Generally, (1) The size of the foundation pit shall meet the construction requirements.
The cofferdam used for groundwater protection should be 0.2-0.4m higher than the water level.
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The buried depth of foundation is very small compared with its width, which belongs to the category of shallow foundation.
C form Vertical pit wall, slope pit wall, ladder pit wall d.
It has a great impact on the safe use of structures and the construction cost.
Foundation positioning and setting out 1).
B Applicable conditions: (1) In dry and waterless beaches and ditches, or in ditches where water can be discharged from surface water through river reconstruction or embankment; (2) The quality of the pit wall will not be affected when the groundwater level is lower than the base or the seepage amount is small; (3) The foundation is not buried deep, the construction period is short, and the excavation of foundation pit will not affect the safety of adjacent buildings.
Construction method: manual construction method (shovel, pick) mechanical construction: excavator, conveyor belt, grader, grab bucket (2) pit wall with support a Applicable conditions (1) pit wall is not easy to be stable and there is groundwater infiltration (loose soil, large water); (2) The slope excavation site is limited (narrow); (3) When the foundation pit is deep and the quantity of slope excavation is large, which does not meet the technical and economic requirements (pit depth and large earthwork volume); B.
2) When the foundation pit is an unstable strongly weathered rock foundation or muddy clay, the anchor rod can be used for shotcrete slope protection.
It is a temporary project.
Foundation pit without support on the pit wall a.
2) Rock foundation pit excavation Rock foundation excavation, pit wall slope is as described in the table, hard rock can be vertically downward, and the general design excavation depth is the thickness of weathered layer.
Fresh bedrock, slightly weathered or weakly weathered rock can be used as the foundation bearing layer.
3) The foundation pit excavation of underwater foundation, bridge pier and abutment foundation are mostly located below the surface water level, and sometimes the water flow is relatively large.
In most cases, it is cheaper and shorter than other types of foundation; 5) , vulnerable to the adverse effects of frost heaving and scouring; 4、 Construction process: foundation positioning and setting out, foundation pit excavation, foundation pit drainage, foundation pit inspection and treatment, foundation masonry and foundation pit backfilling.
The excavated slag and stone must be transported to the place designated by the design, and shall not cause harm to the construction safety or the production, living and environment of the surrounding people.
Generally, the base shall be 0.5~1.0m wider than the plane size of the foundation.
The excavation depth of the foundation pit supported by steel sheet piles should not be greater than 4m, and the water seepage is small.
(4) When there is groundwater in the foundation pit, the part above the groundwater level can be excavated by slope; For the part below the groundwater level, if the soil is easy to collapse or the water level is high above the foundation pit bottom, reinforcement or lowering of the groundwater level shall be adopted for excavation.
2.
1、 The common foundations of bridge engineering are expanded foundation, pile foundation, pipe column foundation, open caisson foundation and underground continuous wall foundation.
1.
Foundation pit excavation type: 1).
When the foundation pit supported by the support structure baffle is excavated deep (more than 5m), the pit wall is not easy to be stable, and there is groundwater influence or the slope is restricted.
(2) The slope of foundation pit wall shall be determined according to geological conditions, foundation pit depth, construction method, etc.
Function: provide a space for the foundation masonry work to be carried out according to the design position.
3、 Features: 1) The construction quality is reliable because it can be carried out under the condition that the supporting foundation can be confirmed by eyes on site; 2) The construction noise, vibration and underground pollution are relatively small; 3) Compared with other types of foundations, the operation space required for construction is small; 4) .
When there is no formwork, the foundation pit can be excavated according to the size of the foundation bottom.
The most common construction method of bridge underwater foundation is cofferdam method.
Under the condition that the foundation soil is good and the water seepage is small, shotcrete or anchor rod (anchor cable) hanging net shotcrete can be used to reinforce the foundation pit wall, excavation layer by layer, and reinforcement layer by layer.
When the foundation pit is a permeable soil base, the size of the pit bottom shall be determined according to the drainage requirements (including drainage ditch, sump, drainage pipe network, etc.) and the size of the foundation pit required for the design of the foundation formwork.
C Support form: straight lining plate, horizontal lining plate pit wall support, frame support, other forms of support (anchor pile type, anchor rod type, anchor plate type, diagonal bracing type).
(3) If the soil humidity may cause the pit wall to be unstable and collapse, the slope of the pit wall of the foundation pit shall be slower than the natural slope under this humidity.
For relatively complete weathered bedrock with excavation depth less than 10m, plain concrete can be sprayed directly.
According to data records, 70%~80% of building accidents are caused by foundation failure.
The bridge expanded foundation load is directly transferred to the natural foundation with better soil quality through the gradually expanded foundation, and its size is determined by the load borne by the foundation bearing capacity.
Shotcrete and anchor rod support 1) When the foundation pit is limited by conditions and the excavation depth is large, it can only be excavated vertically or in a large slope.
2、 Expanded foundation (shallow foundation, open cut expanded foundation) Structural expanded foundation is a foundation form that directly transfers the load from the pier or abutment and the superstructure to the shallower bearing foundation.
Fixing Socket Cross Hole Nail Plate
The construction is expected to be carried out under the condition of no water or static water.
Land (dry) foundation pit excavation (1).
Foundation engineering plays an extremely important role in the design and construction of bridge structures.
(1) Cofferdam is used for waterproofing and water containment, and sometimes also for supporting the construction platform and foundation pit wall.
According to the weathering degree, joint, tendency and development of the rock stratum, appropriate methods shall be adopted for pit wall protection.
Generally, manual excavation is adopted for excavation, and loose blasting can be carried out when necessary, but the blasting depth and dosage shall be strictly controlled to prevent the loosening and damage of bearing stratum caused by excessive blasting.
(2) Requirements for cofferdam a The height of cofferdam shall be 0.5~0.7m higher than the highest water level (including wave height) that may occur during construction.
Foundation pit: temporary pit excavated for building foundation.
Because of its shallow burial depth, simple structural form, simple construction method and low cost, it is the most commonly used foundation type of buildings.
