FR2777305A1 - Earth spoil treatment method for producing back fill material - Google Patents

Abstract

The method for the treatment of earth spoil (10) in order to make back fill (15) involves crushing (12) the earth spoil, followed by a screening (14), the crushing and the screening being in a closed loop. Lime is added to the earth spoil at the start of the treatment and the back fill is recovered. Independent claims are included for an apparatus for implementing the method, and the back fill produced by this method.

Description

A method of processing cuttings to make it into

  embankment, an installation for installation, as well as the embankment obtained by this process and having a predetermined densification capacity and sensitivity to water. In the field of public works, where it is necessary to dig trenches to pass cables, conduits, and this in particular under or along pavements and sidewalks, the excavation material of these trenches is very important and their reuse , to make it backfill, has many advantages. The treatment of cuttings to make it 1o backfill for trenches has therefore become of paramount importance for reasons related to the environment and the need to reduce, on the one hand the discharge of cuttings, and on the other hand the consumption of natural embankments, for example

embankments from quarries.

  From the point of view of filling the trenches, the choice of usable i5 materials and their characteristics must meet precise specifications from the point of view of respect for the environment, the mechanical, physical and chemical properties of the embankment, and these constraints. depend on the use made of it according to the trenches and inside a trench. Thus, for its use as an embankment for the road, for example, the specifications impose the following characteristics in particular on the embankment used: - a densification capacity Q3-Q4, as defined by the standard

NF 11300,

  - a sensitivity to water defined by the IPI and ICBR values, the ICBR / IPI ratio being greater than 1 and the IPI index greater than 15,

  and this whatever the particle size.

  The IPI and ICBR values are defined in NFP 94 093 and 94 078 standards. Embankments and their characteristics according to their use are defined by

NFP 98 331 standard.

2 2777305

  Other compliance criteria may also be taken into account, depending on whether the intended use of the embankment (for the lower part of the embankment or the upper part of the embankment, for example), depending on the nature of the trench, of this

  found there, and according to the constraints linked to the environment.

  The grain size can be predetermined by the use that will be made of the fill in the trench. In the laying area, we generally use a grain size of 0/6 mm to 80% of 0/4 mm, and about 70% of 0/2 mm, for reasons of non-aggressiveness with respect to what we set (pipes, cables, ...), and above, for the upper and lower parts of embankment, less restrictive standards. Thus, in general, material is used for the lower and upper parts whose particle size does not exceed one third of the width of the trench. For example, to fill a trench of cm, for the lower and upper parts of embankment, we will use a

  material with particle size less than 133 mm.

  Generally, the grain size of an embankment is between 0/6

and 0/50.

  It is known from document FR-A-2 729 685 to treat cuttings material to make them usable as backfill material. However, the material obtained remains sensitive to water, with an IPI value of less than 15 and an ICBR / IPI ratio of less than 1, so that the material obtained according to this process cannot be used in the upper part of the embankment or in the lower part of embankment, parts which are in majority majority, in quantity, when one fills a trench. In addition, this method only allows a limited range of

  cuttings, and in particular not clayey cuttings.

  The present invention relates to a new cuttings treatment in a wider range (higher clay and water content), for

  make it an embankment that meets the criteria defined above.

  Thus, the present invention relates to a process for treating cuttings to make it backfill, in which the cuttings to be treated undergo crushing, followed by screening, the crushing and screening being in a loop, and

3 2777305

  lime is added to the incoming cuttings, and the compliant backfill is recovered. Another object of the invention is to provide such a process for treating cuttings to make it backfill, in which the cuttings to be treated are added with lime upstream of a crushing and undergo crushing and loop screening. , the screening residue being recycled to

  upstream of the crushing, and we recover compliant backfill.

  Another object of the invention is to provide such a process for treating cuttings to make it backfill, in which the cuttings to be treated are added with lime upstream of a primary crushing and undergo the primary crushing, then screening, the residue from the screening being recycled upstream of the screening by undergoing a secondary crushing, and

compliant backfill.

  Another object of the invention is to provide an installation for the implementation of a cuttings treatment process in order to make it into compliant backfill. Such an installation comprises a crusher, a screen, means of transporting the cuttings from their source to the crusher, means of transporting the crushed cuttings from the crusher to the screen, means of transporting the residue from the screen to the crusher, means of distribution of lime in the cuttings, arranged at the means of transport of the cuttings from their source to the crusher or at the level of the crusher, with the exception of means of

  scalping of the cuttings and mixing of the fill.

  Another object of the invention is to provide such an installation, that is to say

  say without scalping means or kneading means, making it possible to treat cuttings to make it into compliant fill, installation which comprises a crusher, a screen, means of transporting the cuttings from their source to the crusher, means of transporting the crushed cuttings from the crusher to the screen, means of transporting the residue of the screen upstream of the crusher, and means of distributing lime in the cuttings at the level of the means of

  transport of cuttings from their source to the crusher or at the crusher.

4 2777305

  Another object of the invention is to provide such an installation, that is to say

  say without scalper or kneader, allowing to treat cuttings to make it into compliant embankment, installation which includes a primary crusher, a screen, a secondary crusher, means of transport of the cuttings from their source to the primary crusher, means of transport of crushed cuttings from the primary crusher to the screen, means of transporting the residue from the screen to the secondary crusher, means of transporting the cuttings from the secondary crusher upstream of the screen, and means of distributing lime in the cuttings at the means of transport spoil from their source in

io primary crusher.

  As will be seen below, the installations can of course include other devices customary in the field of cuttings treatment and

backfill.

  For the implementation of this process, the cuttings are however not the subject of what is called scalping within the meaning of the present application, that is to say a selective sorting tending to separate the materials from grain size greater than 60 mm or 40 mm for other materials. Such selective sorting can also be carried out by a screen or bucket screen. This is why the installations of the invention do not include means for scalping the cuttings or for screening. The absence of scalping is an advantage compared to

usual techniques.

  Furthermore, the method is implemented without its own kneading step. In the usual natural embankment treatment techniques, it is known to treat with lime, at the end of the chain, which requires mixing the embankment with lime. In these methods, a kneader is necessary at the end of treatment, because the kneader could not knead the natural fill at the start of treatment, before crushing. In the process of the invention, the crusher

also performs mixing.

  By excavation according to the invention, is meant a mixture of various materials, such as clay, silt, solid or serious elements, or materials with a particle size greater than 60 mm such as bricks, pavers, light foundation concrete.

2777305

  of pavement, agglomerates, flint, asphalt, curbs, and generally what is extracted from the ground and pavements when digging a trench.

  Another object of the invention is to provide compliant backfill, that is

  say that meets the criteria related to trench use, a densification capacity Q3-Q4, as defined by standard NF 11300, a sensitivity to water defined by the IPI and ICBR values, the ICBR / IPI ratio being higher at 1

  and the IPI index greater than 15, and a predetermined particle size.

  For the laying area, as we saw above, a particle size of

  0/6 mm to 80% of 0/4 mm and about 70% of 0/2 mm may be required.

  Thus, in certain laying areas or according to certain constraints related to the use of trenches, it may be necessary to have non-aggressive backfill (due to the particle size), having a pH of less than 10, an electrical resistivity greater than 1000 Qcm. (AFNOR 05-252 standard), which is possible

by implementing the invention.

  A determined thermal resistivity and gas permeability

may also be required.

  The lime introduced into the incoming cuttings is used in an amount of 0.1 to 10% by weight of the cuttings, preferably 0.8 to 3%. Preferably, about 1% lime is used. The amount of this additive obviously depends on

  the quality of the cuttings treated and the qualities required for the backfill.

  As lime, it is possible to use lime of the type used in public works, and in particular so-called "fine" lime. A particle size of

  the order of about 0.1 to 10 mm, preferably about 0.2 mm, is chosen.

  Other details and advantages of the invention will be better understood at

  using the detailed description below, and illustrative examples which

  follow. Reference is made below to the following appended drawings: FIG. 1 shows schematically a treatment installation

  cuttings making it possible to implement the method of the invention.

6 2777305

  Figure 2 shows schematically another cuttings treatment installation allowing to implement a variant of the process

of the invention.

  For the purposes of the invention, the term “crushing and screening” is understood to mean the usual stages of the treatments undergone by recovery materials in an attempt to make it backfill. These methods are implemented in conventional crushers and screeners, as described in the document "Aspects of processing techniques for recycling of building materials" Aufbereitungs-Technick, 32 (1991), Januar N 1, Wiesbaden. Thus, as a crusher, it is known to use sand, impact, cone and ball mills. When only one crusher is used, or as a primary crusher,

  preferably an impact crusher is used.

  The screens are chosen, in the usual way, so as to obtain the desired predetermined particle size. A 6.3 screen can thus be used to prepare the fill for the laying area. The size of the last of the screen grids is indicated here; the screens are in fact generally provided with several stages

  screening, with decreasing grid size on the way down.

  Within the meaning of the invention, the screening residue or the screen is the part of the flow entering the screen which does not pass through it because the pieces are too large, and is discharged therefrom. It must therefore be crushed again, which is achieved by passing through the crushing-screening loop. The other part of the

  incoming flow passing the screen constitutes compliant backfill.

  Furthermore, the means of conveying, transport and supply are usual in this type of installation. These include conveyor belts, belt feeders, conveyor belts, or generally

  conveyors, and dosing hoppers.

  Within the meaning of the invention, the compliant cut is ready for use; its content

  water can however be adjusted, for example by sprinkling.

  A first variant of the process of the invention appears in Figure 1.

  The cuttings to be treated coming from the source 10 are, from a feed hopper 19, conveyed by a conveyor belt 11 to a crusher

7 2777305

  12. The crusher 12 is connected by a conveyor belt 13 to a screen 14 which discharges, on the one hand the compliant embankment 15 and on the other hand, the residue of

  screening which is conveyed by a conveyor 16 upstream of the crusher 12.

  The lime distribution means are constituted by a dosing screw 17 which discharges lime in a controlled manner in the cuttings to

  treat 10 during conveyance on the belt 11.

  To this end, the strip 11 can be equipped with weighing means 18 which, connected to the screw 17 allow the controlled addition of the quantity of

lime, by enslavement.

  In Figure 2 is shown a second variant of the method implemented in an installation according to the invention. The cuttings to be treated 20 are conveyed from a feed hopper 32 on a conveyor 21 to a primary crusher 22. The conveyor 21 is equipped with a dosing screw 30 discharging lime in a controlled manner in the cuttings which are then treated in the primary crusher 22. The crushed cuttings are then conveyed by a strip 23 to a screen 24 which discharges, on the one hand the conforming fill 25, and on the other hand a screening residue which is conveyed by a belt 26 to a secondary crusher 27, the product of crushing by the crusher

  secondary 27 being conveyed by a band 29 upstream of the screen 24.

  A weighing means 33 is installed under the conveyor 21, and in a manner known per se, makes it possible to control the metering by the screw 30, by being connected to it by

control means 34.

  In addition, if the secondary crusher 27 is cone-shaped, a tester 37 can be provided which makes it possible to stop it in the event that metal is present on the

  strip 26. Tester 37 is optional and shown in dotted lines in Figure 2.

  Finally, there may be provided, optionally and preferentially, a rail defender 35, which is disposed before the screen 24 on the strip 23. It may also be provided a buffer hopper 36 which makes it possible to regulate the supply of the secondary crusher 27 screen residue. One can also provide an intermediate storage 28 of the screen residue. Depending on the characteristics of the cuttings to be treated, it is possible, instead of treating the cuttings immediately, to accumulate the cuttings

8 2777305

  from different sites to obtain, by dosing the cuttings compositions from various origins, more homogeneous fill compositions. We

  can thus provide 31.31 'sources of spoil from various sources.

  In a variant of this second method, the dosing screw 30 ′ is installed so as to deliver the lime at the level of the crusher 22 rather than at the level of the conveyor 21. Similarly, in the variant of FIG. 1, the dosing screw 17 so that the lime is added to the

  cuttings in the crusher. One could also provide two dosing screws.

  These variants are represented in Figure 2 in dotted lines for the cuttings to be treated 31, 31 ′ and for the temporary storage of screening residues

  28, the undercarriage 35, the buffer hopper 36, and the dosing screw 30 '.

  Alternatively, the screen can be equipped with anti-

  clogging. Likewise, the entry and exit of the crushers can be

equipped with air cannons.

  These installations can moreover be provided fixed on a site, or

  mobile, to be moved around the site or to other sites.

RESULTS

  Using the installation of the variant in Figure 1 with a 1 m wide impact crusher with a rotor diameter of 1 m, 40 t / h of compliant backfill can be obtained. Using that of the variant of the

  Figure 2, the flow is considerably increased, and up to 70 t / h are obtained.

  In both cases, a 6.3 screen is used to obtain a particle size of 0/4 mm. At the end of the cycle, a fine rate varying from 20 to 30%, a water content of 10 to 16% is obtained, using 1% by weight of lime.

compared to dry cuttings.

  By way of comparison, equipment as described in FIG. 2, without the addition of lime, makes it possible to obtain an embankment of type b5, but this does not meet the criterion of sensitivity to water which is met if the level of fine is less than or equal to 12% by weight, the Vbs <0.2. However, such a b5 type backfill does not

cannot be used in Q3.

9 2777305

  On the other hand, by treating with 1% lime, by a flocculation effect, the same cuttings treated according to the invention can be used as backfill in

class Q3 (standard NF 11.300).

2777305

Claims (12)

  1. A method of treating cuttings to make it backfill, characterized in that the cuttings to be treated undergo crushing, followed by screening, the crushing and screening being in a loop, and in that one   add lime to the incoming cuttings, and recover the fill.   2. Method according to claim 1, characterized in that the cuttings incoming is not scalped.   3. Method according to claim 1 or 2, characterized in that the 1o cuttings to be treated undergo crushing and screening in a loop, the residue of the   screening being recycled upstream of crushing.   4. Method according to claim 1 or 2, characterized in that the cuttings to be treated undergo a primary crushing, then a screening, the residue of the screening being recycled upstream of the screening by undergoing a crushing secondary.   5. Method according to one of claims 1, 2 or 3, characterized in that   that lime is introduced before crushing or during crushing.   6. Method according to one of claims 1, 2 or 4, characterized in that   that lime is introduced upstream of primary crushing or during primary crushing.   7. Method according to one of claims 1 to 6, characterized in that   0.1 to 10% by weight of lime is added relative to the cuttings,   preferably 0.8 to 3% by weight of lime relative to the cuttings.   8. Installation for processing cuttings to make backfill from a source of cuttings comprising at least: - a crusher, - a screen, - means of transporting cuttings from the source to the crusher, - means of transport crushed cuttings from the crusher to the screen, - means of transporting the residue from the screen to the crusher, there 2777305 means of distribution (17,30,30 ') of lime in the cuttings, arranged at the level of the means of transport of the cuttings from source to   crusher, or at the crusher level.   with the exception of means for scalping the cut and mixing the fill. 9. Installation according to claim 8, characterized in that it comprises: - a crusher (12), - a screen (14), - means of transport (11) of the cuttings from the source to the crusher, - means of transport (13) of the cuttings from the crusher to the screen, - means of transport (16) of the residue from the screen upstream of the crusher.   10. Installation according to claim 8, characterized in that it comprises: - a primary crusher (22), - a screen (24), - a secondary crusher (27), - means of transport of the cuttings from the source to primary crusher (22), - means of transport (23) of the crushed cuttings from the primary crusher through a screen, - means of transport (26) of the residue from the screen to the secondary crusher, - means of transport (29) of the crushed cuttings of the crusher secondary upstream of the screen.   11. Embankment, characterized in that it is obtained by the process according to   One of claims 1 to 7 and in that it presents:   - a densification capacity Q3-Q4, 12 2777305   - water stability defined by the IPI and ICBR values, the ratio   ICBR / IPI being greater than 1 and the IPI index greater than 15.