At present, China's socio-economic and urbanization development is constantly advancing and deepening, and the situation of urban land use is becoming increasingly severe. Around the original residential land in the old city, various satellite new cities have been formed. However, in order to protect the existing amount of cultivated land, many land approved by the government are non-cultivated land such as sloping land and tidal flat land, and Bamin land in Fujian is surrounded by mountains and seas. Strive to realize the efficient use of land and the scientific development of urbanization, rely on the original natural landform, do a good job of "relying on the mountain" project, form the local urban green lung, and perfectly realize the harmonious development between man and nature. With the improvement of people's living standards, the requirements for living environment are also constantly improving. More and more mountain buildings that adapt to the natural environment and combine with the terrain appear in new urban areas, which makes the structural design of mountain buildings more presented in the design of civil buildings.
1 project overview
Jianfashan Waishan Project is located in Shili Lanshan Resort, Changtai County, Zhangzhou City. The project is divided into north and south plots and built on the mountain. The south plot is a multi-storey villa without a whole basement, and the north plot is a high-rise residence with a large chassis basement. The elevation difference of the Yellow Sea between the north and south buildings is about 30m. The upper soil layer of the site is mainly artificial fill and Quaternary proluvial, and the underlying bedrock is Yanshanian granite. From top to bottom: ① plain fill, ② silty clay, ③ residual sandy cohesive soil, ④ fully weathered granite, ⑤ gravelly strongly weathered granite, ⑤ fragmented strongly weathered granite and ⑦ moderately weathered granite; The terrain is undulating, with a U-shaped gully in the middle. The maximum difference between the current ground and the designed ground is about 10m.
2 Prior scheme control
The site leveling cost and slope treatment cost of slope buildings account for a large part of the upfront cost. Under the premise of ensuring safety and rationality, make full use of the original landform, avoid large-scale excavation to destroy the natural landform and cause new geological disasters, and better control the project cost. In the preliminary general layout planning and scheme determination, the project cost should be comprehensively considered in combination with the civil engineering cost, and the following factors should be comprehensively considered in combination with the actual situation in the scheme stage:
2. 1 earthwork balance
Consider backfilling the earthwork part of the north slope (step treatment) to the middle gully. In the early stage of the project, the key is to control the earthwork within a reasonable range, and the elevation design in the early stage is very fine. After the architectural scheme is determined, each specialty shall determine the comprehensive index of each single building according to the existing site leveling, balance the building elevation, road slope, whether to set basements and the number and height of basements (considering the buried depth of foundation, the basements are concentrated in the north high-rise building), determine the excavation ratio and slope size, minimize the excavation amount, avoid large excavation and fill, and try to ensure the earthwork balance in the site.
2.2 Retaining wall setting
Retaining wall is an unavoidable difficulty in slope engineering, and the cost of retaining wall itself is high, including digging and filling, tamping soil behind the wall and so on. The best choice of retaining wall is to control its height within a reasonable range, and the height of retaining wall can be reduced by dividing the platform and slope top. The villa on the south side has no basement. Considering the general layout of the building, the height difference between villas is about 4 meters, and the concrete wall on the back side of the villa serves as a retaining wall. The height difference between the periphery of residential area and the outside road is large, and the number of independent retaining walls is reduced by combining the greening and sloping of basement exterior wall and residential area landscape.
2.3 Drainage design
In the process of building design on sloping land, geological disasters are an important factor affecting the safety of building engineering. In the design of building engineering, it is necessary to strengthen the layout of comprehensive pipe network such as drainage. According to the specific trend of the slope, an efficient and reasonable drainage system is designed to ensure timely precipitation and the stability of the building foundation. For southern cities where there is a possibility of rainstorm, in order to ensure that the instantaneous head rise (too late for flood discharge) affects the anti-floating safety of the basement, measures such as setting a drainage blind ditch on the basement side of the dustpan can ensure the timely discharge of surface water, reduce the anti-floating design head and reduce the project cost of setting anti-floating measures.
3 Construction drawing stage control
3. 1 There is a complete basement.
According to the geological regulations, the buried depth of building foundation can be calculated from the outdoor terrace to the bottom of foundation, and it meets the following requirements: ① The buried depth of raft foundation on natural foundation or composite foundation should not be less than115 of the building height; ② The buried depth of pile-raft foundation (less than the pile length) should not be less than118 of the building height. The starting position of the buried depth of the outdoor terrace of the mountain building (not fully buried basement) should not be the 0.00 elevation of the building or the average elevation of the outdoor ground, but the lowest point of the outdoor terrace around the building; When determining the building height, it should also be calculated from the lowest point of the outdoor surrounding ground. The exposed height of the basement is not more than 65438+ 0/3 of the buried depth of the whole basement, and not more than 2m. The free surface of the basement is a reinforced concrete side wall, and there is no big opening arrangement. If the above conditions are met, it can be designed as a complete basement. For the retaining wall on the higher side above the embedded end base, separate retaining wall or concrete retaining wall can be set according to the site conditions.
3.2 High-rise building without basement
According to No.37 [1] of the Civil Engineering Department, basements should be set up in high-rise buildings; For high-rise buildings without basement, the buried depth requirements should be met. When the building adopts rock foundation or other effective measures, it can be appropriately relaxed on the premise of meeting the requirements of foundation bearing capacity and stability. The geological fluctuation of this project is great, and the bearing stratum of foundation changes greatly, from filled soil (foundation treatment) to moderately weathered granite. Combined with the actual situation, the following measures for foundation reinforcement are adopted: ① The structural measures of setting column caps under the wall columns (that is, the local foundation pit is about 0.5 ~ 1.0 m, and there is no slope in the foundation pit when the rock mass is stable, and steps can be set in the local deep foundation pit) are structurally satisfied.
(2) Pull-out anchors are set under the wall column (around the building) to ensure that the embedded end meets the bending bearing capacity, that is, the overall anti-overturning requirements of the structure. For general engineering, the setting of anchor bars can meet the requirements of wind resistance and multi-earthquake. For special projects or key parts in the foundation plane, performance-based design method can be used to meet the checking requirements of fortification earthquake (moderate earthquake), and the strength of anchor bars can be used as the standard value. (3) When the bearing capacity of natural foundations of individual buildings can't meet the requirements of superstructure or the area of zero stress zone of foundation exceeds the requirements of codes, a small number of belled cast-in-place piles or artificial piers are set. Under the action of upper horizontal load, the uplift of surrounding piles and the shear bearing capacity of all piles can meet the anti-sliding and shear requirements of buildings.
3.3 Multi-storey without basement
There are two architectural forms of villas on the south side: landing structure and diaojiao building structure. The first floor of cantilever scaffold structure adopts beam-slab system. The thickness of the first floor of the multi-layer cantilever scaffold structure shall not be less than120mm; ; The upper grounding end of the bottom structure is provided with a grounding layer connected with the bottom part. When the grounding layer is set, the floor thickness of the multi-layer separation structure shall not be less than 120mm, and when the grounding layer is not set, the floor thickness of the upper grounding layer shall not be less than150 mm; ; The reinforcement shall be arranged according to the double-layer bidirectional length, and the single-layer unidirectional reinforcement ratio shall not be less than 0.25%. The stirrups of the leg suspension column, grounding column and upper and lower grounding columns of the bottom structure should be encrypted in the whole column section. When the concrete wall is used as the retaining wall at the back side or falling part of the suspended scaffold building, a matching reinforced concrete outer wall should be set at the opening side (only structural holes should be opened at the passage position required by the building); So as to meet the stiffness balance of the front and rear sides and avoid the torsional damage of the structure under the earthquake.
4 conclusion
The design of sloping buildings should be considered comprehensively at all stages to achieve the optimal project investment cost requirements. In the scheme stage, earthwork, height difference treatment method and anti-floating problem of structure should be considered according to the initial situation. In the construction drawing stage, technical problems such as the buried depth of the structure, the embedded end and the type of retaining wall should be further considered according to the principles determined in the scheme stage.
The above are collected and sorted by Zhong Da Consulting Company.
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