CN109811771B - Simple method for preventing anchor rod steel waist beam from bending during tensioning - Google Patents
Simple method for preventing anchor rod steel waist beam from bending during tensioning Download PDFInfo
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- CN109811771B CN109811771B CN201910038526.1A CN201910038526A CN109811771B CN 109811771 B CN109811771 B CN 109811771B CN 201910038526 A CN201910038526 A CN 201910038526A CN 109811771 B CN109811771 B CN 109811771B
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Abstract
A simple method for preventing an anchor rod steel waist beam from bending during tensioning comprises the following steps: assembling and welding steel beams, tensioning once, and spraying concrete: spraying full concrete to the back of the steel beam to form steel beam back concrete, spraying and filling concrete to an inner cavity between two I-shaped steels from a gap in the front of the steel beam assembly to form steel beam inner cavity concrete, covering, preserving heat and moisture, and solidifying for 24-36 hours; and finally, secondary tensioning: and each anchor rod is tensioned to 1.4 times of the standard value of the axial force. The invention has the advantages that: the method of filling concrete in the back of the steel beam, filling concrete in the inner cavity of the steel beam, and tensioning after the concrete is solidified to reach a certain strength is adopted, so that the tensile strength of the steel beam is greatly improved, the problem that the steel beam is obviously bent when the anchor rod is tensioned is effectively solved, and the method is convenient, rapid, easy to implement, low in cost and very reliable.
Description
Technical Field
The invention relates to a simple method for preventing a steel waist beam of an anchor rod from bending during tensioning, which is used in anchor rod tensioning construction in foundation pit supporting construction of a foundation, and prevents the steel waist beam from bending when an anchor rod grouting body reaches certain strength and needs to be tensioned and locked in a pile-anchor supporting system of foundation pit supporting, and belongs to the field of construction of constructional engineering.
Background
It is known that in the foundation pit supporting construction of foundation in the field of building construction, a pile-anchor supporting system is a very common supporting type, especially in deep foundation pit supporting, for example, the depth exceeds 15m, and the side of the foundation pit has buildings, roads or underground pipelines, etc., the soil nailing wall or composite soil nailing wall is not good at strictly controlling deformation, the pile-anchor supporting saves money, trouble and labor time compared with underground continuous wall and secant pile, and the control of foundation pit deformation is very effective, especially in hard soil stratum areas like Beijing area, the cost performance is very high. Has been widely adopted.
However, with the increasingly complex urban environment, the price of buildings around the foundation pit, especially houses, is increasingly high, the requirements of residents, construction parties, governments and other related parties on the deformation of the foundation pit are increasingly strict, and the deformation of the foundation pit support is changed from the traditional centimeter level to the current millimeter level. The pile designed by people is required to be thicker and longer, the bearing capacity of the anchor rod is larger and larger, the rod body is longer and longer, the construction process is more and more severe, and the locking value is higher and higher in the water-rising ship. The standards (regulations) for retaining and protecting foundation pits are also increasingly required, for example, the technical regulations for retaining and protecting foundation pits in buildings (DB 11/489-: the maximum test load of the anchor rod pullout resistance test is the designed axial tensile bearing force Nd of the anchor rod. And when the revision is in 2016, the following changes are carried out: the maximum test load of the anchor rod uplift resistance detection test is 0.8 time of the limit uplift bearing capacity of the anchor rod. The industry standard "architecture foundation pit support technical regulation" (JGJ120-2012) specifies: for the first-stage foundation pit, the ratio of the anchor rod tension value to the axial tension standard value Nk is not less than 1.4; meanwhile, the specified conditions are that when test data are lacked, the tension of the anchor rod during locking can be 1.1 to 1.15 times of the locking value.
The design requirement of a certain 15m deep foundation pit of Beijing is as follows: the anchor rod is tensioned and locked in two times, the first tensioning is released after the first tensioning is 1.4 times of the standard value of the tension force, and the second tensioning is locked after the second tensioning is greater than the locking value. The deepest part of the foundation pit reaches 16.05m, three anchor rods are designed, wherein the length of the first anchor rod is 23.5m, 4 steel stranded wires with the diameter of 15.2 are matched, the length of a free section is 8m, the aperture is 150mm, the horizontal distance is 1.6m, the standard value of axial tension is 400kN, the locking value is 380kN, the waist beam is two 25B I-shaped steels, and the 32B I-shaped steels are adopted in the design that the distance is larger due to the fact that one pile drilling tool is broken. When the axial tension reaches 1.4 times of 400kN, namely 560kN, the steel beam is bent quite severely, the 32B I-shaped steel beam is only loaded to 552kN, namely 1.38 times of the steel beam is bent severely, the steel beam has to be terminated in advance, obviously, whether the quality of the anchor rod meets the design requirement cannot be checked, and the steel beam of the type used is confirmed to meet the requirement. At this time, it is urgently required that professional subcontracting construction units have a convenient and quick method to put into practice as soon as possible.
Disclosure of Invention
The invention aims to provide a simple method for preventing an anchor rod steel waist beam from bending during tensioning, so as to solve the problem of steel beam bending during the tensioning of an anchor rod in the prior art.
The technical scheme of the invention is as follows: a simple method for preventing an anchor rod steel waist beam from bending during tensioning is characterized by comprising the following steps:
(1) assembling and welding steel beams: after the slope protection piles and the protective layers among the piles are constructed, mutually welding two parallel I-shaped steels by batten plates and inclined cushion blocks to form a steel beam assembly, wherein each inclined cushion block corresponds to each slope protection pile; the steel strand of the anchor rod penetrates between the two I-shaped steels and is placed in place according to a conventional method;
(2) primary tensioning: in order to enable each part of the prestressed anchor rod to be tightly contacted and enable the steel strand to be completely straight, 10-20% of designed tensioning load is adopted, the steel strand is tensioned for 1-2 times, and the steel beam assembly is ensured to be completely hung and positioned;
(3) spraying concrete: repairing the bottom surface of the steel beam assembly to be flat, forming a 'soil mould' between the inter-pile protective layer and the rear side of the steel beam assembly after the side surface is filled with soil, and spraying concrete into the 'soil mould' to fill the space between the rear surface of the steel beam and the inter-pile protective layer with the concrete to form post-steel beam concrete; spraying and filling concrete into an inner cavity between the two I-beams from a gap in front of the steel beam assembly to form steel beam inner cavity concrete, covering, preserving heat and moisture, and solidifying for 24-36 hours;
(4) secondary tensioning: and each anchor rod is tensioned to 1.4 times of the standard value of the axial force.
The sheath between stake include: the steel mesh is arranged between two adjacent slope protection piles, and two sides of the steel mesh are connected with the slope protection piles through implanted steel bars; the steel mesh is sprayed with the spray protection among the piles.
Before the step (2) is carried out, the multi-section steel beam components are welded into a whole, so that the integrity of the multi-section steel beam components is ensured.
In the step (3), a small excavator is adopted to trim the bottom surface and the side surface of the steel beam to be padded with soil, so as to form the soil model; starting an air compressor by using field anchor spraying equipment, mixing a mixture in a background, spraying the concrete behind the steel beam and the concrete in the inner cavity of the steel beam in sequence, and performing steel strand protection and wrapping isolation before spraying the concrete so as not to enable the steel strands to be stained with the concrete; after the spraying, trowels are used for trowelling the concrete so that the appearance is attractive.
The cement used by the post-steel beam concrete and the steel beam inner cavity concrete selects PSA32.5, PSB32.5 or PO42.5, the used stones and sands are the same as the materials of the protective layer between the piles, and the volume ratio is as follows: cement: stone: sand 1: 2: 2.
in order to reduce dust pollution, the step (3) particularly adopts a 'wet spraying' process, namely, the pebble sand is wetted by water, the spraying effect is not influenced, dust flying is avoided, the dust concentration can be controlled within 30mg/m3 and is usually about 15mg/m3 through detection of a CCZ-1000 dust concentration tester, and workers can operate without wearing dust masks.
The I-shaped steel in the steel beam assembly comprises 25B, 28B or 32B, or adopts a smaller type.
The I-steel can also be replaced by two channel steels with opposite notches, and the concrete behind the steel beam and the concrete in the inner cavity of the steel beam are filled with C30-C40 concrete.
The invention has the advantages that: the method of filling concrete in the back of the steel beam, filling concrete in the inner cavity of the steel beam, and tensioning after the concrete is solidified to reach a certain strength is adopted, so that the tensile strength of the steel beam is greatly improved, the problem that the steel beam is obviously bent when the anchor rod is tensioned is effectively solved, and the method is convenient, rapid, easy to implement, low in cost and very reliable.
Drawings
FIG. 1 is a plan view of a foundation pit and surrounding pile-anchor support according to an embodiment of the present invention;
FIG. 2 is a view (partial) taken in the direction F of FIG. 1;
FIG. 3 is an enlarged view at N of FIG. 2;
FIG. 4 is a cross-sectional view E-E of FIG. 2;
FIG. 5 is an enlarged view at P in FIG. 4;
fig. 6 is a schematic top view of fig. 5.
Description of reference numerals: 1-crown beam, 2-retaining wall, 3-retaining wall, 4-filling wall, 5-first anchor rod, 6-second anchor rod, 7-third anchor rod, 8-slope protection pile, 9-bearing plate, 10-anchor head, 11-I-steel, 12-inclined cushion block (angle plate), 13-steel mesh, 14-inter-pile spraying protection, 15-embedded steel bar, 16-steel beam rear concrete, 17-close to foundation pit building foundation, 18-steel strand, 19-batten plate, 20-steel beam inner cavity concrete, 21, inter-pile sheath, A, slope protection pile position (pile hole), B, foundation pit upper opening, C, foundation pit lower opening, D, raft sideline, a, soil model side face, B and soil model bottom face.
Detailed Description
Referring to fig. 1 to 6, the invention relates to a simple method for preventing an anchor rod steel waist beam from bending during tensioning, which comprises the following specific steps: after the slope protection piles 8 and the inter-pile protection layers 21 are constructed, the anchor rod design construction is finished by using an anchor rod drilling machine; the welding is assembled with the girder steel subassembly, promptly: mutually welding two parallel I-beams 11 by a plurality of batten plates (namely connecting plates) 19 and inclined cushion blocks 12 to form a steel beam assembly (the batten plates 19 can be welded on two sides of the I-beams 11), wherein each inclined cushion block 12 corresponds to each slope protection pile 8; and the steel strand 18 of the anchor rod mechanism penetrates between the two I-shaped steels 11 and is placed in place according to a conventional method.
In order to make the prestressed anchor rods tightly contact all parts and make the steel strands 18 completely straight, 10-20% of the designed tension load is adopted to stretch the steel strands for 1-2 times, and the steel beam assembly is ensured to be completely hung and positioned. At the moment, every two sections of steel beam assemblies can be welded into a whole, and the integrity of the steel beam assemblies is ensured.
Correcting the bottom surface a of the steel beam assembly to be flat by using a small excavator, properly filling soil on the side surface b to form a 'soil mold', starting an air compressor by using field anchor spraying equipment, mixing a mixture in a background, spraying concrete, and spraying full concrete behind the steel beam to form steel beam rear concrete 16; and the inner cavity of the steel beam is laterally sprayed, so that the inner cavity of the steel beam is also filled with concrete to form the concrete 20 in the inner cavity of the steel beam. At this time, the protection and the wrapping isolation of the steel strand 18 are needed, and the steel strand 18 is not stained with concrete. After spraying, trowelling to make the appearance beautiful, covering, preserving heat and moisture, and waiting for solidification.
The concrete 16 after the steel beam is formed and the cement of the concrete 20 in the inner cavity of the steel beam can be selected from PSA32.5 and PSB32.5, or in order to shorten the construction period and enable the concrete to be quickly solidified, PO42.5 can be used, and the stone and the sand can be the same as the materials used for spraying the soil, nailing walls and piling spaces on site (the volume ratio is that the cement, the stone and the sand are 1: 2: 2), so that the separate feeding is not needed, and the method is time-saving, simple, convenient, economical and efficient in operation. In order to reduce dust pollution, a 'wet spraying' process is particularly adopted, namely, the stone sand is wetted by water, the spraying effect is not influenced, dust flying is avoided, the dust concentration can be controlled within 30mg/m3 and is usually about 15mg/m3 through detection of a CCZ-1000 dust concentration tester, and workers can operate without wearing dust masks.
After the solidification reaches a certain strength, the anchor rod can be tensioned generally only in 24-36 hours, and the construction period is not occupied independently in the anchor rod maintenance period. Even if each anchor rod is tensioned to 1.4 times of the standard value of the axial force, the steel beam cannot be bent.
Thereby the anchor rod stretch-draw construction is accomplished high-efficiently smoothly, realizes that each anchor rod all stretches to 1.4 times of axial force standard value, and the crooked mesh can not appear in the girder steel.
The construction equipment comprises an air compressor, an anchor spraying machine, a small excavator, a spade, a pipeline, a spray gun, a trowel, a spray head, electric welding equipment and the like.
Another advantage is that deep basal pit anchor rod girder steel can adopt models such as 25B, 28B, 32B, also can adopt more small-size, for example 20B, 22B etc. because light, it not only brings the convenience, but also can save a lot of money, and the economic nature is very showing. For example, 25B I-beam 540.8m, 28B I-beam 1181.6m and 32B I-beam 72m have theoretical weights of 42.03, 47.888 and 57.741kg/m respectively, and 20B has theoretical weight of 31.069 kg/m. 27721.38kg of I-steel can be saved after replacement, and 116429.8 yuan can be saved by 33.2% according to the current market price of 4200 yuan/T. I.e. one third. The steel channel is preferably filled with C30-C40 concrete, and more one-half of the concrete can be saved. Compared with a reinforced concrete waist beam, complex and tedious processes of binding a reinforced bar formwork, pouring concrete and the like are omitted, time for waiting for long-time maintenance and time for waiting for coagulation and strength improvement is omitted, and the time efficiency can be improved by more than half.
4. Examples of the embodiments
4.1 engineering overview
The modification project of the school district hospital of the Zhongguancun of the Beijing university of nursing Engineers is located in the school of the Nanda street of the Zhongguancun of the Haitai province of Beijing university of nursing Engineers No. 5 Beijing university of nursing Engineers, the east side of the school is a hospitality 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 residential buildings No. 1 and No. The engineering + -0.00 ═ 52.700 m. The project consists of a school hospital and a rainwater storage tank.
The foundation pit engineering is temporary support, and the design service life is 1 year.
4.2 ambient Environment
(1) More underground pipelines (thermal pipelines, water supply pipelines and sewage pipelines) and related well valve facilities are distributed on the north side of the foundation pit, the east section of the north side is a number 1 residential building, and the west section of the north side is a number 2 residential building. The nearest distance between the underground pipeline and the outer edge of the proposed structure is about 2.40m, a direct burial mode is adopted, and the burial depth is less than 2.00 m; the nearest distance between the 6 floors of the No. 1 residential building and the outer edge of the proposed structure is about 9.70m, the C10 concrete strip foundation is arranged, and the base elevation is 50.15-49.10 m; the ground of the No. 2 residential building has 5 floors, the nearest distance from the outer edge of the proposed structure is about 6.10m, the C15 concrete strip foundation is arranged, and the base height is 48.80 m.
(2) The east side of the foundation pit is a middle road, a hospitality place and a dormitory of the university of the nursing staff. Burying underground pipelines under the middle road of university of science and engineering, wherein the nearest distance between the underground pipelines and the outer edge of the proposed structure is about 13.0m, and the buried depth is less than 2.00m by adopting a direct burial mode; the nearest distance between the upper 6 floors of the hostel of the accommodation place and the dormitory of the living quarters is about 20.00m, the C20 concrete strip foundation is arranged, and the base elevation is 50.44 m.
(3) More underground pipelines (power electricity, weak electricity, thermal pipelines, water supply pipelines and rainwater pipelines) and related well valve facilities are distributed on the south side of the foundation pit, the east section of the south side is a Kai-Shi building, and the west section of the south side is a playground. The nearest distance between the underground pipeline and the outer edge of the proposed structure is about 4.00m, a direct burial mode is adopted, and the burial depth is less than 2.00 m; 1-4 floors on the floor, the nearest distance from the outer edge of the proposed structure is about 21.50m, the C20 concrete independent foundation is arranged, and the elevation of the foundation is 50.00 m; the playground is a field in use, and the elevation of the field is about 52.40 m.
(4) More underground pipelines (power electricity, weak electricity and rainwater pipelines) and related well valve facilities are distributed on the west side of the foundation pit, the north west side is a manager restaurant and a comprehensive service building, and the south west side is a polygala tenuifolia building. The nearest distance between the underground pipeline and the outer edge of the proposed structure is about 2.80m, a direct burial mode is adopted, and the burial depth is less than 2.00 m; 1-2 floors of the organization restaurant and the comprehensive service floor, the nearest distance from the outer edge of the proposed structure is about 8.30m, the C20 concrete strip foundation is arranged, and the base elevation is 50.40-49.50 m; the nearest distance between the polygala tenuifolia floor and the outer edge of the proposed structure is about 7.30m, and the base height of the C20 concrete strip foundation is 50.60 m.
4.3 engineering and hydrogeological conditions
General description of the Earth's strata
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.
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.
4.4 engineering emphasis and difficulties
The construction project is located in the south street of Guancun in the Haihe district, the workload of foundation pit support and earth excavation is large, and the depth of the foundation pit reaches 15 m. The traffic management along the engineering line and around the engineering is strict, the building structure is complex, the surrounding building is closer to the foundation pit, the deformation control requirement of the soil body around the foundation pit is strict, and the outstanding characteristics of the engineering are that the safety and the stability of the foundation pit and the safety and the stability of the surrounding building are ensured.
4.4.1 protection of surrounding buildings, structures and underground pipelines is of great importance
After entering the field, the method carries out deep and detailed investigation and investigation on the adjacent buildings (structures), further verifies the relationship (including plane relationship, elevation relationship and the like) between the adjacent buildings (structures) and the foundation pit, and further perfects the design. According to our investigation, the surrounding residential buildings have no earthquake resistance, so that effective measures are needed to reduce the earthquake damage to the surrounding buildings as much as possible. The construction can be carried out by adopting the following measures:
1) the construction process of the slope protection pile adopting the rotary drilling rig mud protection wall for hole forming shortens the pile driving construction period and reduces the influence on the surrounding environment in the slope protection pile construction process.
2) In order to avoid hole collapse during the construction of the anchor rod in the sandy gravel layer, a sleeve follow-up construction process can be adopted during the construction of the anchor rod if necessary, and grouting is carried out in time, so that the existence of factors causing instability of the foundation of the adjacent building and the surrounding soil body is reduced as far as possible.
Secondly, monitoring the deformation and settlement of the structure of an adjacent building (structure) by matching with an authoritative monitoring unit (an independent third party) with qualification; the method comprises the steps of embedding an inclinometer in a pile body, installing a bolt shaft dynamometer, adopting an advanced digital level gauge and a foundation pit monitoring and analyzing system, carrying out rapid and accurate processing and analysis on monitoring data, rapidly drawing a curve, and timely providing dynamic information and prediction for the safety of a supporting structure and a nearby building (structure), so that the information-based construction is used as a favorable guarantee for the safety of the engineering supporting structure.
Pre-stressed anchor rod construction attention
The existing buildings are arranged on the north side and the west side of the foundation pit, the foundation pit is close to the foundation pit, and the pre-stressed anchor rods of all supporting sections do not collide with the foundation structure of the adjacent building through calculation of a design unit. When the anchor rod is constructed, jumping construction is adopted for hole forming, three steps are separated, one step is performed, grouting is performed in time, and the adjacent anchor rod can be constructed after the grouting is completed for 24 hours.
Because the underground pipelines around the foundation pit are more, when the anchor rod construction encounters an obstacle, the construction needs to be stopped immediately and the reason needs to be searched, corresponding treatment measures are made, and adverse consequences are avoided.
Selection of the Process
The construction range of the anchor rod is clay, fine sand, silty clay, pebble and the like, the first anchor rod is constructed by dry operation of a common anchor rod drilling machine, and a mud jacking method mechanical hole forming process is adopted to ensure that no mud skin is generated in the construction process. The anchor rod grouting adopts a micro-pressure grouting combined secondary pressure grouting process.
Because of the hard ground layer such as pebbles, the second anchor rod is downward and is constructed by a casing drilling machine. And (3) reserving an anchor rod construction working surface (500 mm below an anchor position) while constructing the earthwork. And dynamic adjustment is carried out on site according to the actual drilling condition of the anchor rod construction, so that the construction speed and quality of the anchor rod are ensured. When different geological layers are involved, the anchor rod trial drilling is carried out in advance, and the type selection of the drilling machine is adjusted in time according to the hole forming condition.
Dry operation construction process flow
Casing wet operation construction process flow
Drilling machine is in place → hole site angle regulation is corrected- → water source is opened → drilling → inner drill rod is repeatedly lifted and washed → inner drill rod and outer sleeve are connected → drilling is continued till design hole depth → hole clearing → water is stopped, inner drill rod is pulled → steel strand bundle and grouting pipe are inserted → cement paste is pressed and grouted → outer sleeve is pulled out by tube drawing machine and secondary grouting is carried out- → secondary pressure grouting is carried out- → maintenance → steel waist beam and anchor head are installed → prestressed tension locking
Tension lock
The bearing surface is flat and perpendicular to the axis direction of the anchor rod. The anchor rod tensioning is carried out when the strength of the grouting body reaches 20 MPa. The main tensioning steps are carried out according to design requirements.
In order to ensure that the stress of each unit anchor rod is uniform, each unit anchor rod is tensioned in a split manner, and when the displacement difference caused by different lengths of free sections of each unit anchor rod under the same load is compensated, the unit anchor rods are tensioned integrally.
And determining the locking load according to the design requirement. If the anchor rod is locked, the change of the prestress value is larger than 10%, and the tensioning needs to be loosened or repeated.
And before the prestressed anchor rod is tensioned, calibrating tensioning equipment. The prestressed anchor rod tensioning is carried out according to a specified program, and the mutual influence of the prestressed anchor rod tensioning of adjacent drilling holes is considered when the tensioning program is arranged. Before the prestressed anchor rod is formally tensioned, 20% of designed tensioning load is adopted, and the prestressed anchor rod is pretensioned for 1-2 times, so that all parts of the prestressed anchor rod are tightly contacted, and the steel strand is completely straight.
In the anchor rod of the engineering, experimental tensioning is carried out according to different anchor rod types, 3 anchor rods of each type are taken, tensioning is carried out until the design load is reached, then locking is carried out, the locking value is given by a design drawing, and then tensioning of the engineering anchor rod is carried out. The anchor rod tensioning and locking are carried out in two times, the first tensioning is released after the tension is 1.4 times of the standard value of the tension, and the second tensioning is locked after the tension is larger than the locking value. In view of the amount of recoil (i.e., loss of a certain locking load) that occurs during bolt tensioning, it is necessary to perform over-tensioning. The specific value of exceeding the tension lock is determined by field tests by using an oil pressure system and a monitoring instrument.
If a significant loss of prestress is found, a compensation stretch should be performed. After the anchor rod is tensioned and locked, the end tensioning section cannot be shortened for supplementing tensioning.
4.4.2 engineering monitoring
According to the design file, before the foundation pit engineering construction, a construction party commissions a third party which supports corresponding qualifications to carry out on-site monitoring on the foundation pit engineering, a construction unit also needs to carry out necessary construction monitoring in the construction process, and the on-site monitoring needs to adopt a method of combining instrument monitoring and inspection tour to monitor the foundation pit according to the technical Specification for monitoring the construction foundation pit engineering (GB 50497-2009).
4.4.2.1 monitoring content
(1) Monitoring horizontal and vertical displacement of the slope top; (2) monitoring horizontal and vertical displacement of the pile top; (3) monitoring horizontal displacement of a deep layer of a support pile; (4) monitoring the internal force of the anchor rod; (5) and monitoring the peripheral surface subsidence.
4.4.2.2 monitoring Instrument
Main monitoring instrument for sequence number monitoring project
1 Displacement monitoring Zhongweg ZT80MR + (Total station)
2 sedimentation monitoring DSZ2 and FS1 (micrometer)
The same observer of the same instrument is always kept during observation, and instrument centering errors and staff collimation errors caused by the exchange of personnel and instruments are avoided.
4.4.2.3 method of monitoring
The engineering horizontal displacement is measured by a total station. In consideration of the monitoring precision requirement, a straight line method is adopted as much as possible (a station is arranged on a straight line with a monitoring body, two direction points are selected to measure 2 angle values far away from the foundation pit, one is used for checking whether the station has variation, and the other is used as an initial value of an orientation point, a measured point and the station). The individual points adopt a small-angle distance method (2 measuring stations are arranged opposite to a monitoring body, the side length of each monitoring point is measured at each measuring station respectively, and the plane position change of each point can be directly reflected by calculating the closing difference and the side length intersection value of a triangle at each point, so that the accuracy of data is ensured).
And measuring and reading twice for the first time, and taking an average value as an initial value of the engineering monitoring data. Each subsequent time, one-way observation can be carried out, and if the data is abnormal, the data is seriously tested. The observation method takes the settlement observation datum point as a starting point, measures the elevation of each point, and then subtracts the last elevation value from the current elevation value to obtain the settlement variation.
(1) Observation of settlement
And measuring by using a precise level gauge. The method is mainly carried out by adopting a precise leveling method, the settlement observation point is directly arranged on the characteristic point of an observed object (such as a soil slope and a building), and the datum point is arranged at a position far away from a foundation pit or a stable position. The observation points should be placed where there are characteristic points (e.g., the external corners of the pit).
(2) Observation of horizontal displacement
And measuring by using a total station. And adopting an axis projection method to connect a line between two stable reference points as a reference line, and measuring the difference and the accumulated displacement. The observation points are directly arranged on the top of the soil slope or the pile top connecting beam.
(3) Anchor rod axial force monitoring
Before the anchor rod is tensioned, an anchor rod stress sensor is installed at the base plate, and then an anchor head is installed outside the anchor rod stress sensor for tensioning and locking.
(4) Deep horizontal displacement of supporting structure
And (3) setting monitoring points on the foundation pit slope protection piles, monitoring by using a JTM-U10A reader of a measuring instrument monitored by a third party, and editing a daily monitoring report form after each period of monitoring is finished. The displacement of each monitoring point in the table is a positive value, which indicates that the monitoring point deviates towards the inner side direction of the foundation pit; conversely, the displacement is toward the outside of the foundation pit.
(5) On-site inspection
Because the construction quality of the supporting structure, the change of construction conditions, the change of the pile load at the side of the foundation pit, the improper discharge of construction water, the leakage of pipelines and the change of weather conditions and engineering hidden dangers such as ground cracks, instability of the supporting structure, cracks close to a building and the like can be found in time during the routing inspection work, the routing inspection is very important and necessary, the routing inspection is carried out by experienced engineers according to time, and the routing inspection work is carried out according to time and kept in records.
Monitoring alarm value and emergency measure
Monitoring frequency
The monitoring average rate of the horizontal displacement is as follows: before excavation to 1/2 of depth: 1 time/2 days; excavating for 1 time/day until the substrate is stabilized; 1 time/3 days after the stabilization is finished and before the structural bottom plate is finished; 1 time/15 days after the structural bottom plate is finished and before the backfilling is finished.
The monitoring average rate of the vertical displacement is as follows: before excavation to 1/2 of depth: 1 time/2 days; excavating for 1 time/day until the substrate is stabilized; 1 time/3 days after the stabilization is finished and before the structural bottom plate is finished; 1 time/15 days after the structural bottom plate is finished and before the backfilling is finished;
the monitoring flat rate of deep horizontal displacement of the supporting structure is as follows: before excavation to 1/2 of depth: 1 time/2 days; excavating for 1 time/day until the substrate is stabilized; 1 time/3 days after the stabilization is finished and before the structural bottom plate is finished; 1 time/15 days after the structural bottom plate is finished and before the backfilling is finished;
the monitoring flat rate of the anchor rod tension is as follows: before excavation to 1/2 of depth: 1 time/1 day; excavating for 2 times/day until the substrate is stabilized; 1 time/day after the stabilization and before the backfill is completed.
Monitoring data must be timely, accurate and complete, abnormal phenomena are found, and monitoring is enhanced;
if the monitoring data reaches or exceeds the alarm value, the monitoring data should inform all the parties in time so as to take effective measures as soon as possible to ensure the smooth progress of the project.
Safety patrol
(1) The inspection tour of the foundation pit engineering comprises the following main contents:
1) supporting structure
a. The forming quality of the supporting structure;
b. whether cracks appear or not;
c. whether the soil body behind the wall sinks, cracks and slides or not;
d. whether accumulated water exists at the top and the bottom of the slope or not and whether underground water leaks from the supporting surface or not.
2) Construction conditions
a. The exposed soil condition after excavation is different from a rock and soil investigation report;
b. whether the length of the excavation segmentation of the foundation pit, the layering thickness and the arrangement of the soil nails are consistent with the design requirements or not;
c. and whether the ground surcharge load around the foundation pit is greater than a design limit value or not.
3) Surrounding environment of foundation pit
a. Whether the underground pipeline is damaged or not;
b. whether new cracks appear in the peripheral buildings or not;
c. the peripheral road (ground) has no crack or subsidence.
4) Monitoring facility
a. The conditions of the reference points and the measuring points are intact;
b. whether there is an obstacle that affects the observation work;
c. and monitoring the health and protection condition of the element.
(2) The inspection method is mainly for visual inspection, and is assisted with tools such as a hammer, a drill, a measuring tape, and a magnifying glass, and measurement such as image pickup and photography.
(3) The inspection tour of natural conditions, supporting structures, construction conditions, surrounding environment, monitoring facilities and the like should be recorded. The inspection records should be sorted in time and comprehensively analyzed in combination with the monitoring data.
(4) The designer and other relevant units should be informed in time when the inspection tour finds abnormal and dangerous situations.
4.5 field implementation and foundation pit monitoring results
Starting the first anchor rod construction from 7 month and 16 days in 2018, tensioning the first anchor rod until 7 months and 23 days, spraying concrete on the back of the steel beam, spraying concrete in the inner cavity of the steel beam, waiting for 36 hours at the shortest time, wherein the tensioning time is 1.4 times of the standard value of the axial force of the anchor rod, and then unloading and tensioning until the axial force is greater than the locking value for locking. Taking the typical cross section as an example:
the standard value of the axial tension of the first anchor rod is 400kN, and the first anchor rod is tensioned to 560 kN;
the standard value of the axial tension of the second anchor rod is 540kN, and the second anchor rod is tensioned to 756 kN;
the third anchor rod axial tension standard value is 610kN, and the third anchor rod axial tension standard value is tensioned to 854 kN.
By adopting the patented technology, the steel beam is sprayed with concrete at the back, the setting time is 36h, then tensioning is carried out, the root reaches 1.4 times of the standard axial tension value of the anchor rod, the steel beam is not bent, the quality of the anchor rod is ensured, the displacement of the foundation pit is ensured within the limited range, and the safety of building road pipelines and the like around the foundation pit is ensured.
And monitoring the foundation pit to be dug to the bottom of the pit by a third party, constructing the floor, wherein only one point of the maximum horizontal displacement reaches 4mm, and the displacement of the other points is 2-3 mm. It can be seen that the excavation support is extremely successful.
Claims (8)
1. A simple method for preventing an anchor rod steel waist beam from bending during tensioning is characterized by comprising the following steps:
assembling and welding steel beams: after the slope protection piles (8) and the protective layers (21) between the piles are constructed, mutually welding two parallel I-shaped steels (11) by using batten plates (19) and inclined cushion blocks (12) to form a steel beam assembly, wherein each inclined cushion block (12) corresponds to each slope protection pile (8); the steel strand (18) of the anchor rod penetrates between the two I-shaped steels (11) and is placed in place according to a conventional method;
primary tensioning: in order to enable each part of the prestressed anchor rod to be tightly contacted and enable the steel strand to be completely straight, 10-20% of designed tensioning load is adopted, the steel strand is tensioned for 1-2 times, and the steel beam assembly is ensured to be completely hung and positioned;
spraying concrete: repairing the bottom surface of the steel beam assembly to be flat, forming a 'soil mould' between the post-pile protective layer (21) and the rear side of the steel beam assembly after the side surface is filled with soil, and spraying concrete into the 'soil mould' to fill the space between the rear surface of the steel beam and the post-pile protective layer (21) with the concrete to form post-steel-beam concrete (16); spraying and filling concrete into an inner cavity between the two I-beams from a gap in front of the steel beam assembly to form steel beam inner cavity concrete (20), covering, preserving heat and moisture, and solidifying for 24-36 hours;
secondary tensioning: and each anchor rod is tensioned to 1.4 times of the standard value of the axial force.
2. The easy method for preventing the anchor rod steel wale from bending during the tensioning according to claim 1, wherein the inter-pile sheath (21) comprises: the steel mesh (13) is arranged between two adjacent slope protection piles (8), and two sides of the steel mesh (13) are connected with the slope protection piles (8) through implanted steel bars (15); the steel mesh (13) is sprayed with inter-pile spraying guards (14).
3. The easy method for preventing the anchor rod steel wale from bending during the tensioning according to claim 1, wherein the multi-sectional steel girder assembly is welded to each other to ensure the integrity thereof before the step (2).
4. The simple method for preventing the anchor rod steel wale from bending during tensioning according to claim 1, wherein: in the step (3), a small excavator is adopted to trim the bottom surface and the side surface of the steel beam to be padded with soil, so as to form the soil model; starting an air compressor by using field anchor spraying equipment, mixing a mixture in a background, spraying the steel beam rear concrete (16) and the steel beam inner cavity concrete (20) in sequence, and performing steel strand protection and wrapping isolation before spraying the concrete so as not to enable the steel strands to be stained with the concrete; after the spraying, trowels are used for trowelling the concrete so that the appearance is attractive.
5. The simple method for preventing the anchor rod steel wale from bending during tensioning according to claim 1, wherein: the cement used by the steel beam rear concrete (16) and the steel beam inner cavity concrete (20) is PSA32.5, PSB32.5 or PO42.5, the used stones and sands are the same as the materials of the sheath layer (21) between the piles, and the volume ratio is as follows: cement: stone: sand = 1: 2: 2.
6. the simple method for preventing the anchor rod steel wale from bending during tensioning according to claim 1, wherein: in order to reduce dust pollution, the step (3) adopts a 'damp spraying' process, namely, the pebble sand is wetted by water, the spraying effect is not influenced, dust flying is avoided, the dust concentration can be controlled within 30mg/m3 and is usually about 15mg/m3 through detection of a CCZ-1000 dust concentration tester, and workers can operate without wearing dust masks.
7. The simple method for preventing the anchor rod steel wale from bending during tensioning according to claim 1, wherein: the I-shaped steel (11) in the steel beam assembly has the type of 25B, 28B or 32B or adopts a smaller type.
8. The simple method for preventing the anchor rod steel wale from bending during tensioning according to claim 1, wherein: the I-shaped steel (11) is replaced by two channel steels with opposite notches, and C30-C40 concrete is filled in the rear concrete (16) of the steel beam and the concrete (20) in the inner cavity of the steel beam.
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| CN114411767B (en) * | 2021-11-30 | 2023-04-11 | 中铁二院工程集团有限责任公司 | Construction method of loose deformation slope reinforcement structure |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1405409A (en) * | 2002-10-11 | 2003-03-26 | 贾金青 | Foundation pit side-wall flexible support method |
| CN102251533A (en) * | 2011-05-12 | 2011-11-23 | 哈尔滨工业大学 | Spiral ribbed steel pipe concrete pre-pressed composite oblique pile foundation and construction method |
| KR20140013300A (en) * | 2012-07-23 | 2014-02-05 | 유호산업개발(주) | Steel pipe pile cap for supporting temporary bridge girder or temporary bent |
| CN108797600A (en) * | 2018-05-21 | 2018-11-13 | 青岛建集团有限公司 | Miniature steel pipe pile prestressed anchor rope combination supporting construction method |
-
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1405409A (en) * | 2002-10-11 | 2003-03-26 | 贾金青 | Foundation pit side-wall flexible support method |
| CN102251533A (en) * | 2011-05-12 | 2011-11-23 | 哈尔滨工业大学 | Spiral ribbed steel pipe concrete pre-pressed composite oblique pile foundation and construction method |
| KR20140013300A (en) * | 2012-07-23 | 2014-02-05 | 유호산업개발(주) | Steel pipe pile cap for supporting temporary bridge girder or temporary bent |
| CN108797600A (en) * | 2018-05-21 | 2018-11-13 | 青岛建集团有限公司 | Miniature steel pipe pile prestressed anchor rope combination supporting construction method |
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