JPH0784731B2 - Ground improvement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for improving soft ground such as clay layers and loose sand layers.

[Problems to be solved by the invention] In order to increase the soil density of clay layers and loose sand layers, embankment is generally used for clay layers and vibration compaction is generally adopted for sand, and rarely absorbs water in the ground of quicklime and expands. Pressure is used.

However, the embankment has drawbacks such as large-scale construction such as large movement of earth and sand, construction of water blocking wall, and inability to effectively transfer load to a deep position, and vibration compaction cannot be adopted in urban areas. In the case of quick lime, there is a concern about long-term strength after it absorbs water, expands, and becomes slaked lime, or there is a drawback that lime components are mixed into groundwater and discharged soil, causing an increase in pH and environmental pollution.

The present invention has been made in view of the above circumstances. The purpose of this is low noise and low vibration, construction can be done even in urban areas, the consolidation load can be applied to the desired depth, and the soil can be efficiently dehydrated to improve the ground in a short period of time. The purpose of the present invention is to propose a ground improvement method in which a composition that generates force can be a stable cement bacillus and can contribute to strength improvement, and there is no fear of contamination of groundwater or discharged soil.

[Means for Solving the Problems]

The ground improvement method according to the present invention is a method of arranging vertical drains on a ground to be improved with a predetermined distance, forming vertical holes, filling a water-soluble container with a composition which becomes water-expand-hardened cement bacillus by absorbing water. Insert into the pit without discontinuity, backfill the pit void, close the pit opening, and allow the composition in the pit to absorb water and expand as a consolidation load on the ground. The water in the ground whose water pressure has risen thereby is discharged via the vertical drain. In this construction method, as the vertical drain for releasing the rising pore water pressure, a sand lane or a packed drain for the clay layer and a plastic drain for the sand layer soil layer are preferably used. Usually, it is arranged in the middle of the vertical holes. The vertical hole is bored to the required depth using a casing or rod.

A composition that absorbs water and expands and cures (hereinafter simply referred to as composition)
Is a dry mixture that produces cement bacillus mainly composed of quick lime, an alumina component, and a sulfate. For example, a mixture of 70% quicklime, 20% alum, and 10% feldspar powder is suitable for this purpose because quicklime heats up and expands when water is absorbed, and alum dissolves well in water to form cement bacillus and expands and hardens. Is.

These compositions are pressure-molded to form tablets or the like, which are filled in a water-soluble container, for example, a capsule-shaped container obtained by pressing a mixture of cellulose and bentonite, and inserted into a vertical hole. Since the premixed composition tends to absorb water and cause a reaction, it is necessary to strictly isolate water from the composition when storing it in a container, storing it, or throwing it into a vertical hole.

The composition packed in the water-soluble container is inserted discontinuously into the pit, avoiding the layer in which groundwater is retained. If the groundwater is made of sand or gravel and is inserted into a water-bearing position, the quicklime component reacts with a large amount of water to form slaked lime, which elutes and the expanding force cannot act as a consolidation load on the ground. In addition, it raises the pH of groundwater and causes environmental pollution.

〔Example〕

The embodiment will be described below. In Fig. 1 and 2, vertical drains 2 are arranged at the base-shaped position while maintaining a predetermined space in the ground to be improved 1, and vertical holes 3 are alternately bored, and the peripheral portion along the site boundary line 4 is The holes 5 were formed.

A shell-shaped container 6 filled with the composition shown in FIG. 3 is provided in the vertical hole 3 to avoid a sand layer 8 in which groundwater is retained and a viscous soil layer 9
It was inserted discontinuously in the position, and the backfill soil 7 was filled and closed in the void and the upper void in the vertical hole 3. This container 6 is made of water-soluble microporous one obtained by pressing a mixture of cellulose and bentonite, and has a composition of 70% quicklime and alum.
A mixture of 20% and 10% feldspar powder was used.

The composition in the container charged into the vertical hole 3 absorbs moisture in the ground formed of the clay layer 9 to generate heat and expand,
The expansion pressure acts as a load that horizontally consolidates the viscous soil layer 9, and the excessive pore water pressure generated by this load is discharged to the surface of the ground or the sand layer 8 via the vertical drain 2, and the viscous soil 9 is quickly discharged. Consolidation dehydration of the ground progressed. The expanded composition hardened into cement bacillus and was converted into a stable and pollution-free artificial stone, which contributed to the improvement of the strength of the ground.

In the process of improving the ground, the holes provided along the boundary of the site exhibit a buffer function against the expansion pressure of the composition, and can prevent the expansion pressure from spreading to the outside of the target ground.

〔The invention's effect〕

The present invention is as described above, and has the following effects. A composition that expands and hardens to become cement bacillus is packed in a container, and an efficient position in the vertical hole is selected and inserted, and it is made to work. be able to. Even if the groundwater is contaminated with water, it can be efficiently consolidated, and there is no risk that the lime component will mix into the groundwater etc. and damage the environment. Workability is good because the composition that easily absorbs water is packed in a container and handled. Low noise·
Since it has low vibration and can prevent the influence on the adjacent land, it can be carried out in urban areas. Consolidation dehydration can be performed to a desired depth to improve the ground in a short time. The hardened cement Bacillus contributes to the improvement of ground strength and does not hinder excavation or pile driving, so the value of land does not decrease.

[Brief description of drawings]

The drawings show examples, and FIGS. 1 and 2 are a plan view and a vertical sectional view of the ground to be improved, and FIG. 3 is a perspective view of a shell-shaped container filled with the composition. 1 ... Ground to be improved, 2 ... Vertical drain, 3 ...
… Vertical holes, 4… Site boundary line, 5… Holes, 6… Cannonball type container, 7… Backfill soil, 8… Sand layer, 9… Cohesive soil layer.

Claims (1)

[Claims] 1. A vertical drain is provided on the ground to be improved while keeping a predetermined interval, and a vertical hole is bored, and a water-soluble container is filled with a composition that absorbs water, expands and hardens, and becomes cement bacillus. Inserted without discontinuity in, backfill the pit void, close the pit opening, let the composition in the pit absorb the water and expand the force to act as a consolidation load of the ground,
The ground improvement method is characterized by discharging the water in the ground whose water pressure has risen by way of the vertical drain.