A method for excavating a deep foundation pit of a dam calcareous cemented sand and gravel

Abstract

The application provides a dam calcareous cemented sand gravel deep foundation pit excavation method, through repeated forms, the calcareous cemented sand gravel is drilled and grouted in batches, the cracks in the drilling depth range are filled and combined into a whole, after repeated drilling to the design elevation, the explosives are filled and loose blasting is carried out, and then excavation is carried out. The method solves the problems of great difficulty in excavation and removal, and the problems of blasting pressure relief in the form of drilling and blasting in the process of excavation of the calcareous cemented sand gravel deep foundation pit, improves the construction efficiency, and saves the cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water conservancy and hydropower engineering construction, in particular to a dam calcareous cemented sand and gravel deep foundation pit excavation method. BACKGROUND

[0002] In the water conservancy and hydropower engineering construction, in the dam foundation pit or downstream apron foundation pit excavation, the foundation pit needs to be excavated to the design rock elevation position of the foundation surface. In the original river channel, under the long-term action of natural factors, pebbles or gravels and minerals with cementing effect, such as calcium, iron and silicon, are condensed into calcareous cemented bodies with certain strength through physical and chemical changes.

[0003] In the foundation pit excavation, the thick calcareous cemented sand and gravel layer above the rock layer needs to be excavated. Since the calcareous cemented sand and gravel is tightly combined, it cannot be directly excavated by the excavator, and it can only be excavated by the hydraulic hammer, which can only remove a little at a time. Compared with the deep foundation pit excavation of large amount of calcareous cemented stone, the efficiency is low and the construction progress is slow.

[0004] If the drilling and blasting method is directly used, since there are gaps between the cemented stones, when drilling to a certain depth, the wind at the drill bit position will leak out from the gaps between the cemented stones, and the dross cannot be blown out along the drill rod. In addition, some calcareous cemented sand and gravel contains large boulders, and when drilling to a certain depth, the drill will be repeatedly stuck. At this time, the drilling efficiency is greatly reduced. Even if blasting is carried out at this time, due to the large gap between the calcareous cement, a part of the energy will leak out from the gap at the moment of detonation, and the effect of shaped charge blasting cannot be achieved.

[0005] How to use an innovative method to improve the drilling speed and overall blasting excavation efficiency is a problem that water conservancy and hydropower engineering technicians need to solve. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a dam calcareous cemented sand and gravel deep foundation pit excavation method which reduces the difficulty of drilling, improves the blasting efficiency, and solves the problems of difficult direct excavation or removal of calcareous cemented sand and gravel layer and easy leakage of drilling blasting energy.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a dam calcareous cemented sand and gravel deep foundation pit excavation method, comprising the following steps:

[0008] Step 1) Preparation, excavate the slope around the deep foundation pit to the original elevation position, level the excavation surface of the deep foundation pit, and provide a drilling platform;

[0009] Step 2) measuring the line, laying out holes on the working platform, drilling holes arranged in a quincunx and numbered, marking the drilling depth data;

[0010] Step 3) according to the number and preset drilling sequence, drilling the hole once, the drilling direction is inclined upstream, and the drilling is stopped when the preset first stroke or the serious jamming cannot continue drilling, the drill bit is lifted and inserted into the flower pipe, and the hole is sealed with mortar;

[0011] Step 4) after a certain number of holes are drilled, start grouting each hole through external equipment and flower pipe, the grouting material is water, cement and sand, the cement is slag portland cement, the sand is fine sand or silt with a fineness modulus less than 2.2, the ratio of cement and silt is cement: silt = 1:1~1:4 by weight, the ratio of water and dry material for mixing slurry is water: dry material = 6:1~1:1 by weight, the grouting pressure is 0.3~0.5MP, the slurry concentration gradually changes from dilute to thick during grouting, the ratio is adjusted in real time according to the slurry condition and grouting pressure; under the preset pressure, the grouting pressure of the grouting hole gradually increases, and finally hovers at a high value, the slurry and back slurry are balanced, and the slurry surface in the slurry tank for stirring slurry no longer falls, and the grouting is finished;

[0012] Step 5) after standing for a certain time, according to the number and preset drilling sequence, secondary drilling is carried out at the original marked hole position, the drilling depth exceeds the drilling depth of the first drilling, and the drilling is stopped when the preset depth or serious jamming cannot continue drilling, the drill bit is lifted and the lower flower pipe is inserted;

[0013] Step 6) for the holes that do not reach the final depth data of the marked drilling, continue grouting according to the method of step 4); repeat steps 5) and 6) until the drilling depth reaches the final depth data;

[0014] Step 7) when all the holes reach the designed final depth data, charge and blast.

[0015] As described above, in step 2), the same row spacing of the hole layout is 2m-3m, and the row spacing is 1.4m-2m.

[0016] As described above, in step 3), during the first drilling, the drilling direction is inclined upstream by 80°-90°, the preset first stroke is 1m-1.5m, and the flower pipe material is PVC material.

[0017] As described above, the drill used for drilling is a full pneumatic down-the-hole drill.

[0018] As described above, in step 6, the number of times of repeating steps 5) and 6) is 2-4 times.

[0019] As described above, in step 7), the explosive is selected as emulsified explosive, the layered interval charging is adopted, the bamboo sheet is used for guiding, the length of the hole blocking should be greater than the minimum resistance shoe, the area of not less than one third of the blast hole depth is filled with fine soil or sand, the non-electric section initiation system is adopted, and the millisecond thunder micro-difference initiation is adopted.

[0020] As described above, in step 1), the slope is excavated, and the protection is simultaneously completed.

[0021] As described above, in step 4, the slag portland cement has a mark of PSA325.

[0022] As described above, the diameter of the flower pipe is 70cm-90cm.

[0023] As described above, in the process of once drilling, the upper 50cm of the flower pipe is not provided with holes, and the holes are provided below 50cm.

[0024] Compared with the prior art, the present application has outstanding substantial features and significant progress, specifically, the present application has the following advantages:

[0025] 1. According to the characteristics that the cemented stones are tightly cemented but have gaps between them, short footage drilling is first carried out at a certain interval, then water, cement and sand are stirred at a certain proportion to fill the gaps and combine into a whole, the original grouting hole position is drilled again to grout again, and the drilling is repeated several times to reach the designed reserved elevation, then the loosening blasting is carried out by using explosives, and the excavated materials are loaded on the transport vehicle by the excavator and transported to the designated waste dump for stacking. Since the cemented stones have high cementing strength and cannot be directly excavated by the excavator, if the hydraulic hammer is used for chiseling, only a little can be chiseled each time, and the progress cannot meet the requirements for large amount of calcareous cemented stone deep foundation pit excavation, and the method can improve the construction progress and save the cost.

[0026] 2. The drilling is carried out at an inclined angle, and when grouting, the slurry can flow out along the flower pipe hole by gravity to fully fill the pores distributed near the flower pipe hole.

[0027] 3. After drilling and before grouting, the flower pipe is inserted into the drilling hole and the hole is sealed, which can prevent the collapse of the broken slag caused by long time standing of the drill bit after being lifted to block the drilling hole.

[0028] 4. The proportion of grouting is adjusted step by step according to the actual situation to adapt to the site situation and achieve good grouting effect.

[0029] 5. The end of grouting depends on the monitoring of multiple indexes such as grouting pressure, balance state maintenance and slurry height maintenance, which can accurately judge whether the grouting degree is sufficient and whether the gaps are fully grouted.

[0030] 6. The drilling and grouting can be performed crosswise to improve efficiency.

[0031] 7. The method has higher construction efficiency than the traditional hydraulic hammer excavation method, and has lower cost than the method of simultaneously using multiple hydraulic hammers.

[0032] 8. The method using drilling and grouting reduces noise and dust pollution, and achieves the effect of green and environmentally-friendly construction. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a hole position and drilling depth diagram of the dam calcareous cemented sand gravel deep foundation pit excavation method in the application.

[0034] Figure 2 is a hole position distribution diagram in the dam calcareous cemented sand gravel deep foundation pit excavation method in the application.

[0035] In the figure, 1. Same row hole distance L; 2. Flower tube; 3. Primary grouting hole; 4. Secondary reaming grouting hole; 5. Hole position bottom elevation; 6. Third reaming grouting hole; 7. Shaped blast hole; 8. Drilling hole; 9. Row distance W; 10. Upstream temporary cofferdam. DETAILED DESCRIPTION

[0036] The technical solutions of the application will be further described in detail through specific embodiments.

[0037] As shown in Figure 1 and Figure 2 , a calcareous cemented sand gravel deep foundation pit excavation method comprises the following steps:

[0038] S1, excavate the slope around the deep foundation pit to the original elevation position of the foundation pit, i.e. the hole position bottom elevation 5 in the figure, and leave an upstream temporary cofferdam 10 upstream, and excavate while protecting to prevent the slope from falling and injuring construction personnel during the subsequent foundation pit excavation process.

[0039] S2, use an excavator to roughly level the foundation pit excavation surface and clean the slag out of the work surface to provide a work platform for drilling.

[0040] S3, measure and mark, a surveyor marks the foundation pit excavation line with red paint according to the design requirements, and then marks the drilling position at a position 1m away from the excavation line, the same row hole distance L1 is 2.4m, the row distance W9 is 1.5m, and the hole is arranged in a plum blossom shape, and the point number and the final depth record required for drilling are recorded, in other embodiments, the hole distance is 2-3m, and the row distance is 1.4-2m.

[0041] S4, use the full wind YQ100 down-the-hole drill in the hole mark position for drilling, one drilling 8 direction is 80° upstream tilt, the diagram is a one-time grouting hole 3, drilling is generally about 1m or deeper, or serious jamming cannot continue to drill, then the drill bit is lifted, and then a Φ75 PVC pipe 2 is inserted into the hole, the first pipe is not provided with a hole in the upper 50cm range, and the pipe hole is provided below 50cm, and the hole mouth PVC pipe is sealed with mortar, the PVC pipe is inserted to prevent the hole from being left for a long time after the drill bit is lifted, the debris collapses and the subsequent grouting.

[0042] S5, move the drill, continue to drill and insert the PVC pipe at the other marked positions, and then seal the hole around the pipe.

[0043] S6, after a certain number of holes are drilled, grouting is started using a mortar pump, the grouting material is water, cement and sand, the cement is slag portland cement with a mark PSA325, the sand is fine sand or silt with a fineness modulus of less than 2.2, the ratio of cement to silt is 1:1 to 1:4 by weight, and the ratio of water to dry material for mixing the slurry is 6:1 to 1:1 by weight, the grouting pressure is 0.3 to 0.5 MP, and the slurry concentration is gradually changed from dilute to thick during grouting, and the ratio is adjusted in real time according to the slurry consumption and grouting pressure.

[0044] S7, the grouting end standard: under the design pressure, the grouting pressure of the grouting hole gradually increases, finally fluctuates at a high value, the slurry and back slurry remain balanced, and the slurry surface in the stirred slurry tank no longer decreases, and the grouting operation can be completed.

[0045] S8, in this construction, drilling and grouting can be performed alternately, after 7 days of grouting at the hole position, the drill can be erected at the original marked hole position, the drill is vertical, the drill is drilled again at the original hole position, the drilling depth reaches the depth of the first drilling, the drilling continues, reaches the design depth or repeatedly jams again, cannot continue to drill, the drill is lifted, a second time drilling grouting hole 4 is formed, and the PVC pipe is lowered.

[0046] S9, after the second time drilling, according to S6, the grouting is performed again for those that do not reach the design hole depth.

[0047] S10, after the grouting reaches a certain strength, according to S9, the hole drilling is performed again for those that do not reach the design hole depth, according to the above construction steps, until the design depth is reached, in this embodiment, the final three times drilling hole is formed, the three times drilling grouting hole 6 reaches the design elevation.

[0048] S11, when the drilling depth reaches the designed depth, the shaped blast hole 7 is formed, the charge blasting is carried out, the explosive is emulsion explosive, according to the situation, layered interval charging can be used, bamboo sheet is used for guiding, the length of the blast hole should be greater than the minimum resistance shoe, and should not be less than 1 / 3 of the blast hole depth, the blast hole is filled with fine soil or sand, a non-electric section initiation system is used, and millisecond delay detonator is used for differential initiation.

[0049] S12, in the blasting stage, the warning and personnel protection work should be well done.

[0050] Through the above excavation method, the problems of high hardness caused by cementation and difficult to excavate or remove, and too many gaps leading to blasting pressure relief during conventional drilling blasting can be solved, so that the difficulty of engineering construction is reduced, and the efficiency is improved.

[0051] Finally, it should be noted that: the above has made a detailed description of the preferred embodiments of the patent, but the patent is not limited to the above embodiments, within the knowledge range of ordinary skill in the art, various changes can be made without departing from the purpose of the patent.

Claims

1. A method of deep excavation of a calcareous cemented sand and gravel dam foundation, characterized in that: The method comprises the following steps: Step 1) preparation, the side slope around the deep foundation pit is excavated to the original elevation position, the excavation surface of the deep foundation pit is leveled, and a drilling operation platform is provided; Step 2) measurement and line laying, line laying and hole arrangement are performed on the operation platform, the holes are arranged in a quincunx shape and numbered, and the drilling depth data are marked; Step 3) according to the number and preset drilling sequence, one-time drilling is performed on the hole arrangement position, the drilling direction is inclined upstream, the drilling is stopped when the preset first stroke or the drill is seriously stuck, the drill bit is lifted and inserted into the flower pipe, and the hole mouth is sealed with mortar; during the one-time drilling, the upper 50 cm of the flower pipe is not provided with a hole, and the hole below 50 cm is provided with a flower pipe hole; Step 4) after a certain number of holes are drilled, one-time grouting is performed on each hole through external equipment and the flower pipe, the grouting material is water, cement and sand, the cement is slag Portland cement, the sand is fine sand or silt with a fineness modulus less than 2.2, the cement and silt are in a weight ratio of cement:silt = 1:1-1:4, the mixing ratio of the slurry is water:dry material = 6:1-1:1, the grouting pressure is 0.3-0.5 MP, the slurry concentration is gradually changed from dilute to thick during grouting, the ratio is adjusted in real time according to the slurry consumption and the grouting pressure, the grouting pressure gradually increases at the preset pressure, finally hovers at a high value, the slurry output and return are balanced, and the slurry surface in the slurry tank for stirring the slurry no longer drops, and the grouting is completed; Step 5) after a certain time, according to the number and preset drilling sequence, secondary drilling is performed at the original marked hole position, the drilling depth exceeds the drilling depth of the one-time drilling, and the drilling is stopped when the preset depth or the drill is seriously stuck, the drill bit is lifted and the flower pipe is lowered; Step 6) for the holes that do not reach the final depth data of the marked drilling, the grouting is continued according to the mode of step 4), and step 5) is repeated until the drilling depth reaches the final depth data; Step 7) when all the holes reach the designed final depth data, the blasting is performed.

2. The method of claim 1, wherein: In step 2), the same row spacing of the hole arrangement is 2-3 m, and the row spacing is 1.4-2 m.

3. The method of claim 2, wherein: In step 3), during the one-time drilling, the drilling direction is inclined upstream by 80-90 degrees, the preset first stroke is 1-1.5 m, and the flower pipe is made of PVC material.

4. The method of claim 3, wherein: The drilling machine used in the drilling is a full pneumatic down-the-hole drill.

5. The method of claim 4, wherein: In step 6, the number of times of repeating steps 5) and 6) is 2-4 times.

6. The method of claim 5, wherein: In step 7), the emulsion explosive is selected, the layered interval charging is adopted, the bamboo sheet is introduced, the stemming length of the blast hole should be greater than the minimum resistance shoe, the area not less than one-third of the blast hole depth is filled with fine soil or sand, the non-elevator section initiation system is adopted, and the millisecond thunder micro-difference initiation is adopted.

7. The method of claim 1, wherein: In step 1), the slope excavation is protected at the same time.

8. The method of claim 1, wherein the deep foundation pit excavation of calcareous cemented sand and gravel of a dam is characterized by: In step 4, the slag Portland cement has a mark of PSA325.

9. The method of claim 6, wherein: The diameter of the flower pipe is 70-90 cm.

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