JP7271836B2 - Soil improvement method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ground improvement method in which a preload is applied using non-discharge type drain construction equipment.

Conventionally, when constructing buildings on the upper part of the ground mainly composed of cohesive soil, the vertical drain construction method and the preload construction method are used together in order to increase bearing capacity and prevent ground subsidence after construction of the building. It is common to

Here, the vertical drain method is to vertically extend water-permeable materials such as sand and board-like cardboard into the ground, and drain the interstitial water in the ground through drainage channels (drains) made of these water-permeable materials. This is a construction method that improves the ground by discharging it to the outside. In the past, the construction method of the earth removal type, in which soil was discharged from the drain, was common, but in order to eliminate the inconvenience of the earth removal, the construction method has changed to the non-discharge type construction method.

In addition, the preloading method is a method of consolidating and hardening the ground at an early stage by applying a load such as earth and sand that is easy to obtain and transport to the ground surface. As preloading methods, (1) embankment method, (2) atmospheric pressure method, (3) groundwater level lowering method, and (4) combination method of (1) to (3) are known. It is

According to the construction method using the vertical drain construction method and the preload construction method together, the ground can be hardened while the moisture in the ground is discharged by the drain.

On the other hand, for example, a bag that expands when a fluid is injected is placed in the ground, the fluid is injected into the bag placed in the ground to inflate the bag, and the pressure of the inflated bag causes the bag to expand. A ground improvement method has also been proposed in which the ground around the body is pressurized (Patent Document 1).

JP-A-2003-293355

However, in the case of a construction method that uses a conventional vertical drain construction method and a preload construction method (for example, an embankment construction method), it is not easy to suppress the construction cost for creating an embankment for preloading, and the construction period tends to be prolonged. There was a problem. In addition, since it is necessary to stack earth and sand vertically upwards in order to increase the load per unit area placed on the ground surface, there is a practical limit to the size of the load, and it is necessary to harden the ground to be improved. In some cases, it was not possible to apply a sufficient load and the ground could not be hardened sufficiently. Furthermore, there is a concern that the ground that receives the load from the earth and sand piled up on the ground surface will sink, and the ground adjacent to the ground that should be improved will sink due to being dragged down.

On the other hand, for example, in the case of the method of Patent Document 1, it is necessary to arrange a special bag in the ground and introduce a separate facility for injecting a solidifying agent such as cement milk into this bag. There is still a problem that the construction cost is still high and the construction period cannot be sufficiently shortened.

The present invention has been made in view of the above circumstances, and provides a ground improvement method that can reduce the construction cost and shorten the construction period in the ground improvement method by the vertical drain method. The challenge is to

The present invention is a ground improvement method for forming a plurality of vertical drains in the ground to be improved by non-discharge type drain construction equipment, and discharging pore water in the ground from the vertical drains,
It is characterized by including a step of vertically driving a long empty casing pipe into the ground near the middle of the adjacent vertical drains by the drain construction equipment to pressurize the surrounding ground.

In this ground improvement method, it is preferable that the drain construction equipment includes a vibro-hammer, and water in the ground is collected around the vertical drain by vibration of the vibro-hammer when driving the casing pipe.

According to the construction method of the present invention, it is possible to reliably consolidate the ground to be improved, reduce the construction cost, and shorten the construction period.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which illustrated the outline|summary of one Embodiment of the ground improvement method of this invention. 2 is a plan view of the embodiment shown in FIG. 1; FIG.

The present invention is a ground improvement method in which a plurality of vertical drains are formed in the ground to be improved by non-discharge type drain construction equipment, and pore water in the ground is discharged from the vertical drains, and adjacent vertical drains. It includes a step of vertically driving a long, empty casing pipe into the ground near the middle of the two using drain construction equipment to pressurize the surrounding ground.

In the conventional construction method, all preloads were static loads, but one of the features of the present invention is to use dynamic preloads in combination.

Hereinafter, one embodiment of the ground improvement method of the present invention will be described with drawings. FIG. 1 is a cross-sectional view illustrating an outline of one embodiment of the ground improvement method of the present invention. 2 is a plan view of the embodiment shown in FIG. 1. FIG.

As exemplified in FIGS. 1 and 2, in the ground improvement method of this embodiment, a plurality of vertical drains 2 are formed by non-discharge type drain construction equipment (not shown). The vertical drain 2 discharges moisture in the ground 1 to the outside of the ground (ground surface) by permeating interstitial water in the ground 1 with a water-permeable material inside.

As in the conventional case, the vertical drain 2 can be formed by a vertical drain construction method using a non-discharging type drain construction equipment (vertical drain driving machine). Specifically, for example, a long casing pipe is cast vertically downward from the ground surface to the vicinity of the lower end of the soft ground 1 to be improved using a drain construction machine, and sand or board-like cardboard is placed inside the casing pipe. The vertical drain 2 can be formed by pulling out the casing pipe after filling with a water-permeable material such as. Also, in this embodiment, a plurality of vertical drains 2 are formed at predetermined intervals.

Furthermore, in the ground improvement method of this embodiment, an empty casing pipe 3 is driven vertically into the ground 1 near the middle of adjacent vertical drains 2 by drain construction equipment.

The casing pipe 3 is a hollow, long, substantially cylindrical member used to form the above-described vertical drain 2, and may have, for example, a lid that can be freely opened and closed at the tip side. In this embodiment, the vertical length of the casing pipe 3 is approximately equal to that of the vertical drain 2 and the diameter of the casing pipe 3 is approximately equal to that of the vertical drain 2 .

As the drain construction equipment for driving the casing pipe 3, the same non-discharge type construction equipment as used when forming the vertical drain 2 can be used. Moreover, it is preferable that this drain construction equipment is equipped with a vibro-hammer. In this case, when the casing pipe 3 is driven into the ground 1, the moisture in the ground 1 can be collected around the vertical drain 2 by the vibration of the vibro-hammer, so the drainage of the moisture from the vertical drain 2 is promoted. and the consolidation speed of the ground 1 can be shortened.

As illustrated in FIG. 2, these vertical drains 2 and casing pipes 3 are arranged in a staggered matrix (lattice) in plan view.

In the ground improvement method of this embodiment, by driving an empty casing pipe 3 into the ground 1 using drain construction equipment, the ground 1 around it can be pressurized to be a preload. That is, by placing the casing pipe 3, it is possible to apply a sufficient pressure to the ground 1 almost uniformly, and the pore water pressure in the ground 1 can be increased, so that the drainage of water from the vertical drain 2 is promoted. and the consolidation speed of the ground 1 can be increased.

In addition, in the ground improvement method of this embodiment, the casing pipe 3 used in the vertical drain construction method is placed in the ground 1 to make it a pre-loaded load, and the drain construction equipment for placing this casing pipe 3 can use the same construction equipment as used when forming the vertical drain 2 . Therefore, since embankment for preloading (preloading), separate equipment, special materials, etc. are unnecessary, the construction cost can be greatly reduced and the construction period can be shortened.

1 and 2 illustrate a state in which the casing pipe 3 is driven into the ground 1. After the pore water pressure in the ground 1 is increased by driving an empty casing pipe 3, It can be withdrawn immediately.

The ground improvement method of the present invention is not limited to the above embodiments. For example, in the above-described embodiment, a plurality of vertical drains and casing pipes are arranged in a staggered matrix in plan view, but the arrangement is not limited to this. That is, it is possible to appropriately design the arrangement so that the driving of the casing pipe into the ground pressurizes the surrounding ground and promotes the discharge of moisture from the vertical drain. Further, in the above-described embodiment, the vertical lengths of the vertical drain and the casing pipe are substantially equal, but the lengths are not limited to such lengths and can be designed as appropriate.

1 Ground 2 Vertical drain 3 Casing pipe

Claims (1)

It is a ground improvement method using the vertical drain method , in which multiple vertical drains are formed in the ground to be improved by non-discharge type drain construction equipment, and pore water in the ground is discharged from the vertical drains to the ground surface. hand,
A long empty casing pipe was driven vertically into the ground near the middle of the adjacent vertical drains by the drain construction equipment to pressurize the surrounding ground and increase the pore water pressure in the ground. After that, including the step of pulling out,
The drain construction equipment includes a vibro-hammer, and when driving the empty casing pipe, the ground is characterized by collecting moisture in the ground around the vertical drain by vibration with the vibro-hammer as a vibration source. How to improve.

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