JPH0814101B2 - Liquefaction control method for sandy ground - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for suppressing liquefaction of sandy ground for suppressing liquefaction of loose sandy ground.

[Prior Art] In the case of loose sandy ground during an earthquake, sand or water may spout to the surface of the ground, structures may sink into the ground, tilt or tip over, or lightly buried objects may surface. The phenomenon of may be seen. This is called the ground liquefaction phenomenon.

The cause of this liquefaction phenomenon will be briefly described as follows.

When groundwater fills the gaps of sand particles in a loose sand layer that is shallow from the surface of the earth, when the sand layer is shaken by an earthquake, the sand particles are disengaged and the sand particles are removed. Becomes suspended in the water, and because it tries to sink rapidly, the excess pore water pressure rises, and as a result, some sand erupts with the water onto the surface. Further, in such a state, the sand layer in the ground is in a liquid state and loses the usual ground supporting force, so that it appears as the phenomenon described above, and as a result, various damages occur.

Therefore, as a countermeasure against liquefaction of such sandy ground, the following construction methods have been conventionally adopted.

It is a method of increasing the density of sandy ground because it is difficult to liquefy when compacting loose sandy ground.

Sand compaction pile is a method of increasing the strength of the ground by making strong sand piles with a large diameter by press-fitting sand into the soft sandy ground by impact or vibration load. Also, the vibro flotation method and the vibro composer method, which are of the same quality as this method, are used.

 This is a method of removing water in the sandy ground.

This is a crushed stone draining method in which crushed stone piles are created with augers to drain water from the sandy ground, and excess pore water pressure generated in the sand layer during an earthquake is quickly removed.

This is a method of improving the ground by injecting a chemical solution into the sandy ground.

It is called the injection consolidation method, and is a method that is carried out by injecting water glass, a polymer chemical solution, etc. into the ground under pressure to increase the strength of the ground and improve the water stopping property.

[Problems to be Solved by the Invention] However, each of these construction methods has the following problems.

That is, in the sand compaction pile method, etc., since vibration construction is used, vibration and noise caused by repeated driving and pulling out of the pile due to vibration become a problem. Also,
In the case of the water pressure removal method, there is concern about the certainty of its effect, and there is also a problem with vibration construction. In addition, in the case of the injection solidification method, there is a problem that the construction is troublesome and that the groundwater is contaminated by the chemical liquid.

As described above, in the conventional technology, vibration, noise during construction,
Problems remain with respect to environmental pollution, complexity of construction, and liquefaction prevention effect.

The present invention proposes a method for suppressing liquefaction of sandy ground that can solve these problems all at once.

[Means for Solving Problems] In this method, piles are formed in groups in the sandy ground at appropriate intervals using a dry cementitious material having water-absorbing, expansive and hydraulic components. There, an improving effect of lowering the water content in the sandy ground by the water absorbing action of the cement-based material, and an improving effect of compressing the peripheral sandy ground by the expanding action of the material to increase the strength of the sandy ground, or Liquefaction is suppressed by the composite improvement effect of sandy ground by forming piles that are hardened by groundwater and exhibit strength.

Here, the cementitious material mainly contains a hydration-hardening component and an expansive component, and further contains a water-permeable component, if necessary. The hydration curable component is a component for exerting water absorbency, expandability to some extent, and hydraulic property, for example, gypsum, blast furnace slag and ordinary Portland cement as main materials, and as a curing accelerator for these. There are solidifying materials that are well mixed by adding halogen compounds or sulfates as needed, such as Osaka ESC.
(Osaka Cement Co., Ltd. product name). This solidifying material is gypsum 15 to 60% by weight which is the main material, blast furnace slag 20 to 60% by weight, and ordinary portland cement 10 to 50% by weight, and these are pulverized to have a specific surface area of 4500 cm ² / g or less. It is prepared by mixing or by adding 5% by weight or less of a curing accelerator to these and crushing and mixing, and it has water absorbability, expandability and hydraulic property. Examples of the expansive component include quicklime and expansive cement. This component is intended to further increase the swelling effect. Furthermore, examples of the water permeable component include dry slag and dry sand. This component has a function of assisting hydration up to the core of the pile, and can be omitted if the pile diameter is small.

Then, the pile formation in the sandy ground with this cement-based material is performed as follows.

Fig. 1 shows the outline of the construction method.
First, as shown in FIG. 3A, the conical casing tube 1 is screwed into the ground 2, and then the cementitious material 3 is put into the casing 1 as shown in FIG. Thereafter, as shown in FIG. 2C, the bottom portion 1a is urged downward while the cement-based material 3 is urged downward by the force of the screw 4 and the compressed air 5 arranged in the axial center portion of the casing tube 1. By pulling up the casing tube 1 that has been opened, the work of forming the cement-based material 3 into a pile shape is completed as shown in FIG.

[Operation] As described above, according to this construction method, the sandy ground can be applied without vibration and noise, and the sandy ground is improved to be a liquid that is hard to be liquefied and at the same time has a strong pile portion. Since it is a composite ground consisting of sand and a sand layer, it secures the ground strength, so it exerts a large liquefaction suppressing effect that resists liquefaction even if pore water does not escape, and further increases environmental pollution and work man-hours due to the use of chemical liquids. Will not invite.

[Examples] The ground improvement effect of the present method will be specifically described below with reference to Examples.

In the soft sandy ground including a layer of sand in an area,
According to the above construction method, dry piles of φ400 mm each with a depth of 1
It was constructed in a regular triangular shape with a pitch of 3m and a pitch of 1.5m. N before and after improvement
The values and the soil column diagram are shown in FIG. From this figure −2.5 to −8
It can be seen that the effect of improving the sand layer up to m is greatly shown.

Also, in the soft sandy ground of another area, φ400mm
Fig. 3 shows N value and soil column diagram before and after the improvement when the dry piles of No. 1 and No. 2 were each installed in the shape of an equilateral triangle with a depth of 9.5 m and a pitch of 1.0 m. According to this result, −5.4
The improvement effect is significant in the sand layer of ~ -8.9m.

The above improvement effects indicate that the relative density of the sandy ground has increased, which is less likely to cause liquefaction because of the risk of liquefaction and the N-value correlation indicated in the building foundation design standard. It means that the ground has been improved.

[Effects of the Invention] As described above, according to the method of the present invention, a pile of dry cementitious material having a water-absorbing component, an expanding component and a hydraulic component is formed in the sandy ground in a group to form a conventional method. It is possible to improve the sandy ground to a composite ground that is unlikely to cause liquefaction while solving the above problems.

[Brief description of drawings]

1 (a) to 1 (d) are schematic cross-sectional views showing construction examples of the present invention. FIG. 2 and FIG. 3 are soil columnar diagrams showing the improvement effect by the embodiment, respectively.

Claims (1)

[Claims] 1. Liquefaction of a sandy ground, characterized in that piles are formed into groups in the sandy ground at appropriate intervals by using a cement material in a dry state having a water absorbing component, an expanding component and a hydraulic component. Deterrent construction method.