CN100387790C - Ground caisson construction technology and ground caisson - Google Patents

Abstract

The invention relates to a construction method of a land caisson and the land caisson. A construction method of a land caisson, which first fully or partially seals the bottom plate of the caisson, and then sinks; a land caisson, which has blade feet around the lower part of the box body, and a plurality of high-pressure water guns and water guns are vertically installed on the bottom of the box body Connected with water pipes. The invention has the advantages of "safe construction, economical construction, short construction period and long structural life".

Description

Land caisson construction method and land caisson

technical field

The invention relates to a construction method of a land caisson and the land caisson.

Background technique

The use of caisson foundations in hydraulic engineering is a common construction technology, but there is no precedent for using caisson construction technology in the construction of deep foundations and deep underground structures on land.

The caisson is the main foundation type for building deep foundations and deep underground structures. It is on the ground or in the pit, firstly make an open reinforced concrete cylinder body, after the cylinder body reaches a certain strength, excavate and transport soil in layers regularly in the wellbore, with the gradual decrease of the soil surface in the wellbore, the caisson It is a deep foundation or underground engineering construction technology that overcomes the friction between the body and the soil wall by its own weight, and continuously sinks and settles in place. However, it is not suitable to adopt the caisson process in the following three cases: (1) the upper part is artificially filled, and the lower part is an extremely weak natural soil layer, and the caisson has a large dead weight. Although the soft soil has been reinforced, However, when the caisson goes down through the artificial filling soil layer, due to the friction between the soil and the wall, the reaction force of the blade and foot, and the buoyancy generated when it is not drained, the combined force cannot make the subsidence coefficient drop to a safe standard, that is, sudden subsidence will occur. In the event of an accident (causing over-sinking, tilting, displacement or even overturning); (2) If the caisson process is used, but the foundation reinforcement treatment is required, the cost of the treatment process is relatively high; (3) when the caisson sinks to the design position, Even if the soil in the well is excavated without drainage, but due to the good fluidity of the outer soil, the external pressure is greater than the internal pressure, and the outer soil can not be cleaned up due to backflow.

Just run into the technical problem that is difficult to overcome the excessive sinking coefficient with caisson sinking technology during the construction of the sewage collection well (referring to accompanying drawing 11～16) of Panyu Huangge sewage treatment plant in Guangzhou City, Guangdong Province. The structure of the sewage collection well is a cuboid 20.8 (length) × 18.2 (width) × 16.79 (height), the thickness of the bottom plate is 1m, the thickness of the weighted concrete under the bottom plate is 2-2.5m, the wall thickness is 60cm-120cm, and the weight is 49970K _N (excluding the bottom plate downweight concrete). The soil layer structure is: the first layer of artificially filled sand is 2.0m thick, the second layer of silt (N=1~4) is 10m thick, and the third layer of silty fine sandy soil (N=2~14) is 8m thick. The design bearing capacity of the bearing layer soil at the foot tread of the designed caisson blade is 150KN/m ² . Under the conditions of the soil layer structure and the caisson structure, if the caisson is changed to a caisson, and the soil outside the box is filled to a height of 2m, and the water storage increases the buoyancy of the box, such a caisson construction technology can greatly reduce the project cost. The construction period is shortened, and there is no safety hazard of subsidence.

Contents of the invention

The purpose of the present invention is to overcome the singleness of the prior art and the use of different construction techniques not adapted to local conditions, so there are disadvantages of unsafe construction, high construction cost, long construction period, and short structural life, and provide a land caisson construction Methods and land caissons.

The technical solution of the present invention is: a construction method of a land caisson, which first fully seals the bottom plate of the caisson, or divides the caisson into three parts, and seals the bottom plates on both sides, and the closed part forms an impenetrable space in the box, and the bottom plate The middle part is not closed, remove the obstacles in the soil layer within the sinking range of the caisson, wash the soil under the fully enclosed caisson into mud with high-pressure water, and then pump the mud away, or directly wash away the mud with high-pressure air; or in the unclosed part In the well, the soil is directly excavated manually or by earth-moving machinery, and as the soil layer under the box descends, the caisson is continuously sunk in place.

The present invention also provides a land caisson, the bottom plate of the box body is completely closed, or the caisson is divided into three parts, the bottom plates on both sides are closed, and the closed part forms an impenetrable space in the box, and the middle part of the bottom plate is not closed. There are blade feet around the lower part of the body, and a plurality of high-pressure water guns are vertically installed on the bottom of the box body, and the water guns are connected with water pipes.

The present invention has the advantages of "safe construction, economical construction, short construction period and long structural life", which are embodied in the following points:

1. The traditional caisson construction technology is to pour concrete separately on the well wall and the bottom plate, the structural integrity is poor, the bottom plate has a large bending distance, and the amount of steel and concrete is large; the joint between the well wall and the bottom plate is prone to leakage, such as the storage in the box will corrode Steel bars, the structural life is bound to be short. The caisson process does not have these disadvantages.

2. The caisson process is to bind the bottom plate reinforcement and pour concrete on the ground, which is easy to construct; the well wall and the bottom plate are poured with concrete at the same time, which saves a construction process compared with the caisson, saving construction time and management costs.

3. There is no need to worry about quicksand or backflow during excavation, and the amount of dredging is small.

4. One section of the well wall can be poured, and one section can sink, with good continuity; when the next section is poured, due to sufficient supporting force, the newly poured concrete will not crack due to uneven settlement when it solidifies, ensuring the quality.

5. There is no need for foundation reinforcement treatment, which saves a lot of construction costs, and the economic benefits are particularly obvious; less construction procedures save construction time and management costs.

6. When sinking, it will not be scrapped due to sudden sinking accidents like caissons. There is no safety hazard, and the construction period plan is guaranteed, which eliminates safety and economic risks.

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Description of drawings

Figure 1a-Figure 1c is a schematic diagram of the irregular caisson structure:

Figure 1a is a perspective view of an irregular caisson

Figure 1b is a fully enclosed section view of the irregular caisson bottom

Figure 1c is a partial closed section view of the irregular caisson bottom

Figure 2 is a schematic diagram of the regular caisson structure

Figures 3a-3c are schematic diagrams of several embedding methods for water guns:

Figure 3a shows the connection of the water gun in the caisson

Figure 3b shows the connection of the water gun in the bottom plate

Figure 3c shows the water gun under the bottom plate

Figure 4 is the plane distribution and cross-sectional view of the water guns connected in the bottom plate

Fig. 5a-Fig. 5d are schematic diagrams of several methods of discharging sludge:

Among them, Figure 5a is the discharge of buried tube in the body

Figure 5b is an in vitro drainage

Figure 5c is natural extrusion + blowing high-pressure air discharge

Figure 5d shows the direct digging of the grab bucket

Figure 6 is a schematic diagram of the sludge discharge pipe buried in the body

Figure 7 is a schematic diagram of the sludge discharge pipe buried outside the body

Figure 8 is a schematic diagram of natural extrusion + blowing high-pressure air sludge discharge pipe

Figure 9 is the effect diagram of sealing pipe grouting

Figure 10 Schematic diagram of obstacle pretreatment (a artificial filling soil layer, b silt soil, c muddy silt soil layer)

Figure 11 is a schematic diagram of the structure of the obstacle treatment water gun

Fig. 12 is the schematic diagram of embodiment irregular caisson

Figure 13 is a schematic diagram of caisson counterweight calculation in the first section

Figure 14 is a schematic diagram of caisson weight calculation after concrete pouring in the second section

Figure 15 is a schematic diagram of the position of the counterweight of the caisson (the caisson in the first section of A, and the combined caisson in the first and second sections of B)

Figure 16 is a schematic diagram for calculating the safety factor of caisson sinking (a artificial filling soil layer, b silt soil layer, c muddy silt soil layer, d heightened filling soil layer, e backfill soil before caisson sinking, f water storage, g positioning sandbags)

In the figure: 1. Fully enclosed caisson with bottom plate, 2. Partially closed caisson with bottom plate, 3. Blade foot of caisson, 4. Main connecting pipe, 5. Branch connecting pipe, 6. Water gun, 7. Nozzle, 8. Main pipe, 9. Stop Water steel plate, 10. @150cm lifting ring, 11. Globe valve, 12. Water pressure gauge, 13. Connected to high pressure gas or water, 14. Shrinking steel plate ring, 15. Connected to mud pump, 16. Wrapped in iron mesh geotextile Filter materials such as sand and stone inside, 17. Mud discharge pipe, 18. Soft mud natural extrusion discharge pipe, 19. Water gun cutting position, 20. Concrete slab, 21. Filled cement slurry, 22. Manual reel, 23. Wire rope, 24. Gun shaft, 25. Extended interface, 26. Pulley, 27. Explosion-proof soft inner tube, 28. Steering knuckle, 29. Spring, 30. Wire rope fixed point, 31. Handle, 32. Drain pipe, 33. Centroid Position, 34. The counterweight of the first caisson, 35. The combined counterweight of the first and second sections, 36. Plastic film, 37. The stop position of the first caisson, 38. The excavation grab, 39. The nozzle.

Detailed ways

If the caisson process is adopted on land, the soil within the subsidence range of the caisson must be removed by mechanical removal or other methods.

The invention provides a method for washing the soil under the box into mud by using high-pressure water, then pumping the mud away, and making the caisson continuously sink into place as the soil layer under the box descends.

Using this method, it is first necessary to judge whether there are obstacles in the soil layer in this range, see Figure 10, the judgment method is: in addition to drilling to understand the soil layer, make a probe point every 1.5 meters, and form a well-shaped distribution. The probe can be connected with iron rods, artificial hammer penetration, or other mechanical detection methods. If there are large boulders or other obstacles in the sinking range of the caisson, the treatment methods are as follows: a. Conduct underground blasting first to decompose the large obstacles into smaller ones. The size and position of the obstacle Adjust the distribution and depth of the water gun at this position to ensure that the depth of the water gun is greater than the size of the obstacle, so that the obstacle sinks enough not to hinder the sinking of the caisson; b. After finding the position of the obstacle, first Use a long-rod high-pressure water gun to impact the bottom of the obstacle to sink the obstacle to a safe depth that does not hinder the sinking of the caisson. The structure of the long-bar high-pressure water gun is shown in Figure 11. This high-pressure water gun includes a gun shaft 24 and a gun shaft head. The first joint top of the gun shaft 24 has a handle 31 and a high-pressure water inlet pipe 13. The gun shaft 24 can be twisted at both ends of a multi-section ordinary seamless steel pipe Teeth are connected, and each joint is about 1 meter long, and the joints are connected with the extension interface 25 of the inner twisted teeth. The last section is that the gun shaft head is made up of explosion-proof soft inner tube 27, steering knuckle 28, spring 29, nozzle 39, pulley 26, steel wire 23, and the two ends of explosion-proof soft inner tube 27 are filled with adhesive to make it connect with extension interface 25 and nozzle 39 tightly bound. One end of steel wire 23 is connected to the manual wheel 22 on the gun shaft 24 first joint, passes the pulley 26 on the gun shaft head in the middle, and the other end is fixed on the steel wire fixing point 30 on the nozzle 39. When in use, the gun rod 24 is continuously added, and when the gun head enters the lower part of the obstacle, the manual reel 22 can be turned, and the steel wire 23 drives the gun head to turn, so that the high-pressure water sprayed from the nozzle 39 can directly impact the lower part of the obstacle , causing the obstacle to sink quickly.

The structure of caisson: caisson comprises irregular caisson (Fig. 1a-Fig. 1c) and regular caisson (Fig. 2), floor fully enclosed caisson 1 and partly enclosed caisson 2; The bottom has a blade foot 3 along the periphery. The depth of the blade foot depends on the soil quality and the length of the water gun. The softer the soil, the longer the blade foot. The main function of the blade foot is to guide the vertical sinking of the caisson and isolate the scour area of the water gun.

The composition of the water gun system (see Figure 3a-Figure 3c): it is composed of the main connecting pipe 4, the branch connecting pipe 5, the gun shaft 6, the water gun nozzle 7, the main pipe 8, the water-stop steel plate 9, the lifting ring 10, and the stop valve 11; the branch connecting pipe 5 Connect each water gun, and the main connecting pipe is passed into high-pressure water; the cross-sectional area of the main connecting pipe 4 is greater than 1.2 times the cross-sectional area of the nozzle 7; the cross-sectional area of the branch connecting pipe 5 is greater than 1.5 times the cross-sectional area of the nozzle 7; The cross-sectional area of the nozzle 7 is greater than 10 times. The design allowable pressure of the water gun system is not less than 16kg. The water guns are distributed on a plane and arranged symmetrically.

The method provided by the invention is described in detail as follows:

1. Pre-embedded installation of high-pressure water guns (as shown in Figure 3a to Figure 4)

(1) Water gun material: D=20mm seamless steel pipe can be selected as the gun shaft of the water gun 6, and a round iron (or water pipe plug) with the same diameter is drilled in its center (aperture 5-8mm) as the nozzle of the high-pressure water gun. The connection method can be welded or screwed.

(2) Water gun connecting pipe: Use a plurality of seamless steel pipes with a diameter > 100mm as branch connecting pipes 5 (select the number and size according to the number of water guns) to connect the water guns 6 into one. The branch connecting pipe 5 can be built in or exposed outside (on or under the board).

(3) Buried position of water gun 6: Install one at intervals of 1m along the centerline position of blade foot 3 around the box body, the gun shaft is buried 20cm in the soil, and connected together with a main connecting pipe 4 controlled by an independent valve; One at intervals of 1m, distributed in a well-shaped pattern, and divided into 5 zones, the main connecting pipe 4 in each zone has an independent valve control.

The connecting pipe can be hidden in the bottom plate or exposed under the bottom plate.

Water gun density and rod length basis: Calculate the size and depth of the impact pit according to the softness and hardness of the soil. The softer and looser the soil, the looser the water guns (can be long or short); the harder and stickier the soil, the denser the water guns and the moderate length; the denser sandy soil, the denser and shorter the water guns.

(4) Embedding depth of the water gun 6: The depth of the water gun in different areas is different, and the depth of the water gun in the middle area is 50 cm, and the surrounding area is 30 cm. The water guns in the middle area are called the main sinking working water guns (that is, they are generally opened continuously when sinking); the water guns in the four surrounding areas are called sinking adjustment water guns (when the caisson sinks unevenly or shifts, it is opened or closed by opening or closing). Turn off the water guns in different areas to adjust the degree of soil erosion in the area, so as to achieve the purpose of adjusting the uniform sinking of the caisson or correcting the deviation).

Note: The depth of the water gun at the bottom plate position cannot exceed the depth of the blade foot (except when encountering obstacles and non-pre-settled obstacles, the length of the water gun shaft at this position must be greater than the maximum diameter of the obstacle); the gun shaft must be installed vertically.

2. Installation of mud discharge pipe 17 (as shown in Figure 5a to Figure 8)

Inside (or outside) the bottom plate are installed 4 pieces of mud discharge pipes 17 made of seamless steel pipes with D = 200mm, and the pipe mouth extends 20cm below the bottom plate, and the diameter of the pipe mouth is reduced by 2 to 3cm with a mouth reducer. The mud discharge pipe meets at the casing position (inside or side) and converges into a D=200mm mud discharge pipe, which is then connected to the outside of the casing to be connected with the mud pump (15). The two mud discharge pipes at the wall position are all equipped with an inclined tee with a stop valve 11 at a position 1.0m high from the plate surface, which is used to connect a high-pressure water pump or a high-pressure air pump (13). When the height of the caisson is not large (that is, the mud discharge head is not high), the mud slurry can be discharged directly by blowing high-pressure air or injecting high-pressure water without a dredge pump.

A shrinking steel ring 14 is welded at the position of the air blowing or water injection port in the pipe, so that this position generates negative pressure when blowing air or injecting high-pressure water.

3. Install the water pressure gauge 12 (as shown in Figures 5a-8)

A water pressure gauge 12 is installed in the middle of the bottom plate, which is used to observe the pressure of the water under the plate, so as to guide high-pressure flushing and pumping out of silt. When the water pressure reaches 8kg, the mud pump is opened, and the mud pumping working pressure is 6-8kg. If it is less than 6kg, stop mud pumping, and if it is greater than 8kg, stop flushing.

4. Irregular caisson counterweight (as shown in Figure 13-15)

When the caisson is irregular or asymmetrical, the center of gravity of the caisson is not at its centroid. At this time, the number of counterweights and the placement of counterweights are determined through moment calculations so that the center of gravity of the caisson falls at the centroid.

In Fig. 13: Calculated according to the specific gravity of reinforced concrete 2.50t/m ³ , the eccentricity M=M1-M2=-23.416×2.50=58.54tm. On the side where the torque is small, leave the inner wall of the well 0.5m (that is, 8.9m away from the centroid of the well) as the center line, push the two ends to the middle to a height of 1m, and the total counterweight is 58.54/8.9 (moment arm)=6.58t.

In Fig. 14: eccentricity M=(M1+M3-M2-M4)×2.50=93.166×2.50=232.92t.m. On the side with the smaller torque, 0.5m away from the inner wall of the well (that is, 8.7m away from the centroid of the well), push the two ends of the center line to a height of 1m in the middle, and the total weight of the gravel bag is 232.92/8.7=26.78t.

G1=7.79×1×18.2×9.9=1403.602

G2＝2×6.8×7.79×0.8×6＝508.531

G3=1.2×4.79×16.6×2.0=190.834

G4=0.8×3×16.6×2.2=87.648

G5＝2×3.7×7.79×0.8×0.75＝34.588

G6=0.6×7.79×18.2×1.4=119.093

G7＝2×8.7×7.79×0.8×6.05＝656.043

G8=1.2×4.79×16.6×9.8=935.085

G9＝0.8×3×16.6×10＝398.400

5. Calculation of subsidence safety factor

The formula for the subsidence safety factor is: $K=\frac{Q-B}{f+R}$

K——Sink safety factor, take 1.15～1.25

Q—the weight of the caisson plus the counterweight

B——The buoyancy acting on the caisson (mud buoyancy is greater than water buoyancy)

F - the friction between the caisson and the soil

R—the reaction force of the soil acting on the bottom of the caisson

According to the condition of the soil layer, the subsidence safety factor is calculated layer by layer. In order to meet the safety range of K in the range of 1.15 to 1.25, various conditions can be changed to adjust the parameters in the formula (such as raising or lowering the filling outside the box, increasing water injection or pumping groundwater. Reduce the water head outside the box, change the soil outside the box to increase or reduce the coefficient of friction, increase the additional load inside the box, etc.).

When the weight of the caisson is too large, for safety considerations, concrete must be poured in sections and submerged in sections. Illustrate with the example of irregular caisson subsidence, as shown in accompanying drawings 12-15 and irregular caisson K value calculation demonstration tables 1-5.

6. Stack and position sandbags g (as shown in Figure 16)

In order to make the caisson less prone to displacement during the sinking process, sandbags are stacked at the four corners of the caisson within 3 meters from the corners. The height of the sandbags is 1.5-2.0 meters, the top width is 1.0 meters, and the side slope is 1:1.5.

7. Fill the outside of the box and increase the water level outside the box (as shown in Figure 16)

a. Before the caisson is prefabricated, it is necessary to calculate the foundation bearing capacity of the fill layer. When the fill layer is thin and the foundation bearing capacity is not enough, it is necessary to thicken the fill; b. When the caisson sinks through the fill layer and enters When the natural soil layer is weak, because the bearing capacity of the soil layer suddenly decreases, the K value suddenly increases. In order to reduce the K value, it is necessary to increase the water head outside the box and increase the side friction of the box, so the box is filled with soil and water is stored.

8. The caisson sinks under the water

After everything is ready, start lowering the caisson. First, turn on the high-pressure pump of the middle water gun, and when the water pressure in the tank reaches 8kg, turn on the mud pump, keep the pressure of 6-8kg to pump out the sludge, and observe the sinking of the caisson. If the pressure drops below 6kg soon, two sets of water gun pumps will be symmetrically turned on, and if the pressure is normal at this time, the other two sets of water gun pumps will be turned on and off in turn. If only 2 sets of water gun pumps are added to adjust the pressure and the pressure cannot be increased, then the 4 sets of water gun pumps are fully turned on. If the sinking speed is not fast, the water gun pump at the blade foot position can be turned on. If the pressure is sufficient, the tee of the mud discharge pipe can be connected to high-pressure water or air to speed up the mud discharge.

In the process of flushing and sinking, if uneven settlement occurs and the left side settles quickly, turn off the left side to adjust the water gun pump, and so on. If offset occurs, turn off the adjusting water gun pump at the offset position and turn on the adjusting water gun pump at the reverse position to make the caisson tilt. When the position of the blade foot returns to half, stop adjusting the water gun pump at the reverse position and turn on the offset Adjust the position of the water gun pump to restore the balance of the caisson. Continuously tilting and balancing the caisson can reset the caisson.

When the caisson sinks to 100cm away from the design elevation, stop the high-pressure flushing, continue to pump out the mud, and pay attention to observe the sinking of the caisson. If the discharged mud concentration is high, the sinking of the caisson is still not in place. The amount of difference, control the time of flushing again, continuously flushing with a small amount of water and mud discharge process, so that the caisson sinks in place.

9. Skills for improving the bearing capacity of the bearing layer: When the bearing capacity of the original soil layer at the bottom of the box is not enough, and the sand content in the soil layer within the subsidence range is high, the water gun rod can be lengthened to a suitable The length is that the dredging pump is not turned on when flushing high-pressure water, that is, the flushing and mud pumping are staggered, the purpose is to allow the coarse sand to settle naturally, continuously accumulate into a sand layer of a certain thickness, and increase the bearing capacity of the bearing layer. The cost of reinforcement treatment at the bottom of the box is saved.

10. The high-pressure water gun pipe and the mud discharge pipe are filled with expanded cement slurry to seal (as shown in Figure 9)

After the caisson is in place, replace the high-pressure water pump with a high-pressure air pump, and blow high-pressure air to the bottom of the caisson to completely remove the silt under the caisson. Empty the mud slurry in the mud discharge pipe, then replace the mud pump with a high-pressure grouting machine, pour the expanded cement mortar from the mud discharge pipe under the bottom plate of the caisson, calculate the amount of grouting, so that the position of the suction port of the mud discharge pipe can form a cement bag , close the mouth of the nozzle; the high-pressure water gun pipe also uses the same method to pour 1: 2.5 expansion cement slurry (with a filter screen to isolate coarse particles) into the seal. After the pressure gauge is removed, the expansion cement slurry is also poured, then the valve is closed, the protruding pipe is cut off, and the reserved pit is filled with concrete.

Calculation basis of grouting amount: (1) The bearing capacity of the bearing layer under the box; (2) The gravity that needs to be increased when there is an anti-floating requirement; (3) If there is no special requirement, the pipe can be filled.

11. Various mud discharge methods (as shown in Figure 5-8)

1. Mud pump pumping mud: The soil is turned into mud under the impact of high-pressure water, and then pumped out by the mud pump.

2. Blowing high-pressure air or injecting high-pressure water to discharge mud: Under the impact of high-pressure water from the water gun, the soil becomes mud, and the high-pressure gas blown by the air gun installed in the mud discharge pipe or the high-pressure water pumped by the water pump pumps the soil into mud. Mud discharge.

3. Natural extrusion + blowing high-pressure air to discharge mud: first open the three-way stop valve of the mud discharge pipe, let the soft soil be discharged naturally by extrusion under the action of the caisson's own weight, and the soil can be immediately removed out of the box , but when the soft soil cannot be extruded by the weight of the caisson alone, the soft soil can be allowed to flow out naturally and temporarily stay in the box to increase the gravity of the box so that the soft soil can be squeezed out naturally again, which saves pumps Water costs are at the same time less effluent. When the soft soil can no longer be extruded, close the three-way stop valve, open the high-pressure water gun to flush water, and at the same time blow high-pressure air or pump high-pressure water at the three-way position to discharge the mud slurry.

4. The partially closed caisson with the bottom plate can directly excavate the soil in the unsealed well with manual or grabbing equipment, and the soil under the other bottom plate is naturally squeezed and moved into the unsealed well by the gravity of the caisson.

Claims (5)

1. land caisson job practices, it is characterized in that carrying out totally-enclosed earlier to Bottom plate of sinkbox, or caisson is divided into three parts, the base plate of closed on both sides part, enclosure portion forms the space that does not connect in casing, and the base plate mid portion does not seal, remove the interior obstruction of soil layer in the caisson sinking scope,, again mud is taken away, or directly washed away mud native scour out mud under the totally-enclosed caisson with water under high pressure with high pressure gas; Or in the well of enclosure portion not, directly cut the earth with artificial or digging machine, along with the decline of soil layer under the case, it is in place that caisson is constantly sunk.

2. land as claimed in claim 1 caisson job practices is characterized in that the sword pin is arranged at said caisson bottom.

3. land as claimed in claim 1 caisson job practices is characterized in that may further comprise the steps:

(1) at caisson body pre-buried installation giant in bottom and mud pipe;

(2) WG is installed in the Bottom plate of sinkbox centre position;

(3) to the caisson center of gravity not in the caisson counterweight of position of form center;

(4) be calculated as follows the sinking safety factor:

Sinking safety factor formula is: $K=\frac{Q-B}{F+R}.$

K---sinking safety factor gets 1.15～1.25

Q---the caisson deadweight adds counterweight

B---act on the buoyancy of caisson

Frictional force between F---caisson and soil

R---soil acts on the counter-force at the bottom of the caisson

(5) stack the location sandbag;

(6) case bankets outward;

(7) improve the outer water level of case;

(8) caisson bath spoil disposal sinks or does not seal in the well and cut the earth;

(9) pre-pipe laying grouting sealing.

4. land caisson, it is characterized in that box bottom is totally-enclosed, or caisson is divided into three parts, the base plate sealing of two side portions, enclosure portion forms the space that does not connect in casing, the base plate mid portion does not seal, and the sword pin is arranged at the bottom around casing, the bottom vertical of casing is equipped with many giants, and water pipe is communicated with between the hydraulic giant.

5. land as claimed in claim 4 caisson is characterized in that the casing center installs a pressure gauge.

Images