JPS5841377B2 - Foundation pit excavation method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for excavating a foundation shaft for a steel tower or the like.

Here, a steel tower foundation will be explained as an example. Generally, when it is necessary to dig a deep foundation shaft for a steel tower or the like, an enlarged bottom section is often provided below the shaft.

This is because steel tower foundations are subject to large uplifting forces in addition to compressive forces due to wind, etc., so in order to increase uplifting capacity, a deep foundation is used.

When excavating a deep foundation pit, the excavation method shown in FIG. 1 or 2 has conventionally been used.

In the construction method shown in FIG. 1, each time a predetermined depth of approximately 0.5 m is excavated, a liner plate 1 is used to form a landslide prevention cylinder (hereinafter referred to as a cylinder) with a predetermined diameter.

) 2 was being formed while excavating.

This cylindrical body 2 naturally withstands earth pressure from the outer periphery.

Here, the liner plate 1 is a corrugated steel plate bent into an arc shape with flange portions 1a on the top, bottom, left and right, as shown in FIG.
was formed.

They are assembled with bolts through bolt holes 1b drilled in the flange portion 1a to form a cylindrical body.

However, with this excavation method, a gap α is created between the cylindrical body 2 and the inner wall of the shaft part 3, making it impossible to retain the soil, which causes the ground to loosen and the earth and sand to collapse, making it difficult to excavate in deep areas. Met.

Furthermore, if an attempt is made to form the widened bottom part 4 below the shaft part 3, the vertical earth pressure above the widened part 4a will be applied directly to this part, requiring an earth retaining device with a very large earth pressure resistance capacity, and sometimes causing severe damage. It also led to an accident.

Here, the earth retaining device is a device that maintains the vertical earth pressure above the expanded bottom portion, and is made of, for example, a wire 9 or the like on which a diagonal pile 8 is stretched and held.

In the construction method shown in FIG. 2, in order to solve the problems of the construction method shown in FIG. , a jack pressure ring (hereinafter referred to as pressure ring) having a cylindrical body 6 attached to its inner periphery.

) 7 to press the outer surface of the cylindrical body 6 against the inner wall of the combing section 3.

In this construction method, the outer surface of the cylindrical body 6 presses against the inner wall of the combing section 3 to maintain earth pressure, so compared to the construction method shown in Fig. 1,
The ground does not easily loosen, making it easy to excavate at deep locations.

However, due to the inaccuracy of the circular dimensions of the combing section 3 and the unevenness of the inner wall due to soil quality, even if the cylinder body 6 is fully expanded by the pressure ring 7, the cylinder body 6 is not flexible. This resulted in uneven pressure and gaps formed at the joints of the corrugated steel sheets.

For this reason, there are parts in the circumferential direction where the earth pressure cannot be maintained, and it cannot necessarily be said that the earth pressure is maintained completely at the outer peripheral portion of the cylindrical body 6.

In view of the above, the present invention is capable of more completely retaining the earth pressure at the outer periphery of the cylindrical body for preventing landslides, making it easier and safer to perform deep excavation work, and furthermore, providing an earth retaining device for the expanded bottom part. The purpose of this invention is to provide a foundation pile excavation method that minimizes the vertical earth pressure resistance of the foundation pile.

Hereinafter, one embodiment of the present invention will be described based on illustrated examples.

Here, we will take as an example a case in which the cylindrical body is formed from the liner plate 1, but there may also be a case in which a flat steel plate is bent at a predetermined curvature and flanges are formed on the top, bottom, left and right sides of the end, or a cylindrical body is formed by the corrugated steel plate 5. It can also be applied to the case where a cylindrical body formed so as to be able to receive earth pressure at its outer circumference, such as one formed to be expandable and contractible and fitted with a pressure ring 7, is used.

The working steps of this embodiment are carried out as follows.

(I) First, a circular comb 3a with a depth of about 0.5 m is excavated.

(FIG. 4A) (It) A ring-shaped tube (flexible) having flexibility as shown in FIG. The liner plate 1 is assembled to form a cylindrical body 2a while the pressurized hollow body 11 is attached through the trough portion 1c of the liner plate 1 as shown in FIG.

(FIG. 4B) (G) Air is simultaneously injected into each tube 11 through the air nozzle 10 using the compressor 12 to bring the tube 11 to a predetermined pressure.

(Fig. 4C) ■ Perform the next stage of excavation, and perform the above (I) to (
Repeat the process in g) to continue excavation.

(Fig. 4D) (V) When providing an expanded bottom portion, after excavating to a predetermined depth, for example, as in the conventional case, a retaining ring 21 is provided at the lowest node of the cylindrical body 2, and the retaining ring 13 is used to secure the diagonal pile 8.
A large number of slanted piles 8 are driven in and hung from above with wires 9.

The expanded bottom portion 4 is excavated while the vertical earth pressure from above is not received by the inclined piles 8.

(Fig. 4E) In the above, the liner plate 1 is a commercially available product, and the size is 0.5 m in length, 1.0 m in width, and 2.7 to 4.5 m in thickness.
Select from mountains depending on soil quality and shaft diameter.

In the left and right flanges 1a of the liner plate 1, cutouts 13 are formed along the troughs 1c at locations corresponding to the troughs 1c of the plate.

In addition, an air nozzle 10 is installed in one part of the liner plate 1.
A hole 1d is made so that it can be protruded inward.

The tube diameter of the tube 11 is approximately 3 to 4 times the depth of the valley portion 1c of the liner plate 1 (15 to 20 cm).

An example of the material for the tube 11 is one made of fibers made of rubber or vinyl to provide airtightness, such as commercially available pump hoses.

The standard air pressure injected into the tube 11 is equivalent to the static earth pressure at the bottom of the combing where the pressure is applied.

The unit weight of soil is γ (t/m'), and the depth of combing is H (m).
, the coefficient of static earth pressure is K.

, if the loss over time is η, then the injection air pressure P.

is as follows. Po−(1+η)γHK.

At this time, η=0.1~0.2, γ=1.8 (t/
m”), H=20m, Ko=0.5, then Po=
:=20t/m' (2kg,/cfIL).

In addition, when forming the expanded bottom part 4 below the leveling comb 3, in order to reduce the withstand earth pressure of the earth retaining device that maintains the vertical earth pressure above the expanded bottom part, the above formula K is used as an intermediate value between the static earth pressure and the passive earth pressure. .

Earth pressure coefficient K corresponding to . p=1.5 to 2.5.

In this way, the tube 11, which is interposed between the cylindrical body 2 formed by the liner plate 1 and the inner wall of the comb 3 and into which air is injected to a predetermined pressure, is connected to each trough 1 of the liner plate 1.
held at c.

Since the diameter of the tube 11 is much larger than the depth of the trough, the outer circumference of the tube 11 presses against the inner wall of the comb 3.

At this time, since the tube 11 is flexible, the combing 3a
Even if the dimensions of the excavation are inaccurate, or even if the inner wall is uneven, the inner wall will be pressed evenly in the circumferential direction, as shown in Figure 8, and the earth pressure at the iron part will be completely eliminated. to hold.

In the above embodiment, air was used as an example of the pressurized fluid, but
It may be a fluid such as water.

Further, although a tube-shaped hollow body is taken as an example, as shown in FIG. 7, the inner side may be shaped along the troughs, and the outer side may be a flat ring-shaped mat 17.

Furthermore, when the outer circumferential surface of the cylindrical body is a flat plate or a spiral recess is formed, the tube may be spirally wound and fluid may be injected from the upper end or the lower end.

In addition, in the above embodiment, the diagonal pile 8 was used as an earth retaining device for the expanded bottom section 7, but any widened bottom excavation method can be applied, such as the method shown in Figs. 9 and 10, since vertical earth pressure can be maintained perfectly. can.

The construction method shown in FIG. 9 involves press-fitting a rectangular cylindrical steel frame 19, then press-fitting a steel plate 20 between the upper ends of the steel frame 19 using an oil jack, and then draining the earth and sand inside the steel frame 14 and below the steel plate 20. Forms an enlarged bottom part.

In the construction method shown in FIG. 10, before driving the diagonal piles, mortar 18 is poured into the outer periphery of the cylinder 2a at the lowest joint to fix the cylinder 2a and the ground.

After the mortar 18 is cured for 24 hours or more, a retaining ring 21 is attached to the cylindrical body 2a at the lowest joint.

Next, the diagonal pile driving hole 23 is opened and the diagonal pile 22 is inserted.

The oblique pile 22 has a hole 22a formed on its outer periphery.

Cement milk is injected into this slanted pile 22 and permeates into the ground through the hole 22a.

After curing the cement milk for more than 24 hours, the inclined pile 22
Firmly fasten using plates, etc.

After this, bottom expansion excavation will be carried out.

Since the method for excavating a foundation pit of the present invention is the method described above, it has the following effects.

(a) Since it is a flexible pressurized hollow body and presses the entire circumference of the inner wall uniformly, earth pressure can be maintained more completely, making it easier and safer to excavate in deep areas.

(b) Fluid pressure can be controlled depending on the depth of the pit, and the soil can be maintained in a manner appropriate to the location.

(c) Since the cylindrical body is not directly pressed against the hole, the number of times the cylindrical body can be reused can be increased.

(a) When applied to expanded-bottom foundation piles, the vertical earth-holding capacity of the earth retention device above the expanded-bottom part is small, and the earth-hold can be maintained according to the depth, so there is almost no worry about soil collapse. Work safety is greatly improved.

[Brief explanation of drawings]

Figures 1 and 2 are schematic sectional views showing the conventional excavation method for foundation shafts, Figure 3 is a perspective view of a liner plate, Figure 4 is a process diagram showing the method of the present invention, and Figure 5 is a diagram of the method of the present invention. A perspective view of the tube used in the method, FIG. 6 is a partially cutaway perspective view of the tube attached to the liner plate, FIG. 7 is a partially cutaway perspective view of the mat used in the method of this invention, and FIG. 8 9 is a sectional view of the main part when the tube is brought to a predetermined pressure, FIG. 9 is a perspective view showing an example of the bottom-expanding excavation method used in the construction method of the present invention, and FIG. 10 is a schematic sectional view showing another example. be. 1...Liner plate, 2...(± collapse prevention) cylindrical body, 2a...Cylindrical body, 3...
...Threading section, 3a... Hole clearing, 4...
Expanded bottom part, 6... Cylindrical body, 8... Oblique pile,
9... Wire, 11... Tube (hollow body for pressurization), 17... Mat, 19...
... Steel frame, 20 ... Steel plate, 21 ... Retaining ring, 22 ... Oblique pile.

Claims (1)

[Scope of Claims] 1. A method of excavating a foundation shaft while forming a landslide prevention cylinder that can withstand earth pressure from the outer periphery to a predetermined depth each time the earthslide prevention cylinder is formed. When doing
A flexible pressurizing hollow body is arranged on the outer periphery of the landslide prevention cylindrical body, fluid is injected into the pressurizing hollow body to bring it to a predetermined pressure, and the inner wall of the pit is moved around the outer periphery of the pressurizing hollow body. A method for excavating a foundation shaft, which is characterized by pressing down on the part. 2. In a method of excavating a foundation pit while forming a landslide prevention cylindrical body that can withstand earth pressure from the outer periphery each time a predetermined depth is excavated, when forming the landslide prevention cylindrical body, A flexible pressurizing hollow body is placed on the outer periphery of the cylindrical body, fluid is injected into the pressurizing hollow body, the pressure is set at a predetermined pressure, and the inner wall of the pit is pressed by the outer periphery of the pressurizing hollow body. A method for excavating a foundation shaft having an expanded bottom portion, characterized in that after preventing landslides in the shaft, the shaft is further excavated, an earth retaining device is installed, and the bottom of the shaft is widened and excavated to form an expanded foundation pile.