What are the common schemes for foundation pit support?

The co-development of rock and soil is very good, and the cases are very good.

First, the common form of foundation pit support

1.Natural grading.

1) Natural grading of earthwork slope.

When excavating the foundation pit (groove), if the geological conditions and surrounding conditions allow, the slope excavation can be carried out; However, in the construction of densely built areas, the slope cannot be graded due to the limitation of the site, so it needs to be supported.

Natural grading can be made into a straight line, a broken line or a stepped shape, the natural grading slope is generally specified in the design documents, if there is no provision in the design documents, it can be implemented in accordance with the provisions of the "Code for Acceptance of Construction Quality of Building Foundation Engineering" GB50202-2002 as shown in the table.

2.Soil nailing wall support.

The natural soil is set up with soil nails (also known as mortar anchors) through drilling, reinforcement and grouting, and combined with the sprayed concrete panel to form a gravity-like retaining wall.

The soil is nailed to the wall to resist the earth pressure behind the wall and keep the excavation face stable. It is also known as spray anchor net reinforcement slope or spray anchor net.

3.Soil bolt support.

Drill (dig) a hole in the soil layer of the vertical wall to the required depth, put steel bars in the hole, and pour cement mortar.

or chemical slurry, which is combined with the soil layer to form a tensile anchor, and transmits the pressure on the side of the vertical wall soil to the stable soil layer.

4.Cast-in-place pile support.

Before excavation, concrete cast-in-place piles are arranged around the foundation pit, and the arrangement of piles is provided with cantilever pile support, double-row pile support and occlusal pile.

The top of the pile is provided with concrete to tie the crown beam or the waist is provided with a waist beam.

The construction is convenient, the safety is good, and the cost is low.

5.Cast-in-place pile + bolt support.

The top of the pile is not provided with anchor piles and tie rods, but is dug to a certain depth, and the anchor rods are driven obliquely to the back of the pile at certain distances, and after reaching the strength, the waist beam is installed, and the tension is locked, and the soil is excavated in the middle of the pile until the design depth.

6.Steel sheet pile support.

When the foundation pit is deep, the groundwater level is high and the precipitation is not constructed, the sheet pile is used as the supporting structure, which can not only retain the soil, waterproof, but also prevent the occurrence of quicksand. Sheet pile support can be divided into two categories: unanchored sheet piles (cantilever sheet piles) and anchored sheet piles.

Second, the scope of application of common support methods

1.Grading:

Applicable conditions: 1) The perimeter of the foundation pit is open and meets the slope conditions;

2) The soil around the foundation pit is allowed to have a large displacement;

3) There is no groundwater or precipitation treatment within a certain range above the excavation face;

4) Can be used independently or in combination.

Undesirable conditions:

1) Silt and flow-plastic soil layer;

2) Groundwater is higher than the excavation surface or has not been treated with precipitation;

2.Soil nailing wall:

Applicable conditions: 1) good geotechnical conditions;

2) The soil around the foundation pit is allowed to have a large displacement;

3) Rock and soil that has been treated with precipitation or water stopping;

4) The excavation depth should not be greater than 12m.

5) Clay, silty clay, silt and sand above the groundwater table;

Foundation pit support, the relevant construction people are still stranger than the sales year, what are the forms of general implementation of foundation pit support? The following is the basic information of Zhongda Consulting for the construction personnel to sort out the characteristics of the relevant foundation pit support, the specific content is as follows:

The characteristics of foundation pit support mainly include: (1) safety and reliability; (2) economic reasonableness; (3) Construction convenience and construction period guarantee.

Then, according to the characteristics of foundation pit support and the construction situation of each foundation pit project, the commonly used forms of foundation pit support include:

1.Slope excavation: the vertical slope excavation depth can generally reach 5 6m, and after a certain angle of grading, the excavation depth of the foundation pit can reach about 15m.

2.Cantilever pile: the foundation pit with a pit depth of 5 10m often uses bored cantilever piles, and a few projects use manual digging piles. The foundation pit with a pit depth of 9 12m adopts a double row of piles, and the application of double row pile support in Beijing is too common.

3.Bolt pile: foundation pit with a pit depth of 10 15m, often using an anchor rod; The pit depth is 15 18m, and two anchors are often used; The pit depth is greater than 18m, and multiple anchors are used.

4.Soil nailing wall: widely used in Beijing, the common support depth is 5 12m, the deepest has reached 17m, the cost is low, the construction speed is fast, and the application unit has created higher economic benefits.

5.Underground diaphragm wall: it has two functions: slope protection and waterproofing.

Finally, we summarize the above content, the form of the foundation pit support project must be based on the situation of the construction site, the technical characteristics of the construction of the foundation pit support project, the construction site is not required and other relevant factors after comprehensive consideration of the construction. Don't be careless!