JPH03156022A - Ground improvement method - Google Patents

Abstract

PURPOSE:To form unsaturated ground without pumping up ground water by erecting injection pipes in bores drilled in the ground, by producing air bubbles in the ground with foamable liquid that is made to get through the pipes and by forming air bubbles in openings among sand particles. CONSTITUTION:The ground is drilled from the surface 1 thereof and from a mat foundation 2 of a building, and bores 3 are provided in necessary numbers and injection pipes 4 are erected in the bores and a filtering material 5 is thrown into the pipes. Foamable liquid with foam regulating agent added is made to get through the injection pipe 4 and is made to penetrate the injection holes 4a to produce air bubbles 8 in the ground. Air bubbling materials 7 infiltrate among sand particles 9 and thereby air bubbles 8 are formed in openings among the sand particles 9. As the occasion demands, the injection pipes 4 may be installed either in perpendicular or aslant, and the injection can be repeated in the case where the air bubbles 8 in the ground decrease. Thereby occurrence of the pressure of excessive porewater can be prevented even in the case where repeated load such as earthquake is applied and, at the same time, unsaturated ground can be created.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention reduces the saturation level of the ground before and after construction of a building, so that the ground does not liquefy even when subjected to repeated loads such as earthquakes. This relates to ground improvement methods for ground improvement.

(Prior Art) Saturated, loose sandy ground causes liquefaction during earthquakes, etc., and there is a high possibility that buildings built on the ground may be damaged. In order to prevent liquefaction, there are ways to reduce the degree of saturation of the ground, which is an absolute condition for liquefaction, or to increase strength through consolidation and compaction. Among these methods, there is a method to reduce the saturation level of the ground by lowering the groundwater level to make the soil unsaturated.

(Problems to be Solved by the Invention) However, many of the above-mentioned consolidation and compaction construction methods involve large-scale construction, and inevitably cause pollution such as vibration and noise.
Moreover, it was difficult to use as a countermeasure method for existing structures.

Although the cementation method by injection can be used as a countermeasure for existing structures, its use is difficult due to economic considerations.

Furthermore, the saturation reduction method has the difficulty of long-term maintenance and management of the groundwater pump.

This invention was developed in view of the above circumstances, and aims to provide a construction method that can be applied to existing buildings, can create unsaturated ground without pumping up groundwater, and is less polluting.

(Means for Solving the Problems) In order to achieve the above object, in this invention, an injection pipe is inserted into the ground from the ground surface, and the foam material is injected into the ground through this injection pipe. .

(Example) Hereinafter, explanation will be given based on the illustrated example. First, as shown in FIG. 1, holes are drilled into the ground by poling from the ground surface 1 and the building mat 2, and a required number of poling holes 3 are provided. Next, an injection pipe 4 is installed in the polling hole 3, and a filter material 5 is inserted into the gap between the polling hole 3 and the injection pipe 4. In addition, an impermeable filling 6 is installed near the ground surface (Figures 2 and 3). By passing a foaming liquid (a foam material 7, a mixture of a surfactant and water) through the injection pipe 4, the foam material 7 is injected into the ground through the injection hole 4a of the injection pipe 4, and bubbles 8 are generated.

In addition to foaming liquids, there are also chemical foaming materials (e.g. diisocyanate + water → carbon dioxide gas) that create air bubbles by chemically reacting with water in the ground, and physical foaming materials that create air bubbles (8) through a physical reaction. For example, CC13F) may be injected directly into the ground, and it is used depending on the injectability of the ground. In any of the above cases, a foam stabilizer is added so that the injected bubbles are stabilized for a long time.

Figure 4 shows the state of the ground when the foam material 7 was injected.
First, before injecting the foam material, as shown in Figure 4 (A), the sand particles 9
0 gap is filled with water 10, and by injecting the foam material 5, sand particles 9 enter the foam material 7 as shown in FIG. 9
(FIG. 4(C)).

FIG. 5 shows the installation pattern of the injection tube 4. In addition to being installed vertically in the ground, the injection pipe 4 may be installed diagonally or horizontally by excavation, backfilling, etc. If the injection pipe 4 is left in the ground after injection, it can be re-injected when the number of air bubbles 8 in the soil decreases.

(Effects of the Invention) As described above, according to the present invention, air bubbles are artificially created between sand particles in the ground, resulting in an unsaturated ground with a reduced value of pore water pressure coefficient, even when subjected to repeated loads such as earthquakes. Generation of excessive pore water pressure can be prevented. It can also be applied to existing buildings, and creates unsaturated ground without pumping up groundwater, so there is no risk of pollution.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view showing the state in which the poling hole has been drilled;
Figure 2 is an enlarged vertical cross-sectional view showing the state where the injection tube is inserted into the poling hole and foaming material is being injected, Figure 3 is a vertical cross-sectional view showing the state after foaming material is injected, and Figure 4 is with foaming. FIG. 5 is an enlarged perspective view showing the condition in the ground from before to after injection, and a vertical cross-sectional view showing the pattern of injection pipe installation. DESCRIPTION OF SYMBOLS 1... Ground surface, 2... Building mat, 3... Polling hole, 4... Injection pipe, 5... Filter material, 6...
... impervious water filling, 7... foam material, 8... bubbles,
9...Sand particles, 10...Water. Figure 4 (A>CB) (C)

Claims (1)

[Claims] (1) A ground improvement method characterized by inserting an injection pipe into the ground from the ground surface and injecting foam material into the ground through this injection pipe.