation pit (3) and a planting soil layer (10) located directly above the cohesive soil layer. The bottom of the foundation pit (3) is the upper surface of the bedrock layer (2). The composite filter structure includes geogrid (6), geotextile (7) and sand and gravel filter layer (9) laid from the inside to the outside along the outer side of the gabions (4) except for the bottom side. The top of the ventilation pipe (8) extends vertically out of the planting soil layer (10) and then bends horizontally. The planting soil layer (10) is planted with green plants.

2. The composite treatment structure for ground subsidence in karst areas according to claim 1, characterized in that: The foundation pit (3) is excavated to the surface of the bedrock layer (2) using the slope method, and the center of the gabion (4) is aligned with the center of the karst cavity (1).

3. The composite treatment structure for ground subsidence in karst areas according to claim 1, characterized in that: The gabion (4) includes a gabion frame (41) made of horizontal, vertical and horizontal steel bars and a gabion mesh (42) installed on the gabion frame (41), thus forming two symmetrical stone placement cells. The stone placement cells are filled with stones (5). The gabion mesh (42) is made of double-twisted hexagonal mesh with a polyvinyl chloride organic coating.

4. A composite treatment structure for ground subsidence in karst areas according to claim 3, characterized in that: The stone material (5) is filled by manual layering and stacking, and the lower layer of stone material (5) has a larger particle size than the upper layer of stone material (5). The stone material (5) is made of weather-resistant hard rock.

5. A composite treatment structure for ground subsidence in karst areas according to claim 1, characterized in that: The geogrid (6) is installed on the outer side of the gabion (4) by binding. The geotextile (7) is applied to the entire geogrid (6) from top to bottom, and the bottom is fixed to the bottom of the foundation pit (3) by U-shaped steel nails. The geotextile (7) is a polyester filament spunbond needle-punched nonwoven geotextile.

6. A composite treatment structure for ground subsidence in karst areas according to claim 1, characterized in that: The cohesive soil layer is compacted in layers with a thickness of 150mm to 250mm.

7. A composite treatment structure for ground subsidence in karst areas according to claim 1, characterized in that: The ventilation pipe (8) has a right-angle bend at the top with the outlet facing the horizontal direction. The top horizontal section is more than 20cm higher than the top of the green plants, and the length of the horizontal section is 20cm to 24cm. The ventilation pipe (8) is made of rigid UPVC pipe with a diameter of 5cm to 10cm.

8. A composite treatment structure for ground subsidence in karst areas according to claim 1, characterized in that: The sand and gravel filter layer (9) includes a medium-fine sand and gravel layer (91) and a fine sand and gravel layer (92) laid horizontally from bottom to top.

9. A composite treatment structure for ground subsidence in karst areas according to claim 1, characterized in that: The planting soil layer (10) is more than 30cm thick, and the greening plants are local dominant species and low shrubs with root systems shorter than 30cm.

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