13?
Chapter six? Deep foundation?
1, what is a deep foundation? What are the types of deep foundation? When do you need to use de
13?
Chapter six? Deep foundation?
1, what is a deep foundation? What are the types of deep foundation? When do you need to use deep foundation? ?
A: Definition: Generally speaking, it refers to a foundation with a buried depth greater than the width of the foundation and a depth greater than 5m. Deep foundation includes pile foundation, open caisson and caisson, diaphragm wall, pile box, pile raft foundation and pier foundation. When the shallow soil in the construction site can't meet the requirements of the building on the bearing capacity and deformation of the foundation, it is not suitable to take foundation treatment measures, so it is necessary to adopt deep foundation. ?
2. What are the characteristics of open caisson? How to choose the type of open caisson? What are blade feet and treads? What effect does the step size have on the sinking of open caisson? How to seal the bottom of open caisson? (pages 265-267)?
Answer: The characteristics of open caisson foundation: firstly, the building or building foundation located in a certain depth underground is made into open caisson on the surface, and then the open caisson, under the protection of the shaft wall, gradually sinks under the free action through continuous excavation from the well, and then the bottom is sealed to carry out the internal structure construction. ?
3. What problems should be paid attention to in the design and construction of open caisson? What should I do if the open caisson inclines during construction? Answer: Note: Before construction, we should fully understand the geological and soil conditions and formulate corresponding construction measures. For open caissons constructed in water, the flood season, riverbed erosion, floating objects and navigation channels of rivers should be investigated and studied. The construction period should make full use of the dry season. If the construction must go through the flood season, reliable measures should be taken to ensure the construction safety. Inclination treatment: If inclination is found, it shall be notified in time and measures shall be taken quickly. For example, step up excavation on the side with small settlement, and add load on the top of open caisson. You can also use a high-pressure water gun to impact in the side well with small sinking of the open caisson, so that the shaft blade foot loses support; Or dig outside the side of open caisson with small settlement to remove part of soil friction; Or pour bentonite mud at the bottom of the foundation pit on the side of the open caisson with small settlement, so as to further reduce the friction resistance of the soil on the outer wall of the open caisson. ? 4. What is the main difference between caisson and caisson foundation? ?
Answer: Open caisson foundation is a kind of deep foundation which takes open caisson as the basic structure and transfers the upper load to the foundation. Open caisson is a cylindrical structure with four walls, with no bottom, no cover at the top and blades at the bottom of the side wall. Caisson foundation, also known as pneumatic caisson foundation, is the foundation of piers or other structures built with pneumatic caissons. Caisson is shaped like a tank with a top cover.
14?
All right. ?
5. What is the pile box (raft) foundation? What kind of engineering geological conditions is this new foundation suitable for? Can this kind of foundation be widely promoted in cities? You can't. ?
Answer: When the foundation soil of high-rise building is weak and the box (or raft) foundation cannot meet the requirements of foundation bearing capacity, bearing pile foundation must be made under the box (or raft) foundation slab. This box foundation (or raft foundation) is added with pile foundation, which is called pile box (or pile raft foundation) for short. When the load of high-rise or heavy building is heavy, and the foundation is thick clay layer, the strength or deformation conditions of the foundation can not meet the design requirements or may cause large settlement, the friction pile group and box foundation (or raft foundation) can be used to share the building load. ?
6. What are the characteristics of large-diameter pier foundation compared with traditional pile foundation? What problems should be paid attention to in the design and construction of this foundation? (P283)？
A: Features: (1) High bearing capacity; (2) It is very difficult to pile in dense sandy pebble foundation, while pier foundation is easy to construct; (3) Compared with open caisson, caisson and other deep foundations, pier foundation construction generally only needs light machines and tools, which has great economic advantages. There is no strong noise such as piling in pier foundation construction, which can reduce noise pollution. In pier hole construction, the sand layer below the groundwater level may cause quicksand, which should be paid special attention to. (4) Pier foundation not only has high vertical bearing capacity, but also can bear large horizontal load. The bell pier can also resist great uplift force. (5) The pier has a large cross section, which is convenient for checking the soil conditions of the bearing layer at the bottom of the pier and the soil layer at the side of the pier after the hole is formed, and verifying the survey and design results. There is a large amount of concrete pouring on piers, so the construction quality must be carefully checked. Bad weather will affect the construction progress and inspection of piers. ?
7. What is the mechanical mechanism of large-diameter belled pier foundation? What is the difference between its side friction and ordinary straight piles? (284 pages)? A:?
8. What are the advantages of belled piles? What are the construction methods of belled piles?
9. What are the application characteristics of the working machine technology of underground continuous wall? Brief introduction of key points of underground continuous wall construction. (29 1~294 pages)?
15?
Chapter seven? Special land base?
1. What is a special land foundation? What types of regional special soils exist in China? (page 296)?
A: China has a vast territory, and the differences in geographical environment, geological structure, geological history, climate environment and stratum material composition in different regions make the soil quality in some areas different from that in general areas, which is commonly called special soil foundation. Such as: soft soil in rivers, lakes and seas, collapsible loess in northwest and central China, frozen soil in northeast and northwest China, expansive soil and red clay in southwest China, saline soil in northwest China, and filled foundation along roads and traffic in cities. ? 2. What is soft soil foundation? Brief introduction of engineering characteristics and treatment measures of soft soil. ?
Answer: Soft soil generally refers to modern sediments which are mainly clay particles and accompanied by microbial action in still water or slow flowing water environment. Soft soil has the characteristics of high natural water content, large void ratio, poor permeability, high compressibility, low shear strength and bearing capacity. Treatment measures: (299 pages)?
3. What is the main difference between self-weight collapsible loess and non-self-weight collapsible loess? (P300) What are the causes and influencing factors of collapsibility? (P302) Briefly describe the engineering treatment measures of collapsible loess foundation. (P304-305)
4. What is expansive soil? What are the engineering characteristics of expansive soil? Briefly describe its harm to engineering buildings. ?
A: Definition: Expansive soil generally refers to cohesive soil whose clay composition is mainly composed of hydrophilic clay minerals, which has obvious expansion, softening, disintegration and rapid shrinkage, cracking and expansion due to water loss. Engineering features: (1) expansibility; (2) Multiple fractures; (3) overconsolidation; (4) disintegration; (5) intensity attenuation. Hazard to engineering buildings: (1) Impact on buildings: Expansive soil foundations are mostly easily destroyed by buildings in shallow strata. There are two characteristics of house damage: seasonality and collectivity. Cracks at the corner of the building wall often show symmetrical or asymmetrical inverted splayed joints and X-shaped cross joints on the gable. Due to the shear force and lateral horizontal thrust generated in the process of foundation expansion, horizontal cracks and displacements appear in the lower part of the external longitudinal wall; Indoor floor and floor heave and crack longitudinally. (2) the impact on road traffic engineering: the roads in the expansive soil area, due to the uneven change of soil moisture content in the subgrade, are not
16?
Uniform expansion and contraction, resulting in large transverse wave deformation. In rainy season, the road surface seeps and the roadbed is soaked and softened, which will cause you to slip under the driving load and splash mud and soil along the cracks and expansion joints of the road surface. (3) Influence on slope stability: The slope in expansive soil area is vulnerable to atmospheric weathering, with strong evaporation and peeling off in dry season. In rainy season, the slope is eroded, and the depth of erosion ditch is generally 0. 1~0.5m, and the maximum depth can reach1.0m. The slope becomes broken and the soil is saturated with water. Under the action of gravity seepage pressure, plastic flow collapse occurs along the slope. When the rainfall is concentrated in rainy season, it will also form mudslides, block culverts, bury roads, and even cause destructive landslides. ? 5. What is the free expansion rate? How to evaluate the expansion and contraction grade of expansive soil?
A: free expansion rate ef? : The ratio of the increased volume to the original volume after the artificially prepared dry soil sample is soaked in water and fully absorbed, expanded and stabilized. 100%VVV0
wef？
. According to the influence of expansion and contraction deformation of expansive soil foundation on buildings, the expansion and contraction grades of foundation are divided into three levels: when 15 mm ≤ SC.
Answer: Saline soil refers to soil with soluble salt content greater than 0.3% and engineering characteristics such as settlement, salt swelling and corrosion. Classification of saline soil: 1. According to the nature of salt, it can be divided into chloride, sulfate and carbonate. 2. Classification according to the degree of salt leaching: According to the salt content in the soil, the salt-soaked soil can be divided into weak, medium, strong and super-strong salt-soaked soil. ? 7. Briefly describe the engineering characteristics of saline soil, and the construction and anti-corrosion measures in saline soil area. ?
Answer: Engineering features: 1. Solubility: in the natural state, the additional deformation of saline soil when it is soaked in water under the action of dead weight pressure or additional pressure is called settlement deformation of saline soil. Only dry or slightly wet saline soil can be dissolved, and most of them are dissolved by their own weight. What is the sinking coefficient under UFIDA load? To measure. 2. salt swelling. 3. Corrosiveness. Anticorrosive measures: (P3 12)?
8. What's the difference between seasonal frozen soil and permafrost? ?
A: Seasonal frozen soil is a kind of soil that is periodically frozen and melted under the influence of seasonal climate. It is frozen in winter and completely melted in summer, which has a great influence on the stability of foundation soil. Permafrost refers to soil that has been frozen for two years or more. many
Please adopt