FI81414B - Method of stabilizing ground - Google Patents

Abstract

Method of stabilizing ground 3, for example fine-grained soil or clay, by producing subsidences in the ground by means of vacuum pumping comprises the formation of vertical drainage holes which are connected to suction pumps 7 in order to carry away drainage water, and bringing about a negative pressure in an area of the ground which is covered by an airtight tarpaulin 6 which is fixed to the ground at its edges, in which way atmospheric pressure contributes to said subsidences. The ground is frozen first so as to form ice beads which grow by virtue of the fact that water is drawn out of the ground/clay between the ice beads which in this way exert a consolidating pressure on the mineral grain aggregate of the ground. The frozen area 2 is then thawed by supplying heat, after which excess water is drawn out of the ground and the drainage holes by means of vacuum pumping in order to produce said subsidences, the treated area then appearing as a depression.

Description

1 81414

The present invention relates to the stabilization of soil, e.g. fine soil or clay, by causing subsidence in the soil as stated in the introduction to the following method requirement 1.

By loading, for example, clay soil, large depressions can form, which increase with the thickness of the clay layer and the magnitude of the load. This can cause large total and differential depressions that can completely or partially damage the structures supported by the clay. For this reason, it would be advantageous to be able to provide depressions in the clay soil before erection of the structure begins or possibly before the structure is brought into such a condition that it may be damaged by subsidence of the soil.

Known methods for accelerating the subsidence of natural clay are, for example, filling (loading the soil with a ballast), lowering the groundwater, vacuum pumping, electroosmosis, vertical drying or a combination of two or more of these methods.

25 All of these methods have advantages and disadvantages, taking into account the time used, the power, the carrying capacity, the simplicity and the general applicability.

Especially soft soil or clay cannot easily form the foundation of a house structure because the load-bearing capacity is too poor. Various methods such as piling, mass transfer and compensated formation have so far been used to increase the structural / payload.

35 In both extremely poor soil conditions and those referred to above, the above methods cannot always be implemented and, despite their feasibility, may be an unfavorable and time-consuming solution for the structure.

2,81414

A building built directly on loose masses, where a larger or smaller part of the masses under the groundwater is clay, is at risk of long-term subsidence damage when the groundwater pressure or level decreases or when the pressure on the grain body increases so that depressions occur in the bulk masses.

As stated above, the prevention of soil subsidence after it has been loaded by erecting housing structures 10 or other forms of loading, such as road construction, etc., is of the utmost importance. As stated, it is advantageous to be able to provide depressions in the soil before it is loaded, and it is an object of the present invention to provide a method as indicated in the introduction so that depressions in the soil can be made more rapidly so that the possibility of additional depressions after loading becomes almost impossible.

According to the invention, this is achieved by means of the characteristic features set out in the characterizing part of the following independent method claim 1 and in the following dependent claims.

An embodiment of the method will now be described with reference to the drawing, in which Fig. 1a shows a section through the original clay soil, Fig. Ib shows a first step of the method in which a desired area of soil is frozen, Fig. 1a shows a second step of a method in which a frozen area is a third step in which excess water is withdrawn from the soil, and Fig. 1e shows a section through a depression in the form of an insert caused to the soil 35 and the top surface of the soil treated by the method.

By means of the method according to the invention, when treating the original clay soil 3 shown in Fig. 3 81414 1a, coaxial freezing pipes 1, 1a are installed in the soil 3 in order to cause clay soil compression and compression, A freezing agent - i.e. whatever causes frost - is then introduced into the freezing pipes 1 so that the area 2 of the clay soil 3 freezes. The water in the clay freezes slowly as it cools into ice lenses, which increase as water is removed from the molten clay near / between the ice lenses. Increasing ice lenses apply solidifying pressure to the mineral aggregates that make up the clay mass. The frozen area 2 is then thawed by introducing the heat which may be obtained / removed from the soil during the freezing of the next adjacent area 2 in the soil 15 3. This can be accomplished by a well-known heat pump technique, which is not explained in more detail here. When the frozen area 2 is thawed, excess water is generated, which must be removed, which is obtained as shown in Fig. Id, in which the freezing pipe 1 is pulled out and at the same time the resulting hole is filled with sand or some other filterable substance. In this case, a vertical drainage hole is made in the frozen and then thawed area 2 of the soil 3. A thin uniform layer of sand 5a 25 is placed on the soil to connect the tops of the drainage holes with sand 5, after which the whole area with Thereafter, a vacuum 30 is created in the drying holes in the sand 5 and in the sand layer 5a on the soil 3 by means of a vacuum pump 7, which is shown in Fig.

Id, which in the situation shown is tightly connected to the tarpaulin 6. This installation of the vacuum pump can of course take place in several different ways, e.g. by a pipe coming from the pump through a tight bushing 35 or through a pipe leading to the tarpaulin edge and several areas under the tarpaulin. possibly down to the sand layer 5a or to the sand 5 in the drying openings. In that case, these pipes, which are suction pipes 4 81414 with suction openings, must be fitted with filters which allow the drying water to flow into the pipe while retaining sand.

In this case, due to the generated vacuum, the excess water is pulled out of the frozen / thawed area 2 of the clay 3 and pumped out. This generation of vacuum as well as the pumping out of the excess water can, of course, take place by means of two sets of pumps, namely a vacuum pump for generating a vacuum and a suction pump for pumping out the excess water.

10

After the above-mentioned treatment of the areas 2 of the soil 3 has been carried out by the method according to the invention, the entire treated area 2 of the soil 3 is submerged and the whole frozen area 2, which has been thawed and subsequently thawed, has gained greater density, less pressure sensitive than the original. The geotechnical properties of this treated soil volume 2 have thus improved.

Claims (3)

1. Method for stabilizing soil, e.g. fine-grained soil or clay by causing depressions in the soil by means of vacuum pumping, comprising generating vertical drainage heels, coupled with suction pumps for drainage of the drainage water, and for generating underpressure in the soil in the area covered by an airtight tarpaulin, is closed to the ground, whereby the air pressure acts in part on said reductions, characterized in that 1) the ground is first frozen to form ice lenses, which become larger by removing water between the ice lenses from the soil or clay, which at the same time direct a consolidating 2. Eat the ground grain mineral aggregate; 2. The frozen area is melted again by conducting heat thereto; 3) Excess water is withdrawn from the soil and drainage heels by means of vacuum pumping to develop said depressions, the area looking like a recess. 20 Method according to claim 1, characterized in that cooling pipes (1) are first installed in the ground (3), which are coupled with a cooling device for freezing the area (2) of the ground (3), after which heating medium is fed to melt the frozen area ( 2), after which the cooling pipe (1) is replaced by sand (5) and a sand layer is laid on the ground to connect the generated drainage heels before the application of the tarpaulin (6) and the start of vacuum pumping. Method according to claim 1 or 2, characterized in that heat extracted from the ground (3) during freezing of its area is used for melting the previously frozen area (2).