Comb-tooth-shaped damping blasting excavation method for foundation pit in underground station top-down excavation

Abstract

A foundation pit comb-tooth-shaped damping blasting excavation method in underground station cover and excavation top-down construction comprises the following steps that S1, before a foundation pit (1) is excavated, sandbags with a certain height are stacked along the edge of the foundation pit, foam plates and protective nets are arranged on the upper portions of the sandbags, and an annular protective belt (2) is formed; s2, a row of deep holes are drilled in the length direction of the foundation pit, a crack is generated, and two main shock insulation grooves (3) are exploded in the crack direction; s3, blast holes are formed inwards along the main shock insulation groove at proper intervals, and an auxiliary groove (5) is formed after blasting excavation; s4, the remaining rock stratum is divided according to areas, blast holes are sequentially and evenly formed in the width direction of the foundation pit, and blasting is sequentially conducted from inside to outside and from the middle to the two sides; s5, after blasting, arranging an excavation and transportation machine in the main shock insulation groove; and S6, repeating the steps S2-S5. According to the method, a comb-tooth-shaped blasting excavation mode is adopted, vibration waves can make contact with the free face more quickly to release energy, and the influence of vibration on station cover and excavation top-down operation is reduced.

Description

Technical Field

[0001] The invention relates to a comb-tooth-shaped shock-absorbing blasting excavation method for a foundation pit in a cover-excavation reverse operation of an underground station, and belongs to the technical field of foundation pit blasting excavation. Background Art

[0002] With the rapid development of urbanization in my country and the increasing maturity of blasting technology, blasting is usually used for high-strength rock formations in the process of foundation pit excavation in cities. There is no shortage of such blasting methods in the construction of underground buildings. This must take into account the impact of rock blasting on the safety of the upper buildings. In the process of blasting and excavating heterogeneous rock formations in foundation pits, there will be certain differences in blasting effects. When the strength and density of the rock formation are relatively low, blasting will cause the broken rocks to fly and the excess energy to be transmitted to the upper buildings of the station. When the strength and density of the rock formation are relatively high, blasting will cause large pieces of rock to be insufficiently blasted. In the process of rock blasting, the ground stress will be released, which will damage nearby buildings and pipelines. In addition, the environment is closed in the construction of cover excavation and reverse construction. The vibration, splashing of gravel, and dust generated by the blasting will have a greater impact on the foundation pit support and the completed structure.

[0003] Therefore, there is an urgent need for a blasting method that is applicable to heterogeneous rock formations and can reduce shock and dust. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems existing in urban foundation pit blasting excavation and to propose a comb-shaped shock-absorbing blasting excavation method for foundation pits in reverse operation of underground station cover excavation.

[0005] The technical solution implemented by the present invention is as follows: a comb-shaped shock-absorbing blasting excavation method for a foundation pit in a cover-excavation reverse operation of an underground station, the steps of which are as follows: (1) Before excavation of the foundation pit, sandbags are piled up to a certain height along the edge of the foundation pit, and foam boards and protective nets are placed on top of them to form a circular protective belt.

[0006] (2) According to the conditions of the foundation pit site, a certain distance of protection zone is reserved, and a row of deep holes is drilled along the length of the foundation pit and a certain amount of expansion agent is added to create obvious cracks. Two main seismic isolation grooves are blasted along the direction of the cracks.

[0007] (3) Arrange blast holes at appropriate intervals along the main seismic isolation groove. The blast hole connection line extends perpendicular to the main seismic isolation groove and reserves an appropriate distance. The main seismic isolation groove is not penetrated. Each row of blast holes is evenly and staggered. After blasting and excavation, a new secondary groove is formed. The overall foundation pit plane shape is staggered like comb teeth.

[0008] (4) The remaining rock formations are divided into regions. The depth of blastholes and the amount of explosives are controlled according to the strength of the rock formations and the vibration feedback after blasting. Micro-difference blasting is used for excavation. The blasting sequence is to start with the blasthole group at the center, and then blast from the inside to the outside and from the middle to the sides. Water-sealed blasting is used in the rock formations, and the blast holes are charged according to the strength of the heterogeneous rock formations.

[0009] (5) After blasting, excavation machinery is arranged in the main seismic isolation trench to process the broken rocks and rock layers that have not been completely destroyed, and to reinforce the foundation pit.

[0010] (6) Repeat process steps (1) to (5), excavate the foundation pit in layers according to the changes in rock stratum strength, and adjust the spacing between construction trenches until the excavation reaches the base surface.

[0011] In step (1), sandbags and protective nets are arranged along the edge of the foundation pit to prevent direct impact from flying rocks during blasting. An anti-seismic groove is provided on the outer edge of the annular protective belt, and an uneven foam board is arranged on the upper part of the anti-seismic groove to reduce some noise impact. The depth of the anti-seismic groove is h 1 Greater than the depth of the main seismic isolation groove h 2, and h 1≥2m, the width of the seismic trench ≥0.6m.

[0012] In step (2), the main seismic isolation groove is excavated in a rectangular cross-sectional shape. h 2 Classification according to rock strata changes, h 2≥1m; Main seismic isolation groove setting depth and width t 2≥2m, which can facilitate the workers and small machinery to enter the site for work and serve as the main open surface for rock blasting.

[0013] In the step (3), the construction of the secondary trench is similar to that of the main trench. A row of deep holes is arranged along the preset secondary trench, and a hydraulic splitter is used to generate cracks in the deep hole connection line. Then, blasting and mechanical crushing are performed along the crack direction to form the secondary trench. The cross-section of the secondary trench is rectangular and the width of the secondary trench is t 3≥0.5m, depth h 3 Less than or equal to the depth of the main seismic isolation groove h 2. The auxiliary trench is not connected to both sides of the foundation pit, leaving part of the original rock layer. The length of the auxiliary trench is L It should be larger than half the width of the foundation pit, and greater than or equal to the spacing between the auxiliary trenches, so that the excavation plane of the foundation pit is comb-shaped, increasing the free surface for blasting; the unblasted area is convenient for mechanical vehicles to enter the site to assist in the work.

[0014] In step (4), micro-difference blasting is adopted for the remaining rock formation. When charging the blasthole, the explosive is divided into two parts, the upper and lower parts, and the middle part is blocked by a buffer water bag. The amount of explosives at both ends can be adjusted according to the upper and lower strength changes of the heterogeneous rock formation. A detonating cord detonator with a delay time of 310ms is installed in the blasthole, and a detonating cord detonator with a delay time of 60ms is used between the blastholes. The time interval between detonations in two adjacent blastholes is between 50 and 150ms. Blast-UM blasting vibration meters are arranged in the prevention area and adjacent buildings to monitor the maximum acceleration and maximum amplitude of blasting vibration, analyze the vibration data obtained from each blasting excavation and form a test result report to guide the arrangement of subsequent blastholes, the adjustment of technical parameters such as depth and charge amount, and form efficient and accurate positive feedback for blasting construction.

[0015] In step (6), during the entire foundation pit excavation process, the strength and type of the rock strata at depth and in plane must be measured in advance before blasting, and the rock strata must be preliminarily divided to prepare for subsequent layered blasting, construction trench adjustment and layout.

[0016] The beneficial effect of the present invention is that the comb-tooth-shaped shock-absorbing blasting excavation method of the foundation pit in the reverse operation of the underground station cover excavation of the present invention uses the main seismic isolation grooves extending from both sides of the foundation pit as the main air-facing surface during the foundation pit blasting process, so that most of the vibration waves generated by the blasting are released into the air from both sides of the long sides of the foundation pit, so that the surrounding sandbags and foam boards can absorb more vibration energy, reduce the direct impact of the blasting vibration on the foundation pit wall and the upper structure, and can also become the working surface for subsequent mechanical construction, which can reduce a certain construction cost and improve the speed of cleaning up the gravel after blasting.

[0017] The present invention adopts a comb-shaped blasting excavation method, which can make the vibration wave contact the free surface faster to release part of the energy. The increase of the free surface improves the blasting effect of the rock layer, which can make the vibration wave after the rock layer is reflected quickly pass through the free surface again to dissipate part of the energy. In addition, most vibration waves and vibration waves reflected on the critical surface will pass through multiple construction grooves during the propagation process, which can greatly consume their energy and reduce the impact of vibration on the reverse excavation of the station cover. The part of the auxiliary groove in the foundation pit that is not connected to the main groove is conducive to the collection and transportation of crushed stone by engineering vehicles in the early stage of blasting, saving construction costs, etc.

[0018] In the layered excavation of the foundation pit of the present invention, as the excavation depth of the foundation pit increases, the strength and stress of the rock formation gradually increase. According to the feedback from the on-site instrument test, an adjustable grooving method is adopted. In order to ensure that the foundation pit is fully blasted without increasing the blasting vibration too much, the subsequent auxiliary grooves are arranged in a more slender and dense shape, and the overall comb tooth shape is denser. For deep excavation, this method can release the stress of part of the rock formation, improve the influence of the increase in rock formation stress on the formation of residual holes during blasting, and improve the blasting effect. The protective measures around the foundation pit can assist the main free surface grooves on both sides to absorb part of the blasting energy. The use of micro-difference blasting and water seal blasting in the foundation pit can effectively control vibration, shock waves, dust, etc., and the degree of rock crushing is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of construction step (1) of an embodiment of the present invention; Figure 2 is a schematic diagram of construction step (2) of an embodiment of the present invention; Figure 3 is a schematic diagram of construction step (3) of an embodiment of the present invention; Figure 4 is a schematic diagram of construction step (4) of an embodiment of the present invention; Figure 5 A schematic diagram of a charge structure according to an embodiment of the present invention; Figure 6 It is a longitudinal cross-sectional layout diagram of foundation pit excavation according to an embodiment of the present invention.

[0020] In the figure, 1 is the foundation pit; 2 is the protection belt; 3 is the main seismic isolation groove; 4 is the blast hole connection line; 5 is the auxiliary groove; 6 is the explosive; 7 is the water bag; 8 is the oblique blast hole; 10 is the protection net; 11 is the foam board. DETAILED DESCRIPTION

[0021] like Figure 1 to Figure 6 As shown, this embodiment is a blasting excavation of a deep foundation pit in a heterogeneous rock layer of an underground station in a certain urban area. The length, width and depth of the foundation pit 1 are a × b × h .

[0022] The steps of the comb-shaped shock-absorbing blasting excavation method for the foundation pit in the reverse operation of the underground station cover excavation in this embodiment are as follows: S1, such as Figure 1 and Figure 6 As shown, sandbags 9 and protective nets 10 are arranged along the periphery of the foundation pit to reduce the damage caused by splashing gravel. Uneven foam boards 11 are arranged on the foundation pit wall to reduce noise, forming an annular protective belt 2 with a width of t 1≥0.6m, the distance between protection zone 2 and main seismic isolation slot shall be selected according to actual conditions.

[0023] S2, such as Figure 2 As shown, a certain distance of protection belt is reserved along the length of the foundation pit, and a row of deep holes is drilled along the length of the foundation pit and a certain amount of expansion agent is added to produce obvious cracks. After blasting and cleaning along the cracks, the main seismic isolation groove 3 is formed. According to the width of the main seismic isolation groove, a single row or multiple rows of deep holes are set to produce more cracks for easy construction. The main seismic isolation groove is distributed to one side of the foundation pit as the main air-facing surface and the construction surface of subsequent machinery, extending from the leftmost protection belt to the rightmost, with a rectangular cross-sectional shape and a height of 1.5 m. h 2≥1m, width t 2≥2.5m.

[0024] The calculation formula for the blasting width of the main seismic isolation slot is: ; Where: c is the number of rows of blast holes; n is the blasting action index, n≤0.75; W is the minimum resistance line, m; ; d is the borehole diameter.

[0025] S3, such as Figure 3 As shown, cavities are arranged vertically along the main seismic isolation slot 3 toward the inside of the foundation pit 1, and obvious cracks are formed by static blasting. Each row of blasthole lines 4 extends relative to the main seismic isolation slot and reserves an appropriate distance without being connected. The spacing between each row of auxiliary slots on the same side is T (0.5b≤T<b) and the length is L (L≥T). The top endpoints of the two adjacent auxiliary slots on the same side form an angle of less than 90° with the midpoint of the connected main seismic isolation slot, which can make the remaining rock blasting vibration wave propagate to the main seismic isolation slot after reflection, and then weaken it again through the auxiliary slot air interface.

[0026] After blasting excavation, the width is t 3≥0.5m, depth h 3 ( h 3≤ h 2) The auxiliary trench 5 has a comb-like staggered shape in the overall foundation pit plane.

[0027] S4, such as Figure 4 , divide the remaining rock layers into regions, and evenly arrange blastholes in sequence along the width of the foundation pit, using the micro-difference blasting method. The blasting sequence starts with the blasthole group at the center, and then blasts from the inside to the outside and from the middle to the sides. On the outside of the rock layer, oblique blastholes 8 are arranged along the inside of the vertical rock layer of the main seismic isolation groove 3 or the auxiliary groove 5. The oblique blastholes 8 are drilled at an angle of 70° downward. In heterogeneous rock layers, spaced charges (explosives 6) are used, and the middle is blocked by a buffer water bag 7, such as Figure 5As shown. The amount and position of the explosive 6 are adjusted by the water bag 7 so that the explosive 6 can fully act on the high-strength rock layer. At the same time, the water bag 7 can absorb part of the impact of the explosive, thereby reducing the blasting dust. The amount of explosives at both ends is adjusted according to the change in the strength of the blasting heterogeneous rock layer and the vibration data analysis report during each blasting excavation.

[0028] In order to ensure the blasting process, it is necessary to control the amount of explosives Q to ensure that the vibration speed of the top building in the underground station cover excavation reverse operation is within a safe range. The calculation formula is: ; Where: R is the safe allowable distance for blasting vibration velocity, m; V is the safe allowable particle velocity of the protected object, cm / s; K and α are coefficients and attenuation indexes related to the topography and geology between the blasting point and the protected object, respectively. They can be obtained through multiple field pre-blasting data. If there is no field data, it can be roughly judged by the lithology of the rock formation. See the table below for details; ; The depth of the blasthole l It is mainly determined by the depth of the main and auxiliary grooves, the over-depth of the blasthole and the inclination of the blasthole. The calculation formula is: ; In the formula, h The depth of the construction groove around the blasthole, mainly on the deeper side, m; is the over-depth of the blasthole, m; d is the hole diameter, m.

[0029] In the arrangement of blastholes, the general hole spacing a 1 Greater than the row spacing b 1 , and its calculation formula is:

[0030] In the formula, m It is better to take 1.2~1.5; W is the minimum resistance line length, m.

[0031] Calculate the amount of explosives required for blasting per cubic meter of rock based on the explosive performance and the auxiliary trough cross section q : ; Where: is the solidity coefficient of the rock formation; S is the area of ​​the vertical section of the auxiliary trough, m 2 ; k o Considering the correction factor of explosive force, k o =525 / p ,p is the explosive force (mL).

[0032]

[0033] The total amount of blasting at each blast Q , Consumption of rock explosives per unit volume q Number of holes in the plane N , the blasting volume of a single rock formation can be obtained V And the amount of drug in a single hole Q i .

[0034] S5. After blasting, arrange excavation and transportation machinery in the main seismic isolation slot, process the blasted rocks and the rock layers that have not been completely destroyed, and reinforce the foundation pit.

[0035] S6. Repeat the process S1 to S5. During the layered excavation of the foundation pit, as the excavation depth of the foundation pit increases, the rock stratum strength gradually increases. The spacing between the construction trenches can be appropriately adjusted to make the subsequent sub-trench layout more slender and dense until the base surface is excavated.

Claims

1. A comb-shaped shock-absorbing blasting excavation method for foundation pits in underground station cover excavation reverse operation, characterized in that: The method steps are as follows: (1) Before excavation, sandbags are piled up to a certain height along the edge of the foundation pit, and foam boards and protective nets are placed on top to form a circular protective belt; (2) According to the conditions of the foundation pit site, a certain distance of protection zone is reserved and a row of deep holes are drilled along the length of the foundation pit. A certain amount of expansion agent is added to produce obvious cracks. Two main seismic isolation grooves are pre-blasted along the direction of the cracks. (3) Arrange blast holes at appropriate intervals along the main seismic isolation groove. The blast hole connection line extends perpendicular to the main seismic isolation groove and reserves an appropriate distance. The main groove is not penetrated. Each row of blast holes is evenly staggered. After blasting and excavation, a new secondary groove is formed. The overall foundation pit plane shape is staggered in a comb-tooth shape. (4) The remaining rock formations are divided into regions, and the depth of blastholes and the amount of charge are controlled according to the rock formation strength and the vibration feedback after blasting. Micro-difference blasting is used for excavation. The blasting sequence is to start with the blasthole group at the center, and then blast from the inside to the outside and from the middle to the sides. Water-sealed blasting is used in the rock formation, and the blasting holes are charged according to the strength of the heterogeneous rock formation. (5) After blasting, excavation machinery is arranged in the main seismic isolation groove to process the broken rocks and the rock layers that have not been completely destroyed, and to reinforce the foundation pit; (6) Repeat processes S1-S5, excavate the foundation pit in layers according to the change in rock stratum strength, and adjust the spacing between construction trenches until the excavation reaches the base surface.

2. The comb-shaped shock-absorbing blasting excavation method for foundation pit in the top-down construction of underground station according to claim 1 is characterized in that: In step (1), sandbags and protective nets are arranged along the edge of the foundation pit to prevent direct impact from flying rocks during blasting. An anti-seismic groove is provided on the outer edge of the annular protective belt, and an uneven foam board is arranged on the upper part of the anti-seismic groove to reduce some noise impact. The depth of the anti-seismic groove is h 1 Greater than the depth of the construction trench h 2 ,and h 1≥2m, the width of the seismic trench ≥0.6m.

3. The comb-shaped shock-absorbing blasting excavation method for foundation pit in the top-down construction of underground station according to claim 1 is characterized in that: In step (2), the main seismic isolation groove is excavated in a rectangular cross-sectional shape. h 2 Classification according to rock strata changes, h 2≥1m; Main seismic isolation groove setting depth and width t 2≥2m, which can facilitate the workers and small machinery to enter the site for work and serve as the main open surface for rock blasting.

4. The comb-shaped shock-absorbing blasting excavation method for foundation pit in the top-down construction of underground station according to claim 1 is characterized in that: In the step (3), the construction method of the auxiliary trench is similar to that of the main trench. A row of deep holes is arranged along the preset auxiliary trench, and a hydraulic splitter is used to generate cracks in the deep hole connection line; then blasting and mechanical crushing are performed along the crack direction to form the auxiliary trench. The cross-section of the auxiliary trench is rectangular and the width of the auxiliary trench is t 3≥0.5m, depth h 3 Less than or equal to the depth of the main seismic isolation groove h 2. The auxiliary trench is not connected to both sides of the foundation pit, leaving part of the original rock layer. The length of the auxiliary trench is L It should be larger than half the width of the foundation pit, and greater than or equal to the spacing between the auxiliary trenches, so that the excavation plane of the foundation pit is comb-shaped, increasing the free surface for blasting; the unblasted area is convenient for mechanical vehicles to enter the site to assist in the work.

5. The comb-shaped shock-absorbing blasting excavation method for foundation pit in the top-down construction of underground station according to claim 1 is characterized in that: In the step (4), micro-difference blasting is adopted for the remaining rock formation; when charging the blasthole, the explosive is divided into two parts, the upper and lower parts, and the middle part is blocked by a buffer water bag; the amount of explosives at both ends can be adjusted according to the upper and lower strength changes of the heterogeneous rock formation; a detonating cord detonator with a delay time of 310ms is installed in the blasthole, and a detonating cord detonator with a delay time of 60ms is used between the blastholes, and the detonation time interval between two adjacent blastholes is between 50 and 150ms; a Blast-UM blasting vibration meter is arranged in the prevention area and adjacent buildings to monitor the maximum acceleration and maximum amplitude of the blasting vibration, analyze the vibration data obtained from each blasting excavation and form a test result report, guide the arrangement of subsequent blastholes, the depth and the adjustment of the technical parameters of the charge amount, and form efficient and accurate positive feedback for blasting construction.

6. The comb-shaped shock-absorbing blasting excavation method for foundation pit in the top-down construction of underground station according to claim 1 is characterized in that: In step (6), during the entire foundation pit excavation process, the strength and type of the rock strata at depth and in plane must be measured in advance before blasting, and the rock strata must be preliminarily divided to prepare for subsequent layered blasting, construction trench adjustment and layout.

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