CN111733794A - A method and grouting device for determining the safe thickness of side walls in karst area of foundation pit - Google Patents

Abstract

The invention discloses a method for determining the safe thickness of a side wall in a karst area of a foundation pit, including determining the length m of the side wall of the foundation pit affected by the karst area, the length n of the karst area, the steel supporting force F ₁ of the side wall of the foundation pit, and the air pressure. F ₂ and the water pressure F ₃ in the karst area; according to the elastic-plastic theory, the energy conservation theory and the catastrophe theory, the axial displacement, potential energy and safety thickness of the side wall in the karst area are calculated; The slurry device includes: a metal mesh, a water stop plate, a grouting pipe, a water pumping pipe and a one-way communication device; the invention can quickly eliminate the risk of water gushing in the karst area of the foundation pit, and solve the problem of difficult injection of slurry during construction, karst water sucking back, etc. The problem is that the karst area is blocked, which saves project investment and ensures construction safety.

Description

A method and grouting device for determining the safe thickness of side walls in karst area of foundation pit

technical field

The invention relates to the field of grouting in foundation pit construction, 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, and water inrush accidents are very likely to occur during excavation of foundation pits. Under the condition that effective protective measures are taken at the water inlet, it will often flood the construction site, destroy machinery and tools, cause equipment and personnel accidents, delay the construction period, increase project investment and other problems.

SUMMARY OF THE INVENTION

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

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

S1: determine the length m of the side wall of the foundation pit affected by the karst area, the length n of the karst area, the steel supporting force F ₁ , the air pressure F ₂ and the water pressure F ₃ of the karst area on the side wall of the foundation pit;

S2: According to the elastic-plastic theory, calculate the axial displacement of the side wall in the karst area, 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 of the karst area, the specific formula is as follows:

W ₀ =W ₁ -W ₂ (2)

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

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

Among them, E is the elastic modulus of the side wall in the karst area, and μ is the Poisson's ratio;

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

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

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 between the water stop plate and the water outlet of the karst area;

The water pumping pipe is used for pumping out the water in 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 connection ends of internal threads;

The end of the one-way communication device is a second connection end provided with an external thread, the second connection end is threadedly connected to the first connection end, and the one-way communication 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 connection end is arranged at one end of the outer member, the outer member is hollow, and the outer member is sealedly connected to the base;

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

The outer member and the side wall of 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 and simultaneously compresses the spring, The plurality of second pulp outlets coincide with the plurality of first pulp outlets, and the slurry flows out.

Further, it also 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 water pumping pipe for pumping out the water in the karst area, one end of the water pumping pipe passes through the said water pump and is 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, which is paired with the other end of the outer member.

Further, the distance between the plurality of first pulp outlets is equal to the distance between 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 problems such as difficulty in injecting the slurry and sucking back karst water during construction, effectively realizes the blocking of the karst area, and has a good construction effect. And save the project investment and ensure the construction safety; the invention analyzes the relationship between each factor and the safety thickness of the side wall in the karst area by constructing a calculation model of the safety thickness of the side wall in the karst area, and provides a reasonable and predictable safety thickness of the side wall in the karst area. The calculation formula can ensure that the water inrush problem of the foundation pit in the karst area can be properly handled.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following will briefly introduce the accompanying drawings used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

Fig. 1 is the flow chart of determining the side wall thickness of karst area according to the embodiment of the present invention;

Fig. 2 is the front view of the foundation pit and the karst area of the embodiment of the present invention;

3 is a side view of a foundation pit and a karst area according to an embodiment of the present invention.

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

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

Fig. 6 is the perspective view of Fig. 2 of the embodiment of the present invention;

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;

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

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

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

At present, the distribution of water 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. Submerge the construction site and destroy the equipment, causing equipment and personnel accidents, delaying the construction period, increasing project investment and other adverse effects; 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 give a reasonable calculation formula that can predict the safe thickness of the side wall in the karst area to ensure that the water inrush problem of the foundation pit in the karst area can be properly handled. Through the mechanical analysis of the water inrush instability failure 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 comprehensively grasped, and preventive measures such as effective disposal structures can be taken 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 from the position of the confined karst area to the surrounding area, and the side walls have obvious damage surfaces; , The thickness of the side wall in the karst area In the process of increasing the pressure in the karst area, the plastic zone has been developing in a diffuse shape from the position of the karst area to the side wall, and the influence range of the plastic zone is a square that expands outward. The profile section of the karst area can be simplified to a square, and the mutation mechanism of this phenomenon can be further analyzed, and the mechanical model shown in Fig. 1-Fig. 3 can be established.

The invention provides a method for determining the safe thickness of side walls in a karst area, comprising the following steps:

The side wall of the karst area is composed _of numerous thin cubes with uniform thickness. The air pressure F ₂ and the water pressure F ₃ in the karst area; the pressure on the side wall of the karst area on the side of the foundation pit is F=F ₁ +F ₂ -F ₃ , and the side wall in the karst area is an elastic-plastic medium. The axial displacement of the side wall in the area, that is, the deflection is:

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

Its boundary conditions are:

From (1) and (2) we get:

where E is the elastic modulus of the side wall in the karst area, c is the slice thickness of the side wall in the karst area, μ is the Poisson’s ratio, since the flexural stiffness

but,

Using the energy conservation theory, the potential energy of the side wall of 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 lateral wall in the karst area, 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 displacement 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;

Let x=w-y again, then:

w=x+y (16)

Among them, x and y are intermediate variables

Substituting (16) into (14) and writing it in matrix form, we get:

Then it conforms to the cusp mutation model;

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

From this, the safe thickness of the side wall in 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 of the water-resistant rock formation, Poisson’s ratio, karst water pressure, steel support axial force, air pressure, foundation pit The influence of the size and the size of the karst area, the larger the elastic modulus of the side wall of the karst area around the foundation pit, the smaller the minimum safe thickness, that is, when the surrounding rock is hard, the water inrush is not easy to occur. The larger the excavation range of the foundation pit and the size of the karst area, the larger the minimum safe thickness of the foundation pit.

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

The present invention also provides a grouting device for a karst area of a foundation pit, as shown in Figures 4-6, comprising: a metal mesh 3, a water stop plate 4, a grouting pipe 1 and a one-way communication device 5; the metal mesh 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 is fixedly connected with the edge of the water outlet 7.1 of the karst area 7 through bolts 8, and the water stop plate 4 does not completely cover the In the water outlet 7.1 of the karst area 7, in order to prevent the water from flowing out of the karst area, a gap is left between the top edge of the water stop plate and the top of the karst area, so that the grouting pipe 1 and the one-way communication device 5 extend into the karst area, so 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 Figure 8, one end of the grouting pipe 1 is open for injecting slurry into the interior, and the side wall of the grouting pipe 1 is provided with a plurality of first connection ends 1-1 with internal threads;

As shown in FIG. 9 , one end of the one-way communication device 5 is a second connection end 5-1 provided with an external thread, and the second connection end 5-1 is threadedly connected to the first connection end 1-1. , the one-way communication device 5 is used to export 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 connection end 5-1 is provided on the outer member 5 -2 One end of the outer member 5-2 is hollow, and 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, which is threaded paired with the other end of the outer member 5-2 connection, so that the outer member 5-2 can be sealed and disassembled at the same time, and the interior of the one-way communication device 5 can be repaired or the spring 5-4 can be replaced; 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 communicates with the outside world, and the other end of the inner member 5-3 is connected to the base 5-5 through a spring 5-4; the outer The side walls of the 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 Under the pressure of the slurry, it moves to the base 5-5 while compressing the spring 5-4, and the plurality of second slurry outlets 5-3-1 coincide with the plurality of first slurry outlets 5-2-1, so that the The slurry flows out.

Further, it also includes: a water pumping pipe 2 for pumping out the water in 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, and the slurry is injected into the grouting pipe 1 while passing through the suction pipe. 2. Pump out the water in the karst area so as not to affect the slurry hanging on the metal mesh 3. The slurry flows from the six first connecting ends 1-1 of the side wall of the grouting pipe 1 into the six one-way communication devices 5, and the one-way communication After the inner member 5-3 in the device 5 is subjected to the pressure of the slurry, the spring 5-4 is squeezed, so that the two second slurry outlets 5-3-1 and the two first slurry outlets 5-2- 1 Overlap, the slurry flows out from the first slurry outlet 5-2-1 and solidifies rapidly near the metal mesh 3. In order to enable the one-way communication device 5 to continue grouting in a fixed position, the outer member 5-2 A magnet 9 is fixed on the outer wall of the metal mesh, and the magnet 9 is a strong magnet, so that the one-way communication device 5 can be adsorbed on the metal mesh 3; The inner member 5-3 is pressed and reset by the spring 5-4; to replace the grouting pipe 3 and the one-way communication device 5 on the metal mesh 3, only grouting is required until the entire metal mesh 3 and its adjacent areas are It is filled with slurry and rapidly solidifies to form a sealing wall that blocks the water outlet 7.1 of the karst zone 7; since the maximum width of the entire device is larger than the maximum width of the metal mesh 3, the metal mesh can be dismantled when the device is placed in the karst zone. , after putting the device in, and finally the remaining ungrouted area of the metal mesh 3 is small, and other damaged areas are connected and repaired with metal wires, and five one-way communication devices 5 are removed, and only one one-way communication device 5 is retained. Grouting, at which point a single one-way communication device 5 can be removed from 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 and causing damage to the device, the outer diameter of the inner member 5-3 and the outer member 5-2 2 have the same inner diameter.

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. Ports 5-3-1 are equally spaced.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but 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 described in the foregoing embodiments can still be modified, or some or all of the technical features thereof 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 sidewall of a karst area is characterized by comprising the following steps:

s1: determining the length m of the side wall of the foundation pit influenced by the karst area, the length n of the karst area and the steel supporting force F of the side wall of the foundation pit₁Air pressure F₂And karst water pressure F₃；

S2: according to the elastoplasticity theory, calculating the axial displacement of the side wall of the karst area, namely the deflection is as follows:

wherein d is the safe thickness of the sidewall of the karst area;

s3: calculating the potential energy of the karst area side wall, wherein the specific formula is as follows:

W₀＝W₁-W₂(2)

wherein, W₁To prevent deformation of the projecting layer, W₂Acting for external force;

s4: calculating the safe thickness of the karst area side wall, wherein the specific formula is as follows:

wherein E is the elastic modulus of the sidewall of the karst region, and mu is the Poisson ratio;

s5: and comparing the calculated safe thickness of the side wall of the foundation pit in the karst area with an actual detection result, and determining a grouting mode.

2. The apparatus of claim 1, wherein the boundary conditions of the deflection in S2 are:

3. a slip casting device for foundation ditch karst area, its characterized in that includes: the device comprises a metal net (3), a water stop plate (4), a grouting pipe (1), a water pumping pipe (2) and a one-way communication device (5) for leading out slurry;

the metal net (3) covers a water outlet (7.1) of the karst area (7); the edge of the water stop plate (4) is fixedly connected with the edge of a water outlet (7.1) of the karst area (7), 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 positioned between the water stop plate (4) and the water outlet (7.1) of the karst area (7);

the water pumping pipe (2) is used for pumping out water in the karst area, and the water pumping pipe (2) penetrates through the metal mesh (3) and is arranged 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 communication device (5) is a second connecting end (5-1), the second connecting end (5-1) is connected with the first connecting end (1-1) through a thread pair, and the one-way communication device (5) is used for guiding slurry out of the metal net (3) to form a blocking wall for blocking a water outlet (7.1) of the karst area (7).

4. Device according to claim 3, characterized in that said one-way communication means (5) comprise: 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 component (5-2), the outer component (5-2) is hollow, and the outer component (5-2) is connected with the base (5-5) in a sealing mode;

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 communicated with the outside, and the other end of the inner member (5-3) is connected with the base (5-5) through a spring (5-4);

the side walls of the outer component (5-2) and the inner component (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) moves towards the base (5-5) under the pressure of the slurry while compressing the spring (5-4), and the plurality of second slurry outlets (5-3-1) and the plurality of first slurry outlets (5-2-1) coincide to allow the slurry to flow out.

5. The apparatus of claim 3, further comprising: and the magnet (9) is used for fixing the one-way communication device (5) on the metal net (3), and the magnet (9) is fixedly connected with the outer side wall of the one-way communication device (5).

6. The device according to claim 2, wherein the inner member (5-3) has an outer diameter equal to the outer member (5-2) inner diameter.

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 internal threads and is connected with the other end of the outer component (5-2) through a thread pair.

8. The device according to claim 5, characterized in that the pitch of the first plurality of outlets (5-2-1) is equal to the pitch of the second plurality of outlets (5-3-1).

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