CN110219300B

CN110219300B - Construction process of partially-bonded prestressed uplift anchor rod

Info

Publication number: CN110219300B
Application number: CN201910444998.7A
Authority: CN
Inventors: 何世鸣; 李江; 田震远; 周与诚; 郁河坤; 陈辉; 黄鑫峰; 贾城; 司呈庆; 梁成华; 王海宁; 王建明; 洪伟; 杜高恒; 郭跃龙; 陈鹏
Original assignee: BEIJING URBAN CONSTRUCTION SCIENCE TECHNOLOGY PROMOTING ASSOCIATION; Zhongcai Geological Engineering Exploration Academy Co ltd; Beijing Building Material Geotechnical Engineering Corp
Current assignee: BEIJING URBAN CONSTRUCTION SCIENCE TECHNOLOGY PROMOTING ASSOCIATION; Zhongcai Geological Engineering Exploration Academy Co ltd; Beijing Building Material Geotechnical Engineering Corp
Priority date: 2019-05-27
Filing date: 2019-05-27
Publication date: 2021-07-02
Anticipated expiration: 2039-05-27
Also published as: CN110219300A

Abstract

A construction process for partially bonding a prestressed uplift anchor rod comprises the following steps: (1) measuring the positioning hole position; (2) drilling; (3) processing and manufacturing a steel strand cage; (4) a steel strand cage is arranged; (5) grouting; (6) and the steel strand is tensioned and locked and is connected with the bottom plate steel bars. The invention has the advantages that: by adding prestress, the stress property of the cement paste is changed, so that the anchor rod body is prevented from cracking; because the acting point is arranged at the lower part of the anchor rod, the characteristic that the prestressed anchor rod is partially bonded is highlighted, the stress between anchor soils is not more and more loose when being pulled, but is in a wedge shape, and the characteristic that the prestressed anchor rod is more and more tight when being pulled is provided, so that the pulling-resistant bearing capacity of the prestressed anchor rod is greatly improved. Convenient construction, safety guarantee, reliable quality and obvious economic benefit.

Description

Construction process of partially-bonded prestressed uplift anchor rod

Technical Field

The invention relates to a construction process for partially bonding a prestressed anti-pulling anchor rod, which is used for the construction of an anti-pulling anti-floating anchor rod in a deep foundation pit and belongs to the field of buildings.

Background

The current measures for solving the anti-floating problem of the underground structure mainly comprise: releasing water buoyancy, increasing weight, and arranging anti-pulling anti-floating pile or anti-pulling anti-floating anchor rod. The anti-pulling anti-floating pile or anti-pulling anti-floating anchor rod and other anti-pulling components are the most common method for solving the anti-floating problem of the underground structure (as the existing anti-floating anchor rod shown in fig. 4 and 5, a reinforcement cage and solidified cement paste are arranged in a drill hole 3, at least three reinforcing steel bars 11 without sleeves and grease are uniformly distributed along the circumference, and are supported and fixed by a plurality of centering brackets 7 which are arranged at intervals along the axial direction, a grouting pipe 10 penetrates through a center hole of each centering bracket 7, and the upper part of each anchor rod is a concrete bottom plate 4 and a cushion layer 5 of a basement). In addition, when some high-rise structures are subjected to large horizontal load, the foundation also has the problem of anti-pulling, and anti-pulling anti-floating piles, anti-pulling anti-floating anchor rods and other anti-pulling members are also commonly adopted. However, the common uplift pile or uplift anchor rod has the disadvantages of low bearing capacity, high cost and the like, and in the uplift working state of the common uplift pile or uplift anchor rod, the pile body concrete or anchor rod grouting body is in a tensile state and is easy to crack, so that the stressed steel bars in the uplift member can be corroded by underground water gradually, the tensile bearing capacity is reduced, and the stressed steel bars can be pulled apart to cause the anti-floating member to fail in serious cases.

In order to solve the problems, the invention provides a partial bonding prestressed uplift anti-floating pile and a series of technologies thereof, wherein the partial bonding prestressed uplift anti-floating pile comprises the following steps: the partially-bonded prestressed uplift anti-floating pile and the construction method ZL 200710065368.6 thereof, the partially-bonded tension dispersion type prestressed uplift anti-floating pile ZL 201310470796.2, the pressure dispersion type prestressed uplift anti-floating pile and the construction method ZL 201310470798.1 thereof, the pile forming method of the stress dispersion type prestressed uplift anti-floating pile and the steel bar strand cage ZL 201310544716.3 thereof have the advantages that: the stress property of the concrete is changed, so that the stress of the concrete is more reasonable, and the uplift-resistant anti-floating pile design can be carried out according to the first-level crack resistance; a large amount of steel bars are saved; the long spiral hole-forming concrete post-grouting steel bar-steel strand cage realizes rapid construction, has high efficiency, and is 5-10 times faster than the construction of a traditional reverse circulation drilling machine; the method has the advantages of no need of slurry wall protection and no slurry pollution, realizes dry operation, is beneficial to safe and civilized construction, and particularly shows the advantages in urban construction. The rotary excavating construction process is adopted on the large-diameter and large-length pile, and the method has obvious advantages.

However, as construction progresses, some problems have been found to occur in construction: (1) the construction of the anti-pulling anti-floating pile in the deep foundation pit needs large machinery, particularly when the construction is close to the tail sound, the berm is retracted, the large machinery needs hundreds of tons or more of cranes to be lifted out, the side of the deep foundation pit needs to bear the large additional load, the potential safety hazard of the foundation pit is increased, and accidents of car passing, people destruction and death occur in serious cases. (2) The foundation pit is narrower, the construction of large machinery is limited, and especially side pile and corner pile can not be constructed. (3) In terms of cost performance of piles and anchor rods, the anchor rods are obviously higher in cost performance, and currently, common anchor rods adopting reinforced cement paste or mortar are more. (4) When the long spiral drilling machine encounters a compact sand-gravel stratum, the long spiral drilling machine cannot drill to the designed depth, the phenomenon of 'failure to drill' occurs, and the application of the long spiral drilling machine is also limited. (5) The method is characterized in that a common anchor rod of reinforced cement paste or mortar is designed in a dense sand-gravel stratum, for example, 3 steel bars with the diameter of 22 steel bars, a follow-up pipe water drill is adopted, a protective layer with the thickness of nearly 1m needs to be reserved for pore forming, otherwise, the operation cannot be carried out when an outer pipe is extracted after a reinforcement cage is filled with cement paste, the anchor rod is slightly longer in length, for example, 12m, the reinforcement cage needs to be arranged under a crane, then the crane is required to be lifted out when the crane is out of the field, and the construction machinery cost and the potential safety hazard of. (6) When the high-rise building is connected with the skirt house and the skirt house is both based on natural foundation, the skirt house is anti-floating and can not adopt uplift piles. Otherwise, the settlement of the skirt house is limited due to the supporting effect of the uplift pile, so that the settlement difference between the high-rise building and the skirt house is increased. All the problems need to invent a new anchor rod, which has high cost performance, can be constructed by small-sized machinery, does not need a crane, and has safe, green and environment-friendly performance quality.

The invention relates to a concrete pole body composite anchor rod and a construction method thereof in the prior art (CN201510360640.8) and a utility model patent of a concrete pole body composite anchor rod (CN201520446623.1), which comprises: the concrete pole body, the pole bone pipe, the grouting body, the pole rib and the positioning guide device; the upper end is an embossing anchor or a clamping piece anchor.

The invention still has insurmountable problems, such as concrete pole body still use the long auger drilling machine to press and pour the concrete construction, it is a large-scale machinery, the large-scale machinery needs hundreds of tons or more of tonnage cranes to hoist out when going out of the deep foundation pit, the side of the deep foundation pit should bear such large additional load, the potential safety hazard of the foundation pit is inevitable to increase; the rod bone pipe is bonded with the concrete in full length, and when the steel strand is pulled, the concrete is inevitably pulled to crack; the steel strand does not apply prestress, does not change the stress property of the concrete, only replaces the steel bar with the steel strand, saves a little steel bar and does not contribute to the crack resistance of the concrete. The concrete plain pile is firstly poured by pressure, then the steel pipe (rod bone pipe) is implanted, then the steel strand is put in, and the cement paste is injected, so the process is complex, and the rod bone pipe cannot be too thick, the internal steel strands can only be spliced together and cannot be effectively separated, so the cementing effect of the cement paste is limited. The connection of the knurling type or the clamping piece type composite anchor rod and the bottom plate is complicated, and the connection of thousands of anchor rods and the bottom plate is complicated. The construction of workers is a very painful affair.

Disclosure of Invention

The invention aims to provide a steel strand cage with a prestressed uplift anchor rod partially bonded, which effectively solves the problems of construction of an uplift pile in a deep foundation pit and adoption of large machinery for the uplift anchor rod at present, avoids the defects of common reinforced cement paste or mortar anchor rods, changes the slurry stress property and avoids cracking of the anchor rod body. The complicated method for connecting the steel strand with the bottom plate is also overcome.

The technical scheme of the invention is as follows: the construction process of partially bonded prestressed uplift anchor rod is characterized by comprising the following steps of:

(1) measuring the positioning hole position: when a hole is positioned, anchor positions are distributed according to a pile position plane diagram provided by design and a measured and placed axis on site, in order to prevent anchor position deviation caused by vehicle rolling in construction, a method of pouring 20-30 cm lime into an opening of a steel pipe is adopted for positioning at the anchor positions, and a marker is arranged in the lime;

(2) drilling: adopting a construction process of a water drilling and pipe following jumbolter;

(3) and (3) processing and manufacturing a steel strand cage: at least three unbonded steel strands are uniformly distributed along the circumference and are supported and fixed by a plurality of centering brackets which are arranged at intervals along the axial direction; removing the sleeve and grease on the surface of a section of the bottom of the steel strand to form a steel strand bonding section; the center of the centering bracket penetrates through a grouting pipe, and the bottom end of the grouting pipe is temporarily closed;

(4) b, steel strand cage setting: feeding the steel strand cage with the grouting pipe into the drilled hole;

(5) grouting: opening a cement slurry pump, injecting cement slurry into the drill hole through a grouting pipe, and grouting the cement slurry to the hole opening; when the cement slurry at the orifice falls below the designed elevation after the outer pipe of the drilling machine is pulled out, secondary slurry supplement is carried out in time;

(6) the steel strand stretching locking and the bottom plate steel bar connection: when the strength of the cement paste meets the design requirement, removing the soil layer around the part above the cushion layer on the upper part of the anchor rod to reach the bottom elevation of the bottom plate, exposing the steel strand at the position, and peeling, degreasing and deoiling; the steel strand is tensioned and then locked on the anchor head and the backing plate, and the elevation of the upper end of the anchor head is the same as the elevation of the bottom of the cushion layer; and binding the top ends of the reserved steel strands with the steel bars of the concrete bottom plate after the cushion waterproof layer is prepared.

The specific manufacturing method of the steel strand cage comprises the following steps: firstly, blanking qualified unbonded steel stranded wires after retesting according to the designed length, peeling, degreasing and deoiling the lower end of the unbonded steel stranded wires with the designed length of 2.5-4.5 m, binding the steel stranded wires with a centering bracket every 2.0m according to the number of the anchor rods, placing the steel stranded wires in side holes of the centering bracket, penetrating a soft plastic grouting pipe into a center hole, and winding the lower end of a steel stranded wire cage by using an adhesive tape so as to be conveniently put into a drill hole; and in order to improve the bond stress between the steel strand and the cement paste, a section of steel bar is bound on the steel strand, and in order to avoid the over-thickness of the whole anchor rod, the steel bar sections are arranged in a staggered manner, and a stress dispersion effect is formed.

Because the long spiral drilling machine cannot drill to the designed depth and cannot move, and the hole is easy to collapse after the drilling is carried out, the construction process of the water drilling and pipe following jumbolter is adopted, the designed depth can be achieved, the hole collapse problem is avoided, and the defect of using large-scale equipment is overcome.

The steel strand is prestressed, so that the stress property of cement paste is changed, and the cracking of the anchor rod body is avoided; because the acting point is at the steel strand bonding section L at the lower part of the anchor rod, the characteristics of the partially bonded prestressed anchor rod are highlighted, and different from the common anchor rod, the stress between anchor soils is not the characteristics of 'radish pulling' and 'loosening along with pulling', but is in a 'wedge shape' and 'tightening along with pulling', so that the pulling resistance bearing capacity is greatly improved.

The steel bar sections on different steel strands are staggered.

The centering brackets are bound together with the steel strand by using burning wires every 2.0 m; the centering support consists of a circular ring and a multi-angle star, the circular ring is connected with the inner corners of the multi-angle star, the grouting pipe penetrates through the circular ring, and the steel strand is placed at the outer concave corner of each multi-angle star.

The top end of the steel strand is mutually locked and connected with the bottom plate steel bar through a U-shaped clamp or a binding wire.

The invention has the advantages that: by adding prestress, the stress property of the cement paste is changed, so that the anchor rod body is prevented from cracking; because the acting point is arranged at the lower part of the anchor rod, the characteristics of the partially bonded prestressed anchor rod are highlighted, and different from the common anchor rod, the stress between anchor soil is not the characteristics of 'radish pulling' and 'loosening along with pulling', but the stress between anchor soil is in a 'wedge shape' and 'tightening along with pulling', so that the pulling-resistant bearing capacity of the anchor rod is greatly improved. The bearing capacity can be improved by more than 50% by the same process with the same pore diameter and the same length and the same stratum. Convenient construction, safety guarantee, reliable quality and obvious economic benefit.

Drawings

FIG. 1 is a flow chart of the construction process of the present invention;

fig. 2 is a schematic view of the overall structure of the embodiment of the invention applied to a rock bolt;

FIG. 3 is a cross-sectional view B-B of FIG. 2;

FIG. 4 is a schematic view of the overall structure of the prior art;

fig. 5 is a sectional view a-a of fig. 4.

Detailed Description

Referring to fig. 1, the concrete construction process flow of the invention applied to the prestressed uplift anchor rod is as follows:

firstly, excavating to a designed elevation, wherein the thickness of the protective layer does not need to be 1m, and only 0.5m can be used.

And (3) placing the steel strand cage into the drilled hole 3, injecting cement paste through the grouting pipe 10, and solidifying to form the anchor rod main body. When waiting that grout intensity reaches the designing requirement, clear away stock main part upper portion soil layer, reach concrete bottom plate 4 bottom elevation, expose partial no bonding steel strand wires 8 and skin the degreasing, lock steel strand wires 8 on anchor head 6 and backing plate 11, guarantee that 6 top elevation of anchor head is the same with the bottom elevation of bed course 5. After the cushion layer 5 (containing the waterproof layer) is made, binding the reserved steel strand 8 with the steel bar 1 of the concrete bottom plate 4 of the basement (the bottommost building).

The specific construction process comprises the following steps:

1) measuring the location of the pilot hole

When the hole is positioned, the anchor positions are distributed according to a pile position plane diagram provided by design and a measured and placed axis on site, in order to prevent anchor position deviation caused by rolling of vehicles in construction, the anchor positions are positioned by adopting a method of pouring 20-30 cm lime into holes of steel pipes, and markers are arranged in the lime.

2) Drilling holes

Firstly, the deviation of an anchor position is less than 50 mm;

the depth of the drilled hole is allowed to deviate by +100 mm;

thirdly, the allowable deviation of the aperture is +/-20 mm;

fourthly, the perpendicularity deviation of the pile hole is less than 1 percent;

3) processing, manufacturing and feeding steel strand cage

The due materials such as the steel strand and the like are proved, and the steel strand can be used after being qualified after being retested on site; binding a group of centering brackets on the main ribs every 2m, wherein the allowable error of the length of the main ribs is +/-100 mm; the central hole penetrates into the grouting pipe, and the front end of the grouting pipe is temporarily closed. The error of the drilling is strictly controlled according to the designed elevation in the drilling process and is not more than 50 mm.

4) Grouting:

the cement quality meets the design requirements, and the cement quality is proved by delivery and retest reports. Preparing cement paste strictly according to the designed water cement ratio, adding additives according to the requirements, and fully stirring. Taking out the inner pipe after the final hole, manually putting a steel strand cage with a grouting pipe, opening a cement slurry pump, and grouting cement slurry to the hole opening; and (5) after the outer pipe is pulled out, the grout at the orifice falls below the designed elevation, and then secondary grout supplementing is carried out in time. 1 group of cement paste test blocks are made for every 30 anchor rods.

5) The steel strand stretching locking and the bottom plate steel bar connection:

and peeling, degreasing and deoiling the exposed steel strand, tensioning and locking the steel strand at the upper end of the anchor rod, wherein the elevation of the upper surface of the anchor is the same as the elevation of the bottom of the cushion layer of the bottom plate. And binding the steel strand with the bottom plate steel bar when the cushion layer, the waterproof layer and the bottom plate steel bar are prepared.

Manufacturing a steel strand cage: firstly, blanking the unbonded steel stranded wires qualified in the retest according to the designed length, peeling, degreasing and deoiling the lower end of the unbonded steel stranded wires, binding the unbonded steel stranded wires and the isolation frame together by using a fire wire at intervals of 2.0m according to the number of the anchor rods, purchasing a finished product support with the diameter of 10cm by the isolation frame, clamping the steel stranded wires in a gap, penetrating a phi 20 soft plastic grouting pipe into the center of the steel stranded wires, and tightly winding the lower end of a rod body by using an adhesive tape so as to enter the bottom of the hole. The lower peeling, degreasing and deoiling section of the anchor rod is only 2.5-4.5 m, a section of steel bar is bound on the steel strand in order to improve the bond stress of the steel strand and cement paste, and the steel bar section is arranged in a staggered mode in order to avoid the fact that the whole anchor rod is too thick, and a stress dispersion effect is formed. Thereby forming a partially bonded prestressed steel strand cage. By applying prestress, the stress property of the cement paste can be changed, so that the anchor rod body is prevented from cracking; because the acting point is arranged at the lower part of the anchor rod, the characteristics of the partially bonded prestressed anchor rod are highlighted, and different from the common anchor rod, the stress between anchor soil is not characterized by 'radish pulling' and 'loosening as the anchor rod is pulled more and more', but is characterized by 'wedge-shaped' and 'tightening as the anchor rod is pulled more and more', so that the pulling-resistant bearing capacity of the anchor rod is greatly improved. The characteristics of convenient construction, reliable quality and obvious economic benefit are highlighted. The bearing capacity can be improved by more than 50% by the same process with the same pore diameter and the same length and the same stratum. The economic benefit is extremely obvious.

Referring to fig. 2-3, the steel strand cage of the invention comprises steel strands 8 and centering brackets 7, wherein at least three steel strands 8 are uniformly distributed along the circumference and supported and fixed by the centering brackets 7 which are arranged at intervals along the axial direction; the upper section of the steel strand 8 is an unbonded steel strand section, the surface of the steel strand is sleeved with a sleeve, and grease is arranged in the sleeve; the bottom section of the steel strand 8 is a bonding steel strand section L, the surface of which is removed with a sleeve and grease, and the steel strand 8 below the cushion layer 5 is provided with an anchor head 6 and a backing plate 11; the grout tube 10 is positioned by the centering bracket 7 (through its central bore) and lies on the axis of the bolt. The top ends of the steel strands 8 are bent towards the horizontal direction and are locked with the bottom plate steel bars 1 after being tensioned; a reinforcing steel bar section 9 is welded on the bonding steel strand section L, so that the bond strength of the steel strand 8 and the cement paste is improved; the steel bar sections 9 on different steel strands are staggered with each other, the stress dispersion effect is formed, and the whole anchor rod is prevented from being too thick; the lower end of the steel strand cage is tightly wound by an adhesive tape, and the bonding steel strand section L at the lower part of the steel strand cage is only 2.5-4.5 m.

The centering brackets 7 are bound together with the steel strand 8 by burning wires every 2.0 m; the centering support 7 consists of a circular ring 71 and multi-angular stars 72, the circular ring 71 is connected with the inner corners of the multi-angular stars 72, the grouting pipe 10 penetrates through the circular ring 71, and one steel strand 8 is placed at the outer concave corner of each multi-angular star 72. The number of corners of the multi-pointed star 72 corresponds to the number of steel strands 8.

The top ends of the steel strands are mutually locked and connected with the bottom plate steel bars 1 through U-shaped clamps or binding wires.

The specific manufacturing method of the steel strand cage comprises the following steps: firstly, blanking the unbonded steel stranded wires qualified in the retest according to the designed length, peeling, degreasing and deoiling the lower end of the unbonded steel stranded wires, binding the steel stranded wires and the isolation frame together by using a fire wire at intervals of 2.0m according to the number of the anchor rods, wherein the isolation frame adopts a finished product support with the diameter of 10cm, the steel stranded wires are placed in side holes, a phi 20 soft plastic grouting pipe penetrates through a central hole, and the lower end of a rod body is tightly wound by using an adhesive tape so as to be placed at the bottom of the hole. The lower peeling, degreasing and deoiling section of the anchor rod is only 2.5-4.5 m, a section of steel bar is bound on the steel strand in order to improve the bond stress of the steel strand and cement paste, and the steel bar section is arranged in a staggered mode in order to avoid the fact that the whole anchor rod is too thick, and a stress dispersion effect is formed. Thereby forming a partially bonded prestressed steel strand cage. By applying prestress, the stress property of the cement paste can be changed, so that the anchor rod body is prevented from cracking; because the acting point is arranged at the lower part of the anchor rod, the characteristics of the partially bonded prestressed anchor rod are highlighted, and different from the common anchor rod, the stress between anchor soil is not the characteristics of 'radish pulling' and 'loosening along with pulling', but the stress between anchor soil is in a 'wedge shape' and 'tightening along with pulling', so that the pulling-resistant bearing capacity of the anchor rod is greatly improved. The characteristics of convenient construction, safety guarantee, reliable quality and obvious economic benefit are highlighted. The bearing capacity can be improved by more than 50% by the same process with the same pore diameter and the same length and the same stratum. The economic benefit is extremely obvious.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

Project for reforming school hospitals in middle-guan village school district of Beijing university of nursing workers

1) Overview of the engineering

The project of the school hospital of the Zhongguancun school district of Beijing university of Rich Engineers is located in the school of the Nanda street of the Zhongguancun of Heijing university of Beijing, the east side of the school is a hospitalization place, the south side is a Kai-Shi building and a playground, the west side is a Polygala tenuifolia building and a shop, and the north side is a residential building No. 2. The engineering + -0.00 ═ 52.700 m. The project consists of a school hospital and a rainwater storage tank. The main technical and economic indexes are shown in the table 1.

TABLE 1 Main technical and economic indexes of modification projects of school hospitals of Zhongguancun school district of Beijing university of nursing Engineers

The top elevation of the anchor rod is respectively-15.15 m, -15.75m and-16.25 m according to subareas.

2) Current situation of engineering site and engineering hydrogeological conditions

The proposed site is located in the southwest part of the Beijing urban area and belongs to the middle-upper part of the Yongding river torrent fan. The terrain of the proposed site is basically flat. The ground elevation at the drill hole opening in the investigation range is 52.33-52.56 m.

Geological conditions of site engineering

According to geotechnical engineering survey reports, the upper part is a fill layer, and the lower part is a newly deposited layer, a general quaternary scouring flood layer. The field stratum is as follows from top to bottom:

1) it is characterized by that it uses artificial soil-filling layer

Clay silty plain filling: brown yellow, mainly comprising clay silt and sandy silt, and locally comprising fine sand, a small amount of brick dregs, ash, plant roots and the like. Wet and loose, and partially filling 1 miscellaneous filling soil. The total thickness of the layer is 1.20-7.20 m, and the elevation of the bottom layer is 45.28-51.15 m. The soil is filled with impurities, has mixed colors, is mainly used for buildings, contains bricks, ash, broken stones and the like, is wet and loose in structure, and has the maximum thickness of 0.70 m.

2) The four stages of the flushing layer

Clay silt and sandy silt: brown yellow, contains mica and iron oxide, is wet, slightly dense to medium dense, high to medium high compressibility, and sandwiches ② 1 powdery clay and heavy powdery clay lenses. The layer is discontinuous in distribution, and generally has a thickness of 0.60 to 5.70m and a layer bottom elevation of 45.14 to 46.76 m. ② 1 powdered clay, heavy powdered clay, brown yellow, mica, ferric oxide, etc., wet-wet, soft-plastic, high-medium high compressibility, maximum thickness of 0.70 m.

Thirdly, fine sand grinding: brown yellow, contains mica and the like, is wet, dense and dense, has the thickness of 5.00-7.70 m and the bottom elevation of 39.03-40.26 m.

Pebble: variegated and sub-circular, the particle size is generally 6-9 cm, the maximum particle size is not less than 11cm, the medium coarse sand is filled by about 30 percent, the wet-saturated sand is slightly dense-medium dense, the thickness is 6.20-7.30 m, and the bottom elevation of the layer is 32.82-33.43 m.

Powder clay and heavy powder clay: brown yellow, contains mica, ferric oxide and the like, is wet to very wet, is plastic, has middle-high to middle compressibility, has the thickness of 1.50-2.40 m and the bottom elevation of 30.75-31.83 m.

Fine sand: brown yellow, contains mica and the like, is wet and compact, the thickness of the layer is 1.90-3.60 m, and the elevation of the bottom of the layer is 27.72-29.23 m.

And (c) pebbles: variegated, sub-circular, generally 6-10 cm in particle size, not less than 12cm in maximum particle size, about 30% of medium coarse sand filling, wet-saturated, medium dense-dense. The layer was not peeled through, the maximum exposed thickness was 11.90 m. .

Site hydrogeological conditions

1) Two layers of underground water are exposed in the drilling depth range during the exploration, the type of the first layer of underground water is diving, the aquifer is a pebble layer, the burial depth of the stable water level is 19.10-19.40 m, and the elevation is 33.14-33.25 m. The type of the groundwater of the second layer is diving, the aquifer is a pebble layer, the burial depth of the stable water level is 29.50m, and the elevation is 23.04 m.

2) The highest diving water level of the site in 1959 is close to the natural earth surface, the highest diving water level elevation is about 38.00m in nearly 3-5 years, and the annual variation range of the water level is about 1.00-2.00 m.

3) Judging according to the analysis result of the groundwater corrosivity: under the condition that the environment type is II type, the first layer and the second layer of underground water in the site have micro-corrosivity to the concrete structure; under the condition of alternation of dry and wet, the underground water of the first and second layers of the site has micro-corrosivity to the steel bars in the reinforced concrete structure.

4) Judging according to the analysis result of soil soluble salt: soil is slightly corrosive to concrete structures; soil is slightly corrosive to steel reinforcement in reinforced concrete structures.

3) General overview of uplift anchor design

Design parameters and indices

1. Extreme side friction resistance standard value q of anchor rod_sik

Soil layer	q_sik(kPa)
		Pebble layer	100
Powder clay and heavy powder clay layer	45
		Fine sand layer	60
Pebble layer	120

2. Underground water in the proposed field area has micro-corrosiveness to a concrete structure, and the underground water has micro-corrosiveness to reinforcing steel bars in the reinforced concrete structure in a dry-wet alternating environment.

3. The engineering anti-floating anchor rod is a permanent anchor rod, the service life is designed to be 50 years, and a secondary high-pressure grouting full-length bonding type anti-floating anchor rod is adopted.

4. The anti-floating anchor rod type

Material

1. The grade of the steel bar is HRB400 (C); the connection of the reinforcing steel bars adopts mechanical connection, and the performance level is 1 grade.

2. The cement is ordinary portland cement, the cement paste strength grade is M30, and the mixing water is preferably tap water.

3. Other materials such as the isolation centering bracket, the grouting pipe and the like all meet the regulations of the current relevant specifications and standards.

Basic test

1. The engineering needs to carry out basic tests, and the number of anchor rods in the basic tests is not less than 3. The type and position of the anchor rod for carrying out the basic test can be carried out after being confirmed by an owner, a supervision and design unit.

2. And during the test, the pulling-resistant limit bearing capacity of the anti-floating anchor rod is determined through a field load test according to the relevant standard requirements and in combination with the construction process.

3. When the uplift limit bearing capacity of the anti-floating anchor rod determined by the test cannot meet the design requirement, the construction unit should be matched with the owner, the supervision and design unit to adjust the design and construction scheme.

4. The construction processes of anchor rod hole forming, rod body manufacturing and installation, grouting and the like all meet the regulations of relevant specifications, regulations and standards.

Acceptance test

1 the uplift bearing capacity of the anchor rod is detected by qualified third party units.

The number of the anchor rods of the 2-proof test and the type of the anchor rods of the project are not less than 5 percent of the total number of the anchor rods and not less than 3.

The maximum test load of the 3 acceptance test is not less than 1.5 times of the designed tension value of the anchor rod.

4) Main construction machinery equipment arrangement and anti-floating anchor rod construction

TABLE 2 machinery arrangement List

Serial number	Device name	Model number	Number of	Power (KW)	Remarks for note
						1	Long spiral drilling machine	CFG30 type	1	150
2	Heel casing drilling machine	MFD-180	2	50
						3	Grouting pump	3SNSA		2	18
4	Slurry stirring machine	YJ-340	2	4
						5	Section bar cutting machine	GQ40-1	1	5.5
6	Steel bar bender	NRB-22 type	1	1.7

Main material supply and test plan

The main raw materials of the engineering are steel bars and cement. Steel strand for comparative test. Designing an anti-pulling anchor rod with the diameter of 150mm, the effective length of 11.0m and 285 anchor rods;

the P.O42.5 Portland cement is planned to be consumed for 250t, and the C22 steel bars are consumed for 31 t. And a small amount of unbonded steel strands.

The engineering cement is bulk cement, and is fed in batches for multiple times, and the reinforcing steel bars are fed in all at one time. The construction materials are required to be tested when entering the site, and the materials qualified by the test are required to be used after supervision and audit of site projects if the unqualified raw materials are not used.

Carrying out a group of raw material inspection on the representative quantity of the entering cement in each batch of time which is not more than 200 t; performing a group of raw material inspection on each batch of reinforcing steel bars with the representative quantity not greater than 60 t; 500 steel bar straight thread sleeve joints are subjected to inspection and grouped; the cement paste test block has at least one group of 30 anchors. And inspecting one group of the unbonded steel strands.

Anti-floating anchor rod construction method

1) Construction survey control

The underground building of the project occupies a large area, the construction site is narrow, the requirement on the measurement precision is high, and the quality of the project is directly influenced by whether the axis is well controlled or not. Therefore, the project establishes a plane control network and an elevation control network on the basis of the original plane control points and elevation control points provided by the owner. The key control elevation of the anti-floating anchor rod project is shown in the following table 3.

2) Instrument device for construction survey

The following table 4 shows the measuring instrument devices used in the construction:

serial number	Main measuring instrument	Number of	Measurement item
				1	Total station	1 table	Construction positioning pay-off
2	Theodolite	1 table	Control of verticality, pay-off, etc
				3	Level (with tower ruler)	1 table	Control construction elevation
4	50m steel ruler	1 to 2 handles	Construction paying-off
				5	5m measuring tape	A plurality of	Construction paying-off

3) Construction measuring method

The project takes a lead point and an elevation control point provided by a proprietor as a first-level control point. According to construction needs, control points are arranged around the building, and a construction plane control net and an elevation control net are arranged by utilizing the points so as to meet the requirements of construction positioning, axis measurement and elevation transmission.

The construction control point is buried outside the deformation area of the construction site, is not interfered by construction, and is easy to protect and convenient to use. The method is implemented according to the technical requirements of I-level building square grids, the error in angle measurement is less than 5 percent, and the relative closing difference is less than 1/20000. During observation, a total station is adopted for observation, one time of measurement is respectively observed at the left angle and the right angle of the horizontal angle, and two times of measurement are respectively measured in a distance reciprocating mode.

The elevation control network is generally measured according to the technical requirements of level measurement such as III, the height difference per kilometer of the elevation control network is less than 6mm, and the closure difference is less than

(L is the number of kilometers of the length of the leveling line). Each elevation control point utilizes the plane control point as much as possible.

4) Anti-floating anchor rod construction

According to the actual condition of the engineering stratum, firstly, a construction process for forming holes by using the anchor rod construction drilling machine for hole forming and pressure grouting cement slurry transformed by the long spiral drilling machine is selected. The construction process for forming the anchor by inserting the reinforcement cage after pumping cement slurry in the pore-forming pipe of the long auger drilling machine avoids the problem of hole collapse and slurry pollution, has high construction speed and convenient construction, and is easy to realize environment-friendly and civilized construction. However, after the test, the drill bit cannot drill and cannot reach the designed depth. The construction of the pipe following jumbolter water drill has to be changed.

As a comparison test, a partially-bonded prestressed uplift anchor rod and a steel strand cage thereof are designed, and the same diameter, the same length, the same stratum and the same process are adopted. A comparative ultimate bearing capacity test was performed.

Construction process flow

(1) The construction process flow of the originally designed common anchor rod (see figure 1):

after the rod body reaches the design strength, bending the upper reinforcing steel bar and anchoring the upper reinforcing steel bar into the bottom plate.

Comparative test

As mentioned above, as a comparative test, we designed a partially bonded prestressed uplift anchor rod and its steel strand cage with the same diameter, the same length, the same ground layer and the same process. A comparative ultimate bearing capacity test was performed.

The diameter is 150mm, 3 three-level steel bars with the diameter of 22 are matched with a common anchor rod, the bonding length is 11m, the test limit value reaches 480kN, three steel strands with the diameter of 1860 level 15.2 are matched with a partially bonded prestressed anti-floating anchor rod, the bonding length is 4.5m, the limit value is not less than 848kN, and the bonding length is increased by 1.76 times. Therefore, the structure of the anchor rod is changed, the stress mechanism of the anchor rod is changed, and the bearing capacity is greatly improved. The economic benefit is obvious.

Claims

1. The construction process of partially bonded prestressed uplift anchor rod is characterized by comprising the following steps of:

(3) and (3) processing and manufacturing a steel strand cage: at least three unbonded steel stranded wires (8) are uniformly distributed along the circumference and are supported and fixed by a plurality of centering brackets (7) which are arranged at intervals along the axial direction; removing the sleeve and grease on the surface of a section of the bottom of the steel strand (8) to form a steel strand bonding section (L); the center of the centering bracket (7) penetrates through the grouting pipe (10), and the bottom end of the grouting pipe (10) is temporarily closed;

(5) grouting: opening a cement slurry pump, injecting cement slurry into the drill hole through a grouting pipe, and grouting the cement slurry to the hole opening; after the outer pipe of the drilling tool is pulled out, the grout at the orifice falls below the designed elevation and then is supplemented for the second time;

(6) the steel strand stretching locking and the bottom plate steel bar connection: when the strength of the cement paste meets the design requirement, removing the soil layer around the part above the cushion layer (5) on the upper part of the anchor rod to reach the bottom elevation of the bottom plate, exposing the steel strand (8) with the removed soil layer part, and peeling to remove grease and oil; the steel strand (8) is tensioned and then locked on the anchor head (6) and the backing plate (11), and the elevation of the upper end of the anchor head (6) is the same as the elevation of the bottom of the cushion layer (5); binding the top ends of the reserved steel strands (8) with the bottom plate steel bars (1) of the concrete bottom plate (4) when binding the steel bars after the cushion waterproof layer is made;

the specific manufacturing method of the steel strand cage comprises the following steps: firstly, blanking qualified unbonded steel stranded wires after retesting according to the designed length, peeling, degreasing and deoiling the lower end of the unbonded steel stranded wires with the designed length of 2.5-4.5 m, binding the steel stranded wires with a centering bracket (7) by using a flame wire every 2.0m according to the number of the anchor rods, placing the steel stranded wires in side holes of the centering bracket (7), penetrating a soft plastic grouting pipe (10) into a center hole, and tightly winding the lower end of a steel stranded wire cage by using an adhesive tape so as to be conveniently put into a drill hole (3); in order to improve the bond stress between the steel strand and the cement paste, a section of steel bar section is bound on the steel strand, and in order to avoid the over-thickness of the whole anchor rod, the steel bar sections on different steel strands are staggered with each other, and a stress dispersion effect is formed; by adopting the construction process of the water drilling and pipe following jumbolter, the design depth can be reached, the hole collapse problem is avoided, and the defect of using large-scale equipment is overcome;

the steel strand is prestressed, so that the stress property of cement paste is changed, and the cracking of the anchor rod body is avoided; because the acting point is at the steel strand bonding section (L) at the lower part of the anchor rod, the characteristics of the partially bonded prestressed anchor rod are highlighted, different from the common anchor rod, the stress between anchor soils is not the characteristics of ' radish pulling ' and ' loosening along with pulling ', but is in the shape of a wedge ' and ' tightening along with pulling ', so that the pulling resistance bearing capacity is greatly improved.

2. The construction process of the partially bonded prestressed uplift anchor rod according to claim 1, wherein the centering brackets are bound together with the steel strands by firing wires every 2.0 m; the centering support consists of a circular ring and a multi-angle star, the circular ring is connected with the inner corners of the multi-angle star, the grouting pipe penetrates through the circular ring, and the steel strand is placed at the outer concave corner of each multi-angle star.

3. The construction process of a partially bonded prestressed uplift anchor rod according to claim 1, wherein the top ends of the steel strands are locked and connected with the bottom plate steel bars (1) through U-shaped clamps or binding wires.