JPS5949968B2 - Sand pile construction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sand pile construction method used in soft ground improvement work, which involves constructing a large number of sand piles in soft ground.

In order to construct sand piles in soft ground, especially sand piles whose diameter is larger than the diameter of the hollow pipe for sand pile construction, conventionally, the hollow pipe for sand pile construction is placed at a predetermined depth in the soft ground. Then, sand is supplied into the hollow tube, and before the hollow tube is pulled out for an appropriate length, the sand inside the tube is discharged into the gap created below, and then the hollow tube is re-penetrated and the discharged sand is removed. In addition to the so-called composer method, which is a construction method in which the operation cycle of compacting and enlarging the surrounding ground is repeated in sequence upwards, sand is often used to fill soft soil with sand into a hollow pipe penetrated to a predetermined depth. Another method is to pull the hollow pipe upwards and forcibly discharge, extrude, and compact the sand inside the pipe from the lower end of the pipe into the soft ground using a vibrating body, a screw, a vertically moving extrusion mechanism, etc. using a device installed in the hollow pipe. ing.

In the process of drawing out the hollow pipe for sand pile creation using the conventional method described above, a considerable amount of driving energy is required to create the sand pile, and the diameter is considerably thicker than the diameter of the hollow pipe (the diameter of the enlarged sand pile). Creation 1. Creation of sand piles from considerable depths in soft ground and construction of sand piles using hollow pipes with a particularly large diameter require a particularly large amount of driving energy.

Furthermore, with regard to the sand facing the bottom end of the hollow tube, consideration has been given to using sand that does not contain water as much as possible in order to ensure smooth discharge from the bottom end of the tube.

The present invention can save the driving energy of the hollow pipe in the construction method of the above-mentioned conventional sand pile, especially the sand pile whose diameter is larger than the diameter of the hollow pipe, and the cost required for using dry sand for the sand. This project provides a sand pile construction method based on a new technical idea that can eliminate the disadvantages of sand pile construction.

That is, the sand pile construction method of the present invention, as illustrated in the explanatory diagram of FIG. ,
Hydrated sand 3 with a water content near saturation is maintained in the hollow tube 1 in a fluid state by vibration, etc., and water is added inside the hollow tube while the hollow tube 1 is being pulled out. The pressure of the sand 3 at the lower end of the hollow tube 1 is controlled to be greater than the passive earth pressure of the soft ground 2 at the lower end of the hollow tube 1, and the hydrated sand 3 in the hollow tube 1 is applied to the soft ground from the lower end of the hollow tube 1. This method is characterized in that a sand pile 3 whose diameter is larger than the diameter of the hollow pipe 1 is created by discharging it into the sand pipe 2.

In addition, in FIG. 2, the hollow pipe 1 for sand pile construction shows one embodiment, 4 is a vibrating pile driver attached to the top of the hollow pipe 1, and 5 is the top of the hollow pipe 1. This is a hopper installed in

The present invention will be further described in detail below.

According to experimental research by the inventor of the present invention, hydrated sand 3 with a water content near saturation becomes fluid due to vibration, etc.
The hydrated sand 3 thus maintained in a fluid state within the hollow tube 1 behaves like a fluid.

Utilizing this property, in the process of pulling out the hollow tube 1 that has penetrated the soft ground 2 to a predetermined depth, the hollow tube 1
The pressure of the hydrated sand 3 at the lower end of the hollow tube 1 is controlled to be greater than the passive earth pressure of the soft ground 2 at the lower end of the hollow tube 1. The basis of the present invention is to discharge water from the lower end of the hollow pipe 1 into the soft ground 2.

Next, first, a description will be given of the balance between the pressure of the hydrated sand 3 in the tube at the lower end surface of the hollow tube 1, that is, the internal pressure, and the pressure of the soft ground 2 at the lower end of the hollow tube 1, that is, the external pressure.

Figure 1 shows the sand length of sand 3 in the pipe (hydrated sand with a water content near saturation maintained in a fluid state) corresponding to the earth pressure at the bottom end of the hollow pipe 1, with respect to the depth 2 at the bottom end of the hollow pipe 1. This is an example of a case where the earth pressure is proportional to depth 2 in a cohesive ground.

Now, at a depth of 2 degrees, the internal and external pressures are balanced at the pipe sand length H8, that is, (HO120) point, which originally corresponds to static earth pressure.

In addition, if there is more sand in the pipe than this, the sand in the pipe exceeds the earth pressure and the sand (hydrated sand) in the pipe is discharged from the lower end of the pipe.The sand length in the pipe is H2, and in the figure (H2, Zo). indicated by a dot,
The earth pressure at this time is called passive earth pressure.

In addition, conversely, the sand length within the pipe that is less than the sand length H8 described above and which is below the earth pressure and causes the soil to flow back into the pipe is Hl, and in the figure, it is the point (Hl, Zo). The earth pressure at this time is called the active earth pressure.

In the figure, ■ is the static earth pressure line, ■ is the passive earth pressure line,
■ is the active earth pressure straight line.

When the above relationship is expressed as a balanced equation, the following relationship holds true according to Rankine earth pressure.

H-1"s=Z-rc !rJ:2C(L-1) where, Z-rc+2C: passive earth pressure, z, rc-2C: active earth pressure, C: ground strength, H: sand length in pipe, 2: depth of the lower end of the pipe, rc: specific weight of clayey soil, rs: specific weight of hydrated sand.

Therefore, the ground strength C is; In general alluvial clay, the depth Z
Since it is proportional to , it can be expressed as C-α2 with α being a proportionality constant, and the above balance equation (1-1) can be expressed as follows.

H-rs = Z (7"c±2α) (1-2) The present invention is based on the above balanced equation (l-2) and applies it to sand pile construction. As illustrated in Fig. 2, a vibrating pile driver 4 is operated to drive a hollow pipe 1 with an open bottom end (see Fig. a) penetrated to a predetermined depth Zd in soft ground 2 and supplied with hydrated sand 3. As the hollow tube 1 is pulled upward, the hopper 5 at the top of the hollow tube 1
The hydrated sand 3 is sequentially supplied into the hollow tube 1 from
is maintained in a fluid state in the hollow tube 1 by vibrations by a vibrating pile driver 4, etc., while at each depth Z of the lower end of the hollow tube 1 being pulled out, the hydrated sand 3 in the tube is placed under the hollow tube 1. The pressure at the end face is controlled to be greater than the passive earth pressure of the soft ground 2 at the lower end of the hollow pipe 1 (see Figure c).
.

Therefore, in the balance equation (1-2), rs and rc1α are assumed to be constants, so this control controls the sand length H of the hydrated sand 3 that is sequentially supplied into the hollow tube 1 according to the depth 2. In this way, a sand pile 3' whose diameter is larger than that of the hollow pipe 1 is constructed up to the ground surface (see Figure d).

Next, regarding the hollow pipe used in the construction method of the present invention, in one embodiment shown in FIG. 2, a vibratory pile driver 4 is attached to the top of the hollow pipe 1, As the punching machine 4 operates, the hollow tube 1 penetrates into the soft ground, and when the hollow tube 1 is pulled out, the hydrated sand 3 supplied into the hollow tube 1 is vibrated and kept in a fluid state. be done.

However, the penetration of the hollow pipe 10 is not limited to the above-mentioned vibrating pile driver 4 (you are free to use any other suitable pile driver, In order to maintain the hydrated sand 3 in the empty tube 1 in a good fluid state, it is also considered to attach a vibrating mechanism or a vibrator to the tube separately from the vibrating pile driver 4.

Furthermore, methods other than vibration may be possible to maintain the hydrated sand 3 in the pipe in a fluid state.

Next, for supplying the water-added sand 3 into the pipe, a pressure-feeding pipe for the water-added sand 3 may be used in place of the pumper 5 shown in FIG. 2.

Next, as a feature of the construction method of the present invention, the lower end of the hollow tube 1 can be made into the simplest cut-off open end, as shown in FIG. In order to penetrate the soft ground 2 to a predetermined depth, as shown in Fig. 3 a, the method for constructing sand piles was applied for a patent on March 25, 1976 by the applicant for the patent of the present invention. During the penetration of the hollow tube, the pressure of the hydrated sand 3 in the hollow tube 1 at the lower end surface of the hollow tube 1 is controlled to be in balance with the earth pressure of the soft ground 2 at the lower end of the hollow tube 1, so that the soil It is possible to use a construction method that prevents the flow from flowing backward into the pipe from the lower end, and when this construction method is used, the state in which the hollow pipe 1 penetrates the soft ground 2 to a predetermined depth is as shown in Figure 2 (a). This is extremely convenient.

In addition, when the hollow pipe of the present invention is pulled upward (in the penetration process prior to the sand pile construction process, if hydrated sand is supplied into the pipe after penetration, it is necessary to prevent soil from flowing back into the pipe; A removable sealing plug may be provided at the lower end of the hollow tube, or a narrow diameter portion 7 may be provided within the tube near the lower end of the hollow tube to form a sand frame 8 by arch action of the sand (see Figure 3). Empty tube-
Means such as providing an opening/closing shoe or opening/closing lid at the top end is used.

Further, during the drawing of the hollow tube 1 in the present invention, the hollow tube 1
Controlling the pressure at the lower end surface of the hollow tube 1 of the hydrated sand 3 to be greater than the passive earth pressure of the soft ground 2 at the lower end of the hollow tube 1 will be described.

That is, the above control is H: 7's=Z (rc
The system is controlled so that the balanced equation 0 (%) is given by ±2α). As shown schematically in Figure 4, compressed air is fed into the hollow tube, and the air pressure P caused by this compressed air causes The pressure of the hydrated sand 3 on the lower end surface of the tube can be assisted.

The control state using this air pressure P can be expressed by the following equation.

H7's+P > Z (rc+2α) (2-1
) Therefore, the sand amount H of the hydrated sand 3 supplied into the pipe and the air pressure P
The internal and external pressure conditions are maintained as shown in the above equation.

However, since the control of the air pressure P is quick and extremely easy, in the implementation of the present invention, it is better to use the air pressure P to assist in controlling this, compared to the case where the sand amount H of the water-added sand 3 is used alone. Easy and reliable.

Furthermore, in the implementation of the present invention, as a method of controlling the diameter of the sand pile created during drawing of the hollow tube, the flow rate q of hydrated sand additionally supplied into the hollow tube, and the drawing speed V of the hollow tube will be described below. This section describes an implementation method for controlling the

FIG. 5 schematically shows a part of the hollow tube being pulled out using the method of the present invention, in which there is a short period of pulling out of △tKA→B, during which time an amount of supplied hydrated sand of △V is added, The amount of sand in the pipe is H
The balance equation here that changes to -4H1 is, at A and H, H-rs=Z (1"c+2ct) (3-
1) H7-rs= (Z-ΔZ) (rc+2α)
(3-i).

Also, the total amount discharged from the lower end of the tube during the short time △l is:
Since it is equal to the amount of sand pile created, the cross-sectional area of the discharged sand pile is A.
s and the cross-sectional area of the pipe is AP, then △z-A82(H-Hl)·AP10△v (3-2).

In this formula, Ho, H from the formula (:1l(), (3-1)')
When A8 is calculated by substituting the value of (rc+2α)
M V A8---=ne ・Ap+Sufu-.

△V △2 Now, q=-1, ■knee, so upper △t
Rewriting the formula for △ yields the following formula.

As is clear from this equation (3-3), by appropriately controlling the hydrated sand flow rate q and the drawing speed V, the hydrated sand can be created by discharging the hydrated sand during drawing of the hollow tube. The diameter of the sand pile can be controlled to a desired diameter.

Therefore, in carrying out the control of the hydrated sand flow rate q and the hollow tube drawing speed V during the hollow tube drawing described above, there are conventionally known means for controlling the hollow tube drawing speed). The flow rate q of hydrated sand, that is, the amount of hydrated sand supplied into the hollow tube can also be controlled by supplying the hydrated sand through a pressure pipe or the like.

Next, to explain the point of setting the water content ratio of the hydrated sand near saturation as described above in the present invention, according to experimental research, if the water content ratio at saturation is 100 parts, even if the water content ratio is about 95 parts, vibrations will occur. It is possible to make this into a fluid state by such methods, and if the water content ratio is set to be higher than saturation, the higher the water content ratio, the easier it is to make it into a fluid state.

However, since the hydrated sand in the pipe is used as sand pile construction in the sand pile construction process, increasing the water content ratio of the hydrated sand in particular will cause problems in sand pile construction, so the water content ratio of the hydrated sand should be adjusted to match the fluid state. The water content ratio is set to a sufficient level that can be achieved, that is, close to saturation.

As mentioned above, the sand pile construction method of the present invention uses hollow pipes with a relatively simple structure to construct sand piles with a diameter larger than the hollow pipe diameter in soft ground compared to conventional construction methods. It has the advantage of being able to be constructed with less energy.

Furthermore, the sand pile construction method of the present invention has extremely excellent advantages such as being able to save construction time, not requiring any particular cost for the sand used, and being able to easily control the diameter of the sand pile.

[Brief explanation of the drawing]

The attached drawings are for explaining aspects of the construction method of the present invention using examples. Figure 1 shows the amount of hydrated sand in the pipe corresponding to the earth pressure of the soft ground at the bottom end of the hollow pipe. Figure 2 is an explanatory diagram illustrating the process of pulling out hollow pipes in sequence in the construction method of the present invention, and Figure 3 is a graph showing the process of pulling out hollow pipes at a predetermined depth in soft ground. Fig. 4 is an explanatory diagram of an embodiment of the penetrating step, and Fig. 4 is a schematic illustration of an embodiment in which compressed air is fed into the upper part of the hollow tube to assist the pressure of the hydrated sand in the hollow pipe with air pressure. , is an explanatory diagram illustrating the relationship between the flow rate of hydrated sand additionally supplied into the hollow tube and the diameter of the sand pile created by the sand discharged from the lower end of the hollow tube by controlling the drawing speed of the hollow tube. 1...Hollow tube, 2...Soft ground, 3...Hydrated sand,
31... Sand pile, 4... Vibratory pile driver, 5... Hopper, 6... Compressed air supply, 7... Small diameter part, 8...
...Sand frame, 2...Depth of the lower end of the hollow tube, H...Amount of hydrated sand in the hollow tube, P...Pneumatic pressure.

Claims (1)

[Scope of Claims] 1. In the process of pulling upward a hollow pipe for constructing sand piles that has penetrated to a predetermined depth in soft ground, hydrated sand with a moisture content near the saturation level of the supply is placed inside the hollow pipe. At the same time, while the hollow tube is being pulled out, the pressure of the hydrated sand on the lower end surface of the hollow tube is controlled so that the passive earth pressure of the soft ground at the lower end of the hollow tube increases. A sand pile construction method characterized in that the hydrated sand inside the hollow pipe is discharged into the soft ground from the lower end of the hollow pipe to create a sand pile whose diameter is larger than the diameter of the hollow pipe. 2. From the top of the hollow pipe. A sand pile construction method according to claim IVc, characterized in that compressed air is introduced into the hollow pipe, and the pressure of the hydrated sand on the lower end surface of the hollow pipe is assisted by the air pressure of the compressed air. 3. Inside the hollow pipe. The diameter of the sand pile to be created is controlled by controlling the supply flow rate of hydrated sand with a water content near saturation, which is additionally supplied above the hollow pipe during drawing, and the drawing speed of the hollow pipe. The sand pile construction method according to claim 1, characterized by: