1. Foundation pit engineering, support and enclosure structure
【Formula】Cantilever single multi-support, external anchor reduction control
The foundation pit engineering is to excavate an underground space from the ground downward, and the vertical retaining enclosure structure is generally set around the deep foundation pit, and the enclosure structure is generally a plate (pile) wall structure with a certain depth of insertion under the base of the excavation face. Plate (pile) walls have cantilever, single-brace, and multi-brace. The supporting structure plays the role of reducing the deformation of the enclosure structure and controlling the bending moment of the wall, which is divided into two forms: internal support and external anchor.
2. Foundation pit enclosure structure system
【Formula】The wall is enclosed by inheritance, and the pit is deep in the environment
(1) The foundation pit enclosure structure system includes slab (pile) wall, enclosure purlin (crown beam) and other ancillary components. The plate (pile) wall mainly bears the earth pressure and water pressure generated by the excavation and unloading of the foundation pit, and transmits this pressure to the support, which is a kind of construction temporary retaining wall structure for stabilizing the foundation pit.
(2) The enclosure structure used in the subway foundation pit should be determined after a comprehensive comparison of technology and economy according to the depth of the foundation pit, engineering geology and hydrogeological conditions, ground environmental conditions, etc. (especially taking into account the characteristics of urban construction).
3. Type of deep foundation pit enclosure structure
【Formula】The ground is connected to the gravity wall, digging and filling the steel workers' piles
The forms of enclosure structure mainly include underground diaphragm wall, manually excavated pile, bored pile, bored occlusive pile, SMW construction pile, I-beam pile and steel sheet pile.
In mainland China, there are more applications such as row piles, underground diaphragm walls, gravity retaining walls, and the combined types of these structures.
4. Precast concrete sheet piles
【Formula】Moment T port connection permanent
There are four commonly used forms of reinforced concrete sheet pile sections: rectangular, T-shaped, I-shaped and mouth-shaped. The rectangular cross-section is more convenient to make, and the groove and tenon joint mode is adopted between the piles, and the joint effect is better, and it is a form that is used the most; the T-shaped section is composed of the flange and the stiffener, and its bending capacity is larger, but it is more difficult to apply, the flange directly plays the role of retaining soil, and the stiffener is used to strengthen the bending ability of the flange, and the lateral pressure on the sheet pile is transmitted to the foundation, and the lap between the sheet piles generally adopts the step-type stop; the cross-sectional shape of the I-shaped thin-walled sheet pile is more reasonable, so the mechanical performance is good, the stiffness is large, The material is provincial, easy to apply, and the soil is less squeezed; the mouth zigzag section is generally composed of two trough plates cast in situ to form a whole, and the stiffness of the trough plate is less before being combined into a mouth grub.
The construction of precast concrete sheet pile is more difficult, the mechanical requirements are high, and the phenomenon of soil squeezing is very serious, and the concrete sheet pile can not be pulled out in general, therefore, it is widely used in the permanent support structure, but the use in domestic foundation pit engineering is not very common.
Self-weight, limited by lifting equipment, is not suitable for large-depth foundation pits.
The joints are sometimes supplemented with water-stopping measures.
5. Advantages and disadvantages of steel sheet piles and steel pipe piles
【Formula】Strong isolation and application of normal, deep lock and fracture structure anchor support, sinking and pulling of water-stopping special angle piles
Steel sheet pile has the advantages of high strength, good water insulation effect, flexible construction, and reusable use of sheet pile, which is a kind of retaining structure commonly used in foundation pits. However, due to the phenomenon of squeezing the soil when the sheet pile is driven in, and the soil will be brought out when it is set out, resulting in a gap in the position of the sheet pile, which will have a certain impact on the surrounding environment. Moreover, the length of sheet pile is limited, and the applicable excavation depth is also limited, and the maximum excavation depth is generally 7~8m. There are many forms of sheet pile locks, and the Larsen type is the most commonly used. When the steel sheet pile is used as the supporting structure, it needs to be connected into a whole with a steel purlin at its upper mouth and the supporting position, and the support or anchor is set according to the depth.
There are many cross-sectional forms of steel sheet piles, and most of the commonly used forms are U-shaped or Z-shaped. U-shaped steel sheet piles are mostly used in the construction of mainland underground railways, and their sinking and uprooting methods and machinery used are the same as those of I-beams, but their composition methods can be divided into single-layer steel plates, double-layer steel sheet piles and curtains. Due to the deep foundation pit during the construction of the subway, in order to ensure its verticality and facilitate the construction and make it possible to close the dragon, the curtain structure is mostly adopted.
Steel sheet piles generally have lower stiffness than other row pile enclosures. Its water-stopping effect is also related to the newness, integrity and construction quality of steel sheet piles. In the construction of sandy soil layer containing groundwater, it is necessary to ensure the occlusion of the tooth mouth, and special corner piles should be used to ensure the water-stopping effect.
The cross-sectional stiffness of the steel pipe pile is greater than that of the steel sheet pile, and the construction difficulty is higher than that of the steel sheet pile.
6. Bored pile enclosure structure
【Formula】Beam diameter mixing machine spacing
Bored piles are generally mechanically formed. Auger drilling rigs, percussion drilling rigs, forward and reverse circulation drilling rigs, rotary drilling rigs, etc. are mostly used in subway open-cut foundation pits. For the positive and reverse circulation drilling rig, due to its use of mud wall protection holes, the noise is low when the holes are formed, which is suitable for urban construction, and has been widely used in the construction of subway foundation pits and deep foundation pits of high-rise buildings.
For cantilever row piles, the pile diameter should be greater than or equal to 600mm, for the anchor type or supported pile row pile diameter should be greater than or equal to 400mm, and the center distance of the row pile should not be greater than 2 times of the pile diameter. The concrete strength grade of the pile should not be lower than C25. Concrete crown beams should be provided at the top of the row piles. Concrete cast-in-place piles should be built in the order of interval piling, and the hole-forming construction of adjacent piles should be carried out after the final setting of concrete.
The enclosure structure of bored piles is often used in conjunction with the final setting of water-stopping curtains, and deep stirring piles are generally used for water-stopping curtains. If the upper part of the foundation pit is limited by environmental conditions, the high-pressure jet grouting pile waterproof curtain can also be used, but the construction quality of the waterproof curtain of the high-pressure jet grouting pile should be ensured. In recent years, bored occlusal piles arranged at intervals between plain concrete piles and reinforced concrete piles have also been widely used, and such structures can be directly used as water-stopping female curtains.
7、SMW工法桩（型钢水泥土搅拌墙）
【Formula】Pile diameter H steel, plugging and unplugging mud strong.
The SMW construction method pile retaining wall is to use mixing equipment to cut the soil on the spot, then inject cement mixture liquid to stir to form a uniform cement-soil mixing wall, and finally insert section steel into the wall to form a rigid composite enclosure structure.
The diameter of the triaxial cement-soil mixing pile in the section steel cement-soil mixing wall should be 650mm, 850mm, 1000mm, and the interpolated section steel should be H-shaped steel. The unconfined compressive strength of the mixing pile at 28 days should not be less than the design requirements and should not be less than 0.5MPa, and the cement should be with a strength grade not lower than P· For ordinary Portland cement of O42.5 grade, the amount of material and the water-glue ratio should be determined through field tests in combination with soil conditions and mechanical properties. In particularly weak soils such as fill-in soil and silty soil, as well as in hard sandy soil and gravel soil, when the drilling speed is slow, the amount of cement should be appropriately increased. In sandy soil, the construction of mixing piles should be supplemented with bentonite.
When the diameter of the mixing pile is 650mm, the interpolated H-shaped steel cross-section should be H500×300, H500×200;when the diameter of the mixing pile is 850mm, the interpolated H-shaped steel cross-section should be H700×300;when the provincial diameter of the mixing pile is 1000, the interpolated H-shaped steel cross-section should be H800×300, H850×300. The spacing and 3 plane layout forms of the steel in the steel cement-soil mixing wall should be determined according to the calculation, and the commonly used interpolation steel layout form can be used in the dense plug type, the plug two jump one type and the plug - jump one three.
The welding head should not be more than two in a single section steel, and the position of the welded joint should be avoided in the support position or near the excavation face and the other section steel is stressed; the vertical position of the joints of the adjacent section steel should be staggered with each other, and the staggered distance should not be less than 2m, and the section steel to be pulled out and recovered should be rusted under dry conditions before insertion, and then brushed with anti-friction material on its surface.
8. SMW construction pile process
【Formula】Groove board machine, recycle after stirring
The excavation of the guide trench → setting of the guiding positioning steel plate→ the erection of the SMW mixer, the positioning → mixing and mixing, the residual soil treatment→ the coating of anti-friction materials, the insertion of section steel, the residual soil treatment→ the completion of the construction → the recovery of the section steel
9. Gravity cement-soil retaining wall
【Formula】Convert the deep embedded strong rib board
The deep mixing pile is to mix cement, lime and foundation soil with a mixing machine to form a grid-like structure that overlaps with each other, and can also overlap with each other to form a solid structural form. When the grid form is adopted, a certain area conversion rate should be satisfied, and it should not be less than 0.7 for silty soil, not less than 0.8 for silt, and less than 0.6 for general cohesive soil and sandy soil. Due to the use of gravity structure, the excavation depth should not be greater than 7m. The embedding depth and the width of the wall should also be limited, for silty soil, the embedding depth should not be less than 1.2h (h is the foundation pit digging depth), the width should not be less than 0.7h, and for the silt, the embedding depth should not be less than 1.3h, and the width should not be less than 0.8h.
The 28d unconfined compressive strength of the cement-soil retaining wall should not be less than 0.8MPa. When it is necessary to increase the tensile performance of the wall, reinforcements such as steel bars, steel pipes or bamboo can be inserted into the cement soil pile. The insertion depth of the rod reinforcement should be greater than the depth of the foundation pit. and should be anchored inside the panel. The thickness of the panel should not be less than 150mm, and the concrete strength grade should not be lower than C15.
10. Types and advantages of underground diaphragm walls
【Formula】The sound of steel concrete is pre-presented, and it is suitable for multiple soil layers
There are two types of underground diaphragm walls: prefabricated reinforced concrete diaphragm walls and cast-in-situ reinforced concrete diaphragm walls, usually underground diaphragm walls generally refer to the latter. The underground diaphragm wall has the following advantages: small vibration, low noise, large wall stiffness, small disturbance to the surrounding strata, can be applied to a variety of soil layers, in addition to the local obstacles such as solitary stone, large particles of pebbles and gravel, etc., which affect the efficiency of groove-forming, can be efficient groove-forming for various strata such as cohesive soil, non-cohesive soil, and gravel layer.
11. The underground diaphragm wall is grooved
【Formula】Special section length, plane shape
The construction of the underground diaphragm wall adopts special trenching equipment, along the perimeter of the foundation pit, according to the pre-divided section, and excavates the narrow trench. At present, the slotting machinery used can be divided into grab, impact and rotary types according to its working principle. The length of the slotted groove section of the underground diaphragm wall should be 4~6m. When the groove construction may adversely affect the surrounding environment or the stability of the groove wall is poor, a smaller groove length should be taken. When necessary, it is advisable to use stirring piles to reinforce the groove wall, and when there are special requirements at the corner of the underground diaphragm wall, the plane shape of the unit groove section can be L-shaped, T-shaped, etc.
12. The process flow of underground diaphragm wall
【Formula】The guide trough is cleared and hung and poured
Excavation of guide trench→ construction of guide wall→ excavation of trench → removal of silt and residue at the bottom of the trench→ lifting of the joint pipe→ lifting of the reinforcement cage→ lower conduit→ pouring of underwater concrete→ pulling out the joint pipe
13. A flexible joint of the groove section of the underground diaphragm wall
【Formula】Circular wave wedge mixing
Flexible joints such as circular lock pipe joints, bellows joints, wedge-shaped joints, I-beam joints or concrete prefabricated joints should be used for underground diaphragm walls; flexible joints can also be used when taking measures such as setting up a long crown beam at the top of the underground diaphragm wall, setting structural pilasters at the joint position of the groove section on the inner side of the wall, and rigidly connecting the foundation floor with the underground diaphragm wall.
14. The channel section of the underground diaphragm wall is a rigid joint
【Formula】Perforated steel plate socket ribs
When the underground diaphragm wall is used as the outer wall of the main underground structure, and the overall wall needs to be formed, it is advisable to use rigid joints, and the rigid joints can be one-word or cross-shaped perforated steel plate joints, steel socket joints, etc.
15. The role of the guide wall
【Formula】Heavy mud blocking base to make up for resistance
The guide wall is the main structure to control the accuracy of the trench, and the guide wall structure should be built on a solid foundation, and its main functions are:
(1) Retaining soil: When excavating the trench of the underground diaphragm wall, the surface soil is soft and easy to collapse, so before the unit groove section is excavated, the guide wall plays a retaining role.
(2) Datum function: the guide wall is used as a benchmark to measure the elevation, verticality and accuracy of the underground diaphragm wall excavation.
(3) Load-bearing: The guide wall is not only the support of the trenching mechanical track, but also the fulcrum of the steel cage joint pipe and other shelves, and sometimes bears the load of other construction equipment.
(4) Storage of mud: The guide wall can store mud and stabilize the mud level in the tank. The slurry liquid level is always kept 20cm below the guide wall surface and 1m above the groundwater level to stabilize the tank wall.
(5) Others: the guide wall can also prevent mud leakage, prevent rainwater and other ground water from flowing into the tank; when the underground diaphragm wall is very close to the existing building (structure), it also plays a certain reinforcing role in construction.
16. Performance requirements for guide walls
【Formula】Strong and precise construction
Generally, it is a cast-in-place reinforced concrete structure, which should have strength, stiffness and precision, and meet the construction requirements of slotting machinery.
17. Factors should be considered when determining the form of the guide wall
【Formula】Influence of ground and water charge
The following factors should be considered when determining the form of the guide wall: the geological conditions of the excavation range, the load situation, the possible impact of the construction of the diaphragm wall on the adjacent buildings (structures), and the condition of groundwater. When the construction work surface is below the ground (such as construction below the road surface), the influence on the construction of the temporary support structure should also be considered.
18. The main technical performance indicators of mud
【Formula】PH value, dense sand
In the excavation process, in order to ensure the stability of the groove wall, a special mud wall protection is adopted. The mud should be determined by trial matching according to the requirements of geological and land subsidence control, and the main technical performance indicators such as relative density, viscosity, sand content and PH value of the mud should be inspected and controlled in the mud preparation and trench construction. The mud surface should be 1m above the groundwater level.
Yesterday 速记口诀5/3
1. The role of precipitation
Intercept seepage and stabilize the slope to prevent flow, and lift the shear pit to stabilize and reduce water power
2. Select the engineering precipitation method
Soil and water infiltration depth
3. Engineering precipitation method
Trap jet pipe latent infiltration
4. Collect water and drain it
Ditch well slope seepage pumping subsidence
5. Well precipitation
The construction site is a deep water pit, and the main pump is far from the deep pipe into the soil
6. Vacuum well point and jet well point well formation method
Drilling and punching deep dilute filter seal
7. a tube well
The bottom of the pipe diameter slurry is made into a hole
8. Irrigation
The water drop needs to be protected, and the depth of the well is pressed at the top
9. Factors influencing the characteristics of groundwater seepage and the distribution of precipitation inside and outside the pit
Destination depth aquifer
10. The water separation (interception) curtain of the foundation pit and the precipitation inside and outside the pit are arranged
The inside and outside of the bottom pit, and the pressure in the pit in the layer is reduced
Three days ago, shorthand mantra 5/1
1. Track (commonly known as line) structure
The rail is connected to the sleeper, and the bed is attached
2. The role of track structure
Guided bearer transmission foundation
3. Requirements for track structure
Strong and stable for a long time, the noise surface is smooth
4. Characteristics of track structure
Vibration damping, low dimensional strength, high insulation of curved rails
5. Wheel type
Positive and auxiliary fields, distance overshift
6. Track bed and sleeper
The long tunnel bridge is U high, the ground station in the library, and the long and short pillows are the whole bed
7. Vibration damping structure
Generally, seamless bullet deduction, high vibration buckle short trampoline, special floating plate whole bed
8. The role of sound barriers
Blocking direct blocking transatterioration diffraction
9. Types of sound barriers
Expansion and reverse vibration absorption active drop, straight folding table tilt semi-completely closed, LTY arc deer
Seven days agoShorthand mantra 4/27
1. The form of urban rail transit
Subway light rail up and down
2. Classification of subway stations according to the relative position of the station and the ground
Under the shelf
3. Classification according to the nature of operation and the form of subway stations
The middle (terminal) zone is replaced by a pivot
4. Classification according to the form of subway stations in cross-section of the structure
Rectangular arch oval hooves
5. Classification according to the form of the platform and the form of the subway station
Island side mixing
6. Structural composition of subway stations
The hall is owned by two rooms, and the road crossing is attached to the cold air
7. The main role of the station
Passenger Operations
8. The function of ventilation duct and ground ventilation pavilion
Viman
9. The entrance and exit of the subway station are set
The side room of the hall is worth 1 for 2 people, and the net distance between the scattered should not be three
10. Factors influencing the selection of subway engineering construction methods
The construction of road pipes and environmental financing, and the technical and economic conditions affect the production
Two weeks agoShorthand mantra 4/20
1. Basic requirements for the production of steel beams
Qualification standards: temperature and humidity, assembly welding test and safety acceptance
2. The process flow of steel beam production
Sample line processing and cutting, hole side assembly and welding, friction and collage, three corrections sent to the factory
3. Steel beam manufacturing enterprises should provide documents to the installation enterprises:
Certificates are puzzled, reports are recorded
4. Steel beam installation method
Self-propelled gantry hangs the whole hole, cable cantilever assembly frame, and bracket towing method
5. Selection of steel beam installation method
Cross-river traffic cranes
6. Check the content of the steel beam before installation
The structure is strong and stable, the elevation of the center line hole span, and the zero structure certificate rod is corrected
7. Key points of steel beam installation
The front is clear and anti-deformation, the material is several diameters and long bolts, and the hook is removed to measure the welding bolt screw
8. The key points of the steel beam falling beam are in place
The seats of the former clearance school are dropped
9. On-site coating construction regulations
The coating is sealed and corroded, the temperature and humidity at the bottom of the rust, the weather is sunny and the wind is level 4, and the board shear is anti-dew
10. Make the main control project for installation quality acceptance
The steel welding and coating are tightly connected, and the anti-slip seam is probed and coated with the detector
五周前速记口诀3/30
1. Engineering soil
Surveying and filling organic soil
2. Classification according to the engineering classification standard of soil
Particle group Particle size range 262 075
3. Soil is classified according to the solidity coefficient
Songpu is hard and soft
4. The engineering properties of the soil
strong
5. Performance parameters of soil
Dense hole water limit finger
6. Special soil types
Wet sticky yellow soft frost heave salt
7. Poor soil subgrade should be prepared before reinforcement construction
Check and edit
8. Characteristics of soft soil
The hole is strong and low and shrinks high
9. Soft soil subgrade treatment method
The table is replaced by heavy hanging, and the plastic weaving sand and stone are pressed into the pile
10. Characteristics of collapsible loess
The quality is well developed with loose pores
11. Collapsible loess subgrade treatment method
Anti-seepage soil replacement, strong compacting, chemical pre-soaking and seepage interception
12. Characteristics of expansive soil
Water absorption, water loss, and shrinkage of plastic fingers
13. Expansive soil subgrade treatment method
Improvement of replacement and pre-compression pile, waterproof and moisturizing adjustment
14. Characteristics of permafrost
Thaw and frost heave
15. Key points of seasonal frozen soil subgrade construction
Anti-seepage increase non-freezing material, thickening temperature insulation and control freezing thickness