Rock foundation pit blasting shock absorption construction method

Abstract

The application discloses a rock foundation pit blasting shock absorption construction method and belongs to the technical field of foundation pit construction. The method comprises the following steps: S1, selecting a foundation pit position, removing the soil on the upper part of the foundation pit to obtain a first layer of rock surface, and excavating a shock absorption groove and an auxiliary blasting foundation pit around the foundation pit; S2, respectively performing vertical drilling on the first layer of rock surface at both ends of the foundation pit, setting a first buffer hole and a blasting hole, setting a TPU pipe in the first buffer hole, setting a joint cutting charge in the blasting hole, performing first blasting, and obtaining a second layer of rock surface; S3, performing vertical drilling on the second layer of rock surface and the two ends of the unblasted first layer of rock surface, repeating step S2, and performing second blasting; and S4, repeating step S3 to perform blasting circulation and obtain the foundation pit. The blasting shock absorption construction method can reduce the damage of the rock mass around the foundation pit and the vibration caused to the buildings near the foundation pit, can reduce the charge amount of the blasting hole, and reduces the construction cost of the foundation pit.

Description

Technical Field

[0001] This invention relates to the field of foundation pit construction technology, and in particular to a method for vibration reduction during blasting construction of rock foundation pits. Background Technology

[0002] The complex geological conditions in southwestern my country, with some areas containing hard bedrock beneath the surface, pose significant challenges to the safe and convenient construction of deep foundation pit projects. For these deep foundation pit projects with underlying bedrock, ordinary mechanical excavation is insufficient to meet the project requirements. The drill-and-blast method, which uses drilling and blasting to break and throw rocks for excavation, is economical, efficient, and adaptable. It offers flexibility and shortens the construction period in urban deep foundation pit projects with tight deadlines, making it a highly efficient and convenient method. However, the vibrations caused by blasting excavation inevitably have adverse effects on surrounding buildings. Therefore, how to safely and efficiently implement drill-and-blast excavation technology in urban rock deep foundation pit projects has become a key research focus for experts and scholars both domestically and internationally. Summary of the Invention

[0003] To address the aforementioned problems, this invention aims to provide a method for vibration reduction during rock foundation pit blasting. This method can reduce damage to the surrounding rock mass and vibrations to nearby buildings during foundation pit blasting, thereby reducing the impact on the surrounding environment. It also reduces the amount of explosives required for blasting holes, thus lowering the construction cost of the foundation pit.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for vibration reduction during blasting in rock foundation pits, characterized by the following steps:

[0006] S1: Select the location of the foundation pit, remove the soil above the foundation pit to obtain the first layer of rock surface, and excavate vibration damping trenches and auxiliary blasting foundation pits around the foundation pit;

[0007] S2: Vertical drilling is carried out on the first layer of rock surface at both ends of the foundation pit. The outer row of holes is set as the first buffer hole and the blasting hole alternately, and the inner row of holes is set as the blasting hole. TPU tubes are placed in the first buffer holes and slotting explosive charges are placed in the blasting holes. The two rows of blasting holes are staggered. Then the first blast is carried out to obtain the second layer of rock surface.

[0008] S3: Drill vertical holes at both ends of the second rock surface and the unblasted first rock surface, repeat step S2, and blast a second time to obtain the third rock surface;

[0009] S4: Repeat step S3 to perform a blasting cycle and obtain the foundation pit.

[0010] Furthermore, the specific operations of excavating vibration damping trenches and assisting in blasting the foundation pit in step S1 include the following steps: using the cutting line along the long axis of the foundation pit as the baseline for positioning, vertically excavating vibration damping trenches into the cutting line, with each layer of cutting depth greater than 1.5 times the depth of the blasting hole, and the width of the vibration damping trench being 1.5-3m. The cutting work is carried out every 15m along the baseline, and the rock in the vibration damping trench is broken and transported out by a rock-breaking machine. After each layer of the vibration damping trench is cut, the slag is cleaned up, and the verticality of the outer side of the vibration damping trench is controlled to achieve vertical excavation of the foundation pit rock wall. The inner side of the vibration damping trench is the blasting area, and the outer side of the vibration damping trench is the protection area.

[0011] Auxiliary blasting pits were excavated at both ends of the long axis of the foundation pit so that the rock at the bottom of the foundation pit would fall into the auxiliary blasting pits during blasting.

[0012] Furthermore, the distance between the auxiliary blasting pit and the end of the adjacent pit is 1 to 5 meters.

[0013] Furthermore, in step S2, all the holes in the first row are set as second buffer holes. The second buffer holes are located between the auxiliary blasting pit and the blasting holes, and the second buffer holes are arranged and distributed along the pit support. TPU pipes are also installed in the second buffer holes.

[0014] Furthermore, the depth of the vertical borehole is 1.5m.

[0015] Furthermore, the number of vertical boreholes in the first blast is at least four rows, and the number of vertical boreholes in the second blast is at least eight rows.

[0016] Furthermore, the number of vertical boreholes in the first blast was six rows, and the number of vertical boreholes in the second blast was twelve rows.

[0017] Furthermore, the length of the TPU tube is the same as the depth of the first buffer hole, and both ends of the TPU tube are sealed.

[0018] Furthermore, during the first blast, the blasting dimensions at both ends of the first layer of rock surface were 3m, resulting in a second layer of rock surface with a length of 6m.

[0019] Furthermore, the amount of explosive charge in each blast hole is 0.7 to 0.8 kg.

[0020] The beneficial effects of this invention are:

[0021] 1. The rock foundation pit blasting vibration reduction construction method of the present invention can block the propagation of seismic waves by setting vibration reduction grooves, without damaging the outer wall of the foundation pit and the rock structure outside the foundation pit, thus ensuring the safety of the buildings around the foundation pit.

[0022] 2. The rock foundation pit blasting vibration reduction construction method of the present invention can provide a free surface for rock fragmentation by setting a first buffer hole and a second buffer hole, and at the same time play a role in vibration isolation and vibration reduction for foundation pit support, and can also reduce the drilling cost of production blasting; setting TPU pipes in the first buffer hole and the second buffer hole can reduce blasting vibration and damage to the rock strata below the foundation pit.

[0023] 3. The rock foundation pit blasting vibration reduction construction method of the present invention uses slotted explosive charges to generate detonation product jets and stress concentration in the slotted direction, while reducing the stress peak and blasting vibration velocity in the non-slotted direction, slowing down the energy propagation speed in the non-slotted direction, and reducing the magnitude of energy propagation in the non-slotted direction, thereby achieving the purpose of directional fracture. The use of slotted explosive charges can reduce the damage to the surrounding rock.

[0024] 4. The rock foundation pit blasting vibration reduction construction method of the present invention, through the setting of blasting holes, first buffer holes and second buffer holes, and the step-type blasting process adopted in the blasting process, the combination of the two can reduce the amount of explosives and the impact on the surrounding environment. At the same time, the added auxiliary blasting pit also reduces the impact of blasting vibration on the surrounding environment, thus making the method economical and environmentally friendly, and reducing the cost of rock foundation pit blasting construction. Attached Figure Description

[0025] Figure 1 This is a schematic diagram showing the planar positional relationship between the auxiliary blasting pit, the vibration damping groove, and the pit in this invention.

[0026] Figure 2 This is a schematic diagram of the auxiliary blasting pit and the blasting direction in this invention.

[0027] Figure 3 This is a schematic diagram showing the arrangement of vertical boreholes on the surface of the first layer of rock in this invention.

[0028] Figure 4 This is a schematic diagram of the directional blasting of the slit explosive charge in the blast hole in this invention.

[0029] Figure 5 This is a top view showing the vertical borehole distribution on the first and second rock surfaces in this invention.

[0030] Figure 6 This is a side view showing the vertical borehole distribution on the first and second rock surfaces in this invention.

[0031] Figure 7 This is a schematic diagram of the arrangement of blast holes and the detonation stage in the comparative scheme of the present invention. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0033] A method for vibration reduction during blasting in rock foundation pits includes the following steps:

[0034] S1: Select the location of the foundation pit, use mechanical equipment to remove the soil above the foundation pit to obtain the first layer of rock surface, and excavate vibration damping trenches and auxiliary blasting foundation pits around the foundation pit;

[0035] Specifically, the specific operations for excavating vibration damping trenches and assisting in blasting the foundation pit include the following steps: using the cutting line along the long axis of the foundation pit as a baseline for positioning, vertically excavating vibration damping trenches into the cutting line, with each layer of cutting depth greater than 1.5 times the depth of the blasting hole, and the width of the vibration damping trench being 1.5-3m. The cutting work is carried out every 15m along the baseline, and the rock in the vibration damping trench is broken and transported out by a rock-breaking machine. After each layer of the vibration damping trench is cut, the debris is cleaned up, and the verticality of the outer side of the vibration damping trench is controlled to achieve vertical excavation of the foundation pit rock wall. The inner side of the vibration damping trench is the blasting area, and the outer side of the vibration damping trench is the protection area.

[0036] At both ends of the long axis of the foundation pit, auxiliary blasting pits are excavated using mechanical equipment. This ensures that rock from the lower part of the foundation pit falls into the auxiliary blasting pit during blasting. The distance between the auxiliary blasting pits and the adjacent ends of the foundation pits is 1–5 meters. The planar relationship between the auxiliary blasting pits, the vibration damping trenches, and the foundation pits is shown in the attached figure. Figure 1 The structural schematic diagram of the auxiliary blasting pit and the blasting direction of the pit shown in the figure is attached. Figure 2 As shown, in the appendix Figure 1 and attached Figure 2 In the diagram, 'a' represents the auxiliary blasting pit, 'b' represents the vibration damping groove, and the arrow indicates the blasting direction of the pit.

[0037] S2: Vertical drilling is carried out on the first layer of rock surface at both ends of the foundation pit. The outer row of holes is set as the first buffer hole and the blasting hole alternately, and the inner row of holes is set as the blasting hole. TPU tubes are placed in the first buffer holes and slotting explosive charges are placed in the blasting holes. The two rows of blasting holes are staggered. Then the first blast is carried out to obtain the second layer of rock surface.

[0038] Specifically, the two ends of the foundation pit are designated as End A and End B. Along the direction from A to B, three rows of holes are drilled vertically into the first layer of rock at End A. Then, along the direction from B to A, three rows of holes are drilled vertically into the first layer of rock at End B. The depth of the vertical drilling is 1.5m. (See attached diagram.) Figure 3As shown, the outermost first and sixth rows of holes are configured as second buffer holes (empty holes), located between the auxiliary blasting pit and the blasting holes, and distributed along the pit support; the second and fifth rows of holes are configured with alternating first buffer holes (empty holes) and blasting holes (solid holes); the third and fourth rows of holes are all blasting holes, and the blasting holes in the second row (second row) and the third row (fourth row) are arranged alternately; TPU tubes are installed in both the first and second buffer holes.

[0039] The TPU tube is the same length as the depth of the first buffer hole, and both ends of the TPU tube are sealed. The explosive charge in each blast hole is 0.7–0.8 kg. Directional blasting is performed using slotted explosive charges within the blast holes, with the slot lines parallel to the direction of the blast hole lines, as shown in the attached diagram. Figure 4 As shown, during the first blast, the blasting dimensions at both ends of the first layer of rock surface were 3m, resulting in a second layer of rock surface with a length of 6m. At this point, the first and second layers of rock formed a stepped shape.

[0040] S3: Drill vertical holes at both ends of the second rock layer surface and the unblasted first rock layer surface. Repeat step S2 to perform a second blast, obtaining the third rock layer surface, as shown in the attached diagram. Figure 5 and attached Figure 6 As shown, the attached Figure 5 This is a top view showing the vertical borehole distribution on the first and second rock surfaces. Rows 1, 2, and 3 represent the borehole locations and types on the second rock surface, while rows 4, 5, and 6 represent the borehole locations and types on the first rock surface. (Attached) Figure 6 This is a side view showing the vertical borehole distribution on the first and second rock surfaces.

[0041] S4: Repeat step S3 to perform a blasting cycle and obtain the foundation pit.

[0042] Example:

[0043] In this embodiment, the selected location of the foundation pit is as follows: the soil from the ground surface to 5m below the pit is weathered soil, and below the weathered soil is moderately weathered rock. The medium parameters are shown in Table 1. The width of the excavated foundation pit is 16m and the depth is 12m. There are buildings located 5m on both sides of the foundation pit. The buildings are 30m long, 15m wide, and 15m high. The building foundation is located 10m below the ground surface.

[0044] Table 1. Medium parameters at the location of the foundation pit

[0045]

[0046] Auxiliary blasting pits were excavated at both ends of the foundation pit to add an open surface for blasting. Then, three vertical holes were drilled on the rock surface to be blasted at one end of the foundation pit. Three vertical holes were drilled on the rock surface at the other end of the foundation pit for the first blast.

[0047] After the first blast, sections 1 through 6 were obtained at both ends of the pit. Vertical holes were drilled at sections 1 through 6, followed by a second blast, and this cycle was repeated to complete the blasting process of the pit. The hole depth was 1.5m. During the same blasting process, the blasting dimensions at the same level at both ends of the pit were 3 meters. The number of blast holes and the amount of explosives at each section are detailed in Table 2.

[0048] Table 2 shows the number of boreholes and the amount of explosive charge at each stage in the implementation plan.

[0049] 1 17 0.788 0 2 17 0.788 25 3 17 0.788 50 4 17 0.788 75 5 17 0.788 110 6 17 0.788 150 total 102 80.33 -

[0050] To verify the technical effectiveness of the construction method in this invention, a comparison of the effects of comparative schemes was also conducted.

[0051] The comparative scheme employs a "V"-shaped blasting method: a trench is created by detonating the first blast hole, and subsequent sections are arranged in a "V" shape, blasted and thrown under the free face created by the previous section. The explosive used is No. 2 rock emulsion explosive, with a blast hole diameter of 35mm and a depth of 3m, employing a decoupled charge structure, excavating 3m in a single blast. The arrangement of blast holes and the detonation sections are shown in the attached diagram. Figure 7 As shown, in the appendix Figure 7 In the table, 1-13 represent the detonation sequence. The charge amount for each borehole section is shown in Table 3.

[0052] Table 3 compares the number of boreholes and the amount of explosive charge at each stage in the different schemes.

[0053] 1 1 2.363 0 2 3 1.575 25 3 5 1.575 50 4 7 1.575 75 5 9 1.575 110 6 11 1.575 150 7 13 1.575 200 8 14 1.575 250 9 14 1.575 310 10 12 1.575 380 11 10 1.575 460 12 8 1.575 550 13 6 1.575 650 total 113 178.76 -

[0054] Results analysis of the blasting methods in the implementation plan and the comparative plan:

[0055] (1) Vibration velocity analysis

[0056] The comparison results of the maximum vibration velocity in each direction in the implementation scheme and the comparison scheme are shown in Table 4 below.

[0057] Table 4 shows the maximum vibration velocities in each direction for the implementation and comparative schemes.

[0058] Comparison Plan 6.14 2.35 4.27 Implementation Plan 0.89 2.39 2.76

[0059] The comparative scheme caused the maximum vibration velocity of the existing building on the right to occur mainly in the foundation section, with minimal impact on the vibration of other parts. The vibration velocity gradually decreased as the building height increased. The maximum vibration velocity caused by the blasting operation on the right side of the building was 7.62 cm / s, while the vibration velocity at the top corner of the building was approximately 2 cm / s. The implementation scheme, on the other hand, caused a more uniform vibration impact on the existing building. The maximum vibration velocity occurred at the top corner, furthest from the blast source, at approximately 3.50 cm / s, while the vibration velocity in the remaining parts was approximately 2 cm / s.

[0060] The comparison scheme caused a significant horizontal vibration velocity of 6.14 cm / s in the existing building on the right, followed by a maximum horizontal vibration velocity of 4.27 cm / s. The maximum horizontal vibration velocity occurred in a small area in the middle of the foundation, while the rest of the building was less affected, with vibration velocities almost zero. The building as a whole was significantly affected by vertical vibration velocities, with the maximum vertical vibration velocity also occurring in the foundation area.

[0061] As shown in Table 4, the horizontal vibration velocity caused by the implementation plan to the existing building on the right is relatively small, with a maximum vibration velocity of approximately 0.89 cm / s. The horizontal longitudinal vibration velocity and the vertical vibration velocity are not significantly different, at 2.39 cm / s and 2.76 cm / s, respectively. The bottom and top corners of the building are the areas where the maximum horizontal longitudinal vibration velocity occurs, while the maximum vertical vibration velocity occurs at the top corner of one side of the building.

[0062] (2) Displacement Analysis

[0063] The maximum displacements in each direction for the comparative and implementation schemes are shown in Table 5 below. Table 5 shows that the comparative scheme causes a larger horizontal displacement of the existing building due to blasting vibration, with a maximum value of 0.29 mm. The displacements in the horizontal longitudinal and vertical directions are smaller, approximately 0.10 mm. The implementation scheme causes a larger horizontal and vertical displacement of 0.32 mm, followed by a smaller vertical displacement of approximately 0.21 mm, while the horizontal displacement component is smaller.

[0064] Table 5 Maximum displacement in each direction for blasting schemes

[0065] Comparison Plan 0.29 0.10 0.13 Implementation Plan 0.09 0.32 0.21

[0066] (3) Stress Analysis

[0067] The maximum principal stresses generated on the building by each blasting scheme are shown in Table 6 below.

[0068] Table 6 shows that the building is affected by the vibration from the blasting construction in the comparative scheme. Both the maximum and minimum principal stresses occur in the middle foundation section at the bottom of the building, with a maximum principal stress of 0.31 MPa and a minimum principal stress of 0.54 MPa. Therefore, the foundation section is prone to cracking due to blasting vibration. Table 6 also shows that the implementation scheme affects the building, with the maximum and minimum principal stresses also distributed in the foundation section, but more evenly than the comparative scheme. The maximum and minimum principal stresses are 0.27 MPa and 0.29 MPa respectively, indicating a smaller impact than the comparative scheme.

[0069] Table 6 Maximum Stress in Various Directions for Blasting Schemes

[0070] Comparison Plan 0.31 0.54 Implementation Plan 0.27 0.29

[0071] Comparison of options:

[0072] From the perspective of blasting scheme design, the comparative scheme involves a single blast excavation of 3 meters, with a total of 113 blast holes and a total charge of 178.76 kg. The implementation scheme involves a single blast excavation of 3 meters, with a total of 102 blast holes and a total charge of 80.33 kg. Given the same blasting excavation depth, the implementation scheme is economically superior to the comparative scheme.

[0073] Analyzing the environmental impact of blasting vibration: The comparative scheme's maximum vibration velocity affecting the existing building on the right occurs horizontally, at 6.14 cm / s; the implemented scheme's maximum vibration velocity occurs vertically, at 2.76 cm / s. According to my country's national standard "Safety Regulations for Blasting GB-6722," the maximum vibration velocity for commercial buildings should not exceed 5 cm / s. Therefore, the implemented scheme is safer than the comparative scheme. Both the comparative and implemented schemes have minimal displacement effects on the existing building, with little difference between them. However, the comparative scheme generates a higher absolute value of the minimum principal stress on the existing building than the implemented scheme; therefore, the comparative scheme is more likely to cause cracks in the building and shorten its lifespan.

[0074] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for vibration reduction during blasting in rock foundation pits, characterized in that, Includes the following steps, S1: Select the location of the foundation pit, remove the soil above the foundation pit to obtain the first layer of rock surface, and excavate vibration damping trenches and auxiliary blasting foundation pits around the foundation pit; Auxiliary blasting pits were excavated at both ends of the long axis of the foundation pit so that the rock at the bottom of the foundation pit would fall into the auxiliary blasting pit during blasting. The distance between the auxiliary blasting pit and the end of the adjacent pit is 1~5m; S2: Vertical boreholes are drilled on the surface of the first layer of rock at both ends of the foundation pit. Three rows of holes are arranged along the direction from the end of the pit towards the middle. The first row of holes are all designated as second buffer holes. The second row of holes consists of alternating first buffer holes and blasting holes. The third row of holes is designated as blasting holes. The second buffer holes are located between the auxiliary blasting pit and the second row of holes, and are distributed along the foundation pit support. TPU tubes are installed inside the first and second buffer holes. The length of the TPU tubes is the same as the depth of the first and second buffer holes. The TPU tubes are sealed at both ends; slit charges are placed inside the blast holes, with the slits of the slit charges parallel to the direction of the blast hole connection; the two rows of blast holes are staggered, and the second buffer hole and the first buffer hole are also staggered; then the first blast is performed, with the blast dimensions at both ends of the first layer of rock surface being 3m, resulting in a second layer of rock surface with a length of 6m; the first and second layers of rock form a stepped shape; the charge in each blast hole is 0.7~0.8kg, and the vertical drilling depth is 1.5m; S3: Drill vertical holes at both ends of the second rock surface and the unblasted first rock surface, repeat step S2, and blast a second time to obtain the third rock surface; S4: Repeat step S3 to perform a blasting cycle and obtain the foundation pit.

2. The method for vibration reduction during blasting in rock foundation pits according to claim 1, characterized in that, The specific operations of excavating vibration damping trenches and assisting in blasting the foundation pit in step S1 include the following steps: using the cutting line along the long axis of the foundation pit as a baseline for positioning, vertically excavating vibration damping trenches into the cutting line, with each layer of cutting depth greater than 1.5 times the depth of the blasting hole, and the width of the vibration damping trench being 1.5-3m. The cutting work is carried out every 15m along the baseline, and the rock in the vibration damping trench is broken and transported out by a rock-breaking machine. After each layer of the vibration damping trench is cut, the slag is cleaned up, and the verticality of the outer side of the vibration damping trench is controlled to achieve vertical excavation of the foundation pit rock wall. The inner side of the vibration damping trench is the blasting area, and the outer side of the vibration damping trench is the protection area.

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