Comprehensive Construction Technology for Deep Foundation Pit of Swimming Hall of Fuzhou Strait Olympic Sports Center
The height difference between the competition pool, practice pool and diving pool of the swimming pool of the Fuzhou Strait Olympic Sports Center is relatively large. The soil of the foundation pit is mainly deep-seated plastic silt layer. The SMW construction method pile enclosure and the layer 1 round reinforced concrete internal support are adopted. Considering the space-time effect, earthworks adopt symmetrical and stratified sectioned excavation to better protect the undisturbed soil on the soil surface of the competition pool, effectively control the deformation of the foundation pit, ensure the construction safety of the foundation pit, and achieve quick construction. 1. Project Overview The Fuzhou Channel Olympic Sports Center is the main venue for the first National Youth Games in 2015. It is located on Fuwan Road in Fuzhou. It consists of stadiums, gymnasiums, swimming pools, tennis halls, and commercial centers. The total project area is 80.54hm2. The swimming pool is located at the northwestern end of the entire Olympic Sports Center. The east side is adjacent to the gymnasium and the tennis hall. The outer outline is a “water drop†shape formed by three sections of different heart arcs tangled together, and the Fuzhou Channel Olympics. The center effect is shown in Figure 1. The swimming pool is 210m long and 90m wide. There is a competition pool (50m x 25m), a training pool (50m x 16m) and a diving pool (25m x 25m). The layout is shown in Figure 2. 2. Engineering geological conditions The project site is a typical silt soft soil layer. The survey report reveals the geological conditions. The soil layer and average thickness from top to bottom are: 1Plant layer 0.45m; 2 silty clay 1.53m; 3 saturated, flow plastic sludge 8.26m; 4 silty clay 7.26mm; 5 saturated flow plastic muddy soil 7.05m; 6 sandy clay 5.12m; 7 residual sandy clay 6.68m; 8 Fully weathered granite 5.49mm; 9 sand-like strong weathered granite 12.72m; 10 pieces of massive weathered granite 16.88m. The foundation pit support adopts SMW method piles, the length of the pile is 21m, the bearing layer of the end of the pile is 4 silty clay layer, and the bearing layer of the pillar end is 9 sand-like strong weathered granite layer. The stable water depth of the site is 0.2-16.70m, and the water level is seasonal. 3. Engineering difficulties 3.1 Pit Support The swimming pool features unique features and a complex structure. The height of the bottom of the diving pool is one 7.200m, the height of the bottom of the sewage treatment plant sewage treatment room is 7.900m, the height of the bottom of other supporting facilities in the basement is 1.600m, the bottom height of the pit is 4.100m, and the bottom height of the practice pool is 3.100m The depth of each part of the foundation pit is different, and the design and construction of the foundation pit support are difficult. The foundation pit support adopts the SMW construction method and the supporting form of the reinforced concrete inner support. It has many construction procedures and complicated technology, and the edge of the pit has an irregular arc shape, which makes construction difficult. 3.2 Indigenous soil protection The floor design of the competition pool, practice pool and diving pool structure is directly supported by the original soil, with large volumes and heavy loads. The depth of each part of the foundation pit is different. After excavation at the design elevation, pits in Taichung and Taichung pits will form. Hang pit conditions. The height of the swimming pool structure is 4.100m, and the height of the surrounding pit is 6.900m. The inner wall of the competition pool is reinforced by 4 rows of West 850mm@600mm unconsolidated cement mixing pile soil, and the vertical height difference is 2.8m. During excavation and structure construction Dirt protection is difficult. 3.3 Pit Deformation Control The silt layer in Fuzhou soft soil area is deep, the fluidity of the soil is large, the lateral pressure is large, the subdivision of the foundation pit construction is not synchronous and the environment is changeable, and the control of the deformation of the foundation pit is difficult. 3.4 Fast and Efficient Construction The Fuzhou Channel Olympic Sports Center is a key construction project. It is necessary to rapidly complete the construction tasks in a short period of time, through the construction of retaining piles and supporting structures, excavation of earthwork, construction of basement structures, backfilling of earth outside the pits, support removal, and steel recycling. The construction schedule is urgent and it is difficult to achieve efficient and rapid construction. 4. Construction Technology and Measures 4.1 support options 1) The shallow pit of the training pool is arranged after the construction of the basement pit in the basement. 2) In order to create a larger working face for the basement construction, the undisturbed soil on the raceway pool platform is protected and a circular internal support is used. 3) The foundation pit support adopts the SMW engineering method pile enclosure with better rigidity and one reinforced concrete internal support. The 10m soil surface around the outer periphery of the foundation pit is reduced to a 3.100m basement of the non-basement part, so as to reduce the construction support of the foundation pit. Temporary time for changing and dismantling techniques required for construction of time and structures. 4) Around the competition pool, 4 rows of West 850mm@600mm and 10m long cement mixing piles are installed to reinforce the soil on the inner wall of the foundation pit, as shown in FIG. 3 . 4.2 SMW Method Pile and Cement Mixing Pile 1) The SMW construction method is adopted for the enclosing of this project. The length of the 850mm@600mm cement mixing pile in the 4th row is 21m and the H-beam HN700×300×13×24 is interpolated. 2) Laying a 12m wide 800mm thick dirt road along the retaining piles. The SMW engineering piles and cement mixing piles shall be constructed as required. 3) According to the coordinate reference point, calculate the coordinates of the corner points of the enclosing center line and accurately locate the center line of the enclosing wall. 4) Dig grooves along the centerline of the retaining piles to a width of 1.0m and a depth of 1.0 to 1.2m. 5) Place two 200mm×200mm long and 2.5m long positioning steels in the direction of vertical grooves. Place two 300mm×300mm long and approximately 8-12m long positioning steels along the direction of parallel grooves, using H-shaped steel positioning cards. Mixing piles with sets of play, pile center distance 600mm. Positioning steel spacing 1 200mm, using red paint to mark the exact positioning. 6) Welded iron ring with a radius of 5cm on the pile machine, hanging line hammer at a height of 10m, and using the theodolite to straighten the verticality of the drill pipe. After the pile driver is moved to the working position, the verticality of the pile frame is adjusted to within 0.5%. 7) Build a well-mixed construction platform and cement warehouse. Pc32.5R composite Portland cement is used for the cement. The water-cement ratio of the cement slurry is controlled at 1.5-2.0% and the cement content is 20% (mass). 8) Adjust the speed according to the soil conditions, loosen the hoist to make the mixing head sink from the top down to the ground mixing until the drill bit sinks to the pile bottom elevation. Drill pipe needs to be injected into the cement slurry during sinking and lifting, spraying 60% each time, and raising the spray rate by 40%. The drilling speed is controlled at 0.5 to 1 m/min, and the lifting speed is controlled at 1 to 2 m/min. The cement slurry is continuously and evenly injected into the slurry. After the drilling rod is lifted, all the cement slurry is finished. 9) Before the inserting of the steel bar, a separating agent is applied to facilitate the extraction and recovery. 10) After the construction of cement mixing piles is completed, a hole with a hole diameter of about 8 cm shall be opened before the steel pile is inserted at a distance of 0.2m from the top of the steel section, and reinforcing plates with thickness ≥ 12mm shall be welded on both sides of the steel section here. pile. The length of H-shaped steel is welded on both sides of a 10mm thick steel plate. The welds are all full-grooved. 4.3 Support beam construction 1) After laying a layer of bituminous felt on a 3.900m concrete pad, the support beam reinforcements will be bundled to prevent the adhesion of concrete and mud in the beam bottom. 2) Peripheral H-section steel and concrete contact surfaces are covered with polyester cotton as a barrier layer to prevent concrete and H-shaped steel from sticking. 3) The key to the construction of supporting beams is to control the construction quality of the reinforcing bars for the intersecting nodes of the supporting beams and the H-shaped steel and the enclosing beams. The supporting beams are shown in Figure 4. 4.4 Foundation Excavation The earth excavation of the foundation pit considers the space-time effect. According to the characteristics of the foundation pit, the excavation is performed in layers according to the principle of symmetry balance. Then the construction parameters of each unit, such as the size of the excavation, the excavation time limit, the support time limit, are determined. Support prestressed etc. The key technical points are to excavate section by section along the prescribed excavation order, excavate in small intervals in each excavation section, and do a good job of excavation drainage to reduce the exposure time of the foundation pit. Each layer is first symmetrically excavated around the earth, and then the middle earthwork is excavated, so that the support structure is evenly stressed. 4.4.1 Earth excavation sequence 1) Within the range of support beams, excavate from natural ground to a 3.000m crown beam bottom to support beam construction. 2) During the construction of the support beam, the basement pit shall be excavated 10m away from the basement, and a 3.100m platform shall be hardened at the bottom of the platform. 3) Excavation of the bottom surface of the support beam to the basement of the basement in the basement is mainly a large area excavation. 4) Excavate the basic earthwork below the elevation of the bottom slab of the raft, such as the bottom of the diving pool, the bottom of the sewage treatment system, and the bottom of the platform. The earth excavation sequence is shown in Figure 5. 4.4.2 Excavation Method for Excavation Earthwork The earthwork adopts a method of layered and symmetrical excavation, which is carried out from the periphery of the pit to the middle. The excavation route is shown in Figure 6. 1) The surrounding support beam grid is dense. The earthwork 2m below the support beam grid is first mechanically excavated to facilitate subsequent earth excavation under the support beam. 2) Earthwork will be excavated from both sides to the two soil outlets. The excavated earth will be transported along with the digging and will not be piled up on the site. 3) The silt layer is deep in this project, and the silt body is soft and slippery. The earth-moving vehicles cannot open to the bottom of the pit. The silt site accumulation will increase the pressure on the earth side, and the slope will easily cause fluid collapse. In order to reduce the damage of the original soil structure, the foundation pit sludge was excavated using three excavator relay methods. l The platform is on the surface, and two are on the steps of different elevations of the foundation pit. The radius of gyration of the two excavators adjacent to each other is within the scope of the working overlap, and the digging edge is passed upwards. The excavator at the top of the surface is loaded with the truck. Take away with a dump truck. The excavator travels with the pad steel plate to prevent the machine from sagging, as shown in FIG. 7 . 4) Take a vertical excavation method on the earthwork near the earth excavation 4m around the earth platform on the side of the earthworks. It is forbidden to destroy the soil of the cement mixing pile by the digging shovel. 4.5 Undisturbed soil protection 1) Protection during earth excavation As the earth moves with the digging, it does not accumulate at the site to reduce the pile of soil, avoid the internal silt overload and pressure, and squeeze and destroy the surrounding cement mixing piles. It is strictly forbidden that the earth-moving vehicles will drive on the soil platform so that the soil on the soil surface of the soil will not be subject to rolling and squeezing. The earth excavation around the soil platform is performed symmetrically, balancedly, and excavated in layers, so that the compressive forces around the platform are released and balanced to avoid stress concentration or partial rolling. 2) Protection and strengthening measures in structural construction The floor structure is divided into 12 blocks by the post pouring belt. The construction of each block has successively, the strength of the structural concrete meets the requirements, and the support of the blocks is not necessarily synchronized. During the support demolition process, the pressure on the muddy side of the pit flow will be transferred in the floor plate of the basement, and the earthen platform of the competition pool will be easily damaged by shearing. Afterwards, the pouring zone of each block will strengthen the overall transmission force. 4.6 Support beam removal The strength of the concrete of the basement floor and the transmission belt is up to the specified strength of the design, so that the support can be dismantled and quickly removed by the mechanical crushing method. 1) Set up eight 150 mm×750 mm×12 000 mm steel box girders on the concrete support beams as a demolition mechanical operation platform, as shown in Fig.8. 2) Before the support beam is dismantled, waste tires shall be spread 3m outside the bottom of the support beam vertically and covered with plywood to prevent concrete fragments from damaging the floor structure, as shown in Figure 9. 3) After each lattice column breaks off the inner support beam, the steamer retreats to the next span and continues operations. 4) Remove from one end to the other end by crushing the roots in order, and cut the reinforcing steel after the entire span beam breaks. 5) An excavator with a long arm of 9m is used on a 3.100m platform in the foundation pit to drive along the side of the foundation pit, and transport the concrete fragment hooks to the dump trucks on the natural ground. 4.7 Deformation monitoring of foundation pit The characteristics of the ring internal support is strong, and the lateral pressure of the pit side soil is transmitted to the internal ring beam through the diagonal braces. The internal bracing beam bears a large internal force. The safety and stability of the foundation pit support must not only focus on the local damage of the side wall of the foundation pit, but also focus on the prevention of the tension and damage of the internal support beam, resulting in the overall destruction of the support system. This project is a first-class pit, and the monitoring items and monitoring points are: 1 The horizontal displacement at the top of the pit is monitored by 12 points; 2 Vertical displacement monitoring at the top of the foundation pit 12 points; 3 Monitoring of deep horizontal displacement of soil outside the enclosure structure 10 points; 4 column horizontal displacement monitoring 15 points; 5 column settlement monitoring 15 points; 6 groundwater level monitoring 7 points; 7 Support beam stress monitoring 14 points. 5. Implementation effect 1) Considering the space-time effect, according to the shape of the foundation pits, the symmetry balance principle should be used to divide the layers into layers, and the undisturbed soil in the competition pool is well protected. 2) The relay excavation method is quick and effective for deep flowing silt excavation, which can reduce landslide accidents caused by silt pile up on the site, and weaken the soft soil structure damage caused by frequent movement of excavation machinery in the silt layer. 3) The monitoring results show that the foundation pit construction method is proper, the foundation pit deformation is controlled within the warning value, and the 25th support beam stress (position of the monitoring point is shown in Figure 6). The monitoring results are shown in Table 1. The construction conditions shown in Table 1 are under the support of the north side, the south side of the support beam is under construction, other side support beam has been excavated to the bottom, the middle part is being excavated. From Table 1, we can see that all the data of the monitoring project did not exceed the warning value to meet the design requirements. 4) The routine construction of this project needs to set up two levels of horizontal support. After the scheme is optimized, only one support will be set, which will save the project cost and save the construction period. The horizontal support adopts the mechanical crusher rapid demolition method. The construction period of the foundation pit is one and a half months ahead of the conventional practice, and more time is required for the subsequent construction of the project. Cinnabar also called zinnober. Because the ancient Chenzhou (now Yuanling) produced by called cinnabar. 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