WO2006037403A1 - Method for de- watering a slurry - Google Patents

Abstract

A method of de-watering a slurry mixture produced from a jet grouting operation, comprising the addition to the mixture of an anionic polyacrylamide in such manner that it is uniformly distributed therein, the anionic polyacrylamide having a high molecular weight and a low-medium charge density. Dewatering is achieved readily and economically.

Description

METHOD FOR DE-WATERING A SLURRY

This imention relates tojet gioutingand to chemical compositions for use in_jel grouting

:> Jet giouting is a soil consolidating teclinique, widely used for many civil engineering applications For example, it can be used to provide foundations for stiuctuics to be erected, to underpin existing sliucluies, to create low peπncdbihtv baπieis, to create ietaining or supporting stnictuies to rcmfoice a soil mass and to complement othci geotechnical structures The jet grouting piocess consists of the disaggregation of the soil or weak rock and its mixing with, and 10 partial replacement by, a cementing agent, normally a cement based giout, the disaggregation is achieved by means of a high energy jet of a fluid which can be watei or the grout itself depending on the system employed

Fust of all, a boie of typically 90-150 mm diameter is drilled in the soil to the depth to which the

\> soil is to be consolidated When the appropπate depth is reached the rod is rotated in piace and a fluid ( water oi the cementing grout itself) is in|ccted at high piessuie through nozzles placed at the end of the rod This has the effect of cutting awav the existing soil and replacing it with a soil-grout mixture which will harden The rod is gradually withdrawn while injection through the rotating rod is continued The result is a cylindrical column of consolidated soil which will 0 harden and foπn a consolidated soil element During the operation the mo\emcnt of the rod can be manipulated to form soil mass of different geometry, such as columns and panels

While much of the soil is used in the consolidation, a large amount is carried away in the form of slurry which is a mixture of soil, cement and water The slum is normallv pumped away 3 from the spot where the jet grouting operation is taking place, so, if the slurry is not fluid enough for pumping using a hydiauhc conventional pump, additional water is normally added The result is a slurry which contains a \eiy large proportion of water, fiequentlv in excess of 80°o Typical contents of a slurry are (b> weight) 50-85% water and 15-50% each of both cement and soil (the latter generally clay oi silty sand) However, it is not unknown for slurries to have 0 compositions Is ing outside these ianges In addition, such slurries can include other ingredients, such as placticiseis, superplasticisers, accelerators and rctardeis, added to modif) the properties of the grout Because of the piesence of cement, such slurries often have high pH, sometimmes in excess of 12

The amount of slurry pi oduced vanes, depending on the type of soil treated Ln clay soil w hei e the jet grouting opei ation is typically much slowei , the amount of slurry produced can be considerable While such slurries can sometimes be utilized in, for example, backfills, iai ge amounts usualh have to be disposed of in landfills, which is expensive for jet grouting conti actois

It has now been found that it is possible to de-water such a slurry miλtuie by a simple, effective ti eatment This invention pio\ ides a method of de-wateπng a slurry mixture produced fiom a jet grouting operation, compi ising the addition to the mixture of an anionic polyacrylamide in such mannei that it is uniformly distributed therein, the anionic polyacryl amide having a high molecular weight and a low-medium charge density

It is surprising to find that an anionic polyacrylamide of low-medium charge densitv has such a good dew ateπng effect in a slurry w ith high pH, because the accepted practice is to use high charge density polyacrylamides

An anionic polyacrylamide for use in this inv ention has a high molecular weight, that is, a weight-average molecular w eight of at least 4,000,000 The molecular weight is prefeiably between 5,000,000 and 20,000,000 In addition, the polyacrylamide has a low -medium chaige density Chai ge density, which is an indication of the number of charged species for a given molecular weight, is a parameter well known to the art and to which theie are frequent references in the commercial hteratui e It is quoted as the percentage of the sodium acrylate content of the polymer For the purposes of this inv ention, a low-medium charge density is one w hich lies within the i ange of from 5-70% Those high MW anionic polyacrylamides having a charge density of from 10%-50% are the most effectiv e and are the prefeπ ed matenals for the purposes of this in\ ention Among the commercially-axailable mateπals which comply with the abovementioned lequirements aie materials in the "Sedipυi" (tiade mark) range of BASF Typical examples of these include "Sedipur" Ap 203 , 1 F2-TR and AF 404

3 The dosage used is fiom 150-500, preferably fiom 200-350, ppm of the sluiry

In the process accoiding to the invention, the polyacrylamide is First dissolved in water, to gi\e a topical!) 05-1% weight solution, and this solution is added to the slurry with stirring This has the effect of separating water out of the soil-cement sluiry, and changing the consistency of

10 the slurry from fluid to mortai-like The sepaiation normally takes less than 5 minutes when some agitation is employed, and the sepaiated water can be simply drained out, or some pressure may be employed to press it out The water which comes out is normally clear, and aftet appropriate neutiahzation can be simply discharged into the sewage system, or where allowed, the open enviionment As a result, the disposal cost such as in a landfill for the abovementioned ; slurry would be diasticalh ieduced, because of the lowei \olume of slurry due to de-wateπng and the lower pi ice for disposing of dry material as opposed to fluid mateπal

For the optimum working of the process according to the invention, the solids content by weight of a slurry to be treated should generally be 50% maximum, prefciably 45% maximum, as υ measuied b\ dning a sample in an o\en at 105⁰C These contents figuies are based on a relatively uniform distribution of particle sizes of clay, silt, cement, etc in the slurry However, when such a slurry contains a minoi proportion of mateπals of largei particle size, such as sand and lumps of clay (as can happen in practice) the measuied solids content of a given sample can be considerably higher hi such a case, the performance of the piocess of the imention is 5 unaffected, and, for the purposes of this invention, such a slurry is consideied to fall within the solids content limits given hereinabo\e

The in\ ention is further described w ith reference to the follow ing non-limiting examples

A seπes of anionic polyacrylamides are tested for dewateπng activity The mateiials tested are as follows Example No, Polvacrylamide Averaεe MW Charge densitv 1 SEDΓPUR APl oo 10,000,000 10% 2 SEDIPUR AF203 5,000,000 20% SEDDPUR AP204 12,000,000 20%

4 SEDIPUR AF205 19,000,000 20% 5 SEDIPUR TF2-TR 1 1 ,000,000 20% 6 SEDIPUR AF404 15,000,000 40% 7 SEDIPUR AF701 13,000,000 70% SEDIPUR AF900 15,000,000 90%

The mateials are tested as follows. A slurry containing 25% fine soil (silt and clay), 15% cement and 60% water is prepared. Each of the polyacrylamides hereinabove mentioned is added with gentle stirring to a sample of this slurry at a rate of 280ppm. The effectiveness of each polyacrylaimide is assessed by how quickly water is removed, how much Water is removed and how quickly the remaining solid forms a stiff mass as a result of this dewatering.

The results obtained by using the various materials are assessed and the results are shown in the following table, where +++ represents excellent, ++ average (but acceptable), + some effect (bit unacceptable) and - no effect.

Example No. Result

1 +++

2 +++

3 +++

4 +++

5 +++

6 ++

7 +

Claims

Claim

1 A method of de-watenng a slurry' mixture produced fi om a jet gioutmg operation, comprising the addition to the mixtuie of an anionic polyacrylamide in such manner that it is uniformly distiibuted therein, the anionic polyacrylamide having a high molecular weight and a low-medium charge density