WO2021248872A1 - Method for determining safe thickness of side wall in karst area of foundation pit, and grouting device - Google Patents

Abstract

Disclosed in the present invention is a method for determining the safe thickness of a side wall in a karst area of a foundation pit, comprising: determining the length m of the side wall, affected by the karst area, of the foundation pit, the length n of the karst area, and steel supporting force F1, air pressure F2 and water pressure F3 of the side wall of the foundation pit; and calculating axial displacement, potential energy and safe thickness of the side wall in the karst area according to the elastic-plastic theory, the law of conservation of energy and the catastrophe theory. Also disclosed in the present invention is a grouting device for a karst area of a foundation pit, comprising a metal net, a water stop plate, a grouting pipe, a water pumping pipe and a one-way communication device. According to the present invention, the risk of water gushing in a karst area of a foundation pit can be quickly eliminated, the problems of slurry injection difficulty, karst water backward suction and the like in construction are solved, a karst area can be blocked, project investment is saved, and construction safety is guaranteed.

Description

Method for determining safety thickness of side wall in karst area of foundation pit and grouting device Technical field

The invention relates to the field of foundation pit construction grouting, in particular to a method and a grouting device for determining the safe thickness of side walls in a karst area of a foundation pit.

Background technique

When excavating foundation pits in karst areas, the distribution of karst water is extremely uneven and difficult to detect. During excavation of foundation pits, water inrush accidents are prone to occur. When effective protection measures are taken at the gushing outlet, the construction site will often be flooded, equipment will be destroyed, equipment and personnel accidents will be caused, construction delays will be delayed, and project investment will increase.

Summary of the invention

The invention provides a method for determining the safe thickness of the side wall in the karst area of a foundation pit to overcome the above technical problems.

The present invention provides a method for determining the safe thickness of side walls in a karst area of a foundation pit, which includes the following steps:

S1: Determine the length m of the sidewall of the foundation pit affected by the karst zone, the length n of the karst zone, the steel supporting force F _{1 of the} sidewall of the foundation pit, the air pressure F ₂ and the water pressure F _{3 of the} karst zone;

S2: According to the elastoplastic theory, calculate the axial displacement of the side wall in the karst zone, that is, the deflection is:

Among them, d is the safe thickness of the side wall in the karst area;

S3: Calculate the potential energy of the side wall in the karst area, the specific formula is as follows:

W ₀ ＝W ₁ -W ₂ (2)

Among them, W ₁ is the deformation potential energy of the anti-outburst layer, and W ₂ is the work done by the external force;

S4: Calculate the safe thickness of the side wall in the karst zone, the specific formula is as follows:

Among them, E is the elastic modulus of the water-resistant rock formation, and μ is the Poisson's ratio;

S5: Compare the calculated safe thickness of the side wall of the foundation pit in the karst area with the actual detection results, and determine the grouting method.

The present invention also provides a grouting device used in the karst area of a foundation pit, including: a metal mesh, a water stop plate, a grouting pipe, a pumping pipe, and a one-way communication device for exporting the slurry;

The metal mesh covers the water outlet of the karst area; the edge of the water stop plate is fixedly connected with the edge of the water outlet of the karst area, the water stop plate does not completely cover the water outlet of the karst area, and the metal mesh is located at the water outlet of the karst area. Between the water stop and the water outlet of the karst zone;

The pumping pipe is used for pumping water out of the karst area, one end passes through the metal mesh, and the other end is placed in the karst area;

The side wall of the grouting pipe is provided with a plurality of first connecting ends with internal threads;

The one-way connecting device end is a second connecting end provided with an external thread, the second connecting end is connected with the first connecting end thread pair, and the one-way connecting device is used to lead the slurry to the metal The net forms a blocking wall.

Further, the one-way communication device includes: an outer member, an inner member, a spring, and a base;

The second connecting end is arranged at one end of the outer member, the outer member is hollow, and the outer member is sealed to the base;

The inner member is arranged inside the outer member, one end of the inner member close to the second connecting end is connected to the outside, and the other end of the inner member is connected to the base through a spring;

The side walls of the outer member and the inner member are respectively provided with a plurality of first slurry outlets and a plurality of second slurry outlets; the inner member moves to the base under the pressure of the slurry while compressing the spring, The plurality of second pulp outlets coincide with the plurality of first pulp outlets, and the slurry flows out.

Further, it further includes a magnet for fixing the one-way communication device on the metal mesh, and the magnet is fixedly connected to the outer side wall of the one-way communication device.

Further, it also includes: a pumping pipe for pumping water out of the karst area, one end of the pumping pipe passing through the karst area and placed in the karst area.

Further, the outer diameter of the inner member is equal to the inner diameter of the outer member.

The other end of the outer member is provided with an external thread; the base is provided with an internal thread, and is connected to the other end of the outer member with a thread pair.

Further, the spacing of the plurality of first pulp outlets is equal to the spacing of the plurality of second pulp outlets.

The invention can quickly eliminate the risk of water gushing in the karst area of the foundation pit. Compared with the existing grouting structure, the invention solves the difficult problems of grout injection and karst water suction during construction, effectively realizes the blockage of the karst area, and has a good construction effect. It also saves engineering investment and guarantees construction safety; the present invention analyzes the relationship between various factors and the safety thickness of the side wall in the karst area by constructing a calculation model for the safety thickness of the side wall in the karst area, and gives a reasonable prediction of the safety thickness of the side wall in the karst area The calculation formula of, to ensure that the water inrush problem of the foundation pit in the karst area can be dealt with reasonably.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor.

Figure 1 is a flow chart of determining the thickness of the side wall in a karst area according to an embodiment of the present invention;

Figure 2 is a front view of a foundation pit and a karst area according to an embodiment of the present invention;

Fig. 3 is a side view of the foundation pit and the karst area in the embodiment of the present invention.

Figure 4 is a schematic diagram of an embodiment of the present invention applied in a foundation pit;

Fig. 5 is an enlarged view of A in Fig. 4 according to an embodiment of the present invention;

Figure 6 is a perspective view of Figure 2 of the embodiment of the present invention;

Figure 7 is a schematic diagram of the combination of a grouting pipe and a one-way communication device according to an embodiment of the present invention;

Fig. 8 is a schematic diagram of the structure of a grouting pipe according to an embodiment of the present invention;

Figure 9 is a schematic structural diagram of a one-way communication device according to an embodiment of the present invention;

detailed description

In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

At present, the water distribution in the karst area 7 in the foundation pit 11 is extremely uneven and difficult to detect. When the thickness of the side wall in the karst area is too thin, it is easy to cause water inrush problems, and water inrush accidents are prone to occur during construction. Submerging the construction site, destroying machinery and tools, causing equipment and personnel accidents, delays in construction, increased project investment and other adverse effects; the present invention analyzes the relationship between various factors and the safe thickness of side walls in karst areas by constructing a calculation model for the safety thickness of side walls in karst areas , Give a reasonable calculation formula that can predict the safe thickness of the side wall in the karst area, and ensure that the water inrush problem of the foundation pit in the karst area can be dealt with reasonably. Through the mechanical analysis of water inrush and instability in the karst area of the foundation pit, the characteristics of the water inrush process of the deep foundation pit in the hidden karst area can be more fully grasped, and preventive measures such as effective disposal structures can be adopted to ensure the safe excavation of the foundation pit.

The range of sudden instability of the foundation pit is mainly concentrated in the karst area, and it is radially damaged around the position of the pressure-bearing karst area, and the sidewalls have obvious failure surfaces; and with different surrounding rock conditions and karst area sizes When the thickness of the side wall of the karst zone increases in the karst zone, the plastic zone develops in a diffuse shape from the position of the karst zone to the side wall, and the influence range of the plastic zone is an expanded square. The profile section of the karst area can be simplified as a square, the mutation mechanism of this phenomenon can be further analyzed, and the mechanical model shown in Figure 1 to Figure 3 can be established.

The present invention provides a method for determining the safe thickness of a side wall in a karst area, which includes the following steps:

The side wall of the karst zone is a prism body composed of countless thin cubes of uniform thickness, which determines the length m of the side wall of the foundation pit affected by the karst zone, the length n of the karst zone, and the steel supporting force F _{1 of the} side wall of the foundation pit. The air pressure F ₂ and the water pressure F ₃ in the karst area; then the side wall of the karst area on the side of the foundation pit is under pressure F=F ₁ +F ₂ -F ₃ , and the side wall of the karst area is an elastoplastic medium. According to the theory of elasto-plasticity, the karst area The axial displacement of the side wall of the zone, that is, the deflection:

Among them, d is the safe thickness of the side wall in the karst area;

The boundary conditions are:

From (1) and (2):

Where E is the elastic modulus of the water-resistant rock layer, c is the thickness of the side wall slice in the karst area, and μ is the Poisson’s ratio.

but,

Using the theory of energy conservation, the potential energy of the side wall in the karst area is calculated, and the formula is as follows:

W ₀ ＝W ₁ -W ₂ (5)

Among them, W ₁ is the deformation potential energy of the side wall in the karst zone, which is the sum of the bending deformation potential energy W ₁₁ and the intermediate strain potential energy W ₁₂ , namely

W ₁ ＝W ₁₁ +W ₁₂ (6)

W ₂ is the work done by the external force, including the radial displacement work W ₂₁ and the axial outward shift work W ₂₂ ;

Bring (9), (12) into (5)

Let w = a ₃ w ³ + a ₂ w ² + a ₁ w (14)

Among them, a ₁ , a ₂ , and a ₃ are intermediate variables;

Then let x=w-y, then:

w=x+y (16)

Among them, x and y are intermediate variables

Bring (16) into (14) and write it in matrix form to get:

It conforms to the cusp catastrophe model;

According to the catastrophe theory, the balance equation of the system is:

From this, the safe thickness of the side wall of the karst area for water inrush can be obtained as:

It can be seen from equation (19) that the safe thickness of the side wall in the karst area is affected by the elastic modulus of the side wall in the karst area, that is, the elastic modulus, Poisson's ratio, karst water pressure, steel support axial force, air pressure, and foundation pit. The size and the size of the karst zone are affected. The larger the elastic modulus of the side wall in the karst zone around the foundation pit, the smaller the minimum safe thickness. That is, when the surrounding rock is hard, water inrush is less likely to occur. The larger the excavation range of the foundation pit and the size of the karst zone, the greater the minimum safe thickness of the foundation pit.

According to the above analysis, the step S5 is further: the corresponding safe thickness can be obtained through calculation based on actual geological survey conditions, and compared with the detected thickness. When the safe thickness is greater than the current detected thickness, the following methods are used The grouting device in the karst area of the foundation pit performs grouting prevention.

The present invention also provides a grouting device used in the karst area of a foundation pit, as shown in Figs. The net 3 covers the water outlet 7.1 of the karst area 7; the edge of the water stop plate 4 made of stainless steel and the edge of the water outlet 7.1 of the karst area 7 are fixedly connected by bolts 8, and the water stop plate 4 does not completely cover the The water outlet 7.1 of the karst area 7 is to prevent the water from flowing out of the karst area, leaving a gap between the top edge of the water stop and the top of the karst area, so that the grouting pipe 1 and the one-way connecting device 5 extend into the karst area. The metal mesh 3 is located between the water stop plate 4 and the water outlet 7.1 of the karst area 7, and the metal mesh 3 is fixed at the water outlet 7.1 of the karst area 7 through the extrusion of the water stop plate 4;

As shown in Fig. 8, one end of the grouting pipe 1 has an opening for injecting grout into the inside, and the side wall of the grouting pipe 1 is provided with a plurality of first connecting ends 1-1 with internal threads;

As shown in FIG. 9, one end of the one-way communication device 5 is a second connecting end 5-1 provided with an external thread, and the second connecting end 5-1 is connected with the threaded pair of the first connecting end 1-1. The one-way communication device 5 is used to lead the slurry to the metal mesh 3 to form a blocking wall.

Further, the one-way communication device 5 includes: an outer member 5-2, an inner member 5-3, a spring 5-4, and a base 5-5; the second connecting end 5-1 is disposed on the outer member 5. -2 one end, the outer member 5-2 is hollow, the other end of the outer member 5-2 is provided with an external thread; the base 5-5 is provided with an internal thread, and the outer member 5-2 has a thread pair at the other end Connect to make the outer member 5-2 airtight, and at the same time it can be disassembled, to repair the inside of the one-way communication device 5 or replace the spring 5-4; the inner member 5-3 is arranged inside the outer member 5-2 One end of the inner member 5-3 close to the second connecting end 5-1 is connected to the outside, and the other end of the inner member 5-3 is connected to the base 5-5 through a spring 5-4; The side walls of the member 5-2 and the inner member 5-3 are respectively provided with a plurality of first slurry outlets 5-2-1 and a plurality of second slurry outlets 5-3-1; the inner member 5-3 Under the pressure of the slurry, move to the base 5-5 while compressing the spring 5-4, the multiple second slurry outlets 5-3-1 overlap the multiple first slurry outlets 5-2-1, so that The slurry flows out.

Furthermore, it further includes: a water pumping pipe 2 for pumping water out of the karst area, one end of the water pumping pipe 2 passes through the 3 and is placed in the karst area.

Specifically, as shown in FIG. 7, the outer member 5-2 and the inner member 5-3 are both cylindrical barrel-shaped structures made of stainless steel. 2 Pump out the water in the karst area so as not to affect the grout hanging on the metal mesh 3. The grout flows into the six one-way connecting devices 5 from the six first connecting ends 1-1 of the side wall of the grouting pipe 1 respectively, and one-way communication After the inner member 5-3 in the device 5 receives the pressure of the slurry, the spring 5-4 is squeezed to make the two second slurry outlets 5-3-1 and the two first slurry outlets 5-2- 1 overlaps, the slurry flows out from the first slurry outlet 5-2-1 and quickly solidifies near the metal mesh 3. In order to enable the one-way communication device 5 to be continuously grouted at a fixed position, the outer member 5-2 A magnet 9 is fixed on the outer wall of the metal mesh. The magnet 9 is a powerful magnet, so that the one-way communication device 5 can be adsorbed on the metal mesh 3. When a region of the metal mesh 3 is hung with slurry, the grouting is stopped. The inner member 5-3 is squeezed and reset by the spring 5-4; the grouting pipe 3 and the one-way communication device 5 are replaced on the metal mesh 3, and only grouting is required until the entire metal mesh 3 and its adjacent area It is filled with grout and solidified continuously to form a blocking wall that blocks the outlet 7.1 of the karst zone 7; because the maximum width of the entire device is greater than the maximum width of the metal mesh 3, when the device is placed in the karst zone, the metal mesh can be dismantled After putting the device in, finally the remaining ungrouted area of the metal mesh 3 is small and the other damaged areas are connected and repaired with metal wires, and five of the one-way connecting devices 5 are removed, and only one one-way connecting device 5 is retained. Grouting, at this time, the single one-way connecting device 5 can be taken out of the grid.

Further, in order to prevent the slurry from flowing out of the gap formed between the inner member 5-3 and the outer member 5-2, causing damage to the device, the outer diameter of the inner member 5-3 and the outer member 5- 2 The inner diameters are equal.

Further, it is convenient for the plurality of first slurry outlets 5-2-1 to allow the slurry to flow out at the same time, thereby improving the grouting efficiency. The distance between the plurality of first slurry outlets 5-2-1 and the plurality of second slurry outlets The spacing between ports 5-3-1 is equal.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. Scope.

Claims (8)

1. A method for determining the safe thickness of a side wall in a karst area is characterized in that it comprises the following steps:

   S1: Determine the length m of the sidewall of the foundation pit affected by the karst zone, the length n of the karst zone, the steel supporting force F _{1 of the} sidewall of the foundation pit, the air pressure F ₂ and the water pressure F _{3 of the} karst zone;

   S2: According to the elastoplastic theory, calculate the axial displacement of the side wall in the karst zone, that is, the deflection is:

   

   Among them, d is the safe thickness of the side wall in the karst area;

   S3: Calculate the potential energy of the side wall in the karst area, the specific formula is as follows:

   W ₀ ＝W ₁ -W ₂ (2)

   Among them, W ₁ is the deformation potential energy of the anti-outburst layer, and W ₂ is the work done by the external force;

   S4: Calculate the safe thickness of the side wall in the karst zone, the specific formula is as follows:

   

   Among them, E is the elastic modulus of the water-resistant rock formation, and μ is the Poisson's ratio;

   S5: Compare the calculated safe thickness of the side wall of the foundation pit in the karst area with the actual detection results, and determine the grouting method.
2. The device according to claim 1, wherein the boundary condition of the deflection in the S2 is:

   
3. A grouting device used in the karst area of a foundation pit, which is characterized by comprising: a metal mesh (3), a water stop plate (4), a grouting pipe (1), a pumping pipe (2), and a grouting pipe One-way communication device (5);

   The metal mesh (3) covers the water outlet (7.1) of the karst area (7); the edge of the water stop plate (4) is fixedly connected with the edge of the water outlet (7.1) of the karst area (7), so The water stop plate (4) does not completely cover the water outlet (7.1) of the karst area (7), and the metal mesh (3) is located at the water stop plate (4) and the outlet of the karst area (7) Water outlet (7.1) room;

   The pumping pipe (2) is used for pumping water out of the karst area, and the pumping pipe (2) passes through the metal mesh (3) and is placed in the karst area;

   The side wall of the grouting pipe (1) is provided with a plurality of first connecting ends (1-1);

   One end of the one-way connecting device (5) is a second connecting end (5-1), and the second connecting end (5-1) is connected with the first connecting end (1-1) by a threaded pair. The one-way communication device (5) is used to lead the slurry to the metal mesh (3) to form a blocking wall for blocking the water outlet (7.1) of the karst zone (7).
4. The device according to claim 3, wherein the one-way communication device (5) comprises: an outer member (5-2), an inner member (5-3), a spring (5-4) and a base (5) -5);

   The second connecting end (5-1) is arranged at one end of the outer member (5-2), the outer member (5-2) is hollow, and the outer member (5-2) is connected to the base (5-2). -5) Sealed connection;

   The inner member (5-3) is arranged inside the outer member (5-2), and the end of the inner member (5-3) close to the second connecting end (5-1) communicates with the outside, so The other end of the inner member (5-3) is connected to the base (5-5) through a spring (5-4);

   The side walls of the outer member (5-2) and the inner member (5-3) are respectively provided with a plurality of first pulp outlets (5-2-1) and a plurality of second pulp outlets (5-3) -1); The inner member (5-3) moves to the base (5-5) under the pressure of the slurry while compressing the spring (5-4), the plurality of second slurry outlets (5 -3-1) overlap with a plurality of first slurry outlets (5-2-1) to allow the slurry to flow out.
5. The device according to claim 3, further comprising: a magnet (9) for fixing the one-way communication device (5) on the metal mesh (3), the magnet (9) It is fixedly connected with the outer side wall of the one-way communication device (5).
6. The device according to claim 2, characterized in that the outer diameter of the inner member (5-3) is equal to the inner diameter of the outer member (5-2).
7. The device according to claim 5, characterized in that the other end of the outer member (5-2) is provided with an external thread; the base (5-5) is provided with an internal thread, and the outer member (5- 2) Threaded connection at the other end.
8. The device according to claim 5, characterized in that the distance between the plurality of first pulp outlets (5-2-1) is equal to the distance between the plurality of second pulp outlets (5-3-1).

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