GB2179080A

GB2179080A - Suspension of powders in liquid for soil injection and the like

Info

Publication number: GB2179080A
Application number: GB08614230A
Authority: GB
Inventors: Daniel Gouvenot; Hubert Vattement
Original assignee: Soletanche SA
Current assignee: Soletanche SA
Priority date: 1985-06-12
Filing date: 1986-06-11
Publication date: 1987-02-25
Also published as: AU5855086A; ATA158786A; GB8614230D0; FR2583441B1; KR930010927B1; JPS6284177A; KR870000408A; DE3619551A1; AT394858B; FR2583441A1; AU582859B2; DE3619551C2; JPH0417997B2; GB2179080B

Abstract

A process for the preparation of a filling, which can be injected into porous or fissured materials or into fine alluvia, comprises mixing a product in particle form with a liquid, e.g. water, in the presence of a deflocculation agent which separates the suspended particles from each other; keeping the suspension deflocculated in this way in a container for a time sufficient to permit the partial sedimentation of it; and drawing off the volume of deflocculated suspension present in the container above a given level.

Description

SPECIFICATION Suspension of powders in liquid for soil injection and the like The object of the present invention is the preparation of suspensions of powders in a liquid, intended to be injected into porous or fissured materials or into fine or very fine soils with the aim in particular of modifying the consistency of them.

It is known that some materials necessitate treatment by injection of cement filling. These are, for example, porous reinforced concretes, reinforced concretes which have been attacked by corrosive liquids, or else cracked concretes. In such cases the penetration of the cement filling into the mass of a material of this kind is limited by the grain size of the unit cement particle and at the same time by the aggregation of these same particles with each other.

Similarly, it is known that alluvia are generally divided into two main types, namely coarse alluvia and fine alluvia.

Coarse alluvia may be readily subjected to injections of cement filling or bentonite-cement filling (a filling in which the cement particles are in suspension in water, the bentonite possibly being added to improve the stability of the suspension).

However, fillings of this kind cannot be injected into fine alluvia, since the soil pores in this are too somali to permit the penetration and circulation of normal cement particles.

This is the reason for which injections can be made into fine alluvia of this kind only if solutions based on silicate or silica which do not contain suspended particles and which are solidified by means of a reagent are used.

This latter procedure may present the disadvantage of causing some pollution of the soil, notably with respect to groundwater and also of having a poor life, in view of the fact that the structure of the gel obtained is likely not to be stable in the course of time. This phenomenon, known by the name of synaeresis, may have a very adverse effect on gels obtained by means of silicate solutions.

For the reasons given above, attempts were already made in the past to inject into porous or fissured materials, or also into fine alluvia, cement fillings, using very finely crushed cements, i.e. cements the particles of which are of a size less than about 15 microns, whereas in normal cements the particles generally have a diameter of between 0 and 100 microns.

Finely crushed cements, however, are difficult to obtain and are high-priced, costing, for example, about twenty times as much as a conventional cement.

Attempts were also made to obtain the required cement from a conventional cement which is transported pneumatically, by subjecting it to a cyclone effect so as to separate the finest particles from the largest particles.

This process is also unsatisfactory, since the application of it is still costly and the results obtained are too irregular for the injections produced with a filling containing cements of this kind to be reliable.

The present invention relates to a process permitting the production of a filling composed of a suspension in a liquid of particles such as cement particles which are sufficiently fine for it to be possible to inject the said filling into fine alluvia, the diameter of the particles being less than the intergranular spaces in the soil into which the injection is made.

The object of the present invention is a process for preparing a filling which can be injected into fine alluvia or porous or fissured materials, characterized in that a product in the form of particles is mixed with a liquid such as water in the presence of a deflocculation agent which separates the suspended particles, that the suspension deflocculated in this way is kept in a container for a time sufficient to permit the partial sedimentation of it, and that the volume of deflocculated suspension in the container is drawn off above a given level.

According to the invention 0.5 to 5% by weight deflocculation agent is used in relation to the weight of the particles in suspension.

It can be understood that by selecting the height of the container, which plays the role of a decantation tank, as well as the time of decantation and the level from which the suspension is drawn off it is possible to determine the maximum diameter of the particles contained in the emptied suspension, which depends on the geometry of the cavities to be injected.

According to the invention, the suspension obtained in this way is used to produce a filling which can be injected into fine alluvia or into fissured or porous materials.

The lower section of the suspension remaining can be used for other purposes or discarded.

In a preferred embodiment of the invention, the solid material occurring in the form of particles is composed of cement and the liquid serving to form the suspension is water.

According to the invention, it is also possible to use instead of cement ashes of silica and crushed calcium carbonate, which are treated according to the invention separately, then being mixed just before injection, or being injected separately into the medium to be treated so that they come into contact with each other in situ.

According to the invention it is also possible to use as the suspension liquid a solution of silicate or a silica liquor, or indeed any other liquid capable of reacting after injection with the solid product present in the form of particles.

The deflocculation agent which is added to the suspension of solid particles may be com posed, for example, of melamine resins, naphthalene sulphonates, sodium polyphosphate, sodium alkyl sulphonate or ammonium polyacrylate.

The object of the present invention is also suspensions of solid products obtained by the process which has just been described.

In order better to understand the invention, several applications of it will now be described with the following examples by way of illustration which are in no way limiting.

Example 1 To produce a filling composed of an aqueous solution of cement intended to be injected into a fine sand, the particle diameters of which are between 0 and 0.3 mm, the following procedure is adopted: 500 kg of CLK 45 cement is dispersed in 830 litres of water contained in a high-turbulence cement-mixer. The mixing is continued for about 3 minutes, after which between 2.5 and 7.5 kg of a melamine resin which acts as a deflocculation agent is added and stirring is continued for about 2 minutes.

The mixture prepared in this way is placed in a tank of cross-section 2 m3 which is fitted with an emptying cock located 25 cm below the surface of the liquid, which is allowed to sediment for one hour.

The emptying cock is then opened and 500 litres of filling is recovered which contains between 30 and 35% of the 500 kg of cement initially used.

The cement particles contained in this filling have dimensions of between 0 and 10 microns, whereas in the cement used initially the particle dimensions were between 0 and 100 microns.

The filling obtained in this way is stored in a tank fitted with stirrers. It can then be injected by conventional processes into a soil composed of a sand, the grain size of which is between 0 and 0.3 mm.

In one variant of the process the sedimentation time is limited to 30 minutes and 500 litres of filling is then drawn off which contains between 50 and 55% of the intial weight of cement with particle sizes between 0 and 15 microns.

Example 2 To produce an aqueous suspension of silica intended to be injected into a fine soil, the grain size composition of which is between 0 and 0.3 mm, 300 kg of silica powder which has a grain size of from 0 to 50 microns is dissolved in 1 cubic metre of water contained in a high-turbulence cement-mixer. The mixture is mixed for about 3 minutes and then 3 to 9 kg of deflocculation agent, composed, for example, of naphthalene sulphonate, is added.

The solution is then placed in a tank with a surface area of 2 square metres which is fitted with an emptying cock located at a distance of 25 cm from the surface of the liquid.

After a sedimentation time of 3 hours the suspension which is above the cock is drawn off.

Whereas the initial suspension has a density of 1.147, the suspension drawn off has a density of between 1.120 and 1.125. It can easily be injected into fine soil such as that in example 1 and seal it.

By way of comparison, it is impossible to inject the initial suspension, since it is selffiltered.

The suspension obtained according to the invention, on the contrary, is injected very easily and under a low pressure. The soil pores are then obstructed by the silica powder and the soil is sealed.

Example 3 To effect an injection of a mixture of silica powder and calcium carbonate powder in suspension into a fine soil the procedure is as follows: A suspension of silica powder is first prepared as described in example 2.

In addition, 300 kg of crushed marble (CaCO,) suspended in 1000 litres of water is then placed in a high-turbulence cement-mixer.

6 kg of naphthalene, which acts as a deflocculation agent, is then added and the mixture is allowed to sediment for about 3/4 of an hour to one hour and the 25 cm of suspension which are below the level of the initial surface is then drawn off.

The grain size of the calcium carbonate initially used is between 0 and 50 microns and the initial density of the suspension is 1.16 to 1.18.

In the suspension obtained according to the invention the grain size of the calcium carbonate is between 0 and 20 microns and the density about 1.14 to 1.16.

The two suspensions which have been obtained as described above are mixed in equal volumes and this mixture is injected into a soil composed of fine sand, the grain size of which is between 0 and 0.3 mm.

In this way a sealed and stable sand is obtained.

In one variant, the two suspensions may be injected in succession into the soil.

Example 4 To produce a suspension of calcium carbonate powder in a solution of silica or sodium silicate which can be injected into a fine soil the following procedure is adoped: A suspension of calcium carbonate is first prepared as described in example 3 above, and then this suspension is mixed with a solution of sodium silicate or silica liquor containing 10 to 25% by weight silica SiO2 in the ratio of one volume of the calcium carbonate suspension to 0.5 to 1.5 volumes of silicate or silica liquor.

The mixture obtained in this way is injected into a soil composed of particles between 0 and 0.3 mm and a sealed and stable soil is obtained.

It is quite clear that the embodiments of the invention described above are in no way limiting and that they can undergo any modification which is desirable without, however, going beyond the scope of the invention.

Claims

1. Process for producing a filling which can be injected into porous or fissured materials or into fine alluvia, characterized in that a liquid such as water and a product in particle form are mixed in the presence of a deflocculation agent which separates the suspended particles; that the suspension thus deflocculated is kept in a container for a sufficient time to permit the partial sedimentation of it; and that the volume of deflocculated suspension which is above a given level in the container is drawn off.

2. Process as in claim 1, characterized in that the product present in the form of particles is composed of cement, silica powder or calcium carbonate powder.

3. Process as in either of claims 1 or 2, characterized in that the liquid is water, a solution of silica or a solution of sodium silicate.

4. Process as in any one of the foregoing claims, characterized in that the deflocculation agent is composed of melamine resin, naphthalene sodium sulphonate, sodium polyphosphate, alylnaphthalene sodium sulphonate, sodium alkyl sulphonate or ammonium polyacrylate.

5. Process as in any one of the foregoing claims, characterized in that the deflocculation agent is used at the rate of 0.5% to 5% by weight in relation to the product present in particle form.

6. Process as in any one of the foregoing claims, characterized in that the sedimentation time and the depth of suspension which is drawn off are determined in order to obtain particle dimensions less than 15 microns and preferably less than 10 microns.

7. Process as in any one of the foregoing claims, characterized in that two suspensions, such as a suspension of silica powder and a suspension of calcium carbonate powder, are prepared separately, these being mixed before the injection of them into the soil.

8. Process as in any one of claims 1 to 6, characterized in that two suspensions, such as a suspension of silica powder and a suspension of calcium carbonate, for example, are prepared separately and these are injected in succession into the soil.

9. Suspensions intended to be injected into fine soils or into porous of fissured materials, characterized in that they are obtained by the process as in any one of claims 1 to 8.

10. A soil when treated with a suspension according to claim 9.