First, the survey points of foundation pit engineering
Foundation pit engineeringCompared with the investigation of buildings, the investigation of the foundation pit has its own characteristics. With the excavation of the soil within a certain range inside and outside the foundation pit, there will be stratum movement. Therefore, there are specific requirements for the scope and depth of investigation and geotechnical index test items.
1Foundation pit engineering investigation needs to find out the situation
(1) Rock and soil distribution and physical and mechanical properties in and around the foundation pit;
(2) Whether the rock and soil have undesirable properties such as expansibility, collapsibility, thixotropy, frost heaviness, and earthquake liquefaction;
(3) the distribution and occurrence, filling condition, roughness and their combination relationship of soft structural plane;
(4(whether there are karst caves, soil caves, civil air defense fortifications and other underground caves in the site and their distribution;
(5) The type, water level, water pressure, water volume, recharge, dynamic changes and permeability of groundwater in each layer;
(6) Considerable depth around the foundation pit 1-2Type and importance of adjacent buildings, subways, roads and pipelines, underground and ground water storage and transmission facilities, and their leakage.
2,Foundation pit engineeringScope of investigation and exploration
The detailed survey of the building is mostly arranged along the contour of the building, resulting in the lack of foundation pit design and construction data. The survey and exploration scope of the foundation pit should be beyond the contour of the building, generally take the foundation pit around the equivalent of twice the depth of the foundation pit. When there are special circumstances, still need to expand the scope.
The spacing of exploration points should be determined according to the complexity of the foundation pit and engineering geology and hydrogeology conditions, which is generally 10m～30m. When the horizontal direction of the stratum changes greatly or there are weak structural planes, exploration points should be added to find out the distribution.
The depth of exploration point should be determined according to the complexity of foundation pit, engineering geology and hydrogeology conditions, and should meet the requirements of design and calculation, generally not less than the depth of foundation pit 2～3 When encountering moderate weathering and breeze rock formation in this depth, the depth can be appropriately reduced according to the type of rock and support requirements.
3,Foundation pit engineeringExploration method and soil property index
The main method of exploration is drilling, supplemented when necessary by pit exploration and geophysical exploration. Standard penetration test should be carried out for sandy soil. Static penetration test or standard penetration test should be done for silt and clay. Cross plate shear test is suitable for soft soil. If necessary, side pressure test and foundation bed coefficient test can be performed.
Through laboratory tests, the physical and mechanical properties of soil, especially the shear strength index, permeability coefficient, compression modulus and springback modulus, were obtained. The method of shear test should be matched with the method of analysis and calculation, which can be triaxial test or direct shear test. The drainage conditions of the test are determined according to the design requirements, and the residual shear strength test and lateral pressure coefficient test are done when necessary.
4,Foundation pit engineeringGroundwater types and dynamics
It is necessary to control the movement of groundwater by means of dewatering or water stoppage during foundation pit construction. So. The hydrogeological conditions such as type, burial condition, recharge condition, hydraulic connection and permeability coefficient of each aquifer should be ascertained during the investigation. The hydrogeological parameters such as permeability coefficient, water storage coefficient and influence radius of aquifer should be determined by field pumping test. The possible influence of convection sand, soil flow and piping is evaluated.
5,Evaluation of engineering geological conditions
In addition to meeting the general requirements, the contents of the survey report of foundation pit engineering should also be evaluated for the following items:
(1) the proposedThe type of support And demonstrate the construction should pay attention to matters;
(2) Provide parameters and indicators required for foundation pit design:
(3) to evaluate the influence of groundwater on foundation pit engineering;
(4) To evaluate the influence of surrounding conditions on foundation pit engineering;
(5) To evaluate the possibility of forming flowing sand, flowing soil, piping and overall instability in the construction process and put forward preventive measures. For SOIL WITH EXPANSIBILITY, COLLAPSIBILITY, FROST HEAVING AND OTHER SPECIAL PROPERTIES, THE INFLUENCE OF THESE SPECIAL PROPERTIES ON FOUNDATION PIT ENGINEERING SHOULD BE DEMONSTRATED, AND corresponding MEASURES FOR design and construction SHOULD be PUT FORWARD.
Second,Foundation pit engineeringEnvironmental survey of
To ensure the safety of the surrounding environment of foundation pit engineering is the basic requirement for the design of foundation pit engineering. Before the design, it is necessary to make a thorough investigation of the environment in the surrounding area of influence of foundation pit.
Generally, it is necessary to investigate the condition of the buildings (structures) and facilities within the influence range of the surrounding construction of the foundation pit, including the number of layers, structural form, buried depth and form of the foundation, and the type, diameter and buried depth of the nearby pipelines.
In order to estimate the ability of resistance to deformation, the quality inspection and appraisal of building structure should be carried out according to relevant regulations for key protected objects.
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