深基坑工程存在的问题和展望

1、深基坑工程存在的问题和展望1 Overview In recent years, with the development of economy and the progress of society, high-rise buildings and underground buildings have been found in big cities, And tunnel projects increased greatly, but at the same time in order to save the land, make full use of underground space

2、, the deep excavation engineering is increasing. The deep foundation pit engineering is a comprehensive ancient and epoch -making characteristics of geotechnical engineering, because it involves not only the soil mechanical strength and deformation of typical problems it relates to the soil and supp

3、orting structure interaction problems. After the analysis is not difficult to see that the development of foundation pit engineering is a new type of support led to the emergence of new analysis methods, and follow the practice, understanding, practice, understanding the law and gradually matured. I

4、n 1930s, the first in the study the foundation pit engineering Terzaghi and Peake,60s in Oslo and other places of excavation began to implement the construction monitoring, from 70s onwards, many countries have formulated the guiding and supporting design of foundation pit excavation Design and cons

5、truction of the regulations in China.In the early 1980s began to appear a lot of excavation. Before 80s, the domestic high-rise building is one of the few in the basement is a layer of deep foundation pit, but 4 m, often used in slope excavation can solve the problem. By 80s, with a large number of

6、high-rise building construction two, began to appear in basement excavation depth is generally around 8 m, a few more than 10 m. in 90s, Chinasrapid development of high -rise buildings, but also around the construction of large underground municipal facilities, underground shopping malls, subway sta

7、tions, leading to the basement layer gradually increased, the excavation depth of more than 10 m meet the eye everywhere the excavation.2 deep foundation pit engineering problemsDesign and construction of foundation pit engineering, both to ensure the whole support structure in the process of constr

8、uction safety, control structure and surrounding soil deformation but also to ensure the surrounding environment (adjacent buildings and underground public facilities) safety. Therefore, how to ensure the excavation safety and economical and practical is feasible a very important and urgent issues i

9、n the construction of the modern city. Especially in twentieth Century, with the increasingly high requirements of foundation pit engineering, along with more and more problems. Some problems of deep foundation pit are discussed below:1. problems existing in construction stageThe quantity, scale and

10、 distribution of deep foundation pit increase rapidly, and the construction technology of deep foundation pit and monitoring technology in construction field should be improved as soon as possible. Moreover, the construction management is poor and the construction qualification is not strictly limit

11、ed. Therefore, many problems should be paid attention to during construction. It is necessary for construction, owners, design and monitoring to cooperate with and cooperate with each other in the excavation of the foundation pit.1) improper treatment of ground water in foundation pit constructionIn

12、 the construction of foundation pit groundwater treatment is a difficult problem, due to differences in soil and groundwater, the excavation construction method is different, especially in the coastal areas with high water level or surface water rich area, medium treatment of groundwater in deep fou

13、ndation pit engineering construction is the key to the success of the project. The survey shows that over the past few years, our country deep foundation pit retaining support system failure or safety and environmental problems resulted from the failure of the part about the total project 10% 15%, t

14、he soft soil with high water table areas up to 20%, in some areas a higher failure rate. These accidents, some very serious consequences, not only to the country caused great the economic losses, but also caused unnecessary casualties, delay and affect the normal life of the residents around the neg

15、ative effects, damage the image of construction enterprises. The cause of these accidents a The main reason is the improper treatment of groundwater. So, in the deep foundation pit engineering many failed, because a lot of groundwater in foundation pit construction drainage not dealt with drainage o

16、f the upper soil layer mainly solves the backwater and rain water drainage, including the precipitation of light well point, spray well point and deep well point precipitation. Land subsidence may lower the underground water level that will cause adverse effects on the environment, especially in the

17、 deep well dewatering effect. 2) the degree of information construction is not high Due to the geological conditions of deep excavation engineering is complicated, and the special characteristics of the force, the calculation in the design phase of the project value and the actual value in the const

18、ruction process there are some differences. Therefore, the deep foundation pit safety depends not only on the reasonable design and construction, but also depends on throughout the engineering design and construction safety monitoring of the whole process. Safety monitoring is one of the important c

19、onditions to ensure the safety of deep foundation pit engineering, design, engineering and construction of foundation pit monitoring is also known asthe three basic elements ofthe construction of deep foundation pit excavation engineering. In the event of an accident before more or less have warning

20、, because the destruction of foundation pit supporting structure to experience a process from quantitative change to qualitative change, through the information construction can optimize design scheme, to ensure safe and reliable and reasonable excavation of foundation pit construction refers to the

21、 information. The collected information, after processing and prediction results by soil parameter inverse analysis obtained with the actual parameters of soil and using the model forecast again next construction stage of retaining structure and soil properties, and collecting relevant information t

22、he next construction stage. This repeated cycle, we collect the information, modify the design and guide construction constantly, will design a dynamic process. Through the analysis and forecast to guide the construction, through the construction of information feedback design, the design and constr

23、uction of gradually approaching the actual and the exclusion of danger, to achieve the best project. This is a new promising technology, with low cost the effectiveness of the advantages, at present has been used in some engineering. There is still no universal stage is key to the following two reas

24、ons: (1) the lack of experts; (2) feedback slow. But with the development of computer technology and the progress of science and technology, these problems will be smoothly done or easily solved.3 development prospect of deep foundation pit engineeringWith the increasing number and depth of foundati

25、on pit engineering, design and construction technology of foundation pit engineering is updated, emerging new retaining structure types and construction process so as to improve the design theory and calculation method of foundation pit engineering.2.1 the selection of retaining structure of deep fo

26、undation pit should be more reasonableAs everyone knows, the foundation soil deep foundation pit type, groundwater level, and the surrounding environment are important factors to consider the selection of retaining structure of deep foundation pit supporting structure, if reasonable, can achieve the

27、 whole foundation and the safety of the building, but also can bring considerable economic and social benefits but if the type of support structure; unreasonable choice, not only will be critical for the foundation pit and the whole building safety, but also affect the surrounding environment, soan

28、inevitable trend in the future development of deep foundation pit ishow to make the selection of retaining structure is more reasonable.2.2, the extensive useof new technologiesThe popularization and popularization of new technology is also a development trend of deep foundation pit engineering1) ar

29、tificial freezing soil deep foundation pit technology is the use of soft soil with high content, inserted into the freezing pipe in the field of soil around to the excavation in the formation of a certain structural strength of frozen soil through the wall, as the retaining structure of foundation p

30、it construction. With the strength of soil improvement, good antiseepage performance, strong adaptability, the environmental impact of small advantages and cost is lower than that of the conventional methods of the technology. To realize the optimization of the freezing pipe layout, temperature and

31、thickness of the wall can be designed with this method. At present, many domestic application of conventional supporting method for the construction of the pit there have been varying degrees of instability of foundation pit collapse accidents, causing huge economic losses. The artificial freezing c

32、onstruction of freezing wall and has the structural strength and anti seepage effects, for digging a shallow, easy to conventional foundation pit supporting method, freezing method efficiency is not very significant; but for digging deep foundation pit depth more than 10 m, the cost is significantly

33、 lower than that of the conventional method, and the effect is very good, this method widely use at home and abroad, has not yet been adopted, should be vigorously promoted in China, to promote the development of foundation pit engineering in our country.2) SMW special construction methods In Japan

34、in 1970s was SMW (SoilMixingWall) method, and the strength of cement soil piles, the soil cement sealing performance and the core material (usually H steel, but also for concrete and other stiff material) retaining structure of high strength effectively formed an anti infiltration good, high stiffne

35、ss, economy, has great economic potential. The research and application of domestic and some progress has been made in the development of.SMW method is mixing piles and underground continuous wall construction method based on the deep level up, compared with other types of retaining, with large thic

36、kness, high depth, excellent technical and economic indexes, environmental protection and other advantages, is widely used in many fields of underground building foundation pit, underground dam, underground disposal, environmental protection engineering. Although the SMW method of retaining wall has

37、 the advantages of simple structure, but the stress mechanism is quite complex, at present, the lack of understanding of the working mechanism of H steel and cement soil composite material on the formation of the SMW method, not from an objective perspective to analyze the working mechanism of the c

38、omposite structure. How to consider the composite pile composite structure stiffness, In order to ensure the safety of the project based on the stiffness contribution of the maximum utilization of cement soil is a difficult problem in engineering design. I think that the SMW method should be studied

39、 in the following aspects: first, the interaction relationship between shaped steel and cement soil. Including steel and cement soil interface friction, sliding contact the cement soil and the failure mechanism of SMW composite structure damage evolution process and mechanism from the role of coordi

40、nation to cement soil cracking. Secondly, the establishment of H type steel pull -out model more accord with the engineering practice, and taking into account the effect of water pressure in the lateral steel and cement soil surface resistance in the presence of bending deformation, analysis pull ou

41、t the mechanism of H steel, and SMW method in deep foundation pit in soft soil area application technology research.3) information construction technologyDue to lack of technical personnel and other aspects of capital construction did not spread over every corner of the pit. But with the increase of deep excavation engi