Foundation pit construction quality control seminar

[Abstract] Deep Foundation Pit stage a temporary project, but the reliability of its construction program and construction quality will directly affect the structure and the basement of the main construction workers exposed to life safety, and the technical complexity of its construction, but some even more than permanent infrastructure or superstructure, the slightest mistake will not only endanger the safety of the pit itself, but also bring disaster to the adjacent structures and a variety of underground facilities, causing huge losses. This paper analyzes the current deep excavation of the safety problem, a deep excavation in the design and construction considerations and preventive measures.

[Keywords] building pit construction; supporting, treatment

1 Introduction
In recent years, the rapid emergence of high-rise buildings, and promote deep excavation technology. Around the deep excavation and shoring technology has accumulated rich experience in the design and construction, new technologies, new structures, new processes continue to emerge, but now the city building space is very small, some of the edge of the pit is only ten meters away from the existing building, or even a few meters, to the great foundation construction difficulties, a serious threat to the surrounding environment, but also corresponding increase in the construction schedule and construction costs. In addition, the original structure of the deep excavation design theory, design principles, computing formulas, construction technology, no longer meet the deep excavation and the support structure of the actual situation, lead to some of the excavation of an accident, resulting in huge losses, so deep excavation safety Engineering and technical personnel should be highly valued.

2 present deep excavation problems
2.1 Middle-earth retaining structure design parameters of physical and mechanical inappropriate choice of
Deep Excavations undertaken by the size of the soil pressure directly affects the safety, but because of ever-changing and complex geological conditions, to accurately calculate the earth pressure is still very difficult, still using the Coulomb formula or Rankine formula. soil physical parameters on the choice of a very complex issue, especially in the deep excavation, the moisture content, internal friction angle and cohesion values ​​of three parameters is variable, it is difficult to accurately calculate the supporting structure actual force.

Deep Excavations in the design, if the foundation soil physical and mechanical parameters values ​​are not allowed, the result will be designed to have a significant impact of soil mechanics test data show that: the value of the difference in friction angle 5 °, which produces active earth pressure is different from the original soil of the soil behind the excavation within the cohesion and solidarity within the body, then the difference is even greater. construction techniques and different forms of the supporting structure of the soil physical and mechanical parameters of the choice also has a great influence.

2.2 Excavation of soil sampling with incomplete
Deep Excavations in the design, you must be the foundation soil sample analysis, in order to obtain a more reasonable soil physical and mechanical properties for the supporting structure is designed Tigong reliable basis, normally in areas of deep excavation period, according to the requirements of national standard drilling sampling order to reduce the workload of exploration and reduce project cost, not too many holes, so the soil samples obtained with a certain randomness and incomplete, but the geological structure is extremely complex, varied, to obtain soil samples can not fully reflect the authenticity of the soil, so the design of supporting structure will not fully meet the actual geological conditions.

2.3 Effect of excavation there is room for ill-considered
Deep excavation of a large number of measured data show that: pit to pit around the horizontal displacement occurred in the middle on both sides is small. Deep pit slope instability, often place the long side of the center position. This is enough to say that the deep excavation when a space is the traditional deep foundation pit structure is designed to be handled by plane strain problem. Excavation of some long and thin, such a plane strain assumption is more in line with practical, while the approximate square or rectangular deep pit is relatively large difference, so, without the space before it is processed while the plane strain assumption design, support structure to appropriate adjustments to meet the requirements of the spatial effect of the excavation .

2.4 retaining structure design calculations and the actual Shouli Bu Fu
At present, the structure of deep foundation pit design calculations are still based on limit equilibrium theory, but the supporting structure of the actual force is not so simple. Engineering Practice has proved that some of the supporting structure designed by the limit equilibrium factor of safety calculated from the In theory it is perfectly safe, but sometimes damage occurs, some supporting structure safety factor, albeit small, or even meet regulatory requirements, but in the actual project is to meet the requirements.

Limit equilibrium theory is the structure of deep foundation pit of a static design, but in fact after excavation of soil is a dynamic equilibrium state, the soil is a process of gradual relaxation over time of growth, soil strength decreased gradually, and have some distortion, so the design must take full account of this.

3 deep foundation pit design and construction of the Notes
3.1 thoroughly change the traditional design
Over the last decade, China's deep excavation technology has accumulated a lot of practical experience collected during the construction of some of the technical data, has been a preliminary exploration of the supporting structure changes in the actual ground by the force of law for the establishment of deep base pit retaining structure design of the new theories and new methods to lay a good foundation, but the structure for deep excavation design at home and abroad has not yet a precise method of calculation, mostly in the exploration and exploratory stage, our there is no unified support structure design specification. Earth pressure distribution is also determined by Coulomb or Rankine theories, supporting piles are still using the "equivalent beam method" to calculate its results with the structure of deep excavation of the actual disparity between the larger force is neither safe nor economical . Thus, the deep excavation retaining structure design should not be using the traditional "structural load method", which should completely change the traditional design concepts, and gradually establish a construction monitoring for the dynamic design-led feedback system, which is Designers need to strengthen scientific research directions. Links to free download http://www.hi138.com
3.2 The establishment of deformation control of the new Engineering design methods
Currently, designers use the limit equilibrium theory is a simple and practical design method used, the results of significant reference value, but this design method for deep foundation pit structure, retaining only a simple meet structural strength requirements, but can not guarantee that the stiffness of the supporting structure. a number of construction accidents is because the supporting structure of the deformation caused by too much, and we can see that the evaluation of a support structure design pros and cons, not only depend on its meets the strength requirements, but also by whether they have environmental problems, the key lies in the deformation size view of the actual deformation in the establishment of a new control design method should be focused on the supporting structure deformation control standards, spatial effects into overload for the plane strain and ground to determine its impact on the supporting structure and other issues.

Vigorously supporting structure 3.3 pilot study
Correct theory must be built on the basis of a large number of experimental studies, but in the deep foundation pit structure, our system has not yet been scientifically studied. Some of the supporting structure project a success, but also lost for the specific functions of the Department , some of the supporting structure project failed, can not tell the real reason for the failure in supporting the process of construction, the accumulation of technical information is very rich, but the lack of scientific test data, not scientific analysis, can not rise to the theory of height, which is a big flaw.

Supporting structure to carry out experimental studies (including laboratory simulation and Engineering field test, although I have to spend some money, but because of deep excavation works great investment, such as through the design of scientific experiments to conduct, will certainly save considerable expense Therefore, Engineering field test is necessary, through the accumulation of a large number of engineering practice, test data, the success of similar projects can lay the foundation for theoretical research and the establishment of a new calculation method provides a reliable first-hand information.

3.4 explore the new method of calculating support structure
The rapid development of high-rise buildings Deep Excavations brought a technological revolution in the steel sheet piling, reinforced concrete sheet piles, bored pile retaining wall, diaphragm walls, etc. After the successful application of support structure, double pile, soil nails, combined arch curtain, jet grouting soil anchors, prestressed concrete plates and other new types of support structure have also come out, but these type of supporting structure calculation model how to create, calculate the diagram how to select, design how to become more scientific, is still the current design of the new support structure needed to solve the problem.

At present, the deep foundation pit structure is the direction toward the comprehensive development of the structure of the force structure and the combination of water, temporary support structure and the combination of a permanent support structure, excavation methods and the combination supporting structure type. combination of these types is bound to force a complex support structure, so the establishment of a new method of calculating support structure has become a deep excavation techniques imperative.

4 Conclusion
Construction pit excavation and support structure is a systematic project, involving engineering geology, hydrogeology, engineering structures, building materials, construction techniques and construction management and other aspects it is a soil mechanics, hydraulics, materials and structures scholarship mechanics is one of the comprehensive discipline. supporting structure is again a number of independent components of the overall functionality of the system. For this reason, both the structural design or construction organization should proceed from the overall function, will coordinate the various components in order to make sure it's safe, reliable, economical and reasonable. Links to free download http://www.hi138.com