Important projects or supporting structures are part of the main structure

Excavation depth is greater than 10m

The distance between the foundation pit and adjacent buildings and important facilities is within the excavation depth.

Within the scope of the foundation pit, there are historical cultural relics, outstanding modern buildings, important pipelines and other foundation pits that need to be strictly protected.

① Start the observation after the foundation is completed and the basement is completed. For high-rise civil buildings, observation is conducted once every 2-3 floors.

② If the construction height increases evenly, the measurement should be performed once each when increasing the load by 25%, 50%, 75%, and 100%;

③Test once each during temporary shutdown, shutdown and resumption of work, and once every 2-3 months during the shutdown period;

④Number of observations during the post-completion operation phase: 3-4 observations in the first year. Observations are made 2-3 times in the second year. Once a year starting from the third year until the settlement reaches a stable state and meets the observation requirements.

⑤ When the maximum settlement rate in the last 100 days is less than 0.01-0.04mm/d, it can be considered that a stable state has been reached

The four corners of the building, the four corners of the core tube, large corners and every 10-20m along the exterior wall or every 2-3 column bases;

(2) Both sides of the intersection of high-rise and low-rise buildings, old and new buildings, and vertical and horizontal walls;

(3) For buildings with a width greater than or equal to 15m, internal wall points should be set in the middle of the load-bearing internal partition wall, and ground points should be set in the center and around the indoor floor;

(4) On each or part of the column base of frame structures and steel structure buildings or along the longitudinal and transverse axes;

(5) The four corners and the middle of the bottom plate of raft-shaped foundation, box-shaped foundation or structural part close to the foundation;

(6) There should be no less than 2 monitoring points for each large structural column of super high-rise buildings and large grid structures, and they should be arranged symmetrically.

① The deformation observation points on the foundation pit retaining wall or the top of the foundation pit slope are arranged along the periphery of the foundation pit, with points set up in the middle of the periphery, at the sun corners, and at locations with large stress changes; The horizontal spacing between monitoring points should not be greater than 20m, and the number of monitoring points on each side should not be less than 3; horizontal and vertical monitoring points should share the same point.

② The horizontal displacement monitoring points of the foundation pit retaining wall or deep soil mass should be arranged in the middle part of the retaining wall, at the sun corners and representative parts. The horizontal spacing between monitoring points is 20-60m, and each side should not be less than 1 indivual.

No less than 3 times

clay

silty clay

Precipitation or water-stopping curtains can be used

Piles should be formed at intervals. The distance between completed piles and adjacent piles should be greater than 4 times the pile diameter or the interval should be greater than 36 hours.

The grouting height at the top of the pile is >=500mm; underwater grouting increases the strength level by one level compared with the design.

The water-stop curtain adopts single-axis, double-axis, or three-axis cement and soil mixing piles; the net distance between the piles and the row of piles is less than 200mm.

Set up guide walls

The length of the tank section is 4~6m. The mud in the tank should not be lower than 0.3m of the guide wall and 0.5m higher than the groundwater level.

Conduit method for pouring mud

grouting

(1) The slope ratio (ratio of vertical height and horizontal width of the wall) of soil-nailed walls and prestressed anchor-composite soil-nailed walls should not be greater than 1:0.2.

(3) The horizontal and vertical spacing of soil nails should be 1-2m; the inclination angle of soil nails should be 5°-20

(4) The diameter of the soil nail hole for the grouting type steel bar should be 70-120mm; the soil nail steel bar should be HRB400 and HRB500 steel bars with a diameter of 16-32mm; the soil nail hole grouting material can be cement slurry or cement mortar, the strength is It should not be lower than 20MPa.

(5) The outer diameter of the steel pipe used for soil nailing should not be less than 48mm, and the wall thickness should not be less than 3mm.

(1) The construction of soil nail walls must follow the principle requirements of “advanced support, layered and segmented, layer by layer construction, time-limited closure, and over-excavation is strictly prohibited”. 【201927】

(2) After the construction of each layer of soil nails, the pull-out resistance of the soil nails should be randomly checked as required.

(3) After excavation, the free surface should be closed in time, and the placement of soil nails and the spray concrete surface layer should be completed within 24 hours. When excavating silty soil, the placement of soil nails and shot concrete surface layer should be completed within 12 hours.

(4) The lower layer of soil can be excavated 48 hours after the grouting of the upper layer of soil nails is completed.

(5) Hole-forming grouting type reinforced soil nails should be constructed using two grouting processes. The first grouting should be cement mortar, and the grouting amount should not be less than 1.2 times the borehole volume. The second grouting can only be carried out after the first grouting has initially set; the second grouting should be pure cement slurry. The grout volume is 30%-40% of the first grouting volume. The grouting pressure should be 0.4-0.6MPa.

(8) The maximum particle size of aggregates in shotcrete should not be greater than 15mm. The operation should be carried out in sections and in sequence, from bottom to top within the same section, and the thickness of one injection should not be greater than 120mm.

(9) The thickness of the protective layer of soil nail reinforcement should not be less than 25mm

(1) The interlocking piles are constructed in two stages: I (Pile A) and II (Pile B, full-length reinforcement). During the construction of the II piles, a hole-forming machine is used to cut the I pile body to form a continuous interlocking pile wall.

(2) Occlusal cutting is divided into soft cutting and hard cutting.

(3) For piles using soft cutting technology, the construction of piles in sequence I should be completed before the final setting of piles in sequence I. Super retarded concrete should be used in sequence I, and the retarding time should not be less than 60h; the 3d strength of concrete should not be greater than 3MPa; soft cutting Ordinary concrete should be used for sequence II piles and hard-cut sequence I and II piles.

(4) During segmented construction, a sand-grouted II sequence pile should be set at the end of the construction section for closing the retaining piles.

The safety level of the side wall of the foundation pit is level two or three; it is suitable for silty soil and silt foundation pits, and the depth should not be greater than 7m.

(1) The steel-cement-soil mixing wall should be constructed using a three-axis mixing pile driver. Construction sequences such as jump drilling, unilateral extrusion, and advance drilling and drilling can be used. The overlap time interval between piles should not be greater than 24 hours.

(2) Before inserting the section steel that is to be pulled out and recycled, it should be derusted in dry conditions and then painted with friction-reducing material on its surface. The gap left after the steel is pulled out should be filled with grouting in time.

(3) The pile body strength of the cement-soil mixing pile should be tested before excavation of the foundation pit. It should be determined by the strength test method of slurry test block, or the strength test method of drilling the pile core.

(1) Foundation pit projects with complex engineering geology and hydrogeological conditions; (2) Neighboring important buildings, Foundation pit projects with serious consequences of damage to facilities, pipelines, etc.; (3) Foundation pit projects that have been reorganized and implemented after serious accidents have occurred; (4) First- and second-level foundation pit projects that adopt new technologies, new processes, new materials, and new equipment. Pit projects; (5) Other foundation pit projects that need to be demonstrated.

Precipitation depth 6, multi-level light well point 6~10m

The machine is simple, the cost is low, and the slope stability is improved

Precipitation depth 8~20m

The equipment is simple, the drainage depth is large, and compared with 1, it has less precipitation equipment, less earthwork excavation, and lower costs, etc.

vacuum

non-vacuum

Depth greater than 6m,

water cutoff curtain

Prevent the impact of water pumping on surrounding buildings

Soil nail wall: advanced support, layered and segmented, layer-by-layer construction, time-limited closure, over-excavation strictly prohibited

When using machinery to excavate foundation pits, in order to avoid damaging the base soil, the foundation pit should be A 200-300mm thick soil layer is reserved above the elevation for manual excavation.

No support: sloping excavation

With support: central island type, basin type excavation, reverse method excavation

The layering thickness is controlled at 3 meters, and the length of layering sections during soil nail wall construction does not exceed 30m.

A single-section pile must be lifted at two points, and the lifting point must be 0.2 pile length from the end. It is strictly prohibited to drag the pile.

The pile end elevation control is mainly controlled, and the penetration is supplemented; the pile end reaches hard, hard plastic clay, weathered rock, etc., and on the contrary

When the penetration reaches the design requirements but the pile end elevation does not, hammering should be continued for 3 cycles, and it shall be confirmed that the penetration of 10 blows per cycle is less than the value specified in the design.

Sudden tilt and dislocation

There are no special changes in soil conditions, and the penetration gradually increases or suddenly increases

When the pile hammer jumps up, the pile body will rebound.

1) When making piles, the bending of the pile body exceeds the regulations, the pile tip deviates greatly from the longitudinal axis of the pile, and the pile body tilts or bends during the sinking process.

2) After the pile is inserted into the soil, it encounters a large hard obstacle and pushes the pile tip to one side.

3) If the stable pile is not vertical, press it into the ground to a certain depth and then use the walking frame method to correct it to make the pile bend.

4) When constructing two-section piles or multi-section piles, the two connected piles are not on the same axis, resulting in bending.

5) The concrete used to make the piles is not strong enough, and cracks or fractures in the piles were not discovered during the stacking and lifting processes.

1) Before construction, the obstacles under the pile positions should be cleared, and if necessary, use a probe to understand each pile position. After inspecting the pile components, it is found that the pile body is bent beyond the standard or the pile tip is not on the longitudinal axis and should not be used. 2) Correct the non-verticality in a timely manner during the pile stabilization process. When connecting the piles, ensure that the upper and lower piles are on the same longitudinal axis. The joints must be constructed in strict accordance with the operating procedures. 3) During the stacking and lifting of piles, relevant regulations must be strictly followed. If cracks exceeding the regulations are found, they must not be used. 4) The processing method should be studied together with the designers. According to the engineering geological conditions, the upper load and the structural part where the piles are located, pile replacement methods can be adopted. One or two piles can be added on both sides of the axis

Dense pile groups should not be operated continuously 24 hours a day, and the daily downtime should not be less than 8 hours.

friction, pile top elevation

End bearing friction: elevation is the main factor, pressure is the auxiliary factor,

End bearing: terminal pressure is the main one, elevation is the supplementary one

The stable pressure pile pressing force is not less than the final pressure

Depth >8m, re-press 2~3 times; <8m, re-press 3~5 times

The specific gravity of mud is not enough,

The water head is not high enough or there is pressurized water in the hole.

The casing is buried too shallowly and the lower hole collapses

The footage speed is too fast or the idle time is too long or the rotation speed is too fast.

Impact cone tilts to impact hole wall

When blasting the isolated rocks and probe rocks in the hole, the amount of explosives was too large, causing great vibrations.

Solution

Raw soil pulping

end bearing pile

friction type

Resistance to pull-out and horizontal load

The amount of grouting meets the design requirements

The grouting pressure reaches the design value and the grouting volume >=80%

Satisfy one of them

Ultimate bearing capacity of single pile

Single pile bearing capacity and pile integrity

Single pile vertical compressive static load test

Single pile vertical pullout static load test

Single pile horizontal static load test

Core drilling method

low strain method

high strain method

sonic transmission method

integrity

summary

Static load test

learn

High strain method vertical compressive bearing

The binding points are formed into a figure eight shape

Same structure

Construction organization design content

construction regulations

1.2 times the amount required per unit time

The dosage of fly ash is not more than 50%, the dosage of slag powder is 40%, and the dosage of the first two together is 50%.

Collapse<180, water<170

1. Large-volume concrete construction should adopt overall layered or push-type continuous pouring construction. 2. When horizontal construction joints are set up in large-volume concrete construction, the location and interval time should be determined according to design regulations, temperature crack control regulations, concrete supply capacity, steel bar engineering construction, embedded pipe installation and other factors. 3. When using the jump method, the maximum one-way size of the jump block should not be greater than 40m, the construction time between jumps should not be less than 7 days, and the jump joints should be set and treated according to the requirements of construction joints. 4. The temperature of concrete entering the mold should be controlled at 5-30℃. 5. Mass concrete pouring should comply with the following regulations: 1) The thickness of the concrete pouring layer should be determined based on the depth of action of the vibrator used and the workability of the concrete. It should be 300-500mm for continuous overall pouring. Over-vibration and leakage vibration should be avoided during vibration. 2) For overall layered continuous pouring or push-type continuous pouring, the interval time should be shortened, and the second layer of concrete should be poured before the initial setting of the first layer of concrete. The interval time between layers should not be greater than the initial setting time of concrete, which should be determined through testing. When the interval time between layers exceeds the initial setting time of concrete, the layers should be treated as construction joints. 3) Concrete pouring should be continuous and orderly, and construction joints should be reduced. 4) Concrete should be pumped and vibrated twice. 6. The large-volume concrete pouring surface should be troweled multiple times in a timely manner. 7. Large-volume concrete should adopt thermal insulation and moisturizing maintenance, and thermal insulation and moisturizing maintenance should comply with the following regulations: 1) A dedicated person should be responsible for the insulation and maintenance work, and test records should be carried out; 2) The duration of moisturizing and curing should not be less than 14 days, the integrity of the plastic film or curing agent coating should be checked frequently, and the concrete surface should be kept moist; 8. When there is sudden heavy rain or strong wind during the large-volume concrete pouring process, construction joints should be left in reasonable parts of the structure in time, and concrete pouring should be stopped; the concrete that has been poured but has not hardened should be covered immediately, and rainwater is strictly prohibited from directly washing the newly poured concrete. of concrete.

Concrete test sampling

Temperature detection and control