JPH0310766B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention improves the ground by using a sand drain method in which soft ground consisting of silty soil and clay soil is covered with a water-permeable cylindrical bag. It's about technology.

(Prior technology) Conventionally, when performing ground improvement by consolidating and dewatering soft ground composed of silty soil and clayey soil using the sand drain construction method, the sand drain was placed in the soft ground during the sand drain construction work. A cylindrical bag is made from a coarse sheet material with good water permeability made of a polymeric material to prevent it from being cut vertically and becomes discontinuous, and sand is filled into the cylindrical bag to create a sand drain. is being created.

(Problem to be solved by the invention) However, sand drains covered with cylindrical bags are created in soft ground at a pitch of about 1 m, and then a consolidation load of earth and sand is placed on top of the area where the sand drains are created. When performing consolidation dewatering of soft ground,
The sand drain containing the cylindrical bag becomes a type of rigid pile-like body, and the consolidation load is supported by the sand drain that has become a pile-like body, and the consolidation load is not sufficiently transmitted to the soft ground. There's a problem.

The reason why the above-mentioned sand drain becomes a kind of rigid pile-like body is that the cylindrical bag covering the sand drain is very strong, so the sand drain is restrained, and the restrained sand drain becomes a type of sand pile. This is because even when the soft ground is further compacted by its own weight and shrinks due to the progress of compaction, the sand drain cannot deform by bending freely in response to the shrinkage. Therefore, since the sand drain becomes a pile-shaped body, the load is reduced and transmitted as it goes deeper into the soft ground, which reduces the loading effect on the important soft soil layer, which is necessary for consolidation dewatering. Excess pore water pressure in the soft soil layer is not sufficiently generated, which has the disadvantage of overriding the ground improvement effect.

In addition to the above drawbacks, there is also the drawback that negative friction (a phenomenon in which the sand drain prevents the soft ground from sinking) occurs when the sand drain is in the form of a pile.

(Means for solving the problem) The soft ground improvement method using a sand drain covered with an expandable cylindrical bag according to the present invention is designed to eliminate these drawbacks. a step of creating a sand drain in soft ground by filling sand into a cylindrical bag formed by suturing with a thread that dissolves in water; It is characterized by comprising the steps of dissolving the sutured threads by moisture in the ground, and expanding the cylindrical bag more than when it was sewn due to contraction of the soft ground.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is a soft layer to be improved, 2 is a sand drain created within this soft layer 1 at a predetermined interval, and 3 is a sheet material with good water permeability covering this sand drain. 4 is earth and sand as a load, and 5 is a sand mat.

In the first embodiment of the present invention, as shown in FIG. 2, the vertical seam 3' of the cylindrical bag made of a water-permeable sheet is made of thread that can be dissolved by absorbing moisture, or The stitches are sutured using threads that partially dissolve as they absorb moisture, reducing their strength and making them easier to break.

In the second embodiment of the present invention, a cylindrical bag with a diameter considerably larger than the diameter of the sand drain is used, and when the sand drain is installed, it is sutured with water-soluble thread so that it has the same diameter as the sand drain. After installation, the threads will melt underground and the sutures will come undone. Specifically, as shown in Fig. 3, a water-permeable cylindrical bag 3 with a diameter larger than the diameter of a sand drain to be constructed in soft ground is used, and the inner side of both longitudinal edges 6 of this bag is drained of moisture. The water-permeable cylindrical bag body 3 is sewn with a thread 7 that dissolves and breaks when absorbed, or a thread 7 that partially dissolves and loses its strength when it absorbs moisture. The diameter of the sand drain is reduced to the diameter of the sand drain at the time of construction.

In the first and second embodiments, the yarn that dissolves and breaks by absorbing moisture, or the yarn that partially dissolves and becomes weaker and easier to break due to absorbing moisture, is as follows: For example, a thread made by connecting short fibers with a water-soluble adhesive can be used.

(Function) When a large number of sand drains are created in soft ground using the cylindrical bag of the present invention, and a consolidation load of earth and sand is applied to the sand drain creation area, the cylindrical bag 3 is sewn together. The suture thread 7 is dissolved by water in the ground and breaks, or its strength is reduced and becomes easy to break, so the suture thread 7 breaks due to the contraction of the soft ground as consolidation dewatering progresses, causing the cylindrical bag 3 to break. The diameter of the sand drain expands more than when it is sutured, and as a result, the restraining force of the sand drain by the cylindrical bag 3 is released, and the sand drain is not compacted, and the sand drain contracts in the soft ground. It can be deformed by bending freely depending on the situation.

(Effects of the Invention) Therefore, according to the present invention, a sand drain covered with a water-permeable cylindrical bag constructed in soft ground is not compacted into a rigid pile as in the conventional case. Therefore, the consolidation load can be sufficiently transmitted into the soft ground, and as a result, the excess pore water pressure in the soft ground necessary for consolidation and dewatering can be sufficiently generated, and good ground improvement can be carried out.

In addition, in the present invention, the cylindrical bag is sewn with thread, so by changing the thickness of the thread and the stitching pitch, the water solubility and mechanical strength can be adjusted.
Adaptability to bending can be freely controlled.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the sand drain construction method, FIG. 2 is an explanatory diagram of a cylindrical bag used in the construction method of the present invention, and FIG. 3 is an explanatory diagram of a cylindrical bag in another embodiment. 1...Soft layer, 2...Sand drain, 3...
Tubular bag body, 3'... seam, 4... earth and sand, 5...
Sand mats, 6...both edges, 7...thread.

Claims (1)

[Claims] 1. A process of creating a sand drain in soft ground by filling sand into a cylindrical bag formed by suturing a water-permeable sheet with thread that dissolves in water, and after creating the sand drain. consisting of a step of dissolving the threads suturing the tubular bag by moisture in the ground, and a step of expanding the tubular bag more than when it was sutured due to contraction of the soft ground. A method for improving soft ground using sand drains.