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Excavation high-rise building design and construction of engineering structures


Abstract: In this paper, and engineering geology engineering examples are described in detail the construction of building foundation engineering support scheme comparison and excavation engineering and construction technology program analysis, based on its construction method SMW continuous wall and the foundation construction techniques described in detail on the construction monitoring were evaluated. Keywords: foundation pit; SMW continuous wall construction method; construction technology; monitoring 1 Project Overview Changsha City, a total construction area of about 19770m land 2 , total construction area of about 32116m 2 , the main building project for 19 high-level, group F, 3 to 4 layers, set up a basement. The deep foundation pit, deepening to a wide range of 6.85m, the local part of the elevator shaft pit depth 8.45m. Basement flat rectangular layout, perimeter 327m, as shown in Figure 1. According to geological investigation report of the project land, the scope of the excavation for the thick muddy clay. Excavation of the soil as the main physical properties of the design criteria such as Table 1. According to local experience, on the table, C, φ value is adjusted. 2 Excavation Project Choice under this project the characteristics of the surrounding environment foundation pit excavation works and the same experience, we have taken into account in the design of several kinds of programs: 2.1 composite soil nail retaining wall support programs. This is a more economical solution, but the project site following the ground 2m thick layer of clay, silt, and the project to dig deep (6.85m) is relatively deep, so the surrounding environment using the program than the conventional envelope must be strengthened. Composite soil nailing walls and can not effectively control program soil displacement and soil nails in the muddy soil little effect. Therefore, the design does not consider the program. 2.2 support using bored pile to add the support and cement mixing pile seal program suitable for the basement excavation, but the program larger than normal quantities, it is not considered in the program. 2.3 envelope method using SMW Engineering program has the following characteristics: ① simultaneously retaining and sealing, takes a small construction site: ② Construction speed: ③ no vibration, no noise, no mud pollution; ④ recycling steel can be pulled out. To this end, we have programs and program ③ ① design calculations are carried out on the comprehensive economic, and social benefits period was compared and found that the project uses SMW bored piles construction method than the method of saving 25% cost, in line with national advocate energy saving, environmental requirements, a better social and economic benefits, so we use the envelope scheme SMW engineering methods. 3 SMW continuous wall construction method works and design of shoring the design of shoring construction method mainly uses the SMW continuous steel wall and steel columns supporting the structure increases. SMW (Soi,[link widoczny dla zalogowanych], Mixing Wall acronym) is a construction method for soil cement mixing pile foundation pit of a construction method, the method of deep through a special multi-axis mixer at the construction site according to the design depth of the soil cut loose at the same time drill mud from the water front into the soil enhancer, and make repeated in situ soil mixing, and then inserted before the cement has not hardened steel or steel H piles as stress strengthen the material, until the cement sclerosis. During the construction plane, overlap between the piles and piles lap, in the ground to form a good impermeability, stiffness, while the H-beam intensity, can withstand greater levels of the underground wall of earth pressure. After the underground structure construction recycling pull H beam. This structure of the economic and rational use of deep mixing piles and H-beam advantage, while recovery of H beam can be pulled out to bring huge benefits, and therefore have a simple structure, good sealing performance, short duration, low cost, environmental pollution small advantages. Support surface elevation of the Foundation for the-0.300m. Natural ground elevation is-0.500m. Natural ground to the steel beam supporting the top surface of the depth of 2.500m, by supporting legislation pile bored pile diameter 700 (Figure 2). Pressure are used around the top beam situ reinforced concrete structure 900 × 500, strength grade C25. Φ630 pipe support section ZC1 as steel pipe,[link widoczny dla zalogowanych], wall thickness 10mm; ZC2 to φ426 pipe, wall thickness 9mm; level ZC3 to φ377 pipe wall thickness of 7mm. 4 foundation of the program's technical analysis applied 4.1 Excavation of this project design considered by the sub back strip for the construction, from west to east into a 8 axis, 8 to 16 axes, 16 to 22 axes of three construction segments were excavated from the east slope; 3.500m above the excavation, digging out a support beam before the Ministry of earth, and then press the top of concrete and steel beams supporting beam. ① segmentation, layered excavation of earth pressure around the top to the bottom elevation-3.500m at the beam, make 60 thick C15 concrete slope protection. ② position by pressing the template top beam, steel construction, pouring concrete top beam pressure. ③ When the pressure of concrete roof beams meet the design requirements of 80%, processes the next construction. ④ After construction steel support beam under the earth excavation support beam.
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; 4.2-3.500m above the earth axis is the line taken by the 11 divided into two sub-blocks of cut slope excavation, excavation elevation control points should be located as far as possible to deepen the level control and accurate. Excavation of soil conditions can be taken according to the field put a 1:1 slope. 4.3-3.500m above the earth excavation, shall take measures to protect the steel support beams, non-excavators and earth-car collision in Kengbian support beam. 4.4 in the pit floor construction is complete,[link widoczny dla zalogowanych], remove the second support beam. Finished basement key plate pouring, removal of excavation support beam for the waterproof outer lining of acceptance and return to earth fill wall only after removal of SMW Support H-shaped steel body. 5 Construction of foundation pit construction process technology 5.1 Actinomyces → → SMW construction method was sub-excavation earth pressure of the top beam to-3.500m → Construction → Concrete revetment the top section of concrete pouring pressure steel support beam → conservation → Construction → dug-3.500m construction of the following sub-section of earth → → increase of pouring the basement floor bracing wall after the removal of support pouring → → removal of roof and waterproofing construction method SMW steel → All backfill around earth. 5.2 Construction Methods 5.2.1 Surveying: According to the project are known to control the axis, release of pit edges, the control point at the edge of angle iron with a 4 × 4 make signs. And in accordance with design requirements to do the monitoring points and laying the initial value measured before the excavation time. 5.2.2 SMW construction method: the construction method for high speed and occupancy characteristics of a small construction site. To speed up the progress of the siege of care and quality assurance, engineering methods pile shaft for the partition of 11 lines. With the pressure and the revetment construction of the top beam is divided into two sections. A11-axis clockwise direction from the construction, drilling engineering methods control the sinking pile and increase speed, and to ask Pile deviation value less than 30mm, the vertical deviation is not more than 1% of the pile in the mixing time, when drilling down poured into 70% to 80% water slurry, poured into the remaining rise in the drill. 5.2.3-3.500m pressure at the top beam Excavation: SMW engineering methods based on the progress of the pile, when the completion of 11 west axis, starting at the top beam to the pressure tank excavation (Figure 3), excavation by the gray line beam excavation, due to-3.500m following mud,[link widoczny dla zalogowanych], ground tank, top sub-beam construction of earth to take the pressure above the top beam-3.500m revetment construction. 5.2.4 press top beam construction: to take sides digging, concrete shop side cushion, while placing pressure roof beam, while moving artificial trimmed the steel mesh slope protection after banding, followed by a 60 thick C15 concrete pouring. ① pressure steel banding and steel roof support beams embedded parts remain set, according to the design and specifications, pre-selling pieces of steel support beam leaving in place, in accordance with the drawings to the top of the beam lead testing to ensure the geometry size, strengthening the measurement of review work. ② pressure pouring concrete reinforced top beam horizontal plate when the first check whether the size of the girder specifications and design requirements. C25 commercial concrete mixing concrete with early strength agent,[link widoczny dla zalogowanych], according to the order of Pouring. ③ After curing concrete pouring can be carried out after the final setting water conservation, to achieve the design value of concrete strength. To the same curing condition of concrete strength test block under the pressure test results to determine the basis for the steel support beam 5.2.5: beam intensity to be pressed to meet the design requirements of the top 80% of the steel support beam construction, steel support beam in place for trench excavation, construction of earth excavation by organizational scheme, the steel support beam positioning, welding. In order to maintain a steel support beam installed the same system as the support, according to the value of axial force in the welding test before welding pull. Should be four weeks full welded seam, steel support beam all the installation is complete, the top beam on the pressure to protect and transport the road and then backfill to ensure that hard pressed steel support beam and the impact of concrete pressure off the top beam. 5.2.6-3.500m less excavation, in accordance with the position after pouring into a construction segment. 5.2.7 steel for concrete wall in the basement to meet the design strength of 80%, with artificial gas welding cutting steel support. 5.2.8 SMW engineering methods in the removal of steel: Basement waterproofing such a good job after passing the test, remove the steel SMW engineering methods. The use of professional equipment for steel removal, removal of the basement during the collision of the structure should be avoided. Meanwhile, the safety of personnel and in the surrounding structure must be specifically responsible for the command. 6 Excavation monitoring the situation 6.1 Content excavation depth according to the project, environmental characteristics, physical and mechanical properties of foundation soil indicators and enclosure design requirements, monitoring as follows: 6.1.1 Deep Soil horizontal displacement: the location of excavation near the building envelope were set up 11 monitoring of the deep hole horizontal displacement of soil, inclinometer hole depth 15m: 6.1.2 support axial observation: the horizontal angle in excavation support system support the main axial support group laid 9 monitoring points, inclined bracing emplaced in the axial force monitoring points 6 groups, mainly observed in the deep foundation support system support during the excavation pit with time and the stress changes in working conditions: 6.1.3 envelope in the top of the pavement and road horizontal and vertical displacement observation: in the pit around the Boulevard and the sidewalk near the pit Top envelope several observation points set up to monitor its changes with the excavation. 6.2 Monitoring frequency and duration of warning values 6.2.1 Monitoring period: from the excavation of buried measurement points the week before admission to brace removal and monitoring data to achieve stability or structure ± 0,00. 6.2.2 Monitoring frequency: press enclosure design, according to the progress of excavation and the foundation of the deformation rate to set. Once daily monitoring of excavation stage, when the excavation near the bottom of the pit than the warning value or in case of fast changes in the abnormal number of observations should be increased, if necessary, twice a day or more. Dismantled during the encryption monitoring frequency. 6.2.3 Monitoring alert value: slant-hole soil monitoring and settlement of the maximum horizontal displacement of alert is 50mm, horizontal displacement and sedimentation rate greater than the warning value is generally taken 3mm / d. Found by monitoring: the horizontal displacement increased rapidly with the construction progress of excavation, the daily average rate of change of about +1.0 mm, in particular, CX4, CX7, CX11, etc. triangular hole in the soil during excavation at the maximum measurement of the incremental is 10mm, horizontal displacement of the total value of more than design alert, but the horizontal displacement rate has not been exceeded. Analysis of the main reason is the larger of its surrounding loads, heavy vehicles during the walk more, which increases the total amount of horizontal displacement. Support the axial force to monitor the excavation process has been relatively stable, the value does not exceed the design requirements. 7 Conclusion In summary, SMW continuous wall construction method with the construction of fast, no vibration, no noise, no pollution, mud, water and good sealing characteristics, is to improve the pit bottom heave effective measures, and can reduce the cost of fencing work (the more common method of drilling piles save 20% to 30% of the cost), in line with national advocacy of building energy requirements, with better social and economic benefits.
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