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

Abstract

The invention discloses a method for determining the safe thickness of the side wall of a foundation pit in a karst area, comprising 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 support force F of the side wall of the foundation pit, and the thickness of the side wall of the foundation pit. 1 , air pressure F 2 and the water pressure in the karst area F 3 ; According to the elastic-plastic theory, the energy conservation theory and the catastrophe theory, the axial displacement, potential energy and safe thickness of the side wall in the karst area are calculated; the present invention also discloses a grouting device for the karst area of ​​a foundation pit, comprising: a metal mesh, a water stop plate, a grouting pipe, a pumping pipe and a one-way connecting device; the present invention can quickly eliminate the risk of water gushing in the karst area of ​​the foundation pit, solve the problems of difficulty in injecting slurry and back-absorption of karst water during construction, realize the blocking of the karst area, save project investment and ensure construction safety.

Description

Technical Field

[0001] The invention relates to the field of grouting in foundation pit construction, and in particular to a method for determining the safe thickness of a side wall in a karst area of ​​a foundation pit and a grouting device. Background Art

[0002] During foundation pit excavation in karst areas, the karst water distribution is extremely uneven and difficult to detect, and water inrush accidents are very likely to occur during foundation pit excavation. If the specific location and area of ​​karst water distribution cannot be ascertained during excavation, and if effective protective measures are not taken for the water inrush, it will often flood the construction site, destroy machinery and tools, cause equipment and personnel accidents, delay construction period, and increase project investment. Summary of the invention

[0003] The present invention provides a method for determining the safe thickness of the side wall in the karst area of ​​a foundation pit, so as to overcome the above technical problems.

[0004] The present invention provides a method for determining the safe thickness of a side wall in a karst area of ​​a foundation pit, comprising the following steps:

[0005] S1: Determine the length m of the foundation pit side wall affected by the karst area, the length n of the karst area, the steel support force F1 of the foundation pit side wall, the air pressure F2 and the water pressure F3 of the karst area;

[0006] S2: According to the elastic-plastic theory, the axial displacement of the side wall in the karst area, that is, the deflection is calculated as:

[0007]

[0008] Where d is the safe thickness of the side wall in the karst area;

[0009] S3: Calculate the potential energy of the side wall of the karst area. The specific formula is as follows:

[0010] W0=W1-W2 (2)

[0011] Among them, W1 is the deformation potential energy of the anti-burst layer, and W2 is the work done by the external force;

[0012] S4: Calculate the safe thickness of the side wall in the karst area. The specific formula is as follows:

[0013]

[0014] Among them, E is the elastic modulus of the side wall of the karst area, and μ is the Poisson's ratio;

[0015] S5: Compare the calculated safety thickness of the side wall of the foundation pit in the karst area with the actual detection results, and determine the grouting method.

[0016] The present invention also provides a grouting device for use in a foundation pit karst area, comprising: a metal mesh, a water stop plate, a grouting pipe, a water pumping pipe, and a one-way connecting device for extracting slurry;

[0017] The metal mesh covers the karst area water outlet; the edge of the water stop plate is fixedly connected to the edge of the karst area water outlet, the water stop plate does not completely cover the karst area water outlet, and the metal mesh is located between the water stop plate and the karst area water outlet;

[0018] The water extraction pipe is used to extract water from the karst area, one end of which passes through the metal mesh and the other end is placed in the karst area;

[0019] The side wall of the grouting pipe is provided with a first connecting end having a plurality of internal threads;

[0020] The one-way connecting device end is a second connecting end provided with an external thread, the second connecting end is connected to the first connecting end thread pair, and the one-way connecting device is used to guide the slurry to the metal mesh to form a blocking wall.

[0021] Furthermore, the one-way communication device comprises: an outer member, an inner member, a spring and a base;

[0022] The second connection end is arranged at one end of the outer member, the outer member is hollow, and the outer member is sealed and connected to the base;

[0023] The inner component is arranged inside the outer component, one end of the inner component close to the second connection end is connected to the outside, and the other end of the inner component is connected to the base through a spring;

[0024] The outer member and the inner member side walls are respectively provided with a plurality of first slurry outlets and a plurality of second slurry outlets; the inner member moves toward the base under the pressure of the slurry while compressing the spring, the plurality of second slurry outlets overlap with the plurality of first slurry outlets, and the slurry flows out.

[0025] Furthermore, it also includes: a magnet for fixing the one-way communication device on the metal net, and the magnet is fixedly connected to the outer side wall of the one-way communication device.

[0026] Furthermore, it also includes: a pumping pipe for pumping water out of the karst area, one end of the pumping pipe passes through the karst area and is placed in the karst area.

[0027] Furthermore, the outer diameter of the inner component is equal to the inner diameter of the outer component.

[0028] The other end of the outer member is provided with an external thread; the base is provided with an internal thread connected to the thread pair at the other end of the outer member.

[0029] Furthermore, the spacing between the plurality of first slurry outlets is equal to the spacing between the plurality of second slurry outlets.

[0030] The present invention can quickly eliminate the risk of water gushing in the karst area of ​​the foundation pit. Compared with the existing grouting structure, it solves the problems of difficulty in injecting slurry and back-absorption of karst water during construction, effectively realizes the blocking of the karst area, has a good construction effect, saves engineering investment, and ensures construction safety. The present invention constructs a calculation model for the safe thickness of the side wall in the karst area, analyzes the relationship between various factors and the safe thickness of the side wall in the karst area, and provides a reasonable calculation formula that can predict the safe thickness of the side wall in the karst area, so as to ensure that the problem of water gushing in the foundation pit in the karst area can be reasonably handled. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 A flow chart for determining the thickness of the side wall in a karst area according to an embodiment of the present invention;

[0033] Figure 2 It is a front view of the foundation pit and the karst area of ​​the embodiment of the present invention;

[0034] Figure 3 It is a side view of the foundation pit and the karst area of ​​an embodiment of the present invention.

[0035] Figure 4 It is a schematic diagram of an embodiment of the present invention applied in a foundation pit;

[0036] Figure 5 For the embodiment of the present invention Figure 1 A magnified view of middle;

[0037] Figure 6 For the embodiment of the present invention Figure 2 perspective drawing;

[0038] Figure 7 It is a schematic diagram of the combination of the grouting pipe and the one-way communication device according to an embodiment of the present invention;

[0039] Figure 8 This is a schematic diagram of the structure of a grouting pipe according to an embodiment of the present invention;

[0040] Fig. 9 This is a schematic diagram of the structure of a one-way communication device according to an embodiment of the present invention; DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] 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 very easy to cause water gushing problems. Water gushing accidents are very likely to occur during construction, which often flood the construction site, destroy machinery and tools, cause equipment and personnel accidents, delay the construction period, increase the investment in the project and other adverse effects; the present invention constructs a calculation model for the safe thickness of the side wall in the karst area, analyzes the relationship between various factors and the safe thickness of the side wall in the karst area, and gives a reasonable calculation formula that can predict the safe thickness of the side wall in the karst area, so as to ensure that the water gushing problem of the foundation pit in the karst area can be reasonably handled. Through the mechanical analysis of the instability and destruction of water gushing in the karst area of ​​the foundation pit, the characteristics of the water gushing process of the deep foundation pit containing the hidden karst area can be more comprehensively grasped, and effective preventive measures such as disposal structures can be taken to ensure the safe excavation of the foundation pit.

[0043] The scope of sudden instability of the foundation pit is mainly concentrated in the karst area, and the pressure-bearing karst area is damaged radially around the center, and the side wall has an obvious damage surface; and with the different surrounding rock conditions, karst area size, and karst area side wall thickness, the plastic zone has been diffused from the karst area to the side wall during the process of increasing internal pressure in the karst area, and the influence range of the plastic zone is an outward-expanding square. The contour section of the karst area can be simplified to a square, and the mutation mechanism of this phenomenon can be further analyzed. Figure 1-Figure 3 The mechanical model shown.

[0044] The present invention provides a method for determining the safe thickness of a side wall in a karst area, comprising the following steps:

[0045] The side wall of the karst area is a prism composed of countless thin cubes with uniform thickness. 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 support force F1 of the side wall of the foundation pit, the air pressure F2 and the water pressure F3 of the karst area are determined; then the pressure on the side wall of the karst area on the side of the foundation pit is F=F1+F2-F3. The side wall of the karst area is an elastic-plastic medium. According to the elastic-plastic theory, the axial displacement of the side wall of the karst area, that is, the deflection is:

[0046]

[0047] Where d is the safe thickness of the side wall in the karst area;

[0048] Its boundary conditions are:

[0049]

[0050] From (1) and (2), we can get:

[0051]

[0052] Where E is the elastic modulus of the karst area side wall, c is the thickness of the karst area side wall slice, μ is Poisson's ratio, due to the bending stiffness

[0053] but,

[0054] The potential energy of the side wall of the karst area is calculated using the energy conservation theory, and the formula is as follows:

[0055] W0=W1-W2 (5)

[0056] Among them, W1 is the deformation potential energy of the side wall in the karst area, and W is the bending deformation potential energy. 11 and the intermediate strain potential energy W 12 The sum of

[0057] W1=W 11 +W 12 (6)

[0058]

[0059]

[0060]

[0061] W2 is the work done by external force, including radial displacement work W 21 and axial outward movement work W 22 ;

[0062]

[0063]

[0064]

[0065] Bring (9) and (12) into (5)

[0066]

[0067] Let w = a3w 3 +a2w 2 +a1w (14)

[0068] Among them, a1, a2, and a3 are intermediate variables;

[0069]

[0070] Let x=wy, then:

[0071] w=x+y (16)

[0072] Among them, x and y are intermediate variables

[0073] Substituting (16) into (14) and writing it in matrix form, we get:

[0074]

[0075] It is consistent with the cusp mutation model;

[0076] According to the catastrophe theory, the equilibrium equation of the system is:

[0077]

[0078] Therefore, the safe thickness of the side wall in the karst area for water inrush can be obtained as:

[0079]

[0080] It can be seen from formula (19) that the safety thickness of the karst area side wall is affected by the elastic modulus of the karst area side wall, i.e. the elastic modulus of the impermeable rock layer, Poisson's ratio, karst water pressure, steel support axial force, air pressure, foundation pit size and karst area size. The larger the elastic modulus of the karst area side wall around the foundation pit, the smaller the minimum safety thickness, that is, when the surrounding rock is harder, water inrush is not likely to occur. The larger the excavation range of the foundation pit and the size of the karst area, the larger the minimum safety thickness of the foundation pit.

[0081] According to the above analysis, the step S5 is further as follows: the corresponding safety thickness can be obtained through calculation according to the actual geological survey conditions and compared with the detected thickness. When the safety thickness is greater than the current detected thickness, the following grouting device for the karst area of ​​the foundation pit is used for grouting prevention.

[0082] The present invention also provides a grouting device for use in a karst area of ​​a foundation pit, such as Figure 4-6 The method comprises: a metal mesh 3, a water stop plate 4, a grouting pipe 1 and a one-way connecting 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 made of stainless steel is fixedly connected to the edge of the water outlet 7.1 of the karst area 7 by bolts 8, the water stop plate 4 does not completely cover 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 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 to the water outlet 7.1 of the karst area 7 by squeezing the water stop plate 4;

[0083] like Figure 8 As shown, one end of the grouting pipe 1 is opened for injecting slurry into the interior, and the side wall of the grouting pipe 1 is provided with a plurality of first connecting ends 1-1 with internal threads;

[0084] like Fig. 9 As shown, one end of the one-way connecting device 5 is a second connecting end 5-1 provided with an external thread, and the second connecting end 5-1 is threadedly connected to the first connecting end 1-1. The one-way connecting device 5 is used to guide the slurry to the metal mesh 3 to form a blocking wall.

[0085] Furthermore, 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 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 connected to the thread pair at the other end of the outer member 5-2, so that the outer member 5-2 is sealed and 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 on the outer member Inside 5-2, one end of the inner component 5-3 close to the second connecting end 5-1 is connected to the outside, and the other end of the inner component 5-3 is connected to 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 component 5-3 moves toward the base 5-5 under the pressure of the slurry and compresses the spring 5-4 at the same time, and the plurality of second slurry outlets 5-3-1 overlap with the plurality of first slurry outlets 5-2-1, so that the slurry flows out.

[0086] Furthermore, it also includes: a pumping pipe 2 for pumping water out of the karst area, one end of the pumping pipe 2 passes through the 3 and is placed in the karst area.

[0087] Specifically, if Figure 7As shown, the outer member 5-2 and the inner member 5-3 are both cylindrical barrel structures made of stainless steel. Slurry is injected into the grouting pipe 1, and water in the karst area is pumped out through the pumping pipe 2 to avoid affecting the slurry hanging on the metal mesh 3. The slurry flows into six one-way connecting devices 5 from the six first connecting ends 1-1 of the side wall of the grouting pipe 1 respectively. After the inner member 5-3 in the one-way connecting 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, and the slurry flows out from the first slurry outlet 5-2-1 and solidifies quickly near the metal mesh 3. In order to enable the one-way connecting device 5 to continuously grout at a fixed position, a magnet 9 is fixed on the outer wall of the outer member 5-2. The magnet 9 is a strong magnet, which enables the one-way connecting device 5 to The connecting device 5 can be adsorbed on the metal mesh 3; when an area of ​​the metal mesh 3 is hung with slurry, the grouting is stopped, and the internal component 5-3 is reset by the squeezing of the spring 5-4; the grouting pipe 3 and the one-way connecting device 5 are replaced on the metal mesh 3, and only grouting is required until the entire metal mesh 3 and its adjacent areas are filled with slurry, and the slurry is continuously and rapidly solidified to form a blocking wall for the water outlet 7.1 of the karst area 7; because the maximum width of the entire device is greater than the maximum width of the metal mesh 3, the metal mesh can be dismantled when the device is placed in the karst area, and then the device is placed in, and finally the remaining un-grouted area of ​​the metal mesh 3 is small and other damaged areas are connected and repaired with metal wires, and five of the one-way connecting devices 5 are removed, leaving only one one-way connecting device 5 for grouting, and at this time the single one-way connecting device 5 can be taken out from the grid.

[0088] Furthermore, 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 is equal to the inner diameter of the outer member 5-2.

[0089] Furthermore, in order to facilitate the multiple first slurry outlets 5-2-1 to allow the slurry to flow out simultaneously and improve the grouting efficiency, the spacing between the multiple first slurry outlets 5-2-1 is equal to the spacing between the multiple second slurry outlets 5-3-1.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the safe thickness of the side wall in a karst area, characterized in that: The following steps are involved: S1: Determine the length m of the foundation pit side wall affected by the karst area, the length n of the karst area, the steel support force F1 of the foundation pit side wall, the air pressure F2 and the water pressure F3 of the karst area; S2: According to the elastic-plastic theory, the axial displacement of the side wall in the karst area, that is, the deflection is calculated as: Where 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: W0=W1-W2 (2) Among them, W1 is the deformation potential energy of the anti-burst layer, and W2 is the work done by the external force; 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 of the karst area, and μ is the Poisson's ratio; S5: Compare the calculated safety thickness of the side wall of the foundation pit in the karst area with the actual detection results, and determine the grouting method.

2. A method for determining the safe thickness of the side wall in a karst area according to claim 1, characterized in that: The boundary condition of the deflection in S2 is:

Images