CN110512594B - Simple method for forming hole and pile in cavity of rotary drilling rig - Google Patents

Simple method for forming hole and pile in cavity of rotary drilling rig Download PDF

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Publication number
CN110512594B
CN110512594B CN201910768974.7A CN201910768974A CN110512594B CN 110512594 B CN110512594 B CN 110512594B CN 201910768974 A CN201910768974 A CN 201910768974A CN 110512594 B CN110512594 B CN 110512594B
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pile
hole
construction
soil
cavity
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CN110512594A (en
Inventor
何世鸣
李江
田震远
周与诚
陈辉
司呈庆
黄鑫峰
郝雨
郁河坤
贾城
洪伟
王海宁
刘志刚
梁成华
杜高恒
王建明
郭跃龙
陈鹏
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BEIJING URBAN CONSTRUCTION SCIENCE TECHNOLOGY PROMOTING ASSOCIATION
Zhongcai Geological Engineering Exploration Academy Co ltd
Beijing Building Material Geotechnical Engineering Corp
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BEIJING URBAN CONSTRUCTION SCIENCE TECHNOLOGY PROMOTING ASSOCIATION
Zhongcai Geological Engineering Exploration Academy Co ltd
Beijing Building Material Geotechnical Engineering Corp
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    • EFIXED CONSTRUCTIONS
    • E02HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02DFOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D3/00Improving or preserving soil or rock, e.g. preserving permafrost soil
    • E02D3/02Improving by compacting
    • E02D3/046Improving by compacting by tamping or vibrating, e.g. with auxiliary watering of the soil
    • EFIXED CONSTRUCTIONS
    • E02HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02DFOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D5/00Bulkheads, piles, or other structural elements specially adapted to foundation engineering
    • E02D5/22Piles
    • E02D5/24Prefabricated piles
    • E02D5/30Prefabricated piles made of concrete or reinforced concrete or made of steel and concrete

Abstract

A simple method for forming a pile by a rotary drilling rig in a cavity comprises the following steps: 1. determining a pile position; 2. constructing a protection pile outside two ends of a hollow in a construction area respectively, and plugging two ends of the hollow; 3. excavating a pile hole which is separated from the protective pile by one pile position, directly filling excavated soil into the protective pile hole at the end head, and tamping the filled soil; 4. adopting a hole isolation construction method, digging the pile hole of each pile in a construction area to be a hollow hole, filling the pile hole with good soil of the adjacent pile hole, and tamping until the pile hole is fully tamped; 5. digging the pile holes dug in the middle, filling soil, and tamping until all the pile holes are constructed; 6. and (4) from the middle of the construction area, completing pile-forming construction in all the construction areas by adopting a conventional process. The invention has the advantages that: under the conditions of hardly increasing the cost and not increasing the construction period, the construction of all the piles at the hollow position is completed. The economic benefit, the environmental protection benefit and the social benefit are obvious.

Description

Simple method for forming hole and pile in cavity of rotary drilling rig
Technical Field
The invention relates to a simple method for forming a pile by a rotary drilling rig in a cavity, belongs to pile forming in building foundation construction, and can be used for construction of slope protection piles, pressure-resistant piles, uplift and floating-resistant piles and the like.
Background
At present, when a rotary drilling rig at home and abroad encounters a soil cave or a karst cave in the drilling process, the first conceivable method is filling, rubbles are thrown and filled into holes, lean concrete is backfilled, pressure grouting is assisted, and a construction process of steel casing follow-up is adopted.
And (3) backfilling with slate, repeatedly adding loess and slate when drilling through the karst cave and leaking slurry, using a drill to impact the loess and slate into the karst cave and karst cracks, and optionally adding cement, caustic soda and sawdust to improve the self-stabilizing capability of the hole wall.
The poor concrete is backfilled by adopting C20 poor concrete, and in order to improve the early strength and save time, an early strength agent is added into the concrete. And the backfill top surface at the karst cave is 50cm higher than the top plate of the karst cave. For the inclined rock surface, in order to correct the hole position, the backfilled lean concrete is level to the top surface of the inclined rock surface. And after backfilling for 48 hours, the drill can be restarted when the concrete strength reaches 70%.
The grouting method is an effective measure for treating the large karst cave, the grouting holes are arranged, the largest karst cave is found out firstly according to design information, and if the karst cave is a communicated karst cave, only the largest karst cave is required to be grouted and reinforced.
A steel casing follow-up process is a Bernout (Benote) construction method abroad, and is a construction method which comprises the steps of utilizing a full-rotation full-casing drilling machine to press a prefabricated steel casing into a stratum to a certain depth through 360-degree rotation, taking out soil in the steel casing through a grab bucket, gradually pressing the steel casing into a casing to form a hole, finally hoisting a steel reinforcement cage, pouring concrete and pulling up the steel casing. This method requires specialized equipment and is currently a relatively expensive process. Especially, the utility model is suitable for small projects, and is a 'cattle knife for killing chicken'.
There is also a method of throwing the 'flying pipe' into the hole, which needs to change the diameter of the hole, or use a large diameter drill hole in advance, and when the flying pipe is dropped into the hole, the diameter is changed to drill, or after the flying pipe is dropped, the smaller diameter drill hole is changed to drill. This method is obviously a relatively troublesome method, and of course, requires the prior machining of thick-walled steel pipes, and if the design is not approved to reduce the diameter, the prior use of a larger diameter opening becomes the only option. However, the complete success cannot be guaranteed, and the lower end of the fly pipe may have a cavity, or the lower end of the fly pipe is not well sealed, and slurry leakage may occur. Furthermore, the drill bit breaks or breaks the flying pipe during drilling.
We have also designed thin steel or iron sheet protecting cylinders fixed on the reinforcement cage, which are put into the holes along with the reinforcement cage, and poured with concrete to form piles, but this method may fail to be supported by concrete, or after the thin steel or iron sheet protecting cylinders are filled, they flow out from the upper end and enter into the holes, wasting concrete, or even not filled. It is of course also necessary to machine thin steel or iron sheet casings beforehand.
It has also been designed to use manual work to insert the cavity side into the hole, but this operation is very dangerous, and once collapsed, people will be buried and obviously, everyone does not agree to take the risk.
The above methods are costly both economically and in terms of construction. It should be possible to invent a more economical and time-saving process.
Disclosure of Invention
In order to compete for time and speed, utilize on-site conditions, use local materials and utilize the existing equipment to solve the problems, the invention provides a simple method for forming a pile by drilling a hole in a cavity by a rotary drilling rig.
The technical scheme of the invention is as follows: a simple method for forming a pile by a rotary drilling rig in a cavity comprises the following steps:
(1) the hole trend and the end position of the area needing construction are found out, the field is leveled, and the pile position is determined;
(2) respectively constructing a protection pile outside two ends of the cavity of the construction area, and plugging two ends of the cavity of the construction area;
(3) excavating a pile hole separated from the protection pile by a pile position, directly filling excavated soil into the protection pile (hole) at the end, tamping the filled soil with strength when a bucket of the filled soil is filled, wherein the upper surface of the filled soil is 0.5-1.0 m above the top of the cavity, and the filled soil can be randomly diffused to the periphery of the cavity until all the soil in the cavity is tamped;
(4) firstly digging the pile hole of each pile in the construction area to the bottom of a hollow hole, filling the pile hole with good soil of the adjacent pile hole and tamping until the pile hole is fully tamped, wherein the upper surface position of the filled soil is the same as that in the step (3);
(5) digging the pile hole dug by jumping in the middle, filling soil, and tamping until all the pile holes are constructed;
(6) and from the middle of the construction area, completing pile-forming construction in all the construction areas by adopting a conventional process.
In the step (2), the construction method of the protection pile comprises the following steps: digging a soil filling hole to the bottom of the cavity, and filling soil into the cavity and tamping.
In the step (3), the pile-forming needs hole-separating construction to avoid perforation, the pile hole can be stopped when being dug to the bottom end of the hollow hole, and the good soil dug by the pile hole and the adjacent pile hole is utilized for layered backfill and tamping; provides a stable foundation condition without collapse when excavating pile holes for formal pile forming.
In the step (6), a pile hole of the pile to be constructed is excavated from the middle to form a hole, and then the hole is inspected, a reinforcement cage is hung, and concrete is poured to form a pile; and adopting the jump beating construction to ensure the minimum disturbance to the hole wall during the hole forming and also ensure the minimum impact to the hole wall during the concrete pouring so as to complete the whole construction of the middle pile.
The invention has the advantages that: under the conditions of hardly increasing the cost and not increasing the construction period, the construction of all the piles at the hollow position is completed. The economic benefit, the environmental protection benefit and the social benefit are obvious.
Drawings
FIG. 1 is a flow chart of the construction process of the present invention;
fig. 2 is a schematic view of the earth-filling process of the present invention (a cross-sectional view along the hollow and pile hole, showing only the structure after filling the pile hole formed in the first round of construction).
Description of reference numerals: 1. a cavity, 2, a protection pile hole, 3, a pile hole skipped by the first round of construction (namely the pile hole of the second round of construction), 4, a pile hole of the first round of construction, 5, a protection pile (formed by filling soil in the protection pile hole), 6, filling soil in the pile hole, 7, filling soil in the pile hole of the second round of construction (only one part is shown), 8 and the ground.
Detailed Description
Referring to fig. 1 and fig. 2, the basic process flow of the simple method for forming the pile by the rotary drilling rig in the cavity comprises the following steps:
1. the simple method for forming the pile by the rotary drilling rig in the cavity is realized by using local materials and utilizing the existing equipment to solve the problem. The method comprises the following specific steps:
(1) the method comprises the following steps of (1) searching the trend and the end position of a cavity (1), firstly determining the position and the trend of the cavity (1), determining the relation between the cavity (1) and a to-be-constructed pile (hole) (how many to-be-constructed piles fall into the range of the cavity (1)), leveling the field, releasing the pile position, and fastening the pile position.
(2) Respectively increasing a protection pile 5 at the hollow 1 outside the two ends of the pile holes 3 and 4 of the piles to be constructed (falling into the hollow range), wherein the construction method of the protection pile 5 comprises the following steps: a protective pile hole 1 to a cavity 1 is dug outside each of the two ends, firstly, the dug soil is stacked beside the protective pile hole 1 at one end until the pile hole is dug to be communicated with the cavity 1. And filling the soil into the soil filling hole by using the separating hole and the soil dug by the soil filling hole and tamping the soil filling hole to form the protection piles 5 at the two ends of the cavity 1, so that the two ends of the cavity 1 are plugged, and the piles at the two ends cannot flow outwards when in construction.
(3) And excavating a pile hole 4 (namely a pile hole formed by the first round of construction) by one pile hole 3, directly filling the excavated good soil into the protection pile hole 1 at the end, and tamping the filled soil by using a rotary excavating bucket as a tamping hammer when filling one bucket of good soil, wherein the soil can be randomly diffused to the periphery of the cavity until the soil in the cavity is completely tamped to form a protection pile 5. The upper surface of the filling (namely the protection pile 5) in the protection pile hole 1 is 0.5-1m higher than the top of the tunnel.
(4) And the other end of the protection pile 5 is tamped by filling soil in the same way.
(5) And (4) constructing the middle pile-forming pile hole 4 to the hollow hole 1 by skipping one pile-forming pile hole 3, filling and tamping the pile-forming pile hole with good soil of the separation hole until the pile-forming pile hole is fully tamped to form pile-forming pile hole filling soil 6.
(6) And digging all pile-forming pile holes 3 skipped in the middle, filling soil, and tamping to form pile-forming pile hole filling soil 7. And finishing the filling treatment of all the pile holes. And then performing construction of concrete pile formation (the concrete pile formation is formed by adopting the conventional pile formation construction process in the following).
(7) And normally digging holes from the middle, checking the holes after hole forming, putting a reinforcement cage into the holes, and pouring concrete to form the pile.
(8) And excavating the separated holes, normally excavating the holes, checking the holes after the holes are formed, putting a reinforcement cage, and pouring concrete to form the pile.
(9) And finally constructing a pile at the end of the hollow hole 1 (namely the pile hole 3). Therefore, all pile construction at the hollow position is completed under the conditions of hardly increasing the cost and not increasing the construction period.
The pile-forming hole 3 skipped in the first round of construction and the pile-forming hole 4 in the first round of construction are firstly used for filling soil into the hollow 1, and then are used for concrete pile-forming construction after the soil filling is finished (the steps 7 to 9).
In the steps (5) and (6), the construction of the planned construction pile needs to be carried out at intervals of holes, perforation is avoided, the pile is dug to be communicated with the cavity 1, and the good soil dug out by the holes and dug out by the intervals of holes is utilized for carrying out layered backfilling and tamping. When the next formal pile-forming excavation is carried out, a stable pile hole without collapse can be formed. The method comprises the steps of forming a hole from an end protective pile to a hollow hole 1, backfilling, tamping, forming the hole to the hollow hole 1 at intervals, backfilling, tamping and sequentially processing, wherein pile positions on all hollow holes to be processed are completely processed in place, and conditions are created for the formal construction of the next pile.
And (7) and (8) starting to excavate the construction-planned pile from the middle, forming a hole, checking the hole, hoisting into a reinforcement cage, and pouring concrete to form the pile. And (3) jumping construction is carried out, so that the minimum disturbance to the hole wall during hole forming is ensured, the minimum impact to the hole wall during concrete pouring is also ensured, and the whole construction of the middle pile is completed. And finally, constructing piles at two ends of the hollow (civil air defense channel).
The present invention will be described in detail with reference to the following specific examples:
1. measuring the paying-off and pile positioning: firstly, the direction and the end position of a cavity are found out, the paying-off and pile positioning positions are measured on a flat field, protective piles are added at two ends of the pile position, positioning piles are manufactured at the two ends by using a measuring instrument, and the pile position is prevented from being rechecked at any time when deviation occurs; the pile location is usually drilled with a deep hole on the ground by a drill rod or a puncher, white lime powder is poured in, and obvious marks such as a steel bar stick are inserted at the pile location. When necessary, the control line is projected to a remote wall for rechecking at any time.
2. The trend and the end of the cavity are confirmed, the existing underground pipeline drawing or manual field exploration is utilized, and the cavity is explored in the cavity if necessary, such as an old or abandoned civil air defense channel, so that the trend and the end of the cavity are determined, and the mutual relation between the cavity and the pile position is clarified. The protection piles are added outside the end heads, and are firstly processed in place, so that the two ends can be firstly plugged, and the loss from the two ends is avoided.
3. Firstly, piling the excavated soil beside the protective pile at one end until the pile is excavated to the upper end of the cavity; then, excavating at intervals of one pile, directly filling excavated soil into the protective pile at the end, using the rotary excavating bucket as a rammer to tamp the filled soil when one bucket of the good soil is filled, wherein the soil can be randomly diffused to the periphery of the cavity until the soil in the cavity is fully tamped. The same method is used to fill and tamp the protective pile at the other end, so that the protective piles at both ends of the hollow space (civil air defense channel) are treated.
4. Digging, filling and tamping the soil of the middle piles, wherein each middle pile is dug to the bottom of the cavity and then stopped, constructing the isolation holes, and filling and tamping the well soil of the isolation holes until the middle piles are fully tamped; and digging the pile dug in the middle, filling soil and tamping. All the pile holes are processed in place.
5. And (4) manufacturing a reinforcement cage, wherein joints of vertical reinforcements of the pile body reinforcement cage are mechanically connected or welded. The welding length is single-side 10d, and the length of the two sides is 5d (d is the diameter of the steel bar). The positions of the welding joints need to be staggered, the joint rate is less than or equal to 50%, the staggered distance is more than 35d (d is the diameter of the steel bar) and is not less than 500 mm. The steel reinforcement cage made by sections should take proper measures to prevent torsion and bending when being carried.
6. Constructing an intermediate pile, normally digging a hole from the middle, checking the hole after forming the hole, putting a reinforcement cage, and pouring concrete to form a pile;
7. and (3) constructing an end pile, constructing a hollow (civil air defense channel) end pile, normally digging a hole, checking the hole after forming the hole, putting a reinforcement cage into the hole, and pouring concrete to form a pile. Therefore, all pile construction at the hollow (civil air defense passage) is completed under the conditions of hardly increasing the cost and not increasing the construction period.
Engineering implementation case
1. Overview of the engineering
The project name is as follows: and (3) performing foundation pit supporting engineering on the Fuli square of Shijiazhuang.
Engineering site: the project is planned to be located in south of the living road of the citizens of Shijiazhuang and is constructed in west of the street.
The site and surrounding environment conditions of the project site are as follows:
1) the conditions of surrounding environment, site removal and land acquisition conditions, tee joint leveling and erection and the like.
(1) The support range is the foundation pit shotcrete retaining wall project of the foundation pit engineering construction drawing confirmed by the Fuli square foundation pit support project Party A of Shijiazhuang.
(2) The site is cleared, the land acquisition is normally finished, and the site does not need to be removed.
(3) The construction site enclosing wall is built except for the east side, the east side is a hardening temporary road, and the road in the site can meet the requirement of heavy-duty vehicle passing.
(4) The construction water uses the electric power A to provide the connection point; temporary construction conditions are provided in the site, and temporary construction can be built on a construction site by worker accommodation.
2) The foundation pit bottom side line, the maximum allowable range of the foundation pit top side line, the absolute elevation of the bottom and the top of the foundation pit, the current supporting range is the foundation pit supporting engineering support of the shijiazhuang rich-strength square, and the depth of the foundation pit is 20.3 m.
3) The conditions of roads, loads and the like around the foundation pit, the civil living road adjacent to the north side of the foundation pit and the great street adjacent to the east side of the foundation pit, and the formed soil road in the site can meet the requirements of passing load construction vehicles, such as a crane 25t, a concrete tank truck 38t, a bulk cement transport vehicle 100t, a steel bar transport vehicle 130t and an earth transport vehicle about 25 t.
4) Precipitation and drainage period and requirements:
according to the geological survey report, the underground water level of the project is below the basement, so that the earthwork excavation of the foundation trench is not influenced, large-area precipitation measures are not needed, and the water collection open drain method can be adopted for draining water.
5) Rainfall condition of area of foundation pit engineering
According to the data, the annual total precipitation of the Shijiazhuang city at the location of the project is 401.1-752.0mm, and is influenced by factors such as special terrains, the annual variation of the precipitation is large, annual distribution is concentrated, annual precipitation is mainly concentrated in 6-9 months, and precipitation in the whole flood season is concentrated in two months, namely 7 and 8.
6) The designed service life of the foundation pit support is one year.
7) The construction content and the construction range of the scheme are as follows:
(1) supporting piles, pile top crown beams and anchor rods (tensioning);
(2) hanging steel bars among the supporting piles and spraying concrete for construction;
(3) constructing a prestressed anchor rod;
(4) and arranging a drain pipe according to the requirements of the drawing.
2. General overview of terrain, geomorphology and terrain
The proposed site is located in the south of the living road of the citizens of Shijiazhuang, the west of the street and about 250m from the south of the northern commercial city.
The regional landform is located in the Hutuo river flood sector. The ground height in the ground is 71.69m at the maximum value, 69.65m at the minimum value, the relative height difference of the ground surface is 2.04m, and the terrain is relatively flat.
3. Site lithology and distribution characteristics
The stratum of the planned site is within the exploration depth range of 90.00m and mainly comprises miscellaneous fill, loess silty clay of the fourth system flood-washing accumulation, loess silty clay, medium sand, silty soil, silty clay, medium coarse sand, silty clay, medium sand, round gravel, silty clay, round gravel, pebbles and the like. The engineering properties of the main foundation soil layer according to the detailed survey report are reviewed as follows:
1) fourth series artificial filling layer (Q4 ml)
Filling with soil: the yellow brown soil is mainly sticky soil and silt, contains a small amount of construction waste, is uneven in soil quality, slightly wet, loose and slightly dense. The layer thickness is 0.90-4.90 m, and the layer bottom elevation is 65.75-69.92 m. The layers are distributed in the field.
2) Fourth system of newly built layers (Q42al + pl)
Yellow brown clay containing ginger stone and with macroporous structure, non-uniform soil, thin yellow clay layer, soft plasticity and hard hardness. The layer had a non-self-weight collapsibility with a collapsibility coefficient s of 0.015, a collapsibility onset pressure of 199kPa, and a slight collapsibility. The compression coefficient a1-2 is 0.08-0.75 MPa-1, the average is 0.28MPa-1, and the soil belongs to foundation soil with low-to-high compressibility. Layer thickness: 0.40-1.90 m, bottom elevation of layer: 66.35-68.73 m. This layer is only seen for individual boreholes.
3) The fourth is the new system Honghua layer (Q4al + pl)
The loess-shaped silty clay is yellow brown, contains ginger stones, is uneven in soil quality, is sandwiched with a loess-shaped silty soil thin layer, and is flow-molded to be hard. The layer has non-self-weight collapsibility, the collapsibility coefficient s is 0.015-0.019, the collapsibility initial pressure is 164-196 kPa, and the collapsibility is slight. The compression coefficient a1-2 is 0.10-0.71 MPa-1, the average is 0.34MPa-1, and the soil belongs to medium-high compressibility foundation soil. Layer thickness: 2.60-6.70 m, bottom elevation: 61.06-63.37 m. The fields are distributed generally, and the layer position is stable.
And the sand in the formula IV is light yellow to grey white, has feldspar and quartz, contains mica, has poor grading, is partially sandwiched with a fine soil thin layer, is slightly wet and is dense in the middle and dense. The measured hammering number (N) of the standard penetration test is 22-37 strokes, and the average value is 27.7 strokes. Layer thickness: 1.90-6.10 m, bottom elevation of layer: 57.27-60.33 m. The fields are distributed universally.
4) The fourth is late update of Tonghua-Hongji (Q3al + pl)
Firstly, pulverizing soil: brown yellow, uneven soil texture, mica, silt and silty clay thin layers, dense-dense in the middle and slightly wet-wet. The compression coefficient a1-2 is 0.17-0.44 MPa-1, the average is 0.29MPa-1, and the soil belongs to medium-compressibility foundation soil. Layer thickness: 1.20-4.50 m, bottom elevation of layer: 55.21-57.74 m. The fields are distributed generally, and the layer position is stable.
The powdery clay comprises: yellowish brown, local inclusion of a thin layer of silt, uneven soil texture, soft plasticity-hard. The compression coefficient a1-2 is 0.12-0.55 MPa-1, the average is 0.30MPa-1, and the soil belongs to medium-high compression foundation soil. Layer thickness: 3.50-6.90 m, bottom elevation of layer: 50.35-52.45 m. The fields are distributed universally.
The method comprises the following steps: yellow brown, containing ginger stone, a thin layer of silt is partially sandwiched, the soil quality is not uniform, and the soil is soft and hard. The compression coefficient a1-2 is 0.13-0.66 MPa-1, the average compression coefficient is 0.30MPa-1, and the soil belongs to medium-high compression foundation soil. Layer thickness: 8.60-12.50 m, bottom elevation of layer: 39.01-42.35 m. The fields are distributed universally.
Fourth, coarse sand (b): brown to grey, feldspar to quartzity, mica-containing, purer sandy, poorly graded, slightly wet, dense. The actual hammering number (N) value measured in the standard penetration test is 33-61 strokes, and the average hammering number is 45.9 strokes. Layer thickness: 3.80-9.90 m, bottom elevation of layer: 32.45-37.14 m. The fields are distributed universally.
Fifth, fifth: yellow brown, containing ginger stone, and having a clay thin layer locally, even soil texture, plasticity to hard plasticity. The compression coefficient a1-2 is 0.12-0.42 MPa-1, the average is 0.29MPa-1, and the soil belongs to medium-compressibility foundation soil. Layer thickness: 0.70-5.70 m, bottom elevation: 30.49-34.85 m. The fields are distributed universally.
Sixthly, the Chinese grit has the following advantages: brown to grey, feldspar to quartzity, mica-containing, partially-sandwiched coarse sand and pebble thin layers, pure sand, poor gradation, slight humidity to saturation and compactness. The measured value of the hammering number (N) in the standard penetration test is 43-62 strokes, and the average value is 52.0 strokes. Layer thickness (layer thickness is disclosed): 0.40-10.80 m, layer (hole) bottom elevation: 23.26 to 31.61 m. The fields are distributed universally.
Farinaceous clay (11) -1: yellow brown, containing ginger stone, a thin layer of local pebbles, uneven soil texture, plasticity to hardness. The compression coefficient a1-2 is 0.22-0.35 MPa-1, the average is 0.38MPa-1, and the soil belongs to medium-compressibility foundation soil. Layer thickness: 0.70-2.50 m, bottom elevation of layer: 20.95-22.79 m. This layer is present in the field predominantly in the form of lenticles.
And pebbles (11): the sand-gravel composite material is characterized by having variegated colors, sub-circular shapes and poor grading, generally having the grain diameter of 2-10 mm, containing cobbles, having the maximum grain diameter of 50mm, partially sandwiching a coarse sand and pebble thin layer, and having a cementing layer in a partial section, wherein the cementing layer is in a saturated and compact state. The corrected impact number of the heavy dynamic penetration is 14.8-20.5 impacts, and the average impact number is 17.8 impacts. Layer thickness: 6.00-14.20 m, bottom elevation of layer: 9.62-18.27 m. The fields are distributed universally.
Self-chalky clay (12): yellow brown, containing ginger stone, uneven soil texture, a cementing layer and a pebble interlayer existing in a local section of the layer, and soft and hard. The compression coefficient a1-2 is 0.05-0.45 MPa-1, the average is 0.24MPa-1, and the soil belongs to low-medium compressibility foundation soil. Layer thickness: 8.40-20.70 m, bottom elevation of layer: 7.34-5.96 m. The fields are distributed universally.
With pebbles (13): the sand-gravel composite material is characterized by having variegated colors, sub-circular shapes and poor grading, generally having the particle size of 5-8 mm, containing pebbles and having the maximum particle size of 60mm, partially sandwiching coarse sand and pebble thin layers, and having a cementing layer in a partial section and being in a saturated and compact state. The correction impact number of the heavy dynamic penetration is 16.0-27.4 impacts, and the average impact number is 21.3 impacts. Layer thickness: 1.90-13.80 m, bottom elevation of layer: -11.54-1.33 m. The fields are distributed universally.
Pebbles (14): the rock matrix is medium weathering quartzite, quartz sandstone and granite, the general grain size is 2-5 cm, the maximum grain size is 15cm, the content is 55%, 45% of medium sand and a small amount of cohesive soil are filled, and the rock matrix is in a saturated and compact state. The correction impact number of the heavy dynamic penetration is 20.5-27.7 impacts, and the average impact number is 23.8 impacts. The layer is not torn through.
4. Underground water condition of planned building area
The major aquifer in the urban region of the Shizhuang is an upper renewal system stratum and a complete innovation system stratum, and is a strong water-rich layer stacked by Hutuo product and the Hutuo river flood product egg gravel-gravel, the north extends towards the south by taking the Hutuo river bed as a center zone, the lithology of the stratum above 20.00-25.00 m below the ground surface is cohesive soil, silt and sandy soil, the lower stratum is a gravel layer, and the cohesive soil, the silt and the sandy soil are sandwiched, and the total thickness reaches about 85.00 m.
In the fifties of the twentieth century, the underground water level in the Shijiazhuang city area is buried about 6.00-7.00 m throughout the year, the flood season can reach 4.00m, and later, due to the fact that the climate is dry, the water consumption of industry, agriculture and living is increased, the underground water exploitation is far larger than the supply amount, the underground water in the Shijiazhuang city declines year by year, and an underground water falling funnel taking the industrial area of the Shijiazhuang city as the center is formed.
The height of the underground water level is 24.86-24.95 m, the buried depth of the underground water level is 45.50-46.80 m, the underground water type belongs to the fourth-series diving, and the buried depth is larger. The highest water level of the exploration site is more in 8-9 months, the low water level is more in 5-6 months, and the annual water level amplitude is about 1.5 m. According to the geological survey report, the underground water level of the project is below the basement, so that the earthwork excavation of the foundation trench is not influenced, large-area precipitation measures are not needed, and the water collection open drain method can be adopted for draining water.
The exploration site is originally residential land, no pollution source exists in and around the site, the site soil is not polluted, and the exploration site has micro-corrosiveness on building materials.
5. General description of the design of the Foundation pit support
5.1 Foundation pit supporting type
The foundation pit engineering is temporary support, the design service life is 1 year, and the safety level of the side wall of the foundation pit is one level. According to the depth and the surrounding environment of the foundation pit, the project is divided into 2 supporting sections of 1-1 and 2-2, wherein:
1-1 supporting section: the supporting depth is 20.3m, pile anchors are adopted for supporting, and five rows of prestressed anchor rods are arranged;
2-2 supporting section: the supporting depth is 20.3m, pile anchors are adopted for supporting, and seven rows of prestressed anchor rods are arranged;
and (3) carrying out no piling load on the pit edge load within 2.0m of the upper opening line of the foundation pit, implementing the rest parts according to the design piling load limiting requirement, and reserving a structural construction fertilizer groove with the thickness of not less than 1500mm in each supporting section according to the supporting depth of the side slope and the surrounding field conditions.
Design parameters of supporting section
The depth of the profile foundation pit is 20.3m, and a pile anchor supporting system is adopted.
Slope protection pile parameters: the length of the embedded section in the supporting pile is 29m, the length of the embedded section is 8.7m, the pile-protecting pile spacing is 1.4m, the pile diameter is 800mm, and the pile body strength is C25.
Crown beam parameters: and (3) manufacturing a crown beam on the pile top, wherein the size of the crown beam is 600mm (height) multiplied by 1000 (width), two sides of a reinforcement are respectively provided with 6 phi 20HRB 400-grade hot-rolled threaded steel bars, the upper part and the lower part of the middle of the reinforcement are respectively provided with 216 HRB 400-grade hot-rolled threaded steel bars, and the stirrup phi 8@ 200.
Flanging parameters: the top of the slope is provided with waterproof concrete water dispersion with the width of 1000 mm. The concrete spraying thickness is 50mm, the strength is C20, and a 50X 50 steel plate net with the width of 1mm and the thickness of 1.0m is added. 1 reinforcing steel bar nail with the length of 0.5m and phi 14 is driven into the outer side of the rainproof concrete slab at intervals of 2.0m, and a phi 14 reinforcing steel bar is transversely arranged and pressed on the steel plate net and welded with the reinforcing steel bar nail.
Anchor cable parameters: 5 rows of prestressed anchor rods are arranged among the piles, the distance between the anchor rods is 1.4m, the pore-forming aperture is 150mm, the downward inclination angle is 15 degrees, the rod body is made of phi s15.2 low-relaxation prestressed steel strands with the strength of 1860MPa, and a centering support is arranged every 1.5 m.
Grouting parameters: pouring P.S.A32.5 slag silicate pure water slurry, wherein the water-cement ratio is 0.5-0.55, the strength M is 20MPa, and adopting secondary split grouting.
Supporting parameters among piles: an HPB300 phi 6.5@200mm multiplied by 200mm reinforcing mesh is hung between supporting piles, the reinforcing mesh is fixed with soil by adopting phi 6.5U-shaped clamps, the distance between the U-shaped clamps can fix meshes, the reinforcing mesh and the slope surface are padded up by using cushion blocks (or small stone blocks), and the thickness of a concrete protective layer is 20 mm. Transverse press bars 1 phi 14 steel bars are arranged outside the steel bar meshes, each steel bar mesh is implanted into two sides of the pile body by 100mm, the longitudinal distance is 1m, then fine stone concrete is sprayed, the thickness of the surface wall is not less than 50mm, and the strength is C20.
Foundation pit monitoring
5.3.1 monitoring items
1. Monitoring the settlement of surrounding buildings, pipelines and roads;
2. the pile top and the soil nailing wall top are horizontally and vertically displaced;
3. monitoring the ground settlement of the pit edge;
4. the axial force of the anchor rod;
5. horizontal displacement of the deep layer.
5.3.2 inspection tour
1) Inspection tour for specially-assigned person
In the whole construction period of the foundation pit engineering, a special person needs to perform inspection every day.
2) The main contents of inspection tour
1 supporting structure
(1) The forming quality of the supporting structure;
(2) whether the soil body behind the wall sinks, cracks and slides or not;
(3) and (5) whether the foundation pit has soil gushing, sand flowing and piping or not.
2 construction conditions
(1) The exposed soil condition after excavation is different from a rock and soil investigation report;
(2) whether the length and the layered thickness of the excavation segmentation of the foundation pit are consistent with the design requirements or not, and whether ultralong and ultradeep excavation exists or not;
(3) whether the discharge conditions of surface water and underground water of the site are normal or not and whether the foundation pit dewatering facility operates normally or not;
(4) and (5) carrying the ground around the foundation pit, and whether the super load exists or not.
3 surrounding of foundation pit
(1) Whether the underground pipeline is damaged or not or the underground pipeline is leaked;
(2) whether cracks appear in peripheral buildings or not;
(3) whether cracks and subsidence exist on the peripheral road (ground);
(4) the construction conditions of the adjacent foundation pit and the building (structure).
4 monitoring facility
(1) The conditions of the reference points and the measuring points are intact;
(2) whether there is an obstacle that affects the observation work;
(3) and monitoring the health and protection condition of the element.
5.3.3 method of inspection tour
The inspection method of the inspection by patrol is mainly performed by visual inspection, and may be performed by using tools such as a hammer, a drill, a measuring tape, and a magnifying glass, and by using equipment such as an image pickup device and a photographing device.
5.3.4 inspection tour record
And the inspection condition of natural conditions, supporting structures, construction working conditions, surrounding environment, monitoring facilities and the like can be recorded in detail through inspection tour. If the abnormity is found, the consignor and the related units should be informed in time. The patrol inspection records should be timely sorted and comprehensively analyzed with instrument monitoring data.
5.3.5 monitoring frequency
1. The monitoring frequency of the monitoring project is determined by comprehensively considering the types of the foundation pits, different construction stages of the foundation pits and underground engineering, the surrounding environment, the change of natural conditions and local experience. When the monitored value is relatively stable, the monitoring frequency can be properly reduced.
2. The monitoring frequency should be increased when one of the following conditions occurs:
(1) monitoring data reaching an alarm value;
(2) the monitoring data has larger change or the speed is accelerated;
(3) existence of unfavorable geology not found by exploration;
(4) construction violating design conditions such as ultra-deep and ultra-long excavation;
(5) a large amount of accumulated water around the foundation pit and the foundation pit, long-time continuous rainfall and municipal pipeline leakage occur;
(6) the ground load near the foundation pit suddenly increases or exceeds the design limit value;
(7) cracking of the supporting structure;
(8) the surrounding ground suddenly sinks greatly or cracks seriously;
(9) sudden large settlement, uneven settlement or severe cracking of adjacent buildings;
(10) the bottom and the side wall of the foundation pit have the phenomena of piping, leakage or quicksand and the like;
(11) and reorganizing construction after the accident occurs in the foundation pit engineering.
5.3.6 others
1. And other matters are not to the utmost, and the requirements of technical Specifications for monitoring building foundation pit engineering (GB50497-2009) need to be met.
2. Besides the monitoring of the construction party, the owner should entrust the unit with corresponding qualification and experience to carry out the third party monitoring.
Slope protection pile construction
5.4.1 construction Process
1. Preparation for construction
1) Technical preparation
Firstly, mastering engineering geology and hydrogeology data of a field.
And secondly, reading design drawings and technical requirements of the slope protection piles, compiling a construction scheme, and carrying out technical bottom delivery, raw material inspection and concrete proportioning application.
And thirdly, the distribution of obstacles (old foundations, underground engineering, pipelines and the like) under the base under the special building distribution condition within the supporting construction influence range of the site and the adjacent area is known.
Preparing various reports and specifications for construction.
2) Main machine tool equipment
The original design adopts a long spiral hole-forming concrete pressure-casting post-inserting reinforcement cage process, and equipment needing preparation is as follows: a long auger drilling machine, a self-unloading concrete tank truck, a crane, an excavator, a vibration cage lowering device, a ground pump, an electric welding machine, a straight thread threading machine, a steel bar bending machine, a steel bar cutting machine and the like.
3) Working conditions
Firstly, a construction site is reasonably arranged, obstacles influencing construction in the site are cleaned, and a low-lying position is backfilled with silt or clay, so that the purpose of 'tee joint leveling' is achieved.
Secondly, the equipment and the machines for entering the field are installed, debugged, checked and run in a trial mode, so that the normal work of the machine is ensured, and enough spare parts are equipped.
And thirdly, a pile position control line and a horizontal elevation control point are guided, so that the protection is good, and the retest is required to be carried out frequently in the construction.
And fourthly, the raw materials are put into the field for standby, and the reinforcement cage is processed according to the design requirement.
And fifthly, trying to form a hole before formal construction so as to know the site stratum condition and check whether the construction process of the selected machine tool equipment is proper or not.
2. Construction process
The construction of the engineering slope protection pile adopts a construction process that a long spiral drilling machine is adopted to form holes, concrete is grouted by pressure, and then a reinforcement cage is inserted reversely to a designed pile top elevation to form the pile. The process has the advantages of short construction period, convenient construction, low cost and easy realization of environment-friendly and civilized construction.
Technical measures for construction
1. Measuring drilling of a fixed hole position:
when positioning the hole, according to the pile position plane diagram provided by design, each pile hole is required to be provided with a reliable pile position center mark.
Drilling:
firstly, pile position rechecking is carried out before drilling, and the allowable deviation of the central position is less than 50mm.
② the drilling hole depth is allowed to deviate by +300mm (only depth is not shallow).
And thirdly, controlling the pile diameter deviation within-20 mm.
Pile hole verticality deviation is less than 1%.
Filling coefficient of the cast-in-place pile is larger than 1;
the drilling machine is in place, firstly, a drill bit is aligned to a pile position, then a drill rod of the drilling machine is tamped, and meanwhile, the verticality of the drill rod is controlled in a two-way mode by using double vertical balls; and (5) checking the hole position again after the drilling machine is supported and stabilized, and if the hole position is unqualified and readjusted, drilling stably if the hole position is qualified.
The depth on the drill rod should be observed during drilling. And controlling the length of the scale or the drill rod, drilling to the designed hole depth, observing again and making a record. After the drill bit drills to the bottom of the hole, the drill bit can stop rotating after idling in situ for 5 seconds.
2. Manufacturing a steel reinforcement cage:
the geometric dimension meets the requirement, namely the die is adopted to ensure that the main rib position is accurate, the hole forming verticality is good, the distortion phenomenon does not exist, and the geometric dimension allows deviation;
(a) the spacing between the main ribs is +/-10 mm;
(b) the distance between the stirrups is +/-20 mm;
(c) the diameter is +/-10 mm;
(d) the length is +/-100 mm;
secondly, arranging a protection device on the reinforcement cage to ensure the thickness of the reinforcement protection layer;
③ the thickness of the main rib protective layer: the allowable deviation of the thickness of the main rib protective layer is +/-20 mm;
derusting and straightening main reinforcements, wherein the reinforcing ring reinforcements are required to be round, main reinforcement joints are connected by adopting straight thread sleeves and are staggered with each other, 2 joints are not required to be arranged on one reinforcement in the range of 35d (not less than 500mm), and the number of the joints on the same section is not more than 50% of that of the main reinforcements;
the steel bar main rib lap joint is connected by adopting a JM rib-stripping rolling straight thread connecting sleeve, the main rib thread head processing and joint assembly are constructed strictly according to the operating rules, thread head operators need to train to be qualified and then take on duty and construct strictly according to the training operating rules, 3 test pieces are manufactured before the joint processing and are subjected to process inspection according to the regulations, and construction can be carried out after the joint is qualified. In the construction process, every 500 joints are used as a test batch for testing. And (5) completing the inspection and filling of a steel bar thread head processing quality inspection record table and a steel bar joint connection quality record.
3. Hoisting a steel reinforcement cage:
firstly, double-point hoisting is adopted;
secondly, transporting by using a flat car with a bracket, strictly prohibiting dragging and rolling, and preventing the reinforcement cage from deforming;
thirdly, the hoisting inlet hole needs to be lifted lightly and dropped lightly, cannot be pressed in forcibly, and needs to be lowered in the middle, so that the verticality and the thickness of the protective layer are ensured;
fourthly, arranging a protection device on the main rib to ensure the verticality and the thickness of the protection layer;
fifthly, the reinforcement cage needs to be positioned strictly according to design requirements, and the installation depth of the reinforcement cage is +/-100 mm.
4. Pouring concrete:
firstly, pouring is carried out by adopting 40-60 pump pressure pouring to form a pile, the relation between the drilling speed and the pump speed is controlled well, the quality of a pile body is ensured, and the accident of pile breakage is avoided.
Secondly, when the part close to the pile top is poured, in order to ensure the quality of the concrete of the part of the pile top, the actual pouring height is 0.5m higher than the designed pile top.
And thirdly, at least two groups of test blocks are made for standard maintenance of each group of piles (every day), one group is used for measuring 28d strength of the piles, and the other group is used for measuring short-term strength to guide construction.
5. Chiseling off a pile head:
and after the pile construction is finished and the design strength reaches 70%, chiseling floating slurry and redundant concrete at the top of the pile head to the design elevation.
Quality assurance measures
In order to ensure the construction quality, the construction quality is generally controlled according to three stages, namely, the quality control in the drilling stage, the quality control in the manufacturing and installation of the reinforcement cage, the quality control in the lowering of the reinforcement cage and the quality control in the concrete pouring.
1. Pile hole positioning quality
Pile hole positioning is carried out by a professional technician, and the measurement calculation result is checked to ensure that the drilling machine can be positioned in place after the drilling machine is accurate and free of errors. When the drilling machine is in place, the drilling machine needs to be strictly aligned, and the error between the central vertical line of the drill bit and the center of the pile hole is ensured to be not more than 50mm.
2. Quality of drilled hole
The verticality deviation of the drilled hole is allowed to be less than 1%;
secondly, a drilling tool with good concentricity is used to reduce the bending of the drill hole and the filling coefficient;
3. steel reinforcement cage assembling and positioning quality guaranteeing measure
The steel reinforcement cage, the core pipe and the vibration hammer form a steel reinforcement cage feeding system, the lower end of the core pipe abuts against the bottom of the steel reinforcement cage, and the upper portion of the steel reinforcement cage is connected with the vibration hammer through a flange plate.
Righting by a special person (2-3 persons) when the reinforcement cage is placed into the orifice, aligning the center of the hole, slowly placing the reinforcement cage, and keeping the reinforcement cage vertical in the hoisting process.
After steel reinforcement cage lower part gets into the concrete, at first slowly transfer the steel reinforcement cage under the dead weight effect of steel reinforcement cage and vibratory hammer, transfer the back that can not sink naturally when the steel reinforcement cage, open the vibratory hammer, along with the height (the vibration in-process) of vibrating the steel reinforcement cage entering concrete, ensure the wire rope area power all the time of hoist and mount steel reinforcement cage, insert in case the steel reinforcement cage slope, the stop vibration after arriving the design height, extract the core pipe, transfer in place in order to ensure the steel reinforcement cage, the vibration that plans to adopt powerful vibratory hammer and the stronger vibration core pipe of rigidity is constituteed sinks the device and is carried out the steel reinforcement cage and transfers.
4. Pouring concrete
Firstly, the qualification of commercial concrete manufacturers needs to be examined before construction. The concrete manufacturer should issue the quality certification data of the mix proportion application form, the open-tray identification, the material quality inspection report, the concrete alkali chlorine content, etc. of the produced concrete;
controlling the slump to be 18-24 cm, and preventing the pipe from being blocked;
thirdly, after the drilling machine drills to the designed depth, the drilling machine sends a signal to the ground pump signal worker, and the drilling rod is correspondingly lifted along with the pumping until the concrete reaches the hole opening.
5. Test plan
Firstly, reinforcing steel bars: according to design requirements, all the raw steel bars enter the field at the same time, field raw material tests (60t is one batch) are carried out after the raw steel bars enter the field, the inspection batch of the steel bar joints is 500 times per batch, and all the tests are 100% witnessed.
Concrete: according to the design requirements, the project adopts commercial concrete, and related data such as material retest, mix proportion application form, open-disc identification and the like are provided by a concrete supply unit.
General description of construction of long-spiral-pressure concrete-poured rear-inserted reinforcement cage
After the long spiral drilling machine is assembled, the power of the power head is 150KW, a drill hole is tried, the footage is found to be still fast, a hole with the depth of 26.5m can be formed in more than one hour, the efficiency is high, and the hole is not easy to collapse. Then, the problem comes that the concrete can not be continuously supplied at all due to serious haze of the Shijiazhuang; another problem is that the delay of the start date can not be determined, the power head of the high-power drilling machine is detached to emergently support another project which starts working immediately, a 110KW power head is replaced, and then the hole is tried, so that the efficiency is low, a hole can not be formed within 3 hours, and multiple times of drill lifting and drill lowering are needed. Even more, when the patient encounters the horizon containing the ginger stone, the phenomenon of immobility appears. The construction period is required to be tight and is difficult to achieve, and a rotary drilling rig is additionally arranged.
Overview of construction of rotary drilling rig
The rotary drilling rig adopts dry hole operation, and one device is used for drilling in the following steps of 6: 00 to night 22: 00, 13-14 holes can be formed, the holes are not influenced by underground ginger stones, the holes can be smoothly formed, the holes are not collapsed, concrete is intensively poured at night, the management and control regulations of a concrete tank truck in Shijiazhuang city are well utilized, the efficiency is improved, and the quality is ensured. However, when the construction is carried out to No. 120 to No. 270 piles, the pile position is found to be just above the underground abandoned air-raid shelter, after a hole is tried to be drilled to the bottom plate of the air-raid shelter, the elevation of the top plate of the hole is about 3m below the ground surface, the top plate is of a bricked structure, the thickness is about 400mm, the height of the hole is about 2m, the bottom of the hole is bricked and coated with a cement mortar thin layer, and the thickness of the bottom plate is about 400 mm. Later, the applicant carries out investigation, and finds that the south and north directions are more than one hundred meters long, and the east is more than 50 meters long until the south and north roads are built, and the south and north roads are communicated in a T shape. After the height, the structure and the trend are found out, a group thinking method is started, and the problem is solved.
Firstly, the suggestion is that after the air-raid shelter is perforated on the pile position, people go down to brick and build the hole wall, but the phenomenon that the work load is too large and unrealistic, the time is too long and the danger is too dangerous is quickly avoided, and no people are willing to go down to dry the air-raid shelter is avoided. So-called shimming, clay re-grouting, etc., are clearly not feasible. Throwing the flying pipe is not feasible, the drill bit runs once, and even if the drill bit does not run, the drill bit is easy to be discounted. Later, the method is realized on the reinforcement cage by commercial quantity, a sheet iron pile casing or a thin steel pile casing can be manufactured and directly sleeved on the reinforcement cage to isolate the section, and after the slope protection pile is completed, the inter-pile protection is slowly processed when a foundation pit is excavated. The method is also rejected quickly, firstly, the processing of the iron sheet pile casing or the steel pile casing is troublesome and laborious, and more importantly, even if the iron sheet pile casing or the steel pile casing is processed and sleeved on the reinforcement cage, the quality can not be ensured during concrete pouring, the iron sheet pile casing or the steel pile casing can be broken, and even if the iron sheet pile casing or the steel pile casing is not broken, concrete can flow out from the upper end of the reinforcement cage pile casing, and the steel pile casing can not be filled. The construction period is not allowed. The result of the final trade is that local materials are used, and the existing equipment is utilized to break through the problem. On site, clay exists, a rotary digging drilling machine exists, and a rotary digging bucket is a 'rammer'.
The following solution is determined, and the specific steps are as follows: firstly, leveling a field, releasing a pile position and fastening the pile position; secondly, further confirming the trend of the cavity (the civil air defense channel) and two ends of the cavity, extending a protection pile outside each direction of the two ends, namely extending the No. 120 pile to the north, adding a protection pile, extending the No. 270 pile to the south, adding a protection pile, firstly stacking the excavated soil beside the protection pile at one end until the pile is excavated to the upper end of the civil air defense channel; and thirdly, excavating at intervals of one pile, directly filling the excavated good soil into the protection pile outside the end head, and tamping the filled soil by using the rotary excavating bucket as a tamping hammer when one bucket of good soil is filled, wherein the soil can be randomly diffused to the periphery of the cavity until the soil in the cavity is completely tamped. Fourthly, the 'protection piles' outside the other end are filled with earth and tamped by the method, so that piles at two ends of the hollow hole (civil air defense channel) are treated; fifthly, constructing the isolation holes, wherein each middle pile is excavated to the top of the hollow hole and then stopped, and the good soil of the isolation holes is filled and tamped until the middle pile is tamped; and sixthly, digging the pile dug in the middle, filling soil and tamping. All the pile holes are processed in place. Seventhly, from the middle, normally digging holes, checking the holes after forming the holes, putting a reinforcement cage, and pouring concrete to form a pile; eighthly, excavating separated holes, normally excavating the holes, checking the holes after the holes are formed, putting a reinforcement cage, and pouring concrete to form a pile; and ninthly, constructing piles at two ends of the hollow cavity (civil air defense channel). Therefore, all pile construction at the hollow (civil air defense passage) is completed under the conditions of hardly increasing the cost and not increasing the construction period.
24 horizontal displacement monitoring points, 24 vertical displacement monitoring points, 8 deep horizontal displacement monitoring points and 27 anchor rod axial force monitoring points are arranged on the foundation pit site, the foundation pit is completely finished within one and a half years, a bottom plate is constructed, and all monitoring data are in a safety range and are far smaller than numerical values allowed by the specification through continuous monitoring. The foundation pit support is safe. The hole handling has also proven to be efficient, economical and fast.

Claims (4)

1. A simple method for forming a pile by a rotary drilling rig in a cavity is characterized by comprising the following steps: the method comprises the following steps:
(1) the hole trend and the end position of the area needing construction are found out, the field is leveled, and the pile position is determined;
(2) respectively constructing a protection pile outside two ends of the cavity of the construction area, and plugging two ends of the cavity of the construction area;
(3) excavating a pile hole which is separated from the protection pile by one pile position, directly filling excavated good soil into the protection pile hole at the end, tamping the filled soil by using a rotary excavating bucket as a tamping hammer when one bucket of good soil is filled, wherein the upper surface of the filled soil is 0.5-1.0 m above the top of the cavity, and the filled soil can be randomly diffused to the periphery of the cavity but is tamped until all the soil in the cavity is tamped;
(4) firstly digging the pile hole of each pile in the construction area to a hollow hole, filling the pile hole with good soil of the adjacent pile hole and tamping, wherein the upper surface position of the filled soil is the same as that in the step (3);
(5) digging the pile hole dug by jumping in the middle, filling soil, and tamping until all the pile holes are constructed;
(6) and completing pile-forming construction in all construction areas by adopting a conventional process from the middle of the construction area.
2. The simple method for forming the pile in the meeting cavity of the rotary drilling rig according to claim 1, which is characterized in that: in the step (2), the construction method of the protection pile comprises the following steps: digging a soil filling hole to the bottom of the cavity, and filling soil into the cavity and tamping.
3. The simple method for forming the pile in the meeting cavity of the rotary drilling rig according to claim 1, which is characterized in that: in the step (3), the pile-forming needs hole-separating construction to avoid perforation, the pile hole can be stopped when being dug to the bottom end of the hollow hole, and the good soil dug by the pile hole and the adjacent pile hole is utilized for layered backfill and tamping; provides a stable foundation condition without collapse when excavating pile holes for formal pile forming.
4. The simple method for forming the pile in the meeting cavity of the rotary drilling rig according to claim 1, which is characterized in that: in the step (6), a pile hole of the pile to be constructed is excavated from the middle to form a hole, and then the hole is inspected, a reinforcement cage is hung, and concrete is poured to form a pile; and adopting the jumping construction to ensure the minimum disturbance to the hole wall during the hole forming and the minimum impact to the hole wall during the concrete pouring so as to complete the whole construction of the pile.
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