CN106907169A - A kind of pressure dispersing anchorage cable and its construction method in Super-large-section tunnel supporting - Google Patents
A kind of pressure dispersing anchorage cable and its construction method in Super-large-section tunnel supporting Download PDFInfo
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- CN106907169A CN106907169A CN201710179054.2A CN201710179054A CN106907169A CN 106907169 A CN106907169 A CN 106907169A CN 201710179054 A CN201710179054 A CN 201710179054A CN 106907169 A CN106907169 A CN 106907169A
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
- E21D21/0026—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection characterised by constructional features of the bolts
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D20/00—Setting anchoring-bolts
- E21D20/02—Setting anchoring-bolts with provisions for grouting
- E21D20/021—Grouting with inorganic components, e.g. cement
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
- E21D21/0006—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection characterised by the bolt material
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
- E21D21/008—Anchoring or tensioning means
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
- E21D21/0093—Accessories
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- Mining & Mineral Resources (AREA)
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- General Life Sciences & Earth Sciences (AREA)
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- Piles And Underground Anchors (AREA)
Abstract
本发明提出一种压力分散型锚索及其在特大断面暗挖隧道支护中的施工方法，属于工程技术领域，包括钢绞线、对所述钢绞线辅以张拉的锚锁、使钢绞线划分为自由段和锚固段的压力分散装置，所述自由段连接于所述锚锁，所述锚固段由至少两个锚固单元组成，所述锚固段的两端、及相邻的两个锚固单元之间均设置有所述的压力分散装置；所述压力分散装置由紧固板、紧固螺杆、P型锚具组成。本发明压力分散型锚索是一种新型的支护技术，目的就是控制岩体的变形，尤其是控制层状岩体蠕滑时，能够有效确保工程岩体的安全运行。
The invention proposes a pressure-distributed anchor cable and its construction method in the support of an extra-large cross-section underground excavation tunnel, which belongs to the field of engineering technology and includes steel strands, anchor locks for tensioning the steel strands, and The steel strand is divided into a free section and a pressure dispersion device for an anchor section, the free section is connected to the anchor lock, the anchor section is composed of at least two anchor units, the two ends of the anchor section, and the adjacent The pressure dispersing device is arranged between the two anchoring units; the pressure dispersing device is composed of a fastening plate, a fastening screw, and a P-type anchor. The pressure dispersion type anchor cable of the present invention is a novel supporting technology, and the purpose is to control the deformation of the rock mass, especially when controlling the creeping of the layered rock mass, so as to effectively ensure the safe operation of the engineering rock mass.
Description
Technical Field
The invention belongs to the technical field of engineering, and particularly relates to a pressure dispersion type anchor cable and a construction method thereof in extra-large section tunnel support.
Background
Greater than 100m according to the International Tunnel Association (ITA) for Tunnel Cross-sectional area size definition2Called as super large section tunnel, with the rapid development of the traffic construction business in China, a plurality of super large section tunnels emerge, for example, the section area of a seven-line twin-well station of Beijing subway is 320m2The north station cross section of Shenyang subway line II is 340m2The section of the station of the big terrace with the second line of the Chongqing light rail is 430m2The section of the station at the Yangjiang gate is 420.9m2Section area of 730m of B type of station of red flag ditch of No. three line of Chongqing light rail2. The subway underground excavation station primary support has various forms, and the condition that the safe pressure dispersion anchor rope is adopted as part of the underground excavation primary support rarely exists, the technology can effectively control the deformation of the rock-soil body on the side wall of the tunnel, and especially under the condition that the surrounding rock has a sliding layer, the technology has great significance for ensuring the safety of tunnel excavation and building construction. However, the anti-pulling force of the safety pressure dispersion anchor cable is greatly influenced by the formation conditions, the material strength, the tensioning machines and the like, so that the phenomenon of insufficient anchoring force is easily caused, the side wall of the tunnel is deformed, the earth surface is sunk, the peripheral building structure is damaged due to too large deformation, the normal use of the tunnel is influenced, and even the peripheral building structure is damaged when the deformation is seriousCausing a collapse. Therefore, ensuring the anchorage force of the anchor cable to reach the designed value in the construction process undoubtedly has a great influence on the safety of tunnel construction.
Disclosure of Invention
In view of the above, the present invention provides a pressure dispersion type anchor cable and a construction method thereof in supporting an extra-large section tunnel.
In order to achieve the purpose, the invention is realized by the following technical scheme:
the invention relates to a pressure dispersion type anchor cable, which comprises a steel strand, an anchor lock and a pressure dispersion device, wherein the anchor lock is used for assisting the steel strand in stretching, and the pressure dispersion device is used for dividing the steel strand into a free section and an anchoring section; the pressure dispersion device is composed of two fastening plates, two fastening screws and a P-type anchorage device, the two fastening plates are sleeved on the steel strand, the fastening screws are used for supporting and connecting the two fastening plates which are distributed at intervals, and the P-type anchorage device which is close to the two fastening plates and sleeved on the steel strand is arranged between the two fastening plates.
Furthermore, the steel strands are unbonded steel strands sleeved with PE pipes, the number of the steel strands is an even number selected from 4-16, and the steel strands are uniformly arranged in an annular shape at intervals in the radial direction relative to a fastening plate of the pressure dispersing device.
Furthermore, the pressure dispersion device also comprises a sealing cover which is positioned between the two fastening plates and sleeved outside the P-shaped anchorage device, and anticorrosion grease is filled in the sealing cover; the steel strand is close to the fastening plate and is wound with a sealing adhesive tape opposite to the fastening plate and the sealing cover.
Furthermore, the anchor cable also comprises a conical guide cap arranged on the pressure dispersion device at one end of the steel strand, which is far away from the anchor lock.
Furthermore, a plurality of positioners which are distributed at equal intervals are sleeved on the free section of the steel strand.
Further, the anchor lock comprises anchor head, bearing plate, apron, tapered iron, backing plate, steel pipe, sets up steel pipe and tapered iron between backing plate and the apron, and the one side that the apron deviates from the steel pipe sets gradually bearing plate and anchor head, and the steel pipe is used for the suit steel strand wires, the anchor head is used for the anchor steel strand wires, the tapered iron is used for supporting the steel pipe.
The invention also provides a construction method for the pressure dispersion type anchor cable in the ultra-large section underground excavation tunnel, the construction method adopts a reverse method for construction, and the construction is carried out in a segmented and layered manner, namely, one section of the anchor cable is excavated and used as one section of the anchor cable, and the method specifically comprises the following steps:
step 1), excavating a tunnel soil body to reach the elevation of a top row anchor cable, and installing, tensioning and locking the top row anchor cable;
step 2), continuing to excavate the soil body to the elevations of the two rows of anchor cables, and installing, tensioning and locking the two rows of anchor cables;
and 3) repeating the step 2) to perform soil body excavation and lower row anchor cable construction until the tunnel is excavated to the designed elevation.
Preferably, after the anchor cables of each row are installed, grouting the anchoring sections of the steel strands by adopting a twice grouting method, wherein the primary grouting material is cement mortar with a sand-lime ratio of 1: 0.5-1: 1, and the grouting pressure is 0.5-1.5 MPa; the secondary grouting material adopts pure cement slurry with the water cement ratio of 0.45-0.50, and the grouting pressure is 2.5-3.0 MPa.
Preferably, after grouting of each row of anchor cables is completed, free section tensioning locking is carried out on the steel strands by adopting a super-tensioning method, the super-tensioning value is 1.1-1.2 times of the designed tensioning value, three times of tensioning operation construction are carried out, namely the first tensioning operation value is 1/2 of the designed tensioning value, the second tensioning operation value is 1/3 of the designed tensioning value, the third time of tensioning operation value is up to the super-tensioning value, and the stability of each time of tensioning operation is 4-6 minutes.
Preferably, after tensioning and locking of the anchor cables of each row are completed, free-section grouting is performed on the steel strands, the grouting material is cement paste with a water-cement ratio of 0.45-0.5, and the grouting pressure is 2.5-3.0 MPa.
Compared with the prior art, the invention has the advantages that: the invention relates to a safe pressure dispersion anchor cable, which is a novel supporting technology and aims to limit the deformation of a rock body, and can effectively ensure the safe operation of a project especially in the geology with bedding.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.
Drawings
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings, in which:
fig. 1 is a schematic structural view of a cable bolt according to the present invention;
FIG. 2 is a schematic view of the pressure dispersion apparatus of the present invention;
FIG. 3 is a cross-sectional view of the anchor lock of the present invention;
FIG. 4 is a schematic view of the positioner of the present invention;
FIG. 5 is a layout of the positioner of the present invention on a steel strand;
FIG. 6 is a layout view of the anchor cables of the present invention in an oversized cross-section undercut tunnel;
FIG. 7 is an actual measurement curve of anchor cable prestress variation monitoring;
FIG. 8 is a graph of the monitored axial force of the cable after compensation tensioning;
FIG. 9 is a graph of an elevated lock load versus conventional lock load axial force monitoring;
reference numerals: 1-steel strand, 2-pressure dispersing device, 3-conical guide cap, 4-positioner, 5-anchor lock and 6-grouting pipe; wherein, 11-free end, 12-anchoring section, 12 a-anchoring unit I, 12 b-anchoring unit II, 12 c-anchoring unit III, 12 d-anchoring unit IV; 21-fastening plate, 22-fastening screw and 23-P type anchorage device; 51-anchor head, 52-bearing plate, 53-cover plate, 54-oblique iron, 55-backing plate and 56-steel tube.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings; it should be understood that the preferred embodiments are illustrative of the invention only and are not limiting upon the scope of the invention.
As shown in fig. 1-4 below, the anchor cable of the present invention comprises a steel strand 1, an anchor lock 5 for assisting the steel strand with tension, and a pressure dispersing device 2 for dividing the steel strand into a free section 11 and an anchoring section 12, wherein the free section 11 is connected to the anchor lock 5, and the anchoring section 12 is composed of at least two anchoring units, in this embodiment, four anchoring units are respectively an anchoring unit i 12a, an anchoring unit ii 12b, an anchoring unit iii 12c, and an anchoring unit iv 12d, such that the anchor cable forms five prestressed anchor cables of 4 (anchoring units) +1 (free section); the pressure dispersion devices 2 are arranged at two ends of the anchoring section 12 and between two adjacent anchoring units; the pressure dispersion device 2 comprises two fastening plates 21, two fastening screws 22 and two P-shaped anchors 23, the two fastening plates 21 are sleeved on the steel strand 1, the fastening screws 22 are used for supporting and connecting the two fastening plates 21 which are distributed at intervals, and the P-shaped anchors 23 which are close to the two fastening plates 21 and sleeved on the steel strand 1 are arranged between the two fastening plates 21 respectively. By adopting the scheme, the safe pressure dispersion anchor cable is a novel supporting technology, aims to limit the deformation of a rock body, and can effectively ensure the safe operation of a project especially in the geology with bedding.
In this embodiment, the steel strands 1 are unbonded steel strands sleeved with PE pipes, the number of the steel strands is an even number selected from 4 to 16, and the plurality of steel strands 1 are uniformly arranged in a ring shape at intervals in the radial direction with respect to the fastening plate 21 of the pressure dispersing device 2.
In this embodiment, the anchor lock 5 is composed of an anchor head 51, a bearing plate 52, a cover plate 53, an oblique iron 54, a backing plate 55 and a steel pipe 56, the steel pipe 56 and the oblique iron 54 are arranged between the backing plate 55 and the cover plate 53, the bearing plate 52 and the anchor head 51 are sequentially arranged on the side, away from the steel pipe 56, of the cover plate 53, the steel pipe 56 is used for sleeving the steel strand 1, the anchor head 51 is used for anchoring the steel strand 1, and the oblique iron 54 is used for supporting the steel pipe 56. The gap between the backing plate 55 and the cover plate 53 may be filled with M40 cement mortar.
In another embodiment, the pressure dispersing device 2 further includes a sealing cover 24 located between the two fastening plates 21 and sleeved outside the P-type anchorage 23, and the sealing cover 24 is filled with anti-corrosive grease; the steel strand 1 is wound with a sealing tape 25 on the opposite side of the fastening plate 21 from the sealing cover 24 near the fastening plate 21.
In another embodiment, the cable bolt further comprises a tapered guide cap 3 provided on the pressure dispersion means at the end of the steel strand remote from the anchor lock. Thus, when the anchoring is difficult, a conical guide cap can be arranged at the front end of the anchoring section so as to facilitate the smooth anchoring.
In another embodiment, the free section of the steel strand is sleeved with a plurality of locators 4 which are distributed at equal intervals. The free section of the steel strand anchor is in a structural form of arranging a positioner, so that the steel strand is centered in the anchor hole, the thickness of the steel strand is uniform, and the distance between the positioners is 2 m. In addition, the positioner and the steel strand can only be wedged tightly and cannot be welded.
The invention also provides a pressure dispersion type anchor cable and a construction method thereof in the support of the tunnel with the extra-large section, the construction method adopts the reverse construction method and is constructed by sections and layers, namely, one section of the anchor cable is excavated and used as one section of the anchor cable, and the construction method specifically comprises the following steps:
step 1), excavating a tunnel soil body to reach the elevation of a top row anchor cable, and installing, tensioning and locking the top row anchor cable;
step 2), continuing to excavate the soil body to the elevations of the two rows of anchor cables, and installing, tensioning and locking the two rows of anchor cables;
and 3) repeating the step 2) to perform soil body excavation and lower row anchor cable construction until the tunnel is excavated to the designed elevation.
It should be noted that the anchor cable uses the bedrock landslide body as the anchoring section, and the length of the free section of the anchor cable is required to be not less than 5 m. In the drilling process, if a hole collapses, the hole is treated by adopting a method of additionally arranging a steel sleeve, and the rock mass around the anchoring section is required to be a complete rock mass. In addition, an anchor cable basic experiment is required to be carried out before the anchor cable construction, and the standard value of the bonding strength of the bedrock landslide body and the anchoring body is required to be not less than 400 kPa.
In the method, after the anchor cables of each row are installed, the steel strand is subjected to anchoring section grouting by adopting a twice grouting method, cement mortar with a sand-lime ratio of 1: 0.5-1: 1 is adopted as a primary grouting material, and the grouting pressure is 0.5-1.5 MPa; the secondary grouting material adopts pure cement slurry with the water cement ratio of 0.45-0.50, and the grouting pressure is 2.5-3.0 MPa.
In the method, after grouting of each row of anchor cables is completed, free section tensioning locking is carried out on the steel strand by adopting a super-tensioning method, the super-tensioning value is 1.1-1.2 times of the designed tensioning value, three times of tensioning operation construction are carried out, namely the first tensioning operation value is 1/2 of the designed tensioning value, the second tensioning operation value is 1/3 of the designed tensioning value, the third tensioning operation value is up to the super-tensioning value, and the stability of each time of tensioning operation is 4-6 minutes.
In the method, after tensioning and locking of the anchor cables of each row are finished, free-section grouting is carried out on the steel strands, the grouting material adopts cement paste with a water-cement ratio of 0.45-0.5, and the grouting pressure is 2.5-3.0 MPa.
The present invention will now be described in detail with reference to certain engineering.
Geological conditions and geological survey data show that the buried depth of a subway station is 20-32.4 m, tunnel surrounding rocks are mainly sandy mudstone and sandstone, the surrounding rocks are basically classified into IV grades, the rock surface of the wall on the left side of the tunnel is exposed to the air in the forward direction, bias exists, and the crack on the right side wall J1 is exposed to the air in the forward direction. The bearing capacity of the safe pressure dispersion anchor cable mainly depends on the pulling resistance of the anchor body, the buildings and the environment around a certain subway station are extremely complex, the deformation and the lateral displacement of a foundation pit need to be strictly controlled, and therefore the bearing capacity of the engineering anchor body is mainly controlled by the deformation. And the anti-pulling performance test is carried out on the safe pressure dispersion anchor cable before construction to be used as the basis for checking and designing various data and engineering anchor cable construction.
According to the adopted anchor cable parameters, the left side and the right side of the tunnel are supported by a profile steel arch frame and are provided with five pre-stressed anchor cables (taking K17+ 193.942-DK 17+353.942 as an example), the distance between the anchor cables is 3m multiplied by 3m, the included angle between the left anchor cable and the horizontal direction is set according to 25 degrees, and the included angle between the right anchor cable and the horizontal direction is set according to 15 degrees. The left anchor cable adopts 12 strands of unbonded steel stranded wires with phi 15.2, the right anchor cable adopts 8 strands of unbonded steel stranded wires with phi 15.2, the hole diameter of the anchor cable drill hole is phi 170mm, and the concrete position is shown in figure 6.
The anchor cable structure and assembly, safe pressure dispersion anchor cable is by the free section 11 and anchor section 12 is constituteed, and wherein anchor section 12 divide into four anchor units, therefore each anchor unit length diverse, settle the direction cap in the anchor section front end so that the anchor is smooth down. The space between the positioners is 2000mm, the structural structure of the safety pressure dispersion anchor rope is shown in a large scale in figure 1, the structure of the safety pressure dispersion device is shown in figure 2, the cross section of the anchor is shown in figure 3, and the specific type of the safety pressure dispersion anchor rope is shown in a table 1-1.
Table 1-1 specific types of safety type pressure dispersion anchor cable are shown in the table
And (3) tensioning and locking the anchor cables, starting tensioning and locking when the strength of the anchoring body is greater than 15.0MPa (7d), wherein the tensioning design value of the anchor cable on the left side of the tunnel is 1600KN, the locking load is 800KN, the lengths of the anchor cables are different from 18.1m to 29.8m, the tensioning design value of the anchor cable on the right side of the tunnel is 1050KN, the locking load is 525KN, and the lengths of the anchor cables are different from 13m to 20.1 m.
Firstly, a construction process for refining a safe pressure dispersion anchor cable is as follows: arranging a working face → paying off a measurement group to determine a hole position → placing a drilling machine → correcting a drilling angle → drilling → cleaning the hole → withdrawing the drilling machine → manufacturing an anchor rope → installing the anchor rope → cleaning the hole → grouting → tensioning → locking → secondary grouting. Wherein,
1. drilling holes
And drilling construction is carried out by adopting a geological drilling machine on a construction site, and the inclination angle error is strictly controlled to be not more than +/-1 degree in the construction process.
(1) General requirements
1) The borehole must not disturb the surrounding substratum.
2) The hole distance allowable deviation position in the horizontal and vertical directions of the drilled hole is +/-50 mm, and the diameter of the drill bit is not less than the designed drilled hole diameter by 3 mm.
3) The rate of deviation of the borehole axis should not be greater than 2% of the anchor line length.
4) The drilling depth should exceed the design length by 0.5-1.0 m.
5) Drilling requires that the hole wall is smooth and straight, and the diameter of the drilled hole is 170 mm.
(2) Drilling accuracy requirement
The diameter of the drilled hole is designed to meet the requirements of construction and the anchoring performance of the anchor cable, the diameter is too small, construction difficulty is easily caused or the performance of the anchor cable is influenced, waste is caused if the diameter is too large, and the drilled hole is an inclined drilled hole in the engineering. The drill holes are drilled downwards, a small amount of waste slag is inevitably gathered at the bottoms of the holes, and the scraps occupy a certain depth in the holes, so that the drill holes are prolonged, and the length of the prolonged drill holes is controlled to be 0.5-1.0 m. The downward angle of the anchor cable on the left line of the station is 25 degrees, and the downward angle of the anchor cable on the right side is 15 degrees. The anchor cable angle and length are shown in figure 6.
(3) Drilling equipment: the selection of the drilling tool should select the drilling equipment according to the category of the anchoring stratum, the aperture of the anchor hole, the depth of the anchor hole, the construction site condition and the like. The rock stratum needs to be punched by down-the-hole, and the pipe drilling technology is needed in the stratum which is easy to collapse holes and drill stuck and buried such as broken rock stratum or soft and water-saturated stratum.
(4) Cleaning and inspecting an anchor hole: and after the drilling reaches the designed depth, stably drilling for 1-2 minutes. After drilling, high-pressure air (wind pressure of 0.2-0.4 Mpa) is used for discharging rock powder and water in the hole out of the hole. After the product is qualified by on-site supervision and inspection, the next procedure can be carried out. The hole diameter and hole depth inspection is generally carried out by adopting a designed hole diameter drill bit and a standard drill rod under the condition of a site supervision side station, the drill bit is required to be smoothly pushed in the hole inspection process, no impact or shake is generated, the inspection length of a drilling tool meets the designed anchor hole depth, the drill withdrawal requirement is smooth, and the phenomena of obvious flying base dust and water body are not detected by blowing high-pressure air. Meanwhile, the hole position, the inclination angle and the direction of the anchor hole are required to be rechecked, and after all anchor hole construction items are qualified, the anchor hole drilling inspection is qualified. (the deflection of the bottom of the anchor hole should meet the design requirements and can be controlled and detected by a drilling inclinometer.)
2. Anchor cable manufacturing and installation
(1) Before the anchor cables are bundled, each steel strand needs to be guaranteed to be straight, does not twist or cross, is uniformly arranged, is fed strictly according to the design size, the length error of each strand is not more than +/-50 mm, the steel strand is strictly forbidden to be connected, mechanical cutting is needed, and welding gun material cutting is strictly forbidden. The steel strand adopted by the anchor cable must be subjected to surface decontamination and rust removal treatment. The anchor cable steel strands should be arranged straightly, a positioning frame is arranged every 2m along the axis direction of the rod body, and the specific structure of the anchor cable is shown in an attached drawing 1.
(2) Plastic casing pipe: the plastic sleeve has the advantages that the material, specification and model of the plastic sleeve can meet the design requirements, the plastic sleeve has enough strength, and the plastic sleeve cannot be damaged in the processing and installation processes. The shearing and the joint are avoided, if the joint is provided with the joint, the joint is firmly bound and sealed, and the phenomena of pulling-off and breakage are avoided. The inner diameter of the plastic sleeve is preferably 5-10 mm larger than the outer diameter of the rib strand, so that smooth threading and bundling are ensured, and tension and bursting are prevented. The plastic sleeve has water resistance and chemical stability, and has no adverse reaction when being contacted with cement mortar and a preservative.
(3) Grouting pipes: the grouting pipe is provided with a common grouting pipe according to the design requirement, and has enough strength to ensure smooth grouting in the grouting construction process without blockage, pipe explosion or breakage and breaking. The grouting pipe is tied up at the center shaft part of the anchor tendon body, passes through the middle of the bearing body and is tied up at the edge of the bearing body, and the head of the high-pressure grouting steel pipe extends into the guide cap and is preferably 50-l 00mm away from the inner tail end of the anchor tendon body. The pipe orifice is tightly sealed by an adhesive tape, and a perforated pipe hole and a grout stopping device are reserved according to the design requirement. The length of the anchor cable body is as follows: the length of the anchor cable body is strictly manufactured according to the design requirement, the manufacturing tolerance of the length of the anchoring section is +/-50 mm, and the length of the free section meets the design requirement and is generally reserved with the overlength of 1.0-1.5 m for fully considering the requirements of tensioning equipment and construction process.
(5) And (3) testing an anchor cable body: and after the anchor cable body is manufactured, performing appearance inspection and inspection of each part of the anchor cable body. The anchor cable binding and binding frame meets the design requirements, the tendon strands are straight, do not twist or cross, are not attached to each other, are uniformly arranged, and the binding frame is firm. The anti-rust paint, the anti-corrosion oil and various winding sealing measures at the free section of the anchor cable meet the design requirements, and the anti-rust paint is uniformly brushed to cover without black bottom; the anti-corrosion oil completely covers and fills the space between the anchor cable material and the outer ring layer; the winding sealing is firm and tight. The binding response of the plastic sleeve, the grouting sleeve, the isolation (centering) bracket and the guide sharp shell at the free section of the anchor cable meets the design requirement, the plastic sleeve is stably bound and tightly plugged, the strength is sufficient, the appearance is intact, and no damage repairing trace exists; the grouting pipe is correctly arranged, and is uniformly bundled and appropriately tightened; the isolation (centering) bracket is uniformly distributed, the positioning is accurate, and the binding is firm and stable. And the number is required to be numbered and the brand is required to be hung according to the length and the specification of the anchor cable body, and the anchor cable body is required to be approved by a field supervision engineer before use.
(6) Storage, transportation and hoisting of the anchor cable body: the storage, transportation and hoisting of the anchor cable body are made into a planned scheme according to the ground.
The assembled anchor cable body is separately placed in a ventilated and dry place in a straight and straight manner, and can not be directly contacted with the ground when being stored or manufactured in the open air, and a covering measure is adopted. When the anchor cable is horizontally transported, the distance between the fulcrums is not larger than 2m, the bending radius of the anchor cable body is not too small, and the limit is that the structure of the steel bar body is not damaged. During vertical transportation, except the main hoisting point, other hoisting points are required to ensure that the anchor cable body is quickly and safely unhooked. In the transportation and hoisting process, the anchor cable body, the protective medium and the component parts thereof are not damaged by careful operation.
(7) And (3) anchor cable body installation: before the anchor cable body is placed into the anchor hole, the manufacturing quality of the anchor cable body is checked, the anchor cable body is assembled to meet the design requirement, and the anchor cable body is approved by site supervision. The sundries in and around the anchor hole are required to be cleaned. The length of the anchor cable body is consistent with the designed anchor hole concentration, the anchor cable body has no obvious bending and twisting phenomena, the protective medium of the anchor cable is not damaged, and the damaged anchor cable needs to be repaired. When the anchor cable body is placed, the anchor cable body is prevented from being extruded, bent or twisted, the inclination angle and the direction of the anchor cable body hole are consistent, smooth pushing is required, shaking, twisting and moving are strictly forbidden, and beam scattering and blocking in the midway are prevented. The length of the anchor cable body inlet hole is required to meet the design requirement, and after the anchor cable body is installed, the anchor cable body cannot be knocked randomly and cannot suspend heavy objects.
3. Grouting anchor cable
(1) The cement is preferably 42.5 grade or above ordinary portland cement.
(2) And grouting the anchor section of the anchor cable by adopting a secondary grouting method. The primary grouting adopts cement mortar, is strictly executed according to the test proportion, and can be added with a certain amount of additive or admixture if necessary, the grouting pressure is preferably 0.5-1.5 MPa, and the strength of the grouting body is not less than 25 MPa. And after the strength of the cement bonded stone formed by the primary grouting reaches 5.0MPa, performing secondary grouting, wherein the secondary grouting adopts pure cement slurry with a water cement ratio of 0.45-0.50, and a certain amount of additive or admixture can be added if necessary, and the grouting pressure is preferably 2.5-3.0 MPa and the pressure is stabilized for two minutes. The secondary grouting is splitting grouting, which aims to perform grouting to the anchoring section again to split the grouting body for the first time, and the grout is diffused between the anchoring body and the contact surface of the stratum under high-pressure operation to enlarge the diameter of the anchoring body and increase radial stress; due to the extrusion effect, the stratum around the anchoring body is compressed, the void ratio is reduced, the water content is reduced, and the shearing strength index of the stratum and the bearing capacity of the anchor cable are improved. In order to achieve the design effect of the secondary grouting, the anchoring section must be completely filled with the grouting during the primary grouting.
(3) The grouting pipe is preferably placed in the center of the rod body and is placed into the hole along with the rod body, a grout outlet of the grouting pipe is inserted into a position 300-500 mm away from the bottom of the hole, grout is continuously poured from bottom to top, and smooth water and air drainage in the hole is ensured. The grout outlet and the end of the secondary grouting pipe are sealed, so that grout does not enter the secondary grouting pipe during primary grouting.
(4) When the rod body is placed, the grouting pipe is prevented from being pulled out, and if the length of the grouting pipe pulled out exceeds 500mm, the rod body is pulled out and placed again after being repaired.
(5) In the grouting process, if the grouting amount is greatly reduced or a grouting pipe bursts, the rod body and the grouting pipe are pulled out, and the rod body is lowered after grouting is replaced; if the delay time in the midway exceeds the initial setting time of the slurry, the rod body is lowered after the hole is cleaned again, and the slurry is re-injected.
(6) The grouting slurry is uniformly stirred, is used along with stirring, is used up before initial setting, and is forbidden to mix stones and impurities into the slurry.
4. Construction of anchor cable waist beam
And after the grouting of the anchor cable is finished, the construction of the anchor cable waist beam is immediately carried out. The anchor cable waist beam and the cast-in-situ bored pile are connected by a bar planting method, a combined steel template is adopted for molding, a steel pipe fastener is adopted for reinforcing the template, concrete is put into the mold by a pump truck, and the concrete is vibrated by an inserted vibrating rod. The anchor cable waist beam concrete is C30 concrete, and the slump is 120 +/-10 mm. In order to realize tensioning and anchoring as soon as possible and guarantee the progress of the engineering, the concrete is doped with an early strength agent. When the waist beam is manufactured, the anchor cable is sleeved by a PVC pipe so as to prevent reinforced concrete from being bonded with the steel strand.
5. Tensioning locking anchor sealing of anchor cable
And after the tensioning tool is detected to be qualified, converting an actual display value according to an equation given by the detection report.
(1) And after the anchor cable is grouted, performing tensioning locking when the concrete strength of the anchoring body and the waist beam reaches over 90 percent. The anchor cable is tensioned by adopting a super-tensioning method, the super-tensioning force value is 1.1-1.2 times of the design tension value, and the tensioning operation is applied in three times. The first tensioning operation value is 1/2 of the designed tensioning value, the second tensioning operation value is 1/3 of the designed tensioning value, the third tensioning operation is carried out until the tensioning value is exceeded, and the time of each stage of tensioning is 5 minutes after the tensioning is finished and stable.
(2) When the anchor cable body is stretched, the stress of the anchor cable body is uniform.
(3) In order to avoid the stress loss after the adjacent anchor cables are tensioned, the anchor cable tensioning construction is carried out by adopting a 'jump tensioning method', namely a method of pulling every two anchor cables; if obvious prestress loss is found, the tensioning should be compensated in time.
(4) And after the anchor cable is tensioned and locked, grouting is carried out on the free section, and grouting materials are the same as the anchoring section.
(5) After the anchor cable is tensioned and locked, the residual anchor cable needs to be mechanically cut, arc burning is strictly forbidden, and the exposed anchor cable with the length of 5-10 cm is reserved to prevent dragging and slipping. And finally, cement paste is used for filling gaps of the anchor backing plate and the anchor head, the anchor is sealed according to the design requirement, and C25 fine aggregate concrete is adopted to wrap the anchor head, so that the corrosion is prevented, and the appearance is attractive.
And secondly, in the tensioning and locking processes of the anchor cable, reserving a slurry sample during grouting of the anchoring section, and starting tensioning and locking when the strength is greater than 15.0MPa (7 d). The stretching adopts a feed-through jack matched with an OVM anchor. According to the relevant regulations of technical Specifications of geotechnical anchor rod and shotcrete support engineering (GB 50086-2015) [5], the tensioning mode is carried out according to the following modes:
eliminating differential load increment
Taking 10% -20% of design tension load. Pretension the steel strand for 1-2 times to make each part tightly contact and make the steel strand completely straight. The pressure dispersion anchor cable has different anchor cable lengths, the stretching is carried out by adopting differential step-by-step stretching according to different design sequences, calculating and determining differential load according to design load and anchor bar length, and carrying out the tension according to the calculated differential load, wherein the stretching sequence is as follows: first unit anchor → second unit anchor → third unit anchor → fourth unit anchor. I.e. first long unit and then short unit.
The calculation formula of the differential elongation and the differential load increment of each unit of the safe pressure dispersion anchor cable is as follows:
(1) differential elongation:
△Ln-n+1＝△Ln-△Ln,△Ln＝(σLn)/E
△Ln+1＝(σLn+1)/E,σ＝P/A
(2) differential load increment:
△Pn＝(2EA△Ln-n+1)/L1
△Pn+1＝{(EA△Ln+1-n+2)/Ln+1+(EA△Ln+1-n+2)/Ln}×2
wherein: ln and-are the lengths of the anchor cables of the nth unit respectively, and Ln is greater than Ln +1 and Ln + 2;
delta Ln is the differential elongation of each unit anchor cable under the action of given final tension (design locking) load;
sigma-the load of a single steel strand under the action of a given final tension (design locking) load;
a is the sectional area of a single steel strand (A is 140mm 2);
e — elastic modulus of the steel strand (E ═ 1.97 × 105 MPa);
delta Pn is the first and second step tension load increment of step-by-step differential tension.
And (3) obtaining a linear equation of the jack according to detection data when the jack and the oil pressure gauge are calibrated: P-0.03339F-0.047
In the formula: f-standard force value KN, P-pressure gauge indication value MPa
The values of tension readings of incremental oil meters for eliminating differential loads are determined and shown in the table 2-1 (taking the first layer of anchor cable on the left and right lines of the tunnel as an example)
TABLE 2-1 statistical chart of oil meter tension reading value (eliminating differential load increment)
The first unit is pulled to the corresponding load of the step load (the difference load of the tension units of the first tension group), then the first unit and the second unit are pulled to the corresponding load of the second unit (the difference load of the tension units of the second tension group), and then the first unit and the third unit are pulled to the corresponding load of the third unit (the difference load of the tension units of the third tension group);
and at the moment, a fourth unit of anchor cable is added, and cyclic loading tensioning is carried out.
② tensioning by cyclic loading
After the difference load is complemented, the prestress of the anchor cable is applied in 5 stages according to relevant specifications or regulations, namely 25%, 50%, 75%, 100% and 110% of the designed load, each stage of load is stable for 2-5 min during tensioning, and the load of the last stage of load is unloaded and locked after being stable for 10-15 min. And respectively recording the elongation and stress conditions of the steel strand during each stage of tensioning, and verifying the consistency of the elongation and the stress value. And within 48 hours after the anchor cable is locked, if obvious prestress damage phenomenon is found, compensating and tensioning in time. The specific tension lock load is shown in Table 3-1.
Table 3-1 tension lock load meter (first layer anchor cable of tunnel left and right line as example)
And thirdly, basic tests, namely, the basic tests of the anchor cable are required to be carried out before the anchor cable is constructed so as to determine the standard value of the bonding strength between the bedrock landslide body and the anchoring body, and the standard value of the bonding strength between the bedrock landslide body and the anchoring body is required to be not less than 400kPa required by the design. 424KN is taken for the engineering test load, and after the test result meets the design requirement, the subsequent construction of the anchor cable is carried out.
Fourthly, stress loss of the safe pressure dispersion anchor cable:
influence of tension and locking on prestress loss
From the monitoring results in table 4-1, it can be seen that the safety type pressure dispersion anchor cable shows a certain prestress loss after being tensioned and locked. After tensioning is finished, the anchor clamps installed when the anchor cable is locked can be pulled in when the anchor cable contracts, so that certain locking prestress loss is caused.
TABLE 4-1 Anchor line tension, locking detection data
Influence of prestress on prestress loss
In order to analyze the influence of the prestress on the prestress loss, monitoring results are uniformly sorted. To make the results comparable, the loss rate is redefined, and the new loss rate is defined as the ratio of the difference between the load on the load cell and the lock on load to the tendon pre-stressed tension tonne value, with the results shown in Table 4-2. As can be seen from table 4-2, the average loss of prestress of the 800kN grade cable is 15.5kN compared with the 525kN grade cable, while the average loss of prestress of the 525N grade cable is 11.33kN, and the corresponding loss rates are 1.92% and 2.16%. It can be seen that the loss rate of the prestressed anchor cable with high tonnage is lower although the loss value is larger.
TABLE 4-2 Anchor line loss Rate data
Influence of anchor cable material relaxation on prestress loss
The anchor cable can deform under the action of huge tensioning prestress, so that relaxation loss is generated, and under the condition that the length of the anchor cable is not changed, the loss of internal stress of the steel strand can be caused along with the increase of time, which is a main reason for generating prestress loss of a prestress anchor cable system.
Influence of construction factors on prestress loss
The loss of the prestress of the anchor cable is inevitably caused in the construction engineering of the anchor cable, such as hole sealing and grouting of the outer anchor section of the anchor cable, drill hole inclination and the like. When the hole sealing and grouting of the outer anchor section are carried out, the temperature of the grouting body is higher than that of the anchor cable, so that the anchor cable body expands, and the prestress is reduced. Meanwhile, the partial stress loss has a great relationship with the fracture degree of the rock mass, and if the number of the fractures in the rock mass is large, slurry fills the fractures in the rock mass during grouting, so that the rock mass is subjected to expansion deformation, and the prestress is improved. The inclination of the drill hole during the construction of the anchor cable is inevitable, but the excessive inclination leads to the loss of the prestress of the anchor cable. The field test shows that the larger the hole inclination of the drilled hole is, the larger the prestress loss of the anchor cable is.
Change rule of prestress loss
Through analysis of monitoring results of engineering examples, the prestress changes after anchor cable anchoring locking generally go through three stages, as shown in fig. 7.
The first stage prestress rapid loss stage: at this stage, the anchor cable prestress is lost rapidly, the loss value is second to the locking loss, the duration is short, the duration is about two weeks generally, and the lithology is good for the hard rock.
The second stage is a prestress fluctuation stage: the prestress fluctuation change stage can be found from the anchor cable prestress change curve monitored on site. The change characteristic is represented by high-frequency low-amplitude fluctuation of the prestress value. The main reason for this is that the rock mass and anchor cable are adjusted in internal stress to produce repeated engineering of compression and rebound, thereby causing the prestress of the anchor cable to change. The duration of this phase is typically around 3 weeks.
The third stage is a smooth change stage: the law of the prestress change at this stage is relatively stable, although the prestress change generally shows a descending trend, the descending amplitude is not very large, the deformation of the rock mass under the anchoring effect of the anchor rope tends to be stable and the deformation amount is not large.
Fifth, compensation of anchor cable prestress
Through the analysis of the loss and the change rule of the prestress of the anchor cable, different measures are adopted to compensate the loss of the prestress of the anchor cable aiming at different influence factors.
1. Reasonable selection of materials and equipment
The stress loss of the material under different breaking loads is much smaller than that of a common steel stranded wire, and the loss of the internal stress of the steel stranded wire is much smaller than that of the common steel stranded wire along with the increase of time.
And reasonable drilling equipment is selected, so that the hole inclination of the drilled hole is reduced as much as possible.
2. Selecting proper tension mode
From the above analysis, it can be seen that the cable has a relatively large loss of prestress during tensioning and locking, and therefore, the cable should be tensioned and locked at a proper time during the tensioning and locking operation. The field practice proves that the loss of prestress can be greatly reduced by carrying out necessary and repeated super-tensioning on the anchor cable body. Meanwhile, the anchor cable can be compensated and tensioned after being locked to make up for the stress loss, but the compensation tensioning time is not too long, and the compensation times are more, so that the effect is better. After the anchor cable is subjected to two times of compensation tensioning, the stress loss of the anchor cable can be compensated by more than 90% as shown in fig. 8.
3. Properly increasing the tension lock value
According to the analysis of the influence of the prestress on the prestress loss, the locking value of the anchor cable during tensioning is properly improved, and the reduction of the axial force loss percentage of the anchor cable is facilitated. According to the analysis result of fig. 9, in the construction process of the safe pressure dispersion anchor cable, material equipment needs to be selected at first, a basic anchor cable test is made, influence factors of prestress of the anchor cable are analyzed, and the stress stability of the anchor cable in the later period is ensured by controlling tensioning locking load, performing tensioning supplement in time and the like.
The safe pressure dispersion anchor cable is one new kind of support technology, and aims at limiting the deformation of rock mass, especially in bedding geology, and ensuring the safe operation of engineering. Factors influencing the supporting effect of the safety pressure dispersion anchor cable mainly include geological conditions, the length of an anchoring section of the anchor cable, the mechanical properties of a pull rod material and the like. The anchoring force provided by the anchor cable is a factor directly influencing the safety and stability of engineering, so that the research on the stress loss of the safe pressure dispersion anchor cable of the anchor cable is a very meaningful subject and the quality of the anchoring effect of the safe pressure dispersion anchor cable is directly influenced. The factors influencing the prestress loss of the anchor cable are preliminarily determined by analyzing the factors influencing the prestress change of the anchor cable, corresponding compensation measures are provided, and the method has certain reference significance for designing the pressure dispersion type anchor cable for station underground excavation engineering.
Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.
Claims (10)
1. A pressure dispersion type anchor cable comprises a steel strand (1) and an anchor lock (5) for assisting the steel strand in stretching, and is characterized by further comprising a pressure dispersion device (2) for dividing the steel strand into a free section and an anchoring section; the free section is connected to the anchor lock, the anchoring section is composed of at least two anchoring units, and the pressure dispersion devices are arranged at two ends of the anchoring section and between two adjacent anchoring units;
the pressure dispersion device is composed of two fastening plates (21), two fastening screws (22) and a P-type anchorage device (23), the two fastening plates are sleeved on the steel strand, the fastening screws are used for supporting and connecting the two fastening plates which are distributed at intervals, and the P-type anchorage device which is close to the two fastening plates and sleeved on the steel strand is arranged between the two fastening plates.
2. The pressure dispersion type anchor cable according to claim 1, wherein the steel strands are unbonded steel strands sheathed with a PE pipe, the number of the unbonded steel strands is an even number selected from 4 to 16, and the steel strands are uniformly arranged in a ring shape in a radial direction relative to a fastening plate of the pressure dispersion device.
3. The pressure dispersion type anchor cable according to claim 1, wherein the pressure dispersion device further comprises a sealing cover (24) positioned between the two fastening plates and sleeved outside the P-type anchor, and the sealing cover is filled with anti-corrosion grease; and a sealing adhesive tape (25) is wound on the steel strand close to the fastening plate and opposite to the fastening plate and the sealing cover.
4. A pressure dispersing cable bolt according to claim 1 further including a tapered guide cap (3) provided on the pressure dispersing means at the end of the steel strand remote from the anchor lock.
5. A pressure dispersion cable bolt according to claim 1 wherein the free end of the steel strand is provided with a plurality of spaced apart locators (4).
6. The pressure dispersion type anchor cable according to claim 1, wherein said anchor lock is composed of an anchor head (51), a bearing plate (52), a cover plate (53), a wedge (54), a backing plate (55) and a steel tube (56), wherein the steel tube and the wedge are arranged between the backing plate and the cover plate, the bearing plate and the anchor head are arranged on the side of the cover plate opposite to the steel tube in sequence, the steel tube is used for sleeving the steel strand, the anchor head is used for anchoring the steel strand, and the wedge is used for supporting the steel tube.
7. A construction method of a pressure dispersion type anchor cable in extra-large section underground excavation tunnel support, which is characterized in that the anchor cable according to any one of claims 1-6 is used, the construction method adopts a reverse method for construction, and is implemented by subsection and layering, namely, a section of the anchor cable is excavated and implemented as a section of the anchor cable, and the method comprises the following steps:
step 1), excavating a tunnel soil body to reach the elevation of a top row anchor cable, and installing, tensioning and locking the top row anchor cable;
step 2), continuing to excavate the soil body to the elevations of the two rows of anchor cables, and installing, tensioning and locking the two rows of anchor cables;
and 3) repeating the step 2) to perform soil body excavation and lower row anchor cable construction until the tunnel is excavated to the designed elevation.
8. The construction method of the pressure dispersion type anchor cable in the ultra-large section underground excavation tunnel according to claim 7, characterized in that after the anchor cables of each row are installed, the steel strand is grouted at the anchoring section by adopting a twice grouting method, cement mortar with a sand-lime ratio of 1: 0.5-1: 1 is adopted as a primary grouting material, and the grouting pressure is 0.5-1.5 MPa; the secondary grouting material adopts pure cement slurry with the water cement ratio of 0.45-0.50, and the grouting pressure is 2.5-3.0 MPa.
9. The construction method of the pressure dispersion type anchor cable in the ultra-large section underground excavation tunnel according to claim 8, characterized in that after grouting of each row of anchor cables is completed, a super-tensioning method is adopted to tension and lock the free section of the steel strand, the super-tensioning value is 1.1-1.2 times of the design tensioning value, three times of tensioning operation construction are carried out, namely the first tensioning operation value is 1/2 of the design tensioning value, the second tensioning operation value is 1/3 of the design tensioning value, the third tensioning operation value is up to the super-tensioning value, and the stability of each tensioning operation is 4-6 minutes.
10. The construction method of the pressure dispersion type anchor cable in the ultra-large section underground excavation tunnel according to claim 9, characterized in that after tensioning and locking of each row of anchor cables are completed, free section grouting is performed on the steel strand, the grouting material adopts cement slurry with a water cement ratio of 0.45-0.5, and the grouting pressure is 2.5-3.0 MPa.
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| CN112112676A (en) * | 2020-09-18 | 2020-12-22 | 中铁隧道集团一处有限公司 | One-time tension structure and construction method for secondary grouting of unbonded anchor cables in the cave |
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