1 project overview
Xinjiekou Station, the first phase project of Nanjing Metro Line 2, is located in Xinjiekou, Nanjing Commercial Center. The station is divided into two sections with Xinjiekou roundabout as the center and arranged in the east-west direction. The west end is arranged on Hanzhong Road, and the east end is arranged on Zhongshan Road. The ground traffic is very busy and the traffic density is high. It crosses the North-South Line 1 Xinjiekou Station in a "T" shape and transfers to each other. Under the roundabout are the underground structures of 1 Line and Line 2, which have been completed with Xinjiekou Station of 1 Line. The total construction area of Xinjiekou Station is 249 18m2, of which the main building area is 22275m2, the auxiliary building area is 2644m2, the stationmaster is 4 14.4m, the width is 2 1.6m, the total height is about 12.69m, and the top cover is about 2.836m The effective platform width of the station is 14m. The center of the first underground floor is the station hall floor, the two ends are commercial areas, and the second underground floor is the platform floor. The main structure of the station is constructed by the beam paving method of the whole army, and the bored occlusal pile (diameter? 800, bite thickness 200mm) is used for the station enclosure structure. In order to minimize the influence of station construction on ground traffic and meet the requirements of station construction period, Xinjiekou Station adopts military beams and other components that meet the requirements of urban A-class road load and traffic capacity to quickly form a temporary pavement system, and the main structure of the east and west sections is paved with military beams, which ensures the traffic capacity of east-west 15m wide (4 lanes). The military beams of this station are all single-layer reinforced June 4th military beams with spans of 24m and 28m respectively. The main structure of the station adopts the military beam with a span of 24m (except the east and west end wells), and the center distance of the military beam is 1.0m (3.52m and 0.6m locally). 28m-span military beams are used in the east and west end wells, with the spacing of 0.6m There are 139 24m-span military beams in the east section and 35m-span 28m-span military beams in the east section, and there are four excavation openings with the size of 8.85m×3.0m The excavation openings are about 23.5m away from both ends of the east section. Spacing is 40.0m: 185 pieces of 24m-span military beams and 12 pieces of 28m-span military beams are set on the west side of cushion engineering, and five excavations are set, the excavation size is also 8.85m× 3.0m, and the spacing is 40.0m. Now, taking the 24m-span military beams as an example, the construction design scheme is introduced. The width of the foundation pit in this project is 23.3 meters, and the reinforced June 4th military beam with a length of 24.3 meters is proposed for the enclosure structure. The reinforced June 4th military beam is a self-developed medium-span railway bridge emergency repair equipment in China, and it is a detachable through steel truss beam with all-welded frame, pin-jointed assembly and single-layer or double-layer multi-piece steel bridge deck system. This design adopts single-layer structure, and adopts reinforced single-layer June 4th military beam (composed of reinforced tripod and auxiliary end frame). Before the construction of the main structure, the underground pipeline under the north 15.0m wide military beam laying project should be handled first, and then the bored bite pile construction should be carried out there. After the construction of bored bite pile is completed, the construction of pile top beam should be carried out. After the structural concrete reaches the strength, the first layer of earthwork in this section will be excavated, military beams will be erected and temporary pavement will be laid. Then it is necessary to restore the ground traffic of the Northern Army Beam Paving Agency, and then reverse the remaining 9.3m-wide Army Beam Paving Project in the South. The inverted military beam is constructed in two phases, and the enclosure in 1 phase adopts a four-lane temporary paving project, with a width of 15.0m on the north side. The total length of each temporary military beam is 24.3 m, and the length of each military beam laid in 1 stage is 15.0m, and the spacing is 1m (near the excavation). In the second stage, the enclosure is constructed in the south clinical project, and each clinical military beam is 9.3m long. The 9.3m-long military beam within this range is connected with the 1 5.0m military beam constructed in stages according to the specifications, and finally a 24.3m-long military beam cushion system project is formed. 3. Detailed design scheme of temporary cushion engineering of station 3. 1 Design scheme of military beam structure and bridge deck system According to the sequence of cover and excavation, the components of military beam are transported to the site by flat trailer, and the assembly construction is completed at the site. After the completion of earthwork excavation and steel support construction on the first floor, it will be hoisted in place with a 25t crane. Structural form design of temporary paving system of military beam temporary bridge: The reinforced June 4th military beam support form and bridge deck system are adopted in the main structure construction of the station. Military beams are only used to support temporary cushions and ground vehicles. 3.2 Design of reinforced June 4th military beam structure and its bearing platform The military beams of this station are all single-layer reinforced June 4th military beams with a span of 24m, which are applied to the main structure of the station. The center distance of the military beam is 1.0m (the width of the excavation hole is 3m, and the center distance of the military beam around the excavation hole is 0.6m); The structure of the military beam system adopts oblique and longitudinal connection systems to strengthen the overall stability of the military beam, and all longitudinal connection members are military beam series finalized products. In order to meet the stability and safety of the temporary cushion engineering in the paddock in 1 phase, the fixing scheme for both ends of the military beam of the temporary cushion in the paddock in 1 phase is: L-shaped retaining pile cap at the northern end, steel sheet pile retaining wall at the southern end, 1000mm×600mm concrete pier with reinforced triangular lower fulcrum opposite to the military. During the construction of temporary covering the military beam in the paddock in phase II, it is necessary to The housings of phase 1 and phase 2 are shown in Figure 1 and Figure 2.
3.3 Bridge deck system design
According to the design documents and the usage specification of the reinforced June 4th military beam deck system, in order to reduce the load on the military beam as much as possible and meet the requirements of vibration reduction and safety, it is considered to set the walking deck system only on the temporary pavement with a width of 15m on the north side of the road to meet the requirements of Class A load. Therefore, the bridge deck system on the north side of the station main body 16m wide should be paved with wooden boards with a width of 40cm, a thickness of 5cm and a spacing of 3m along the east-west direction of the station (located under the steel plates to reduce vibration and noise), then a single layer of non-slip steel plates with a thickness of 2cm (A3 steel plate with a specification of 12m×2m) should be paved along the north-south direction, and finally another layer should be paved along the east-west direction according to the design calculation, so as to meet the requirement of gantry crane hoisting to the ground.
3.4 Take the temporary column in the middle as the dividing line between the design and construction of cover-digging support, and hoist the steel supports on both sides with two electric hoists. Before erecting the military beam, the steel support cutting, the guide beam and the L-shaped support cap should be completed first, then the military beam should be erected, and the bridge deck system should be laid, so as to complete the temporary paving project and quickly form road traffic. For the support erection under the military beam in the cover excavation section, in order to meet the needs of steel support erection, four east-west guide beams are also set. The guide beam is made of I20 type I-beam, which is located under the military beam and the first steel support and close to the first steel support. The guide beams on both sides are welded with the bracket by pre-embedded hooks under the crown beam, and the electric hoist is installed. The middle two guide beams are fixed on the military beam with U-clips, steel beams and bolts, and each guide beam is equipped with 1 set 10t electric hoist, which is beneficial to the assembly and erection of steel supports. During construction, the temporary column in the middle is used as the dividing line, and two electric hoists are used on both sides to hoist the steel support. Before the erection of the military beam, the steel support cutting, the guide beam and the L-shaped support cap are completed first, then the military beam is erected and the bridge deck system is laid to complete the temporary paving project. After the temporary cushion system is completed, the steel support erection, earthwork transportation, formwork, reinforcement and other materials of the station will be carried out through the cooperation of the guide beam arranged along the longitudinal direction of the station and the 10t electric hoist suspended under the beam of the truss car. Excavators are mainly used to assist excavation and transportation during earthwork excavation.
3.5 Load checking calculation of military beam when driving and piling up soil 3.5. 1 The precondition of load checking calculation is that the materials are 15MnVq and 16Mnq steel, the vehicle speed is not more than 3km/h, and the urban class A load. 3.5.2 The calculation model adopts MidasCivil67 1 software from Korea to calculate the traffic and temporary earth-piling force of a single-story 24m-span reinforced June 4th military beam. Midas is a universal finite element calculation software for spatial structures, which contains various materials and loads specified in domestic codes, including A Cheng and various steels and profiles. The calculated load is the reinforced June 4th military beam structure.
This structure is modeled by one beam, the spacing between each beam is 1m, and each beam is connected by a transverse connection system. In structural calculation, 1m is taken along the longitudinal direction (vehicle direction) to simplify the load. The calculation structure model is shown in Figure 3, and the calculation condition is the second phase enclosure of this bid. The left side of the calculation model 15m (north of junliang) is a two-way four-lane vehicle range, and the live load of the vehicle is considered as urban class A load. The temporary pavement system is considered to be a steel plate with a thickness of 2 cm. In each excavation area, because the span between beams is 3m, it is necessary to lay another steel plate 6m wide, 9m long and 2cm thick on it for local reinforcement. 9m on the right side of the calculation model (south of the military beam) is the excavation scope. In order to temporarily pile soil on the military beam, a layer of steel plate with a thickness of 1.2cm was laid on the military beam, and excavation earthwork with a certain height was temporarily laid on both sides of the excavation. 3.5.3 Load (1) deadweight of structure: the bulk density of steel is 78.5kN/m3. Weight of deck steel plate: 2cm thick steel plate, 15 m wide steel plate, 1.2 cm thick steel plate, 9m wide. q 1 = 78.5×0.02 = 1.57 kn/m； Q2 = 78.5×0.0 12 = 0.942 kn/m. Self-weight of soil: if the thickness of loose soil is 1.8m and the average bulk density of loose soil is 16kN/m3, Q3 =1.8×/kloc. Longitudinal distribution coefficient: the vehicle load in city A is between wheels 1.8m and between lanes1.3m.. The longitudinal motorcade takes two heaviest axles, axle weight 140kN, wheel weight 70kN, and the distance between the two axles1.2m. Considering the horizontal contact position, it takes 4m, that is, a total of ***4 beams bear it. Longitudinal distribution coefficient =2/4=0.5. Impact coefficient μ=0.6686-0.3032×lg(24)=0.25. 3.5.4 Dead weight of steel plate, dead weight of soil and dead weight of vehicle on deck of load combination structure × 0.67× 0.5× (1.25). 3.5.5 Calculation result of internal force of unit
The numerical value of the calculated results is positive for the tensile force and negative for the pressure. See table 1 for the calculation results. 3.5.6 Conclusion Under the condition that the allowable average thickness of pile-up soil on both sides of excavation is 1.8m, all the above bars meet the bearing capacity requirements, among which the outer diagonal bars of the outermost reinforcement triangle are the overall bearing capacity control bars. The structure is calculated as 4m in the longitudinal direction (vehicle direction). If the covering soil is not concentrated within 4m wide, the allowable covering soil thickness can be increased according to the volume. When the average pile thickness is 1.8m, considering that a single excavation opening can excavate 300m3 per day in peak period, the allowable pile width on both sides of the excavation opening is 300/(9×1.8) =18.5m, that is, 9.3m on one side of the excavation opening can meet the requirements of excavation in peak period. In actual construction, we can consider laying steel plates in other parts for stacking steel supports and other building materials. Conclusion The military beam cladding method is adopted in Xinjiekou Station of Nanjing Metro Line 2, which is seldom used in China. Through semi-cover excavation, semi-open excavation and chamfering construction, the temporary pavement truss beam covering system is formed in stages. The reinforced military beam of June 4th Railway has been well applied in the cladding scheme because of its good bearing capacity and simple disassembly. Compared with the underground excavation method and the full cover excavation method, this scheme reduces the engineering difficulty and cost, saves the construction period, minimizes the impact of subway construction on ground traffic, surrounding buildings and the environment, truly embodies the new concept of modern construction technology, and has high scientific research, economic and social promotion value. References: [[ 1] CJJ77—98-98, Design Load Standard for Urban Bridges [S]. [2] GBJ500 17-2003, Code for Design of Steel Structures [S]. [3] Xue rang. Construction technology of cover excavation in Shenzhen subway station [J]. Modern
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