Rotary drilling dry-method hole-forming construction method under waterproof silt geological condition

Abstract

The invention discloses a rotary drilling dry-method hole-forming construction method under a waterproof silt geological condition. The rotary drilling dry-method hole-forming construction method comprises the following steps: step 1, construction preparation; 2, according to the depth of the pile; 3, after the pile bottom anti-gushing reinforcing layer is solidified; 4, after the steel casing is inserted, a rotary drilling machine is adopted for drilling; 5, the reinforcement cage is hoisted and placed; 6, concrete is poured, and vibration is conducted while pouring is conducted; 7, after the cast-in-place pile is constructed, the steel casing is pulled out for turnover use; the problems that a traditional slurry wall protection complete device occupies a site and the slurry monitoring work in the construction process is tedious are solved, and the conditions that a hole body is unstable and the bottom is settled too thick due to the dead time process after hole forming are avoided; and meanwhile, overexcavation and pouring hyper-square caused by drill suction and bottom reverse surging generated by construction of the rotary drilling drill under the silt geological condition can be effectively solved, the pile forming quality of a pouring pile is efficiently controlled, the cost is saved, and the construction efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pore-forming construction, in particular to a rotary drilling dry pore-forming construction method under impermeable silt geological conditions. BACKGROUND

[0002] As a common foundation structure of building engineering, the borehole cast-in-place pile has various pore-forming methods. For projects with fast construction period requirements, a rotary drilling rig is often selected for pore-forming.

[0003] The rotary drilling rig is a construction machine suitable for pore-forming operation in building foundation engineering, and has the advantages of fast pore-forming speed, less pollution, strong mobility, etc. It is often used in combination with bentonite mud wall protection in sand, clay, silt and other soil layers, and is widely used in municipal construction, highway bridges, technology, civil buildings, underground continuous walls, water conservancy and anti-seepage slope protection and other foundation construction. The conventional pore-forming method is mud wall protection pore-forming construction. The mud wall protection pore-forming construction needs to set up a complete mud manufacturing device and a circulating storage device, which occupies a large area of site, the process construction mud index detection work is tedious, and more time and manpower are consumed. The process connection requirements are high, and the stagnant time process is easy to cause the hole bottom sediment to be too thick, affecting the pile quality at the hole bottom. When the rotary drilling rig is used for construction in some flowable silt geological layers, the phenomena of drill suction, hole shrinkage and hole collapse are easy to occur, causing engineering quality problems and cost increase. SUMMARY

[0004] The purpose of the present application is to provide a rotary drilling dry pore-forming construction method under impermeable silt geological conditions, to solve the problem that when the rotary drilling rig is used for construction, the phenomena of drill suction, hole shrinkage and hole collapse are easy to occur, causing engineering quality problems and cost increase.

[0005] To achieve the above purpose, the present application provides the following technical scheme: a rotary drilling dry pore-forming construction method under impermeable silt geological conditions, comprising the following steps: Step 1, construction preparation, first hardening treatment is performed on the construction site, then the ground after hardening treatment is leveled, then the construction related parameters are determined, and the pile position is measured and placed; Step 2, according to the depth of the pile, a pile bottom anti-overflow reinforced layer is formed below the pile bottom by using grouting reinforcement measures, and a pore-forming buffer layer is formed between the pile bottom and the pile bottom anti-overflow reinforced layer. The mud used for grouting comprises the following components by weight: MOF-5 20-25 parts, Portland cement 20-25 parts, polypropylene fiber 10-12 parts, early strength agent 3-5 parts, and water 80-90 parts. In the grouting process, an ultrasonic vibration rod is inserted into the grouted mud for vibration treatment, and vibration is performed while grouting, The preparation method of the mud comprises the following steps: S1. Dissolve a certain proportion of the early strength agent in a small amount of water, and then add MOF-5 in proportion to obtain a mixture A; S2, mixing Portland cement, polypropylene fiber and remaining water to obtain mixture B; S3, adding mixture A to mixture B, stirring evenly to obtain the slurry; Step 3: After the anti-surge reinforcement layer at the bottom of the pile solidifies, align the pile position and insert the steel casing into the silt geology; Step 4. After the steel casing is inserted, use a rotary drilling machine to drill. When drilling, first use light pressure and slow rotation, then gradually increase the rotation speed and rotation pressure. During the drilling process, the footage speed is controlled according to the geological conditions: when drilling from hard strata to soft strata, the drilling speed is accelerated; when the soft stratum becomes hard stratum, the speed is reduced and the advance is slow; in strata that are prone to shrinkage after hole formation, the number of hole sweeps should be appropriately increased to prevent shrinkage; high-speed drilling is used for hard plastic layers to improve drilling efficiency; slow drilling is used for sand layers, and the mud density and viscosity are appropriately increased. Drill to the designed pile bottom elevation, and then discharge slag and clean the hole; Step 5: Hang the steel cage. When installing the steel cage, align it with the hole, hang it straight and steady, and slowly lower it to avoid hitting the hole wall. After the steel cage sinks to the designed position, fix it immediately to prevent it from moving; Step 6: pouring concrete. A steel conduit is used for concrete discharge. The bottom of the steel conduit is 30cm-40cm away from the bottom of the pile. A funnel is installed on the top of the steel conduit. A round steel plate plug with a hook is installed on the neck of the funnel to temporarily block the opening of the steel conduit. After a sufficient amount of concrete is filled in the funnel, the steel plate plug is lifted with a steel wire rope and concrete is poured into the funnel at the same time. Under the action of gravity, the concrete is poured into the pile along the steel conduit, and vibration is performed while pouring. Step 7: After the bored pile construction is completed, before the concrete begins to set, pull out the steel casing for recycling.

[0006] The length of the steel casing is greater than the length of the bored pile, the top of the steel casing is higher than the top of the bored pile, the bottom of the steel casing exceeds the bottom of the bored pile, and the bottom of the steel casing extends into the borehole buffer layer.

[0007] The steel casing is driven into the muddy geology by a pile driver.

[0008] The drilling speed of the rotary drilling machine is 0.2-0.4 m / min, and the rotation speed of the rotary drilling machine is 30-50 rpm.

[0009] The inner diameter of the steel casing is larger than the diameter of the cast-in-place pile, and the steel casing is made of Q345B steel.

[0010] The diameter of the rotary excavator drill bit is smaller than the inner diameter of the steel casing, and the diameter of the rotary excavator drill bit is equal to the diameter of the cast-in-place pile.

[0011] The length of the steel casing is L1, the length of the cast-in-place pile is L4, and the length of the hole-forming buffer layer is L3, and L3+L4<L1.

[0012] The method for hardening the construction site is as follows: first, 10cm-thick fine soil is laid on the surface of the construction site, and then the 10cm-thick fine soil is tamped to form a base layer, then a layer of 3cm-thick fine sand is laid on the base layer, and the 3cm-thick fine sand is tamped to achieve the purpose of hardening the construction site.

[0013] The method for deslagging and hole cleaning is as follows: during drilling, the flushing record is kept, the hole bottom elevation is calculated using the flushing depth at the end of the hole, and the measuring rope is used for rechecking, when the rotary drill hole reaches the design elevation, after the end hole inspection, hole cleaning is performed; after hole cleaning, the well bottom elevation is 20cm-30cm lower than the design pile bottom elevation.

[0014] The inner diameter D of the steel casing is calculated according to the following formula: D=R+0.01(R+L4) Wherein, R is the design diameter of the cast-in-place pile, and L4 is the design length of the cast-in-place pile.

[0015] Compared with the prior art, the beneficial effects of the present application are: The present application adopts a full-length steel casing as a hole-forming support, which replaces the mud wall protection function to perform dry hole-forming operation, and after construction, the steel casing is pulled out before the cast-in-place pile is initially set, and is used again, so that rapid construction is achieved, and the site occupation and the complicated mud monitoring work in the construction process are reduced; before the cast-in-place pile is constructed, grouting reinforcement measures are used in a certain range below the bottom of the steel casing to form a pile bottom anti-overflow reinforcement layer, and after the strength of the pile bottom anti-overflow reinforcement layer meets the requirements, the steel casing is inserted and driven, so as to prevent the overflow of the bottom silt during the hole-forming process, avoid the expansion of the bottom of the steel casing and the waste of the subsequent cast-in-place pile; and a section of the steel casing is reserved between the bottom of the cast-in-place pile and the pile bottom anti-overflow reinforcement layer, forming a hole-forming buffer layer, which plays a buffering role when the rotary drill reaches the pile bottom, avoiding the damage of the drill bit to the pile bottom anti-overflow reinforcement layer at the bottom of the steel casing; the problems of site occupation and complicated mud monitoring work in the construction process of the traditional mud wall protection complete device are solved, and the instability of the hole body and the excessive thickness of the bottom settlement during the standby time after hole-forming are avoided; at the same time, the over-excavation caused by the suction of the rotary drill and the overflow of the bottom in the silt geological conditions is effectively solved, the pile-forming quality of the cast-in-place pile is efficiently controlled, the cost is saved, and the construction efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only represent some of the embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0017] Figure 1 It is a schematic view of the front view structure of the present application. Figure 2 It is a schematic view of the top view structure of the reinforcing layer of the present application.

[0018] In the figure: 1, pile bottom anti-overflow reinforcing layer; 2, hole-forming buffer layer; 3, cast-in-place pile; 4, steel casing. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments only represent some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort belong to the scope of protection of the present application.

[0020] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0021] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be understood broadly, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solutions.

[0022] Embodiment 1 Please refer to Figure 1-2 The present application provides a technical solution: a dry hole-forming construction method of rotary drilling under impermeable silt geological conditions, comprising the following steps: Step 1, construction preparation, first hardening treatment is performed on the construction site, then the ground after hardening treatment is leveled, then the construction related parameters are determined, and the pile position is measured and placed; According to the geological conditions, when the steel casing 4 is pressed into the ground, especially when it penetrates the gravel layer, it will be deformed, and the rotary drilling machine will inevitably collide with the steel casing 4 when it lifts the rotary drill bit. If the lower opening of the steel casing 4 is deformed too much, it will be more likely to cause damage to the rotary drill bit. To reduce the wear and tear of the steel casing 4 and the drill bit, the inner diameter of the steel casing 4 is larger than the diameter of the cast-in-place pile 3, and the steel casing 4 is made of Q345B steel.

[0023] Step 2, according to the depth of the pile, a layer of anti-overflow reinforcement layer 1 is formed at the bottom of the pile by grouting reinforcement measures, the height of the anti-overflow reinforcement layer 1 is L2, and a hole forming buffer layer 2 is formed between the bottom of the pile and the anti-overflow reinforcement layer 1; The length of the steel casing 4 is greater than the length of the cast-in-place pile 3, the top of the steel casing 4 is higher than the top of the cast-in-place pile 3, the bottom of the steel casing 4 exceeds the bottom of the cast-in-place pile 3, and the bottom of the steel casing 4 extends into the hole forming buffer layer 2; The length of the steel casing 4 is L1, the length of the cast-in-place pile 3 is L4, and the length of the hole forming buffer layer 2 is L3, L3+L4 The steel casing 4 in this application is a full-length casing. In the dry construction of rotary drilling, the rigidity of the steel casing 4 resists the surrounding soil pressure to avoid hole expansion and shrinkage, plays a safety role in hole forming, and at the same time plays a guiding and fixing role in rotary drilling hole forming, ensuring the verticality. It replaces the role of mud wall, reduces the occupation of site and the tedious work of process mud monitoring, and also avoids the problem of excessive thick bottom sediment caused by long stagnation after hole forming. After the cast-in-place pile 3 is constructed, the steel casing 4 is pulled out before initial setting, and is used again; The anti-overflow reinforcement layer 1 is set below the bottom elevation of the steel casing 4. Before the construction of the steel casing 4, grouting reinforcement measures are taken within a certain range below the bottom of the steel casing 4 to form the anti-overflow reinforcement layer 1. After the strength of the anti-overflow reinforcement layer 1 meets the requirements, the steel casing 4 and the rotary drilling hole are inserted and drilled. When the rotary drilling construction reaches the bottom of the pile, the anti-overflow reinforcement layer 1 with certain strength can resist the bottom silt from flowing back into the steel casing 4, avoiding over-excavation during hole forming and subsequent over-excavation during pouring. And a section of the steel casing 4 is reserved between the bottom of the cast-in-place pile 3 and the anti-overflow reinforcement layer 1 to form a hole forming buffer layer 2, which plays a buffering role when the rotary drilling construction reaches the bottom of the pile, avoiding damage to the anti-overflow reinforcement layer 1 at the bottom of the steel casing 4 by the drill bit.

[0024] Step 3, after the anti-overflow reinforcement layer 1 is solidified, the steel casing 4 is inserted into the silt geology by aligning the pile position, and the steel casing 4 is inserted into the silt geology by the driving and pulling pile machine; Step 4, after the steel casing 4 is inserted, the rotary drilling machine is used to drill the hole, and when drilling, the rotary drilling machine is first lightly pressed and slowly rotated, and then the rotation speed and pressure are gradually increased. During the gradual drilling process, the drilling speed is controlled according to the geological conditions: when drilling from hard stratum to soft stratum, the drilling speed is increased; when the soft stratum becomes hard stratum, the drilling speed is reduced; in the stratum which is easy to shrink after the hole is formed, the hole sweeping frequency should be appropriately increased to prevent shrinkage; for the hard plastic layer, fast rotation speed is used for drilling to improve the drilling efficiency; for the sand layer, slow rotation speed is used for drilling, and the mud specific gravity and viscosity are appropriately increased. The hole is drilled to the designed pile bottom elevation, and then the residue is discharged and the hole is cleaned. The diameter of the rotary drilling machine drill bit is smaller than the inner diameter of the steel casing 4, and the diameter of the rotary drilling machine drill bit is equal to the diameter of the cast-in-place pile 3. The drilling speed of the rotary drilling machine is 0.2-0.4 meters per minute, and the rotation speed of the rotary drilling machine is 30-50 revolutions per minute. After drilling to the designed depth, the rotary bucket is used to clean the hole, and the depth display value on the computer is closely observed. When the display value is the drilling depth display value, the rotary bucket is rotated 4-5 times in place, the sediment at the bottom of the hole is rotated into the bucket, and the bottom of the hole is cleaned to a flat bottom using the flat bottom bucket teeth of the rotary bucket, and then the rotary bucket is removed to unload the sediment.

[0025] Step 5, hoist the reinforcement cage. When installing the reinforcement cage, align the hole position, hoist the straight support, slowly sink, avoid collision with the hole wall, and immediately fix the reinforcement cage after sinking to the designed position to prevent movement. Step 6, pour concrete. The concrete is discharged using a steel guide pipe, the bottom of the steel guide pipe is 30-40 cm from the pile bottom, and a hopper is installed at the top of the steel guide pipe. A circular steel plate plug with a hook is installed at the neck of the hopper to temporarily seal the steel guide pipe. After a sufficient amount of concrete is poured into the hopper, the steel plate plug is lifted using a steel wire rope, and concrete is poured into the hopper. Under the action of gravity, the concrete is poured into the pile along the steel guide pipe, and the concrete is vibrated during pouring. Step 7, after the cast-in-place pile construction is completed, the steel casing is pulled out before the concrete is initially set for reuse.

[0026] In step 1, the method for hardening the construction site is to first lay a 10 cm thick layer of fine soil on the surface of the construction site, then compact the 10 cm thick layer of fine soil to form a base layer, then lay a 3 cm thick layer of fine sand on the base layer, and then compact the 3 cm thick layer of fine sand to achieve the purpose of hardening the construction site.

[0027] The method for discharging residue and cleaning the hole is to record the flushing depth during drilling, calculate the bottom elevation of the hole using the flushing depth at the end of the hole, and recheck using a measuring rope. After the rotary drilling reaches the designed elevation and is checked at the end of the hole, the hole is cleaned. After cleaning the hole, the bottom elevation of the well is 20-30 cm lower than the designed pile bottom elevation.

[0028] The calculation formula of the inner diameter D of the steel casing is as follows: D = R + 0.01 (R + L4) Wherein, R is the design diameter of the cast-in-place pile, and L4 is the design length of the cast-in-place pile; Since the pile hole after rotary digging will appear shrinkage hole phenomenon, the inner diameter of the steel casing is set to be larger than the design diameter of the cast-in-place pile, and since the shrinkage hole of the pile hole is related to the length and diameter of the cast-in-place pile, as the length and diameter of the cast-in-place pile increase, the inner diameter of the steel casing also increases, so as to ensure that the inner diameter of the steel casing meets the diameter requirement of the cast-in-place pile.

[0029] In summary, by adopting the full-length steel casing as the hole-forming support, the mud wall effect is replaced by dry hole-forming operation, after the construction is completed, the steel casing is pulled out before the initial setting of the cast-in-place pile, and the steel casing is recycled, so as to achieve rapid construction, reduce site occupation and complicated mud monitoring work in the construction process; before the construction of the cast-in-place pile, grouting reinforcement measures are adopted in a certain range below the bottom of the steel casing to form a pile bottom anti-overflow reinforcement layer, after the strength of the pile bottom anti-overflow reinforcement layer meets the requirements, the steel casing is inserted and driven, so as to prevent the bottom silt from overflowing during the hole-forming process, avoid the expansion of the bottom of the steel casing and the waste of the subsequent cast-in-place pile; and a section of the steel casing is reserved between the bottom of the cast-in-place pile and the pile bottom anti-overflow reinforcement layer, forming a hole-forming buffer layer, which plays a buffering role when the rotary drilling construction reaches the pile bottom, avoiding the drill bit from damaging the pile bottom anti-overflow reinforcement layer at the bottom of the steel casing; the problems of site occupation and complicated mud monitoring work in the construction process of the traditional mud wall forming device are solved, and the instability of the hole body and the excessive thickness of the bottom settlement caused by the stagnation time after hole-forming are avoided; at the same time, the over-excavation caused by the suction of the rotary drill and the bottom overflow in the silt geological conditions during the construction of the rotary drill is effectively solved, the pile-forming quality of the cast-in-place pile is efficiently controlled, the cost is saved, and the construction efficiency is improved.

[0030] Example 2 During grouting, the setting speed of the mud is accelerated, and an early strength agent is usually added to the mud, but after adding the early strength agent, the setting speed of the mud is reduced, and the transportation and grouting difficulty is increased. Based on this problem, the mud combination formula is changed based on example 1, and the grouting mud includes the following components by weight: MOF-520-25 parts, Portland cement 20-25 parts, polypropylene fiber 10-12 parts, early strength agent 3-5 parts, and water 80-90 parts. During the grouting process, an ultrasonic vibration rod is inserted into the grouted mud for vibration treatment, and vibration is performed while grouting. The preparation method of the mud includes the following steps: S1, dissolve a certain proportion of early strength agent in a small amount of water, then add MOF-5 in proportion to obtain mixture A; S2, mix Portland cement, polypropylene fiber and the remaining water to obtain mixture B; S3, the mixture A is added to the mixture B, and stirred to obtain the slurry.

[0031] In the embodiment, the early strength agent is dissolved in water first, and then mixed with MOF-5, so that the early strength agent is adsorbed in the voids of MOF-5, and then the slurry is prepared. In this way, the early strength agent does not react with the materials in the slurry first, and cannot accelerate the solidification of the slurry, so as to ensure that the slurry can be normally transported and grouted. After grouting, the ultrasonic vibration rod is inserted into the grouted slurry for vibration treatment, and vibration is performed while grouting. Then, the early strength agent adsorbed in the voids of MOF-5 diffuses and is released into the slurry, reacts with the materials in the slurry, thereby accelerating the solidification of the slurry and speeding up the solidification of the anti-overflow reinforcement layer at the bottom of the pile. According to the embodiment of the application, the MOF-5 can be 20, 21, 22, 23, 24, 25 parts; According to the embodiment of the application, the silicate cement can be 20, 21, 22, 23, 24, 25 parts; According to the embodiment of the application, the polypropylene fiber can be 10, 11, 12 parts; According to the embodiment of the application, the early strength agent can be 3, 4, 5 parts; According to the embodiment of the application, the water can be 80, 82, 85, 88, 90 parts, etc.

[0032] The early strength agent can be dissolved in water, and the early strength agent can be triethanolamine.

[0033] In summary, the pores on the surface of MOF-5 can adsorb the dissolved early strength agent. Before vibration, the early strength agent does not react with the materials in the slurry, so as to avoid premature solidification of the slurry and ensure that the slurry can be normally transported and grouted. During the grouting process, the ultrasonic vibration rod is inserted into the grouted slurry for vibration treatment, and vibration is performed while grouting. Then, the early strength agent adsorbed in the voids of MOF-5 diffuses and is released into the slurry, reacts with the materials in the slurry, thereby accelerating the solidification of the slurry and speeding up the solidification of the anti-overflow reinforcement layer at the bottom of the pile.

[0034] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A rotary drilling dry hole construction method under impermeable silt geological conditions, characterized in that: The following steps are involved: Step 1: Prepare the drilling site by hardening and leveling the site, then measure and place the piles. At the same time, prepare the slurry. The slurry used for grouting includes the following components by weight: 20-25 parts of MOF-5, 20-25 parts of Portland cement, 10-12 parts of polypropylene fiber, 3-5 parts of an accelerator, and 80-90 parts of water. Step 2: Grouting reinforcement: Use a rotary jet pile machine to pour the prepared mud into the pile hole. During the grouting process, insert a vibrating device into the mud for vibration treatment, and vibrate while grouting; Step 3: Rotary drilling, align the pile position and insert the steel casing into the silt geology; Step 4: After the steel casing is inserted, a rotary drilling rig is used for drilling; Step 5: Hoist the steel cage into the pile hole using lifting equipment; Step 6: pouring concrete. A steel pipe is used for concrete discharge, and a funnel is installed on the top of the steel pipe. Then, concrete is poured into the pile hole through the funnel; Step 7: After the bored pile construction is completed, before the concrete begins to set, pull out the steel casing for recycling.

2. The rotary drilling dry hole construction method under impermeable silt geological conditions according to claim 1 is characterized in that: In step 1, the slurry preparation method includes the following steps: S1. Dissolve the early strength agent in a small amount of water, and then add MOF-5 in proportion to obtain mixture A; S2, mixing Portland cement, polypropylene fiber and remaining water to obtain mixture B; S3. Add mixture A to mixture B and stir evenly to obtain the slurry.

3. The rotary drilling dry hole construction method under impermeable silt geological conditions according to claim 1 is characterized in that: In step 2, according to the depth of the pile, a grouting reinforcement measure is adopted below the pile bottom to form a pile bottom anti-surge reinforcement layer.

4. The rotary drilling dry hole construction method under impermeable silt geological conditions according to claim 3 is characterized in that: After the pile bottom anti-surge reinforcement layer is formed, grouting is continued to form a porous buffer layer between the pile bottom and the pile bottom anti-surge reinforcement layer.

5. The rotary drilling dry hole construction method under impermeable silt geological conditions according to claim 1 is characterized in that: The length of the steel casing is greater than that of the bored pile, the top of the steel casing is higher than the top of the bored pile, the bottom of the steel casing exceeds the bottom of the bored pile, and the bottom of the steel casing extends into the borehole buffer layer.

6. The rotary drilling dry hole construction method under impermeable mud geological conditions according to claim 5 is characterized in that: The inner diameter of the steel casing is larger than the diameter of the cast-in-place pile.

7. The rotary drilling dry hole construction method under impermeable mud geological conditions according to claim 6 is characterized in that: The length dimension of the steel casing is L1, the length dimension of the cast-in-place pile is L4, and the length dimension of the porous buffer layer is L3, where L3+L4<L1.

8. The rotary drilling dry hole construction method under impermeable mud geological conditions according to claim 6, characterized in that: The calculation formula of the inner diameter D of the steel casing is as follows: D=R+0.01(R+L4) Among them, R is the design diameter of the bored pile, and L4 is the design length of the bored pile.

9. The rotary drilling dry hole construction method under impermeable mud geological conditions according to claim 1, characterized in that: In step 4, the drilling speed of the rotary drilling machine is 0.2-0.4 m / min, and the rotation speed of the rotary drilling machine is 30-50 rpm.

10. The rotary drilling dry hole construction method under impermeable mud geological conditions according to claim 9, characterized in that: The diameter of the drill bit of the rotary drilling machine is smaller than the inner diameter of the steel casing, and the diameter of the drill bit of the rotary drilling machine is equal to the diameter of the cast-in-place pile.

Images