JP2794309B2 - Ground improvement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a ground improvement method by dewatering.

<Prior Art> At present, as a method for improving soft ground, a vertical drainage method represented by a sand pitting method and various draining methods is known.

In this method, a permeable layer of sand pit or drain material is formed vertically in the ground to be improved, and pore water between soil particles is collected in the permeable layer by loading from the ground surface and drained to the ground. ,
This is a method for improving the consolidation of the ground.

<Problems to be solved by the present invention> The above-mentioned conventional ground improvement technology has the following problems.

<A> Since this type of conventional improvement method is a method of forming a permeable layer in the vertical direction in the ground, it is necessary to narrow the gap between the permeable layers in order to improve the ground improvement.

 For this reason, the construction period and construction cost tend to increase at present.

<B> When the improved ground is a viscous soil or silt having a high water content, a method of replacing granular material such as sand in a cavity formed by jetting jet water into the ground has been proposed.

However, since it is impossible to avoid mixing viscous soil or silt between the granular materials, the water permeability of the formed water-permeable layer is significantly reduced, and as a result, the ground improvement effect is low.

<C> At present, there is no suitable improvement method capable of effectively improving the ground over a large depth.

<Object of the present invention> The present invention has been made in view of the above points, and an object of the present invention is to effectively improve a soft clay soil, which has been considered difficult to improve, and has a large depth. It is an object of the present invention to provide a ground improvement method suitable for improvement of ground.

<Means for Solving the Problems> That is, according to the present invention, in a ground improvement method for improving the ground by drainage, a small hole is excavated to a predetermined depth, and a wide hole extending horizontally from the inside of the small hole is excavated. This is a soil improvement method that replaces the soil removal inside the hole with a mixture of granular material and a water-absorbent resin that has the property of contracting by absorbing seawater, and constructing a permeable layer that extends horizontally in the ground. .

<Description of the present invention> Hereinafter, before describing the present invention, a water-absorbing resin used for construction will be described.

The water-absorbent resin has a property of gelling with fresh water and contracting in volume when absorbing seawater. For example, a polymer absorbent such as Sunwet manufactured by Sanyo Chemical Industries, Ltd. can be used.

<Construction method> Next, the construction method will be described.

<A> Excavation of small holes The present invention is effective for improving the ground containing seawater such as a beach area or a delta.

As shown in FIG. 2, a small hole 10 is excavated to a predetermined depth in the ground to be improved.

As a means for excavating the small hole 10, a known excavator equipped with an injection nozzle 21 that can adjust the injection direction of the high-pressure water at the tip of the rod 20 can be used.

<B> Excavation and excavation replacement Next, the injection nozzle 21 is rotated by 90 ° at the deepest portion of the small hole 10 to adjust the injection direction horizontally, and then the rotation is given to excavate the expansion hole 30.

When excavating the widening hole 30, a mixture 40 of sand and a water-absorbent resin is injected from the injection nozzle 21 together with high-pressure water.

The water-absorbent resin in the injected mixture 40 takes in sand and gels.

As in the past, the mixture 40 is mixed with viscous soil or silt having a high water content, and it is inevitable that the mixture 40 will be impermeable. it can.

When the drilling 30 is drilled at the lowermost stage and the replacement of the shavings and the mixture 40 is completed, the injection nozzle 21 is raised to the drilling position of the next drilling as shown in FIG. At the same time as the excavation, the mixture 40 is filled in the hole 31.

By repeating the above steps, as shown in FIG. 5, the mixture 40 is replaced with the excavated soil while excavating the hole 32 sequentially and hierarchically toward the surface of the earth.

Then, finally, the mixture 40 that is hierarchically replaced in the under-holes 30, 32, 33 and the small holes 10 has continuity.

Also, as shown in FIG. 1, the small holes 10 are excavated at a plurality of points, and the excavation 30 and the replacement of the mixture 40 are performed for each small hole 10 to form a horizontal layer of the mixture 40 in multiple stages. .

Of course, the number of horizontal layers of the mixture 40 may be one or four or more.

<C> Providing Water Permeability The mixture 40 gelled as described above remains impermeable as it is.

Therefore, drainage is forcibly used from the ground surface using the small holes 10.

Then, when the underground seawater passes between the mixtures 40, the water absorbent resin reacts with the seawater and shrinks.

As a result, voids are generated in the mixture 40 only at locations where the water-absorbent resin has shrunk, and a skeleton of sand particles is completed.

The generation of countless voids in the mixture 40 gives the mixture 40 water permeability.

The mixture 40 in the pores 30, 31, 32 provided with water permeability,
As shown in FIG. 1, it becomes a permeable layer A spreading in the horizontal direction,
The mixture 40 in the small holes 10 connects the respective permeable layers A in the vertical direction to form a communication path B for draining to the ground.

<D> Drainage As shown in Fig. 1, underground seawater and groundwater are collected in a horizontally permeable permeable layer A, and then drained to the ground via a communication path B, and ground improvement proceeds.

In the present invention, since the permeable layer A is interposed in the horizontal direction in the ground, the consolidation drainage distance is reduced.

Therefore, the ground improvement can be performed very advantageously as compared with the prior art in which the water-permeable layer is formed in the vertical direction.

As the drainage means, a natural drainage method, a method of applying a load such as embankment, or a method of forcibly sucking with a water suction pump is appropriately selected and adopted.

<Effects of the Present Invention> The present invention is as described above, and the following effects can be obtained.

<A> Conventionally, it has been almost impossible to form a water-permeable layer having excellent water permeability in the horizontal direction.

In the present invention, a water-permeable layer having excellent water permeability can be formed in a horizontal direction by using a water-absorbing resin having a property of shrinking when absorbing seawater.

 Therefore, the effect of improving the ground can be significantly improved.

<B> Even in the case of a viscous soil or silt having a high water content, which has conventionally been considered very difficult to improve, it can be satisfactorily improved.

<C> Conventionally, the ground improvement method using vertical drainage is not suitable for deep ground improvement because the distance between drainage layers is long and the construction machine becomes larger as the depth increases.

In the present invention, since the distance between the drainage layers formed in the horizontal direction is short, and it can be adapted to a large depth with a small construction machine,
Suitable for deep ground improvement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1: Longitudinal sectional view of the ground improved by the ground improvement method according to the present invention FIG. 2: Explanatory drawing when excavating small holes FIG. Fig. 5: Explanatory diagram when the replacement of the mixture is completed

Claims (1)

(57) [Claims] In a ground improvement method for improving the ground by drainage, a small hole is excavated to a predetermined depth, a widened hole extending horizontally from the inside of the small hole is excavated, and the shaving in the widened hole is removed by a granular material. A ground improvement method that replaces a mixture of water-absorbent resin that absorbs and shrinks seawater with water to build a permeable layer that extends horizontally in the ground.