A construction method for sectional blasting on the upper steps of a new tunnel

Abstract

The present invention discloses a construction method for zoning and segmenting blasting on steps of a newly built tunnel, belonging to the technical field of engineering construction blasting. The method comprises the following steps: 1. setting monitoring points at equal distances within an existing line; 2. determining a suitable blasting footage; 3. determining blasting parameters under various construction methods; and 4. dividing areas according to blasting data. The method solves the problem of reducing the impact of blasting on an existing line when a newly built tunnel is approaching construction, ensures the structural safety and durability of the existing line, and improves engineering construction efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of engineering construction blasting, in particular to a construction method for zoning and segmenting blasting on steps of a newly built tunnel. Background Art

[0002] With the large-scale construction of transportation railways in my country, the environment faced by tunnel blasting is becoming more and more complex. There are more and more engineering examples of new tunnels passing through existing tunnels. Reducing blasting vibration has become a major challenge in the excavation of these tunnels. On-site monitoring is a common method for studying blasting control issues during tunnel construction. It facilitates timely grasp of dynamic information on blasting effects and has the advantage of real and intuitive data. It has become an indispensable research method.

[0003] The close-to-blasting construction of a new tunnel in a three-dimensional intersection tunnel will, on the one hand, cause the deterioration of the mechanical properties of the underground cavern rock mass, such as the opening and expansion of existing cracks, the generation of new cracks, the reduction of rock mass acoustic wave velocity, the increase of permeability coefficient, etc.; on the other hand, it will change the stress state of the existing tunnel, and the additional dynamic load will act on the support structure of the existing tunnel, which will also have various adverse effects on the existing tunnel support structure, such as reduced structural bearing capacity, damage and spalling of the support structure (secondary lining), excessive deformation and intrusion into the limit, etc.; in order to ensure the operational safety of the existing line and the durability of the tunnel structure when the tunnel is close to construction, it is necessary to impose certain restrictions on the blasting vibration velocity of the new tunnel.

[0004] When a tunnel is approaching construction, if traditional blasting is used for excavation, the strong blasting vibration may have a destructive impact on the existing tunnel. In order to reduce the vibration of the existing tunnel during blasting construction, it is necessary to find a blasting construction method based on existing blasting technology that can not only ensure the construction quality and progress, but also reduce the impact of construction on the existing tunnel, so as to ensure the safety of the lining structure and line of the existing tunnel and not affect the normal operation of the existing tunnel. Summary of the Invention

[0005] In order to overcome the defects of the existing technology, the technical problem to be solved by the present invention is to propose a construction method for zoning and segmented blasting on the steps of a new tunnel, which solves the problem of reducing the impact of blasting on the existing line when the new tunnel is approaching construction, ensures the safety and durability of the structure of the existing line and improves the efficiency of engineering construction.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] The present invention provides a construction method for sectional blasting on the upper steps of a newly constructed tunnel, comprising the following steps:

[0008] Step 1: Set up monitoring points at equal intervals within the existing line: Set up several groups of monitoring points within a 25D radius of the new tunnel. The intervals between the groups of monitoring points are 20m. These monitoring points are used to monitor blasting indicators including vibration velocity, settlement, and acceleration. The monitored blasting indicators are mainly blasting vibration velocity.

[0009] Step 2: Determine the appropriate blasting footage: The blasting footage for the new tunnel is determined based on multiple factors, including steel frame spacing, surrounding rock properties, construction schedule, and blasting vibration limits on existing lines. Dynamic adjustments are made during actual excavation, and reasonable adjustments are made within the blasting vibration speed limits of existing lines.

[0010] Step 3: Determine blasting parameters for each method: Based on the differences in blasting vibration effects and face preparation conditions of each method, design blasting parameters for different footage conditions and surrounding rock grades, mainly including the number of blastholes of each type, the maximum charge per hole, and blasthole arrangement;

[0011] Step 4: Divide the area based on blasting data: Set up four zones on each side of the intersection of the new tunnel and the existing line, and the four zones are set symmetrically. The corresponding sizes of the zones on both sides are different, and different vibration reduction methods are used for the four zones. Influenced by the surrounding geological conditions, the demarcation point is the mileage value corresponding to the blasting vibration speed exceeding the blasting vibration speed control value within the operating window point of the existing line. When constructing within the symmetrical zone range, corresponding preparations can be made based on the determined zones;

[0012] Based on the changes in monitoring indicators such as blasting vibration velocity, settlement, acceleration, and blasting vibration characteristics obtained from monitoring points arranged on the existing line, the upper steps of the new tunnel are zoned blasting in the spatial domain. In order to ensure the diversity and effectiveness of the zoned blasting, different controlled blasting methods need to be adopted in each zone; the blasting vibration velocity control value within the operating skylight point of the existing line is used as the dividing point, and symmetrical zoning is carried out with the intersection of the existing line and the new tunnel as the center, and four controlled blasting methods are adopted. The later the method is listed, the more significant the controlled blasting effect is, and the blasting vibration velocity of each monitoring point is significantly reduced compared with the previous use of traditional controlled blasting. At the same time, the impact on surrounding buildings is also weakened, which can effectively improve construction efficiency; at the same time, it can be widely used in controlling the impact of blasting vibration in mining construction when the new tunnel approaches the existing line, to prevent adverse effects on the operation of the existing line, so as to avoid damage to the structure and affect its durability and safety.

[0013] The preferred technical solution of the present invention is that in step 1, several groups of monitoring points are arranged at equal distances in the tunnel, and their spacing is adjusted according to the angle between the newly built tunnel and the existing line. The larger the angle, the larger the spacing, so as to adapt to the construction requirements of different newly built tunnels approaching the existing line, and has a wide range of applications.

[0014] The preferred technical solution of the present invention is that in step 4, the sign of the appearance of the dividing point is that under the same blasting parameters, the following three groups of data appear: the first group of data is qualified but close to the blasting vibration speed control value, the second and third groups of blasting vibration speeds have exceeded the blasting vibration speed control value, and the third group of data is a verification group for the second group of data. At this time, the dividing mileage is taken as the mileage corresponding to the second group of blasting. The dividing point is combined with different blasting vibration reduction methods to control the blasting construction and ensure the blasting effect.

[0015] The preferred technical solution of the present invention is that in step 4, the four partitions are respectively the explosion-controlled shock-absorbing hole rope saw method partition, the explosion-controlled rope saw method partition, the explosion-controlled shock-absorbing hole method partition and the explosion-controlled method partition, and the corresponding shock-absorbing methods are the explosion-controlled shock-absorbing hole rope saw shock-absorbing method, the explosion-controlled rope saw shock-absorbing method, the explosion-controlled shock-absorbing hole shock-absorbing method and the explosion-controlled shock-absorbing method. Different shock-absorbing methods are adopted for different partitions to ensure good blasting effect while reducing vibration and line safety of existing tunnels without affecting the normal operation of existing tunnels.

[0016] The preferred technical solution of the present invention is that the controlled explosion and vibration reduction method adopts high-precision millisecond-level electronic digital detonators to implement single-hole and single-shot submersible controlled blasting, with precise blasting by detonators, more drilling and less charging, reducing the maximum single-hole charging amount and effectively reducing the blasting vibration speed.

[0017] The preferred technical solution of the present invention is that, in the controlled explosion and shock absorption method, the delay time for detonating adjacent blast holes is set to 10ms-15ms, so as to increase the free surface when subsequent blast holes are detonated. The blast holes are in the form of peripheral holes and auxiliary holes, which can effectively prevent the superposition of vibration velocity peaks generated by each detonation point. The blasting vibration velocity is small, the disturbance to the surrounding rock is reduced, and the blasting effect can be effectively improved.

[0018] The preferred technical solution of the present invention is that in the shock absorption method of controlled explosion and shock absorption holes, while achieving a single-shot blast in a single blast hole, several groups of shock absorption holes are excavated at equal intervals along the entire contour of the new tunnel. The diameter of the shock absorption hole is 108 mm, and the center spacing of the several groups of shock absorption holes is 30 cm. The center of the shock absorption hole is 20 cm away from the center of the peripheral eye on the new tunnel. The depth of the shock absorption hole is determined according to the blasting footage, which can further reduce the maximum amount of explosives in a single hole and increase the shock absorption effect.

[0019] The preferred technical solution of the present invention is that in the controlled blasting rope saw shock absorption method, when achieving a single-hole single-shot blast, a rope saw machine is used instead of a groove, and the rope saw machine is used to cut out the area required for the rope saw groove, thereby avoiding large-volume groove blasting, thereby improving the rock breaking efficiency of subsequent blasting and significantly increasing the shock absorption effect.

[0020] The preferred technical solution of the present invention is that, in the controlled blasting rope saw shock absorption method, the size of the rope saw groove cut by the rope saw machine is adjusted according to the size of the new tunnel face, and a plurality of groups of groove holes are opened on the rope saw groove. The groove depth corresponds to the excavation footage, thereby avoiding large-volume groove blasting and improving subsequent blasting efficiency.

[0021] The preferred technical solution of the present invention is that the controlled explosion and shock-absorbing hole rope saw shock-absorbing method adopts the superposition of three single shock-absorbing methods to reduce the number of required blastholes, with significant shock-absorbing effect, reducing the impact on existing tunnels and ensuring their safety.

[0022] The beneficial effects of the present invention are as follows: when a new tunnel passes under an existing tunnel, the tunnel plane intersection angle is 32.6°, the spacing directly below the underpass section is 6.9m, and the surrounding rock grade is Class VI. To ensure smooth construction of the underpass section, a trial blasting is carried out before the formal underpass. Based on the changes in monitoring indicators such as blasting vibration velocity, settlement, and acceleration obtained from monitoring points arranged on the existing line and the blasting vibration characteristics, the upper steps of the new tunnel are partitioned and blasted in the spatial domain. To ensure the diversity and effectiveness of the partitioned blasting, different controlled blasting methods are required for each partition.

[0023] The blasting vibration velocity control value within the existing line's operating skylight point is used as the dividing point. Symmetrical partitioning is carried out with the intersection of the existing line and the newly built tunnel as the center. Four controlled blasting methods are used. The later the method is listed in the order, the more significant the controlled blasting effect is. That is, the smaller the maximum single-hole charge on the face, the more effective the blasting effect is. The impact of blasting on the existing line is controlled within the specified indicators. Compared with the previous use of only traditional controlled blasting, the blasting vibration velocity at each monitoring point has been significantly reduced. At the same time, the impact on surrounding buildings is also reduced, which can effectively improve construction efficiency.

[0024] At the same time, it can be widely used in controlling the impact of blasting vibration during mining construction when a new tunnel approaches an existing line, preventing adverse effects on the operation of the existing line, thereby avoiding damage to the structure and affecting its durability and safety.

[0025] The present invention provides a construction method for blasting in sections and stages on the steps of a new tunnel, which solves the problem of reducing the impact of blasting on existing lines when a new tunnel is approaching construction, ensures the safety and durability of the existing line structure and improves the efficiency of engineering construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the construction of a new tunnel in sections and segments provided in a specific embodiment of the present invention;

[0027] Figure 2 This is a tunnel face layout diagram when using the controlled explosion and shock absorption hole shock absorption method provided in a specific embodiment of the present invention;

[0028] Figure 3 This is a tunnel face layout diagram when using the controlled explosion rope saw vibration reduction method provided in a specific embodiment of the present invention;

[0029] Figure 4 This is a tunnel face layout diagram provided in a specific embodiment of the present invention when using the explosion-controlled shock-absorbing hole wire saw shock-absorbing method.

[0030] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0031] 1. New tunnels; 2. Existing lines; 3. Monitoring points; 4. Zones for blast-controlled shock-absorbing holes and rope sawing; 5. Zones for blast-controlled shock-absorbing holes and rope sawing; 6. Zones for blast-controlled shock-absorbing holes and rope sawing; 7. Zones for blast-controlled shock-absorbing holes; 8. Shock-absorbing holes; 9. Peripheral holes; 10. Auxiliary holes; 11. Grooving holes; 12. Grooving with rope sawing. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0033] A construction method for sectional blasting on a step in a newly constructed tunnel comprises the following steps:

[0034] Step 1: Set up monitoring points 3 at equal intervals within the existing line 2: Set up several groups of monitoring points 3 on the existing line 2 within a 25D range from the new tunnel 1. The spacing between the groups of monitoring points 3 is 20m. These monitoring points are used to monitor blasting indicators including vibration velocity, settlement, and acceleration during blasting. The monitored blasting indicator is mainly blasting vibration velocity.

[0035] Step 2: Determine the appropriate blasting footage: The blasting footage for the new tunnel 1 is determined based on multiple factors, including steel frame spacing, surrounding rock properties, construction schedule, and blasting vibration limits on the existing line 2. Dynamic adjustments are made during actual excavation to ensure reasonable adjustments within the blasting vibration speed limits on the existing line 2.

[0036] Step 3: Determine blasting parameters for each method: Based on the differences in blasting vibration effects and face preparation conditions of each method, design blasting parameters for different footage conditions and surrounding rock grades, mainly including the number of blastholes of each type, the maximum charge per hole, and blasthole arrangement;

[0037] Step 4. Divide the area according to the blasting data: set up four partitions on each side of the intersection of the new tunnel 1 and the existing line 2, and the four partitions are set symmetrically. The corresponding sizes of the partitions on both sides are different, and different vibration reduction methods are used for the four partitions. Affected by the surrounding geological conditions, the dividing point is the mileage value corresponding to the blasting vibration speed exceeding the blasting vibration speed control value within the operating skylight point of the existing line 2. When constructing within the symmetrical partition range, corresponding preparations can be made according to the already determined partitions.

[0038] When the new tunnel 1 passes under the existing tunnel, the tunnel plane intersection angle is 32.6°, the spacing directly below the underpass section is 6.9m, and the surrounding rock grade is grade VI. In order to ensure the smooth construction of the underpass section, a trial blasting is carried out before the formal underpass. According to the changes in monitoring indicators such as blasting vibration velocity, settlement, acceleration, etc. obtained at the monitoring point 3 arranged on the existing line 2 and the blasting vibration characteristics, the upper steps of the new tunnel 1 are partitioned and blasted in the spatial domain. In order to ensure the difference and effectiveness of the partitioned blasting, different controlled blasting methods are required for each partition; the blasting vibration velocity control value within the operating skylight point of the existing line 2 is used as the dividing point, and the existing line 2 and the new tunnel are separated by a vertical axis. The tunnel is symmetrically divided with the intersection of Road 1 as the center, and four controlled blasting methods are adopted. The later the method is listed in the order, the more significant the controlled blasting effect is, that is, the smaller the maximum single-hole charge on the face is, and the impact of blasting on the existing line 2 is controlled within the specified indicators. The blasting vibration velocity at each monitoring point is significantly reduced compared with the previous use of traditional controlled blasting. At the same time, the impact on surrounding buildings is also weakened, which can effectively improve construction efficiency. At the same time, it can be widely used in controlling the impact of blasting vibration in mining construction when the new tunnel 1 approaches the existing line 2, to prevent adverse effects on the operation of the existing line 2, so as to avoid damage to the structure and affect its durability and safety.

[0039] As a possible implementation method of this scheme, preferably, in step 1, several groups of monitoring points 3 are arranged at equal distances in the tunnel, and their spacing is adjusted according to the angle between the newly built tunnel 1 and the existing line 2. The larger the angle, the larger the spacing, so as to adapt to the construction requirements of different newly built tunnels 1 when approaching the existing line 2, and has a wide range of applications.

[0040] As a possible implementation of this scheme, preferably, in step 4, the sign of the appearance of the demarcation point is that under the same blasting parameters, the following three groups of data appear: the first group of data is qualified but close to the blasting vibration speed control value, the second and third groups of blasting vibration speeds have exceeded the blasting vibration speed control value, and the third group of data is a verification group for the second group of data. At this time, the demarcation mileage is taken as the mileage corresponding to the second group of blasting. The demarcation point is combined with different blasting vibration reduction methods to control the blasting construction and ensure the blasting effect.

[0041] As a possible implementation method of the present scheme, preferably, in step 4, the four partitions are respectively explosion-controlled shock-absorbing hole rope saw method partition 4, explosion-controlled rope saw method partition 5, explosion-controlled shock-absorbing hole method partition 6 and explosion-controlled method partition 7, and the corresponding shock absorption methods are explosion-controlled shock-absorbing hole rope saw shock absorption method, explosion-controlled rope saw shock absorption method, explosion-controlled shock-absorbing hole shock absorption method and explosion-controlled shock absorption method. Different shock absorption methods are adopted for different partitions to ensure good blasting effect while reducing vibration and line safety of existing tunnels and not affecting the normal operation of existing tunnels.

[0042] As a possible implementation method of this scheme, preferably, the controlled explosion and shock absorption method adopts high-precision millisecond-level electronic digital detonators to implement single-hole and single-shot submersible controlled blasting, with precise blasting by detonators, more drilling and less charging, reducing the maximum single-hole charging amount and effectively reducing the blasting vibration speed.

[0043] As a possible implementation method of this scheme, preferably, in the controlled explosion and shock absorption method, the delay time for detonating adjacent blast holes is set to 10ms-15ms, so as to increase the free surface when subsequent blast holes are detonated, wherein the blast holes are in the form of peripheral holes 9 and auxiliary holes 10, which can effectively prevent the superposition of vibration velocity peaks generated by each detonation point, and the blasting vibration velocity is small, reducing the disturbance to the surrounding rock, and can effectively improve the blasting effect.

[0044] As a possible implementation of this scheme, preferably, in the shock-absorbing method of controlled explosion and shock-absorbing holes, under the condition of achieving a single-hole single-shot blast, several groups of shock-absorbing holes 8 are excavated at equal intervals along the entire circle contour of the newly built tunnel 1, the diameter of the shock-absorbing holes 8 is 108 mm, and the center spacing of several groups of shock-absorbing holes 8 is 30 cm, the center of the shock-absorbing hole 8 is 20 cm away from the center of the peripheral eye 9 on the newly built tunnel 1, and the depth of the shock-absorbing hole 8 is determined according to the blasting footage, which can further reduce the maximum amount of explosives in a single hole and increase the shock-absorbing effect.

[0045] As a possible implementation method of this scheme, preferably, in the controlled blasting rope saw shock absorption method, when achieving a single-hole single-shot blast hole, a rope saw machine is used instead of a groove, and the rope saw machine is used to cut out the required area of ​​the rope saw groove 12, avoiding large-volume groove blasting, thereby improving the rock breaking efficiency of subsequent blasting and significantly increasing the shock absorption effect.

[0046] As a possible implementation method of this scheme, preferably, in the controlled blasting rope saw shock absorption method, the size of the rope saw groove 12 cut by the rope saw machine is adjusted according to the size of the heading face of the newly built tunnel 1, and a plurality of groups of groove holes 11 are opened on the rope saw groove 12, and the groove depth corresponds to the excavation footage, thereby avoiding large-volume groove blasting and improving subsequent blasting efficiency.

[0047] As a possible implementation method of this scheme, preferably, the controlled explosion and shock-absorbing hole rope saw shock-absorbing method adopts the superposition of three single shock-absorbing methods to reduce the number of required blast holes, with significant shock-absorbing effect, reducing the impact on existing tunnels and ensuring their safety.

[0048] The present invention is described through preferred embodiments. Those skilled in the art will appreciate that various modifications or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. The present invention is not limited to the specific embodiments disclosed herein; other embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A construction method for sectional blasting on the upper steps of a newly constructed tunnel, characterized by: The following steps are involved: Step 1, setting monitoring points (3) at equal distances within the existing line (2): several groups of monitoring points (3) are arranged on the existing line (2) within a 25D range from the new tunnel (1), with the spacing between the several groups of monitoring points (3) being 20m, for monitoring blasting indicators including vibration velocity, settlement and acceleration during blasting, wherein the monitored blasting indicator is mainly blasting vibration velocity; Step 2: Determine the appropriate blasting footage: Determine the (1) blasting footage for the new tunnel based on various factors, including the spacing between steel frames, surrounding rock properties, construction period control, and existing lines (2) blasting vibration limits, and make dynamic adjustments during actual excavation, making reasonable adjustments within the existing lines (2) blasting vibration speed limits; Step 3: Determine blasting parameters for each method: Based on the differences in blasting vibration effects and face preparation conditions of each method, design blasting parameters for different footage conditions and surrounding rock grades, mainly including the number of blastholes of each type, the maximum charge per hole, and blasthole arrangement; Step 4: Divide the area according to the blasting data: set up four zones on each side of the intersection of the new tunnel (1) and the existing line (2), and the four zones are symmetrically arranged. The corresponding sizes of the zones on both sides are different, and different vibration reduction methods are used for the four zones. Affected by the surrounding geological conditions, the demarcation point is the mileage value corresponding to the time when the blasting vibration speed exceeds the blasting vibration speed control value within the operating skylight point of the existing line (2). When constructing within the symmetrical zone range, corresponding preparations can be made according to the already determined zones; In step 1, a plurality of groups of monitoring points (3) are arranged at equal distances in the tunnel, and the intervals between them are adjusted according to the angle formed between the newly constructed tunnel (1) and the existing line (2), and the larger the angle, the larger the interval; In step 4, the four zones are respectively the explosion-controlled shock-absorbing hole rope saw method zone (4), the explosion-controlled rope saw method zone (5), the explosion-controlled shock-absorbing hole method zone (6) and the explosion-controlled method zone (7), and the corresponding shock-absorbing methods are the explosion-controlled shock-absorbing hole rope saw shock-absorbing method, the explosion-controlled rope saw shock-absorbing method, the explosion-controlled shock-absorbing hole shock-absorbing method and the explosion-controlled shock-absorbing method.

2. A construction method for zoning and segmented blasting on the upper steps of a newly constructed tunnel according to claim 1, characterized in that: In step 4, the sign of the appearance of the dividing point is that under the same blasting parameters, the following three groups of data appear: the first group of data is qualified but close to the blasting vibration speed control value, the second and third groups of blasting vibration speeds have exceeded the blasting vibration speed control value, and the third group of data is the verification group of the second group of data. At this time, the dividing mileage is taken as the mileage corresponding to the second group of blasting.

3. A construction method for zoning and segmented blasting on the upper steps of a newly constructed tunnel according to claim 1, characterized in that: The controlled explosion and shock absorption method adopts high-precision millisecond-level electronic digital detonators to implement single-hole, single-shot submersible controlled blasting, with precise blasting by detonators, more drilling and less charging.

4. A construction method for zoning and segmented blasting on the upper steps of a newly constructed tunnel according to claim 1, characterized in that: In the explosion control and shock absorption method, the delay time of detonation of adjacent blast holes is set to 10ms-15ms, so as to increase the free surface when subsequent blast holes are detonated, wherein the blast holes are in the form of peripheral holes (9) and auxiliary holes (10).

5. The construction method for zoning and segmented blasting on the upper steps of a newly constructed tunnel according to claim 1 is characterized by: In the controlled explosion and shock absorption hole shock absorption method, under the condition of achieving a single-hole single-shot blast, a plurality of groups of shock absorption holes (8) are excavated at equal intervals along the entire contour of the newly built tunnel (1), the diameter of the shock absorption holes (8) is 108 mm, and the center spacing of the plurality of groups of shock absorption holes (8) is 30 cm. The center of the shock absorption hole (8) is 20 cm away from the center of the peripheral hole (9) on the newly built tunnel (1), and the depth of the shock absorption hole (8) is determined according to the blasting footage.

6. A construction method for zoning and segmented blasting on the upper steps of a newly constructed tunnel according to claim 1, characterized in that: In the controlled explosion rope saw vibration reduction method, when achieving a single blast hole with a single blast, a rope saw machine is used instead of a groove, and the rope saw machine is used to cut out the area required for the rope saw groove (12).

7. A construction method for zoning and segmented blasting on the upper steps of a newly constructed tunnel according to claim 1, characterized in that: In the controlled explosion rope saw vibration reduction method, the size of the rope saw groove (12) cut by the rope saw machine is adjusted according to the size of the tunnel face of the newly built tunnel (1), and a plurality of groups of groove holes (11) are opened on the rope saw groove (12).

8. The construction method for zoning and segmented blasting on the upper steps of a newly constructed tunnel according to claim 1, characterized in that: The described explosion-controlled shock-absorbing hole rope saw shock-absorbing method adopts the superposition of three single shock-absorbing methods to reduce the number of required blast holes.

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