The invention relates to a method for making a contaminated site suitable for building purposes, in which site foundation piles must be placed, and which site is or can be sealed off from the surrounding area by sheet piling or sheeting walls.

In the last few decades great attention has been focused on the problem of contaminated soil in large parts of the world, in particular in the Netherlands. The Dutch government commissioned a survey on the extent of contamination throughout the Netherlands, in the course of which a classification without degree of contamination was made. The contaminated soil can be cleansed by means of separate storage, incineration or steaming. Very highly contaminated sites are being increasingly sealed off completely from the surrounding parcel of ground by means of an impenetrable vertical screen and an impermeable layer of soil. A great disadvantage in this case is that these sealed-off sites are unsuitable for building purposes, in particular where a pile foundation is necessary. In this last instance the sealing soil layers (usually clay) would be penetrated, with the result that full screening- off of the contaminated parcel of ground cannot be guaranteed. In this situation placing foundation piles is therefore not permitted.

The invention provides a solution to this problem. The object of the invention is to provide a method of the type described in the preamble, which method makes it possible to place a foundation in contaminated sites without the risk of the parcel of contaminated ground being brought into contact with the uncontaminated or less contaminated surrounding area when the sealing clay layer is penetrated.

To this end, the method according to the invention is characterized in that: a casing is placed in the ground to a depth at which the bottom edge of the casing is embedded in a watertight layer, a foundation pile is placed by way of the empty or emptied casing to such a depth that the bottom part of said pile is embedded in a load-bearing soil layer, and a plastic and/or elastic material which seals off the space around the foundation pile in a liquid-tight manner is placed

around the foundation pile, at least in the section where the casing passes from a non-watertight layer into said watertight layer.

The liquid-tight plastic and/or elastic material can be in many different forms and of many different compositions. It can be made of, inter alia, a clay-containing gel, a mixture of bentonite, sand and polymer, and of a rubber or rubber-like material. Above the liquid-tight plastic and/or elastic layer, the casing will be filled with a heavy material, such as concrete or vibrated sand, which itself is not suitable for a liquid-tight seal.

The water below the clay layer can sometimes be at raised pressure, as a result of which there is a risk of said water spouting up when a foundation pile penetrates the ground. In order to avoid this, the water pressure can be relieved below said watertight layer of clay by means of a pressure drainage operation.

A guide can be suspended in the casing, in order to guide a foundation pile inside the casing. A pile driver with a so-called passe¬ partout can be used instead of such a guide.

Another method of placing the foundation pile is to seal off the casing in an airtight manner at the top end by means of a blind flange, to pull the casing out of the ground, and during the pulling to introduce a mixture under pressure into the casing, which mixture forms a watertight mass which ensures complete sealing-off of the foundation pile relative to sealing soil layers. The top layer of soil is generally replaced beforehand by a thick layer of clean soil.

It is pointed out that it is known per se (see, for example, GB-A-215-4630) to introduce a screw pile into the ground by way of a casing screwed into the ground beforehand, to fill the space between the pile and the casing with cement and, finally, to pull the casing out of the ground. The purpose of this is to prevent noise or vibration nuisance. This known method is not suitable for making highly contaminated sites suitable for building purposes, because no plastic and/or elastic watertight plug is used around at least part of the height of the foundation pile.

The invention will now be explained in greater detail with reference to the figures.

Figure 1 shows a perspective view of foundation piles placed in the ground by a first method, at the position of an imaginary ground

cross-section.

Figures 2, 3 and ^ show views of ground cross-sections in which the various stages of the first method are shown.

Figures 5. 6, 7 and 8 show views of ground cross-sections in which the various stages of a second method for placing a foundation pile are shown.

The site shown in the figures is highly contaminated and is completely sealed off from the surrounding area by means of sheeting walls or sheet piling 1. Foundation piles 2 are placed in such a way in this area that no risk of contamination of the surrounding area arises.

The soil layers shown are:

a clean covering layer which has replaced an excavated contaminated layer a thin sealing layer a contaminated soil layer a sealing clay layer a non-load-bearing soil layer a load-bearing sand layer

The abovementioned sheeting walls or sheet piling 1 are embedded in the sealing clay layer 6.

A number of drainage pipes are indicated by 9- In the first phase (Figure 2) of the method, a casing 10 which is open at both ends is placed in the ground to a depth at which the bottom end of said casing is embedded in the sealing clay layer. The soil in the casing is removed by means of a soil drill. It is quite possible for the casing to have at its bottom end a sealing cone which tapers to a point, so that no material passes into the casing while it is being placed in the ground.

In the second phase, a foundation pile guide 11 is suspended in the casing. Said guide has a central channel of essentially the same peripheral shape and size as the foundation pile to be placed in the ground (Figure 3) • A pile driver with a so-called passe-partout can be used instead of a foundation pile guide 11.

In the third phase, a foundation pile 2 is placed in the ground by way of the guide 11 until the bottom part thereof is embedded in the load-bearing sand layer 8 (Figure 3) • Where screw piles or piles poured in situ are used, the guide 11 will be replaced by a suitable guide or

formwork .

In the fourth phase, the foundation pile guide 11 is removed, and a liquid-tight plastic and/or elastic material is placed around the casing 10 in the section where the casing passes from a non-sealing soil layer into a watertight layer 6. This plastic and/or elastic plug is indicated by 13- Above this layer the casing is filled with sand 14 or concrete (Figure 4).

The water pressure below the watertight clay layer 6 can be relieved beforehand by means of a pressure drain 15 provided outside the sealed area, next to the sheet piling 1. This prevents soil and water from rising up in the casing.

In the second method, illustrated in Figures 5 to 8, a casing 10 is placed in the ground in the manner described above, and a . foundation pile guide 11 is suspended in the empty casing. The foundation pile 2 is guided into the ground by way of the casing until its bottom end is embedded in the soil-bearing layer 8. Unlike the first method, in this case the casing has a flange 17, provided with lugs 16, at its top end. After the foundation pile 2 has been placed in the desired position in the ground in the manner described above, and after the guide 11 has been removed, a blind flange 18, which seals the casing in an airtight manner, is attached to the flange 17. An inlet 19 and a manometer 20 are provided on said blind flange (Figure 7)-

As can be seen from Figure 7. pulling elements (see the arrows 21) are attached to the lugs 16, and while the casing is being pulled out of the ground a mixture of materials is introduced under high pressure by way of the inlet 19 into the space around the foundation pile 2. This mixture 22, for example consisting of cement, sand and a polymer, can be a rubber-like material which causes the foundation pile to be completely sealed off from the sealing layer. As in the case of Figure 4, said layer can be of only a limited height, and sand or concrete can be introduced above the layer 22.

Figure 7 also shows that the space around the foundation pile is filled up with the mixture from the underside of the casing, and the casing 8 is pulled out of the ground at a speed which corresponds essentially to the speed at which the level of said mixture rises. The result can be seen in Figure 8. The isolation of the contaminated parcel of ground surrounded by sheet piling has not been jeopardized at any time by placing the foundation pile in the ground. Consequently, such screened-off contaminated sites can be used for

building purposes.

There are various possibilities for the composition of the foundation pile coverings 13 and 22. The materials can be a clay and/or polymer-containing gel or a rubber or rubber-like material loaded by a weight. It is essential that the material should have sufficient plasticity or elasticity to enable it to adapt to the possibly changing shape of the hole, so that there can be no upward and downward liquid leaks for a very long period of time. A suitable material for use as a liquid-tight elastic material is a clay gel which is being marketed by the company "General Industrial Developments Benelux B.V. (G.I.D.) under the names TONPLAST and TRISOPLAST.