I. Introduction
In recent years, China has formed a scientific and reasonable and widely used method of deep foundation pit support in the practice of deep foundation pit.
In the concrete engineering construction, we should combine the actual situation of the project, in addition to the objective analysis of the basic project of the various problems, but also deep foundation pit supporting construction technology is skilled use, and effectively improve the quality and safety of construction engineering.
Two, construction engineering deep foundation pit supporting construction technology application status
After many years of deep foundation pit supporting technology use of practical experience in the industry has formed a unified theory; that is, according to the different terrain, geological conditions, the surrounding environment, water permeability coefficient and economic conditions using different deep foundation pit supporting technology system.
Currently widely used techniques mainly include: soil nail wall support, peristyle perfusion pile, underground continuous wall, steel sheet pile and steel pipe pile supporting technology.
Three, construction engineering deep foundation pit supporting technology requirements
1 according to the area of the building, the depth of the foundation pit, the water level, the seepage coefficient, the edge distance, the geological conditions and the surrounding environment, the construction scheme is more scientific and more scientific and operable.
2 select the appropriate, scientific, reasonable, safe and economical deep foundation pit supporting technology, can ensure the smooth development of the project and the basic quality. In practical engineering, because of the existence of objective conditions and various unfavorable factors, deep foundation pit support is often used a variety of techniques of complex, so for the construction and technical personnel not only to understanding, familiar with all kinds of construction technology characteristics and advantages and disadvantages, and scientific and reasonable operation applied to specific engineering.
3. Deep foundation pit support are often associated with around the pit sealing role. Therefore, in addition to considering the four surrounding foundation pit slope bearing capacity and stability, should also give full consideration to the technology of waterproof and sealing effect, only way to truly ensure foundation pit supporting quality and safety.
Four, Luoyang new area to open up the avenue of Cross River Bridge Engineering Survey and natural environment conditions
1 Engineering Survey
(1) the project is located in Luoyang new district development avenue north, the river downstream of iraq. Full bridge length of 492 meters, the width of the bridge is 45 meters, deck area 22140 square meters of bridge with double tower and double cable planes, self anchored suspension bridge, tower height of 56.5 meters, the bridge span arrangement: 70.5m+175m+70.5m=316m. on both sides of the bridge with three holes, a prestressed concrete continuous box girder, its span is set to:
29m+29m+30m=88m.
2 natural conditions and environmental conditions
(1) the Luoyang new area is a temperate continental monsoon climate zone, four seasons, the highest temperature 39.80C, the lowest temperature -14.10C, the average annual temperature of 14.70C, the average rainfall is: 692.6mm to 703.4mm, extreme rainfall is: 119.1mm, heavy rain and more concentrated in late July to early August.
(2) the location of the proposed bridge based on the drilling revealed that in the depth of exploration, formation is divided into four layers, from top to bottom: (1) the fine sand Qml4 thickness 1.2m to 1.8m; pebble Qal+pl4 thickness 8.7m to 10.3M; (3) pebble Qal+pl4 m to 22.3m; pebble Qal+pl3 thickness to the 27.2m 28.0m. groundwater and Yi River of concrete are no corrosion, the permeability coefficient of groundwater for 250m/d.
Five, the main construction method
Support technology for deep foundation pit of 1.5# axis
(1) in from the excavation pit around 2.5 meters set "geotechnical cloth mud wall water stop curtain curtain depth of 6 meters, 293.6 meters in length, prevent or to reduce the amount of excavation around the periphery of the upper part of the groundwater flow toward the direction of the foundation pit.
(2) in 7.5 meters away from the outer edge of the cap set ouside diameter 400mm double grouting CFG pile support, pile 13 meters long, plane layout of double plum shaped arrangement, there are 558 in total, increase the slope stability, to ensure the construction safety.
(3) away from the excavation around the pit at 1.0 m layout diameter ouside 400mm of dewatering, tube well depth of 22 meters, well spacing 5 meters, a total of 53, ensure in the foundation pit water level dropped to at the bottom of the pile cap under the elevation of 0.5 meters.
(4) the excavation of foundation pit with two steps, 1: 1 of the slope, the middle platform width of 4 meters, the first grade of 5 meters, second meters depth of 8.4 meters.
(5) foundation pit on the surface of the steel mesh and shotcrete, mesh ouside 8@180mm * 180mm, concrete C20 label, divided into two times injection, concrete thickness of 110mm, ensure slope surface has a certain strength and stability.
Support technology for deep foundation pit of 2.4# axis
(1) in the 12 meters around the pile cap, the use of high pressure jet grouting technology, as an increase in the stability of the foundation pit slope and prevent the flow of groundwater to the foundation pit. The jet grouting technology of high pressure jet grouting wall is made of 0.8 meters, three meters in diameter, 1 meters in diameter, I, II, >800mm. and 42.5Mpa, and the water cement ratio is 355: 1.
(2) at a distance of bearing Tainan, position of 2.2 meters on both sides of the north, set the ouside diameter 400mm of dewatering, 9.8 meters away from the well, well depth 24 meters, a total of 12 wells to ensure within the pit, the groundwater down to at the bottom of the pile cap under the elevation of 0.5 meters.
(3) the excavation of the foundation pit is 1: 1, the slope is excavated, and the excavation is layered, and the depth of each layer is about 3 meters.
(4) surface of foundation pit with steel mesh and shotcrete, mesh ouside 8@180mm * 180mm, concrete C20 label, divided into two jet, concrete thickness 110mm to ensure slope surface has a certain strength and stability.
Six, conclusion
Through the analysis of the current situation of deep foundation pit supporting construction technology in our country, combined with the specific case of Luoyang new area, we can clearly see that the 5# axis of the main tower cap deep foundation pit supporting construction technology, in the construction process of precipitation difficulty, quality, safety risk factor, construction period and project cost is much higher than the 4# axis main tower cap deep foundation pit supporting construction technology. Therefore, for the same geological conditions and construction environment and other factors, the use of different deep foundation pit supporting construction technology, to achieve the effect of different, so we have a comprehensive understanding of deep foundation pit supporting construction technology, fully understand the characteristics of its construction technology, the main points and points, also has scientific significance. However, we should also realize that the deep foundation pit supporting construction technology still has broad development space, for this purpose, in order to make deep foundation pit supporting construction technology better effect in our country's construction, save energy, green environmental protection, safe and reliable, we should strengthen the research and exploration of this technology, for China's overall construction project developed a force, do some things.