Hole guiding auxiliary method for gravel-cobble layer and three-shaft stirring pile construction method

Abstract

The invention relates to the technical field of building foundation pit waterproof curtains, in particular to a guide hole auxiliary method for a gravel-cobble layer and a three-axis stirring pile construction method, and aims to solve the problem that a constructed three-axis stirring pile curtain is prone to water leakage due to the fact that existing gravel-cobble layer construction cannot reach the design depth of the three-axis stirring pile curtain. According to the method, a mode of repeatedly lifting a drill and reversely lifting the drill is adopted, drilling is carried out for multiple times, three-shaft stirring pile construction hole guiding assistance is carried out in a hole separation punching and hole guiding mode, a channel is created in a gravel-cobble layer in advance, guidance is provided for three-shaft stirring pile construction, meanwhile, the dense gravel-cobble layer in the construction direction is loosened, and the construction efficiency is improved. It is ensured that the three-shaft stirring piles can evenly and deeply penetrate through a gravel-cobble layer, and a continuous anti-seepage wall is formed; the construction method is easy to operate, the extra cost caused by construction blocking, water leakage repairing and the like of the three-shaft stirring pile can be effectively reduced, the construction efficiency is improved, and the construction period and the construction quality are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of water-stop curtains for building foundation pits, and in particular to a hole-guiding auxiliary method for gravel layers and a three-axis mixing pile construction method. Background Art

[0002] At present, three-axis mixing piles or multi-axis mixing piles are very mature technologies in curtain construction in soft soil areas. They are good in terms of construction efficiency and water-stopping reliability, and are widely used. They can also insert steel sections to achieve the effect of supporting and water-stopping in one, that is, the rigid cement soil mixing pile (Soil Mixing Wall, SMW) method is also widely used. The SMW method uses a special multi-axis mixer to drill and cut the soil on site, and inject cement slurry into the soil at the end of the drill bit. After sufficient mixing, H-shaped steel or other profiles are inserted into the mixing pile body to form an underground continuous wall. The wall has a certain strength and rigidity, and is continuous, complete, and seamless, and can be directly used as a retaining and water-stopping structure. However, this method is not ideal in hard soil areas, especially when encountering medium to dense gravel layers. Due to the high density of the gravel layer and the close bonding between the particles, the three-axis mixer cannot effectively cut the soil during drilling, and the cement slurry cannot evenly penetrate between the gravel particles, resulting in the problem of being unable to construct to the target depth; for example, a 23m deep foundation pit is designed with a 29m long three-axis mixing pile curtain. When the construction reaches 23m, it just enters the gravel layer about 1m, and mixing becomes difficult. The mixer cannot continue to construct downward, and thus cannot reach the designed three-axis mixing pile curtain depth. In this case, it is very easy to leak if a circle of curtain piles is barely constructed. Therefore, in response to the above problems, the construction workers laid a circle of high-pressure jet grouting piles at the location of the fertilizer trough and used a relay method to stop water; however, in the later stage of trough cleaning and excavation of water pits and elevator shafts, local jet grouting pile curtains were required to cooperate with local deep pit dewatering wells for pumping water. This method not only failed to fundamentally solve the problem of water leakage in the three-axis mixing pile curtain, but also increased the construction cost and construction period, and the quality after construction could not meet the construction requirements. In addition, the site also adopted a solution of drilling holes with bentonite mud wall protection by rotary drilling rigs, backfilling the soil, and then implementing three-axis mixing. It was found that this method had serious string holes, easy collapse and difficult to control, and low efficiency, high cost, and mud pollution, which also failed to truly solve the above problems. Summary of the invention

[0003] In view of the problem in the prior art that the density of the gravel layer is large and the particles are tightly bound together, the construction cannot reach the designed depth of the three-axis mixing pile curtain, resulting in the three-axis mixing pile curtain leaking easily after construction, the present invention provides a hole-guiding auxiliary method for the gravel layer and a three-axis mixing pile construction method.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a hole-guiding auxiliary method for a gravel layer, comprising: The construction locations are leveled and measured and laid out in turn, and the lead hole pile positions are determined according to the three-axis mixing pile construction design; At the location of the lead hole pile, drilling to a target depth by drilling several times and reversing and lifting to obtain a lead hole; the target depth is greater than the depth of the gravel layer; The guide hole is backfilled and the construction location is leveled for a second time to complete the auxiliary guide hole for the gravel layer.

[0005] Optionally, the location to be constructed is leveled and measured and laid out in sequence, and according to the three-axis mixing pile construction design, the method for determining the lead hole pile position is: Level the construction site and then tamp or compact it to obtain a compacted or compacted site; Carry out layout measurement on the site after tamping or compaction, and mark the location where the guide hole is required according to the position of the three-axis mixing pile in the three-axis mixing pile construction design to determine the guide hole pile position.

[0006] Optionally, when measuring the layout of the site after tamping or compaction, the control line is projected onto a nearby wall to facilitate review at any time.

[0007] Optionally, a spiral drill is used at the location of the guide hole pile to drill to the target depth by drilling and reversing and lifting several times to obtain the guide hole.

[0008] Optionally, the power head of the auger drilling rig has a power of ≥180kW.

[0009] Optionally, the power head of the auger drilling rig has a power of 250 kW to 300 kW.

[0010] Furthermore, the method of drilling a hole at the position of the lead hole pile by drilling several times and reversing and lifting to obtain the lead hole is as follows: At the location of the pilot hole pile, drill until the drill can no longer drill; After drilling until the drill cannot drill any further, lift the drill and reverse it upwards; After reversing and lifting, continue drilling until the drill bit can no longer drill, repeatedly lift the drill bit and reverse and lift it until it reaches the target depth and a guide hole is obtained.

[0011] Furthermore, the depth of the guide hole is 1 to 2 meters deeper than the designed depth of the three-axis mixing pile.

[0012] The present invention also provides a method for constructing a triaxial mixing pile in a gravel layer, comprising: The construction locations are leveled and measured and laid out in turn, and the lead hole pile positions are determined according to the three-axis mixing pile construction design; At the location of the lead hole pile, drilling to the target depth by drilling several times and reversing and lifting to obtain the lead hole; wherein the target depth is greater than the depth of the gravel layer; Backfill the lead hole and level the construction site for the second time to complete the auxiliary lead hole for the gravel layer; after completing the auxiliary lead hole for the gravel layer, conduct secondary measurement and layout, and determine the position of the three-axis mixing pile according to the construction design of the three-axis mixing pile; After the position of the three-axis mixing pile is determined, the trench is excavated according to the three-axis mixing pile construction design, and the guide frame is set; After the guide frame is set up, the three-axis mixing pile construction is carried out; After the three-axis mixing pile construction is completed, the drilling tools are cleaned and inspected.

[0013] Furthermore, the secondary measurement layout and the measurement layout are on the same straight line.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for assisting hole introduction in a gravel layer. The method sequentially performs leveling and measurement and laying out of a construction position, and determines the lead hole pile position according to a three-axis mixing pile construction design, thereby providing an accurate reference for subsequent drilling work, reducing repeated labor caused by inaccurate positioning, and thus improving overall construction efficiency; drilling to a target depth by drilling several times and reversing and lifting at the lead hole pile position to obtain a lead hole; wherein, drilling several times and reversing and lifting to open a hole can gradually penetrate into a dense gravel layer, reduce the resistance of a single drilling, and make the construction process smoother; backfilling the lead hole, and secondarily leveling the site, and completing the work of drilling for the gravel layer. Hole-guiding assistance for gravel layer: This hole-guiding assistance method provides guidance for the construction of three-axis mixing piles by creating a channel in the gravel layer in advance. At the same time, it loosens the dense gravel layer in the construction direction for the three-axis mixing pile construction in advance, so that during the construction of the three-axis mixing pile, the three-axis mixing pile can be ensured to penetrate the gravel layer evenly and deeply to form a continuous anti-seepage wall, thereby avoiding the problem of water leakage caused by the difficulty of the three-axis mixing pile to reach the depth designed for the construction of the three-axis mixing pile due to the high hardness of the gravel layer; This hole-guiding assistance method for gravel layer is simple to operate, and can effectively reduce the additional costs caused by the obstruction of the construction of the three-axis mixing pile and the repair of water leakage, improve construction efficiency, and ensure the construction period and construction quality. This hole-guiding assistance method for gravel layer is not only applicable to gravel layer, but also has a certain reference value for other similar complex geological conditions, which helps to ensure the overall quality and safety of the project and provides a new solution for construction under similar complex geological conditions.

[0015] The construction location is leveled and then compacted to obtain a compacted or compacted site, that is, the construction location is thoroughly cleaned, all obstacles and debris are removed, the site is leveled, and it is ensured that there are no obvious ups and downs and potholes on the ground. The leveled site is compacted or compacted to improve the bearing capacity and stability of the ground, providing a solid foundation for subsequent construction; the site is laid out and measured after compaction, and the positions of the three-axis mixing piles designed for the three-axis mixing pile construction are marked at the positions where holes need to be bored, and the positions of the hole-drawing piles are determined, that is, according to the design drawings and construction plans, precise laying-out and measurement are performed using total stations, levels and other measuring tools, and the positions where holes need to be bored are marked to ensure the accuracy and consistency of each hole-drawing pile position.

[0016] When measuring the layout of the site after tamping or compaction, the control line is projected onto the nearby wall for easy review at any time. During the layout measurement process, the measurement results may be biased due to various factors, such as weather and equipment accuracy. By projecting the control line onto the wall, construction personnel can review the lead hole pile position at any time with simple tools (such as tape measure, laser rangefinder, total station, etc.), and promptly discover and correct deviations, thereby improving measurement accuracy.

[0017] The auger drill is used at the location of the lead hole pile, and the lead hole is obtained by drilling to the target depth by drilling several times and reversing and lifting. The auger drill can quickly form a lead hole at the specified location through its unique drilling method. By reversing and lifting, the debris on the drill tool of the auger drill is thrown off to reduce the resistance of drilling again, and the hole diameter and depth can be effectively controlled to ensure the quality of the lead hole.

[0018] The power head of the spiral drilling rig has a power of ≥180kW. The high-power power head can drive the drill bit to drill at a higher speed and with a greater torque, thereby helping to overcome the resistance of the dense gravel layer and ensuring smooth drilling, which can greatly improve construction efficiency and shorten construction period.

[0019] The power head of the auger drill has a power of 250kW to 300kW. The high-power power head enables the auger drill to cope with more complex geological conditions. Whether it is a pebble layer or other hard strata, the power of 250kW to 300kW can provide sufficient drilling force and torque to ensure the smooth progress of construction. In addition, this high-power auger drill has better stability and reliability during the drilling process, reduces construction interruptions caused by equipment failure, and improves construction flexibility and adaptability.

[0020] The method of drilling to the target depth by drilling and reversing and lifting several times at the position of the lead hole pile position to obtain the lead hole is as follows: drilling until the drill tool cannot drill at the position of the lead hole pile position; after drilling until the drill tool cannot drill, lifting the drill tool and reversing and lifting; after reversing and lifting, continuing to drill until the drill tool cannot drill, repeatedly lifting the drill tool and reversing and lifting until drilling to the target depth to obtain the lead hole. This method can not only gradually drill into the gravel layer and the soil layer by drilling and reversing and lifting several times, making the drilling smoother, ensuring the smooth progress of the construction, and providing a solid foundation for the subsequent construction steps, but also the reversing and lifting action helps to clean the drill residue and soil in the hole, reduce the collapse and block falling of the hole wall, help maintain the stability of the hole wall, and improve the quality of the lead hole.

[0021] The depth of the guide hole is 1 to 2 meters deeper than the design depth of the three-axis mixing pile, so that the three-axis mixing pile can be more fully mixed with the surrounding soil when pouring cement slurry, reducing the voids and gaps inside the pile body, thereby enhancing the continuity and integrity of the pile body, improving the density and strength of the pile body, and forming a more stable curtain wall structure.

[0022] The present invention also provides a method for constructing a three-axis mixing pile for a gravel layer. The method sequentially levels and measures the construction position, and determines the lead hole pile position according to the position of the three-axis mixing pile in the three-axis mixing pile construction design, so as to ensure the accuracy of the lead hole pile position and the three-axis mixing pile position, thereby helping to reduce errors in the construction process and improve the accuracy of the overall construction; and by drilling to a target depth in the position of the lead hole pile position by drilling several times and reversing and lifting, a lead hole is obtained, so that the lead hole can be gradually adapted to the geological conditions of the gravel layer during the drilling process. Features: Drill to the designed depth smoothly; backfill the guide hole and level the site for the construction location for the second time, complete the guide hole assistance for the gravel layer, lay a good foundation for the smooth construction of the three-axis mixing pile, and ensure the smooth construction of the three-axis mixing pile in the gravel layer; complete the guide hole assistance for the gravel layer, conduct secondary measurement and layout, and determine the position of the three-axis mixing pile according to the construction design of the three-axis mixing pile, and excavate the trench and set the guide frame according to the construction design of the three-axis mixing pile, and carry out the three-axis mixing pile construction. After the construction of the three-axis mixing pile is completed, clean the drill and inspect it. This construction method is specially designed for the dense gravel layer, which can fully adapt to this complex geological condition, ensure that the construction of the three-axis mixing pile can effectively mix the cement slurry with the soil in the gravel layer, and form a cement soil consolidation body with certain strength and stability, avoiding the problem of water leakage repair in the later stage due to the inadequate construction depth of the three-axis mixing pile, thereby improving the construction efficiency and construction quality.

[0023] The secondary measurement and layout are on the same straight line as the measurement and layout, which not only ensures the accuracy of the layout, but also guarantees the guiding effect of the subsequent lead hole on the three-axis mixing pile, facilitating the smooth construction of the three-axis mixing pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a schematic flow chart of a method for assisting hole-guiding in a gravel layer.

[0025] Figure 2 The present invention is a schematic flow chart of a method for constructing triaxial mixing piles in a gravel layer.

[0026] Figure 3 It is a process diagram of a method for constructing triaxial mixing piles in a gravel layer in an example of a specific implementation of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0028] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0029] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0030] See also Figure 1 The present invention discloses a method for assisting hole introduction in a gravel layer, comprising: S11: Level and measure the construction locations in turn, and determine the leveling of the lead hole pile position according to the three-axis mixing pile construction design. The specific method is as follows: Level the construction site and then tamp or compact it to obtain a compacted or compacted site; After leveling, the site is laid out and measured after tamping or compaction, and according to the position of the three-axis mixing piles in the three-axis mixing pile construction design, marks are made at the positions where the guide holes are required to determine the guide hole pile positions; when determining the guide hole pile positions, the pile positions for verification can be prepared with measuring instruments at both ends of the lay-out measurement, and the guide hole pile positions can be verified at any time if there are deviations; a deep hole can be drilled in the ground with a steel chisel or a punch, white lime powder can be poured in, and obvious marks such as disposable chopsticks or steel bars can be inserted to mark the required positions to determine the guide hole pile positions; when necessary, the control line of the lay-out measurement can be projected onto the distant wall for verification at any time.

[0031] S12: At the location of the lead hole pile, drill to the target depth by drilling several times and reversing and lifting to obtain the lead hole, wherein the target depth is greater than the gravel layer depth, specifically: Use the spiral drill to drill into the lead hole pile position until the drill can no longer drill; After drilling until the drill cannot drill any further, lift the drill 1 to 2 meters and reverse it to lift it up 5 to 10 meters. After reversing and lifting, continue drilling until the drill tool cannot drill any further, repeatedly lift the drill tool and reverse and lift it until the target depth is reached to obtain a guide hole; preferably, the power head power of the spiral drill rig is ≥180kW, and more preferably 250kW to 300kW; preferably, after the initial drilling until the drill tool cannot drill any further, lift the drill tool by 1 to 2m, reverse and lift it by 5 to 6m, continue drilling until the drill tool cannot drill any further, lift it again by 1 to 2m, reverse and lift it by 9 to 10m, and repeat the above operation until the drill tool is 1 to 2m deeper than the designed depth of the three-axis mixing pile to obtain a guide hole. Preferably, the interval between adjacent guide holes is equal to the distance between two adjacent mixing piles, and the diameter of the guide hole is close to the diameter of the three-axis mixing pile. Preferably, the difference between the two is 0 to 100mm; S13: Backfill the lead hole and level the site for the construction location for the second time to complete the lead hole assistance for the gravel layer. The specific method is as follows: After obtaining the guide hole, use excavators, forklifts, bulldozers and other machinery to carry out secondary leveling of the construction site to prepare for subsequent construction and complete the guide hole assistance for the gravel layer.

[0032] The hole-guiding auxiliary method for the gravel layer provides guidance for the construction of the three-axis mixing pile by pre-creating a channel in the gravel layer, and pre-loosens the dense gravel layer in the construction direction for the three-axis mixing pile construction, so that during the construction of the three-axis mixing pile, the three-axis mixing pile can be ensured to penetrate the gravel layer evenly and deeply to form a continuous anti-seepage wall, thereby avoiding the problem of water leakage during the construction of the three-axis mixing pile due to the difficulty in constructing to the target depth during the construction of the three-axis mixing pile. The hole-guiding auxiliary method for the gravel layer is simple to operate, can effectively reduce the additional costs caused by the obstruction of the construction of the three-axis mixing pile, water leakage repair, etc., improve construction efficiency, and ensure the construction period and construction quality.

[0033] See also Figure 2 The present invention also provides a method for constructing a triaxial mixing pile in a gravel layer, comprising: S21: Level and measure the construction locations in turn, and determine the lead hole pile position according to the three-axis mixing pile construction design; S22: drilling to a target depth at the location of the lead hole pile by drilling several times and reversing and lifting to obtain a lead hole; the target depth is greater than the depth of the gravel layer; S23: backfilling the lead hole and leveling the construction location for a second time to complete the lead hole assistance for the gravel layer; S24: After completing the auxiliary hole guiding for the gravel layer, conduct secondary measurement and layout, and determine the position of the three-axis mixing pile according to the construction design of the three-axis mixing pile. During the secondary measurement and layout, pay attention to ensure that it is on the same straight line as the aforementioned measurement and layout, so as to ensure the guiding effect of the hole guiding; S25: After the position of the three-axis mixing pile is determined, the trench is excavated according to the three-axis mixing pile construction design, and the guide frame is set; S26: After the guide frame is set up, three-axis mixing pile construction is carried out; preferably, during the three-axis mixing pile construction, the cement slurry pump and the air compressor are started to spray and spray downward for mixing. If mixing difficulties are encountered during the downward process, the drill bit can be stirred and lifted, and then stirred downward again, and the cycle is repeated until the gravel layer is penetrated and the lower clay layer is entered to reach the designed depth of the three-axis mixing pile construction; for the water hole section, the drill bit can be sprayed and lifted again to 1 to 1.5 m above the water level, and then it can be lowered again to the designed depth of the three-axis mixing pile construction, and then sprayed and lifted to the hole mouth to complete one section of mixing pile construction, clean the drill bit and inspect it, and then construct the next section of mixing pile positions in turn until the construction of all three-axis mixing pile positions is completed.

[0034] S27: After the three-axis mixing pile construction is completed, clean the drilling tools and inspect them.

[0035] This construction method is specially designed for the gravel layer and can fully adapt to this complex geological condition. It ensures that the construction of the three-axis mixing piles can effectively mix the cement slurry with the soil in the gravel layer to form a cement-soil consolidation body with certain strength and stability, avoiding the later leakage repair caused by the insufficient construction depth of the three-axis mixing piles, thereby improving the construction efficiency and quality.

[0036] Take the construction at a certain place as an example: a project covers an area of ​​32.56 acres, with a planned net construction area of ​​21,703.44 square meters (approximately 32.56 acres), and a total construction area of ​​126,157.60 square meters, of which: the above-ground construction area is 89,583.54 square meters, including: 82,032.09 square meters of residential buildings, 402.61 square meters of property management rooms, 3,712.74 square meters of supporting facilities and service rooms, and 36,574.06 square meters of underground construction area.

[0037] There is no underground pipeline network within the construction range around the foundation pit. Before excavating the foundation pit, further investigation and confirmation of the surrounding pipeline conditions should be carried out, and corresponding protection measures should be taken. The composition and distribution of the foundation soil should be obtained. According to the geological survey report, the lithology of the foundation soil on the site is the mixed fill and plain fill of the Quaternary Holocene artificial fill layer (Q4ml), and the silt, fine sand and pebbles of the Quaternary Holocene alluvial layer (Q4al). The soil layer characteristics are described from top to bottom as follows: Quaternary Holocene artificial fill layer (Q4ml): Miscellaneous fill soil: variegated, loose, slightly wet, mainly composed of broken bricks, tiles, plastics and other construction and domestic garbage, with some pebbles and gravels, filled with clay and medium and fine sand, and poor soil uniformity. This layer comes from the accumulation of abandoned soil in the surrounding engineering construction, with an accumulation period of 4 to 5 years and is under-consolidated. This layer is mainly distributed in the middle and eastern part of the north side of the site. The layer thickness revealed in this survey is 1.00m to 4.50m.

[0038] Plain fill: variegated, loose, slightly to wet, mainly composed of pebbles and silt, followed by boulders and round gravel, with a small amount of bricks and tiles in some parts, and the soil is relatively uniform. This layer comes from the accumulation of abandoned soil in the surrounding engineering construction, with an accumulation period of 4 to 5 years and is under-consolidated. It is distributed in a large area in the east of the site and in strips on the west and southwest sides. The layer thickness revealed in this survey is 0.70m to 5.00m.

[0039] Quaternary Holocene alluvial and diluvial layers (Q4al): Silt: gray-brown, brown, slightly dense, slightly wet to wet, low toughness, low dry strength, dull cut surface and shaking reaction. It is widely distributed in the site under the surface layer and artificial fill layer. The layer thickness revealed in this survey is 0.80m to 3.90m.

[0040] Fine sand: gray-black, wet, slightly dense to medium dense, mainly composed of quartz, feldspar, mica and other minerals, with a fine grain content of 10% to 15%, and the particles are uniform and round. This layer is mainly distributed in the pebble layer in the shape of a lens, and the thickness of the layer revealed in this survey is 0.50m to 1.50m.

[0041] Pebbles: variegated, slightly dense to dense, mainly composed of boulders, pebbles, gravels, and sand. The coarse-grained parent rock is mainly granite, diorite, sandstone, quartzite, etc., slightly to moderately weathered, and locally strongly weathered; the roundness is good, mainly round to sub-round; the sorting is medium. The boulder content is 10% to 20%, and the general particle size is 200 to 400mm; the pebble content is 40% to 60%, and the general particle size is 20 to 150mm; the gravel content is 10% to 15%; it is filled with medium-fine sand and a small amount of powdery clay, and the sand is locally enriched into lenses, with a thickness generally less than 1.50m. This layer is widely distributed in the middle and lower parts of the site, with a maximum exposure thickness of 24m. According to the content and density of pebbles, it can be divided into the following three sublayers: Slightly dense pebbles: particles are arranged in a disordered manner, most of them are not in contact, the skeleton particle content is 50-60%, and N120 is 4-7 hits / 10cm; Medium-dense pebbles: particles are staggered, mostly in contact, with a skeleton particle content of 60-70%, and N120 of 7-10 hits / 10cm; Dense pebbles: particles are arranged in an alternating pattern and in continuous contact, the content of skeleton particles is >70%, and N120 is >10 hits / 10cm.

[0042] The main type of groundwater in the site is Quaternary loose layer pore water, which is mainly stored in the pores of the Quaternary Holocene sand and gravel layer and is groundwater. It is replenished by atmospheric precipitation and groundwater runoff, and the water level changes with the seasons.

[0043] During the survey period, it was in the flat water period. According to the visit survey and exploration measurement, the groundwater depth was 6.40m~9.60m, the water level was 518.26m~521.66m, and the annual fluctuation of the groundwater level was about 1m~2m. Before the development of this area, the groundwater depth was only 1m~3m. Later, due to the influence of factors such as urban construction and engineering precipitation, the groundwater level decreased year by year. According to the investigation, the highest historical water level in the field area was about 526.00m.

[0044] The main aquifer in the site is the pebble layer, which has strong permeability and water-bearing capacity. The permeability coefficient (K) of the aquifer in the site is recommended to be 25m / d.

[0045] The groundwater on site is slightly corrosive to concrete structures and the steel bars in reinforced concrete structures.

[0046] The design of the construction plan layout takes into account the principle of three separations, that is, the living area, production area and processing area are set up separately. Each area does not interfere with each other to ensure safe production and civilized construction; set up construction site entrances and exits and site road systems; set up major machinery layouts, material yards and processing sites, etc.

[0047] According to the above-mentioned stratum conditions, obtain construction requirements and related data; See also Figure 3 First, the site is leveled, surface obstacles in the construction area are cleared, the soil is backfilled and compacted, and the roadbed load is based on the walking heavy pile driver; The survey and layout shall be carried out according to the coordinate reference points provided by the design and the design drawings, and the positioning and elevation measurement shall be carried out, and permanent and temporary marks shall be made to determine the lead hole pile position. The verification deviation value of the lead hole pile position shall be less than 5cm; According to the positioning surface height and the designed curtain depth, mark the corresponding position of the drill rod of the three-axis drilling rig to control the curtain construction depth.

[0048] Then, according to the on-site stratum conditions, the long spiral drill was installed and debugged. The long spiral drill was used to drill holes with a hole spacing of 1200mm (the distance of the three-axis mixing piles was 1200mm) and a hole diameter of 800mm (the diameter of the three-axis mixing piles was 850mm). When drilling, the drill could not drill further after drilling to the dense gravel layer of 3m. At this time, the drill was lifted 1-2m and reversed upward for 5-6m. The second drilling was carried out. When drilling to the dense gravel layer of 5-6m, the drill could not drill further. The drill was lifted 1-2m and reversed upward for 9-10m. The third drilling was carried out. Drill through the gravel layer into the clay layer until it reaches 1 to 2 meters deeper than the construction depth of the three-axis mixing pile, obtain the first guide hole, and move to the next guide hole. Repeat the above operation until all the guide holes are drilled to obtain the guide holes; backfill the guide holes, and level the construction position for the gravel layer for the second time to complete the auxiliary guide hole for the gravel layer; after completing the auxiliary guide hole for the gravel layer, perform secondary measurement and layout. The secondary measurement and layout are on the same straight line as the measurement and layout, and determine the position of the three-axis mixing pile according to the construction design of the three-axis mixing pile; according to the construction design of the three-axis mixing pile, according to the foundation pit enclosure, The side control line is followed, trenches are excavated with excavators, and underground obstacles are cleared. Excavated trench surplus soil should be handled in time to ensure normal construction of three-axis mixing piles. The three-axis mixing pile driver should be stable and level, and the pile frame should be straightened with a theodolite or level, and then a hanging hammer should be installed to control the verticality. During the construction of three-axis mixing piles, up and down mixing should be repeated. For the water hole section, "two sprays and two stirs" should be implemented, that is, the mixing drill bit sprays and stirs for the first time when sinking, and then sprays and stirs again when rising; for the upper waterless clay hole section, "one stir and one spray" can be used, that is, the mixing drill bit only sprays once during the sinking or rising process, and Accompanied by a mixing action; the grouting speed should be synchronized with the mixing and lifting speed, the grouting must be continuous and uninterrupted, and the outlet pressure of the grouting pump should be maintained at 0.4-0.6MPa to ensure that the rated slurry volume is evenly distributed within the length of the three-axis mixing pile body, and the grouting volume in each three-axis mixing pile must be sufficient; the curtain pile uses P.O42.5 ordinary silicate cement, the water-cement ratio is 0.6-0.8, and the cement content is 20%-25% of the natural mass of the soil; before the construction of the three-axis mixing pile, the applicability of the construction process and the construction parameters such as water-cement ratio and cement content should be determined through field tests. During the construction of the three-axis mixing pile, an appropriate amount of bentonite can be added according to the empirical value to ensure the construction quality of the mixing pile in the pebble layer. The overlap time between the three-axis mixing pile groups shall not exceed 24h. If it exceeds 24h, a construction joint of the concave and convex interface of the pile group shall be reserved. When connecting the piles, the cement content of the new overlapped piles shall be increased to 25%, and the mixing and lifting speed of the mixing head shall be slowed down. In addition, pile filling measures shall be adopted at the joints.

[0049] The on-site construction follows the sequence of three-axis drilling, and the three-axis mixing pile construction follows the skip-type double-hole full-set remixing connection construction to ensure the continuity of the mixing wall and the construction quality of the joints to achieve the effect of water stopping. By analogy, the cement soil mixing pile is completed. Clean the three-axis mixer and move to the next mixing pile position, and repeat the above steps for construction. After acceptance, the curtain piles meet the acceptance standards for curtain piles. Not only does it overcome the difficulty of three-axis mixing piles to penetrate the gravel layer for curtain construction, but it also increases from 1 to 2 sections per day for a traditional three-axis mixer to 7 to 8 sections per day, greatly improving the construction efficiency. It fully proves the feasibility, reliability and guarantee of construction quality and speed of this method.

[0050] In summary, the present invention provides a method for assisting hole introduction in a gravel layer and a method for constructing a three-axis mixing pile. The method adopts the form of repeatedly lifting the drill and reversing and lifting it up, and drilling several times, and assists the construction of the three-axis mixing pile by drilling holes in alternate holes. A channel is created in the gravel layer in advance to provide guidance for the construction of the three-axis mixing pile, and the dense gravel layer in the construction direction is loosened in advance for the three-axis mixing pile construction, so that during the construction of the three-axis mixing pile, it can be ensured that the three-axis mixing pile can penetrate the gravel layer evenly and deeply to form a continuous anti-seepage wall; the operation is simple, and the additional costs caused by the obstruction of the construction of the three-axis mixing pile and the repair of water leakage can be effectively reduced, so as to improve the construction efficiency and ensure the construction period and construction quality. The method for assisting hole introduction in a gravel layer is not only applicable to the gravel layer, but also provides a new solution for construction under similar complex geological conditions.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and substitutions, and these modifications and substitutions are also within the scope of protection covered by the claims.

Claims

1. A method for assisting drilling of gravel layers, characterized in that: include: The construction locations are leveled and measured and laid out in turn, and the lead hole pile positions are determined according to the three-axis mixing pile construction design; At the location of the lead hole pile, drilling to a target depth by drilling several times and reversing and lifting to obtain a lead hole; the target depth is greater than the depth of the gravel layer; The guide hole is backfilled and the construction location is leveled for a second time to complete the auxiliary guide hole for the gravel layer.

2. The method for assisting hole insertion in a gravel layer according to claim 1, characterized in that: The method of leveling and measuring the construction location in turn and determining the lead hole pile position according to the three-axis mixing pile construction design is as follows: Level the construction site and then tamp or compact it to obtain a compacted or compacted site; Carry out layout measurement on the site after tamping or compaction, and mark the location where the guide hole is required according to the position of the three-axis mixing pile in the three-axis mixing pile construction design to determine the guide hole pile position.

3. The method for assisting hole drilling in a gravel layer according to claim 2, characterized in that: When measuring the layout of the site after tamping or compaction, the control line is projected onto the nearby wall to facilitate review at any time.

4. The method for assisting hole drilling in a gravel layer according to claim 1, characterized in that: Use an auger drill to drill to the target depth at the guide hole pile position by drilling and reversing and lifting several times to obtain the guide hole.

5. The method for assisting hole-drilling in a gravel layer according to claim 4, characterized in that: The power head of the auger drill has a power of ≥180kW.

6. The method for assisting hole insertion in a gravel layer according to claim 4, characterized in that: The power head of the spiral drilling machine has a power of 250kW to 300kW.

7. The method for assisting hole drilling in a gravel layer according to claim 1, characterized in that: The method of drilling a hole at the position of the lead hole pile by drilling several times and reversing and lifting to obtain the lead hole is as follows: At the location of the pilot hole pile, drill until the drill can no longer drill; After drilling until the drill cannot drill any further, lift the drill and reverse it upwards; After reversing and lifting, continue drilling until the drill bit can no longer drill, repeatedly lift the drill bit and reverse and lift it until it reaches the target depth and a guide hole is obtained.

8. The hole-guiding auxiliary method for gravel layer according to claim 1, characterized in that: The depth of the guide hole is 1 to 2 meters deeper than the design depth of the three-axis mixing pile.

9. A method for constructing triaxial mixing piles in a gravel layer, characterized in that: include: The construction locations are leveled and measured and laid out in turn, and the lead hole pile positions are determined according to the three-axis mixing pile construction design; At the location of the lead hole pile, drilling to the target depth by drilling several times and reversing and lifting to obtain the lead hole; wherein the target depth is greater than the depth of the gravel layer; Backfill the lead hole and level the construction site for the second time to complete the auxiliary hole for the gravel layer; After completing the auxiliary hole for the gravel layer, conduct secondary measurement and layout, and determine the position of the three-axis mixing pile according to the construction design of the three-axis mixing pile; After the position of the three-axis mixing pile is determined, the trench is excavated according to the three-axis mixing pile construction design, and the guide frame is set; After the guide frame is set up, the three-axis mixing pile construction is carried out; After the three-axis mixing pile construction is completed, the drilling tools are cleaned and inspected.

10. The method for constructing triaxial mixing piles in a gravel layer according to claim 9, characterized in that: The secondary measurement layout and the measurement layout are on the same straight line.

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