Retaining and protection of foundation pit

The purpose and effect of retaining and protection of foundation pit

1. Ensure the stability of the soil around the pit, at the same time there is enough space to meet the basement construction requirements, This is a necessary condition for earth excavation and construction of the basement.

2. Guarantee pit surrounded by adjacent buildings and underground pipelines and other facilities in the basement during the retaining and protection of foundation pit and construction will not be harmed, That Pit soil  deformation ,  including Vertical and horizontal displacement of surface and subsurface soil to be controlled within the allowable range

3.Through cut the water, rainfall, drainage and other measures,  Ensure that foundation pit engineering construction work surface above the underground water level.

The type of foundation pit supporting structure and its applicable conditions

1. Grading excavation

Advantage : Only requires stable, the price is the cheapest.

Disadvantage: Backfill earthwork is larger.

Application: the space is wide, no major building projects around.

2. Enclosure wall Deep mixing cement soil

Deep mixing cement-soil enclosure wall is to use deep mixer in situ soil and the input of the slurry forced mixing,  Forming a continuous overlapping soil cement pillar plus solid retaining wall.

Advantage : Due to the general pit without support, Facilitate rapid mechanization excavators; Has retaining soil , waterproof the dual function; Under normal circumstances the more economical; construction no vibration, no noise, less pollution, soil compaction mild.

Disadvantage: Relatively large displacement thickness , For the length of the large foundation pit, take the middle pier and arch camber To limit excessive displacement; construction should pay attention to prevent affecting the surrounding environment.

Application: Downtown project

3. High pressure jet grouting pile

High Pressure Jet Grouting pile materials are also used in grout, It is through the use of high pressure rotating nozzles grout is injected into the soil and the soil mix to form a soil cement plus solid, Overlap each other to form a row of piles for retaining soil and waterproof.

Advantage : Construction equipment compact structure, small volume, strong maneuverability, covers an area of less, and small construction equipment vibration, noise is also lower, without bring vibration and noise of the surrounding buildings, etc.

Disadvantage: The construction of a large number of sludge discharge, easy to cause pollution. For groundwater flow rate is too large stratigraphic, No filler in karst area of permafrost and the severe corrosion of cement soil, Because of the jet grout can't around the grouting pipe solidification, unfavorable use this method.

Application: the smaller space construction project.

4. Channel steel sheet pile

This is a simple steel sheet pile enclosure wall, by channel composed of positive and negative side buckle or lap. Channel steel length 6 ~ 8m, the model is determined by calculation.

Advantage : Good durability, the second high utilization; easy construction, short construction period.

Disadvantage: Can't block the tiny particles in water and soil, resisting or precipitation measures to be taken in areas of high groundwater levels; Flexural capacity is weak, Supporting small rigidity, large deformation after excavation.

Application: Used for shallower depth ≤4m pit or trench.

5. Bored pile

bored pile with high load capacity, settlement and other small features.

The construction of  bored piles, because the formation of different selected Wall, There are two ways Slurry Wall Construction Law Act and a full pipe.

Advantage : No construction vibration, noise and other environmental hazards, no soil compaction phenomenon, little impact on the surrounding environment; Wall body is high strength, stiffness big, support good stability and deformation of small; When the engineering pile for filling pile construction, you can synchronize the construction, which is conducive to the construction organization construction, short construction period.

Disadvantage: The gap between piles easily cause soil erosion, Especially in high-water areas of soft clay, Need to be taken in accordance with the conditions grouting works, cement mixing pile, jet grouting pile other construction measures to address the problem of retaining water.

Application: It’s the one of the most widely application in row pile, Usually for 7 ~ 15 m deep foundation pit engineering, Suitable for soft clay and sandy soil area.

6. Diaphragm Wall

Advantage : Stiffness is big, waterproof effect is good, is the strongest support form in supporting structure.

Disadvantage: Higher cost, construction require used special equipment.

Application: Poor and complicated geological conditions, foundation pit is deep, the foundation pit is high demand with Environment surrounding.

7. Soil nail wall

Soil nail wall slope stability is a type of support, Its role and passive soil retaining effect of the enclosure wall is different, it is embedded solid active role, Increase the stability of the slope, so that after excavation slope stability.

Advantage : Stable and reliable, easy construction and short time limit, the effect is good, economy good, in good soil region should be actively promoted.

Disadvantage: Poor soil areas is difficult to use.

Application: The main application is the better soil area.

8.The SMW method

SMW method, also known as strength of the cement mixing pile, In inserting h-beam in cement-soil pile, etc (most for h-beam, insert the also have tensile steel sheet pile, steel pipe, etc.), Will bear the load and seepage retaining combine, making enclosure wall also has support force structure and permeability of the two functions.

Advantage : Almost no noise during construction, little impact on the surrounding environment; Reliable structural strength, any application for cement mixing pile occasions can be used; Retaining seepage good performance, do not separate retaining curtain; Can be used with multi-channel support is applied to the deep pit; This construction method under certain conditions can replace underground continuous wall as underground Enclosure wall, If the cost of construction can take certain measures, such as the successful recovery of H-shaped steel tensile material is much lower than the diaphragm wall, and thus have greater prospects for development.

Application: Can be applied in clayey soil, silt, sand, gravel, soil, etc.