EP0257382B1 - Method for stabilizing the soil - Google Patents

Abstract

The stabilising of piled-up soil (E) is performed by means of tubular reinforcing elements (1), which are laid in the soil. A flexible, tubular infiltration reinforcement (2), which is permeable to a binder suspension and is preferably produced from a geotextile, encloses a rigid feeding tube (3), which does not collapse under soil pressure. The aqueous binder suspension is fed to the infiltration reinforcement (2) through outlet openings (3a) in this feeding tube. The said suspension flows through the permeable infiltration reinforcement (2) and seeps in the direction of the arrows into the surrounding soil, where the binder solidifies. The reinforcing elements consequently serve at the same time for binder distribution and as a safeguard against tensile stress. <IMAGE>

Description

The present invention relates to a method for stabilizing soil material with the addition of an aqueous suspension of a binder.

Modern road construction has created a large number of relatively steep slopes in recent decades, the stabilization of which has been causing serious problems for several years. The interaction of different, often still unknown factors, which experts believe includes the washing out of the binding, calcareous parts of the soil, leads to landslides and subsidence, which can only be achieved with considerable effort using the currently known methods and means replenish time, material, stabilize and consolidate. The investigation of a possible cause of the loss of stability of such slopes and embankments can be found, for example, in an article by Dr.-Ing. Lutz Wichter under the title "Weathering stability of embankments in sedimentary rocks", which appeared in No. 4/82 of the magazine TIS.

Soil stabilization problems arise not only on slopes, but also wherever the soil loses strength due to environmental influences, in particular by washing out the binding soil, and has to be subjected to greater loads, as is the case, for example, on driveways, parking lots, etc. .

In the past few years it has been shown that the previously generous use of high-quality building materials - especially sand and gravel - can no longer be continued to the same extent. On the one hand, these high-quality materials are too expensive for many applications of soil stabilization; on the other hand, it is becoming increasingly clear that the large-scale mining of sand and gravel deposits leads to a serious lowering of the groundwater level.

DE PS 3 127 350 describes a method for soil stabilization, according to which the soil to be stabilized is first excavated, then sprayed with a stabilizing agent, then mixed and finally poured back into the trench. Although this method can be used for soil stabilization in flat terrain, it was not able to assert itself due to the disadvantages inherent in it. On the one hand, the entire process is quite expensive, since an addition of 100 to 130 kg of cement must be expected per cubic meter of soil and, furthermore, the material treated in the manner described has a very low tensile strength, which is particularly important on slopes.

From US-A-3 518 834 a method for consolidating the soil in untreated sections of soil, in particular those which are adjacent to excavation sites or other excavations, is known. When carrying out the method, boreholes are first made in the untreated floor sections. A reinforcing element consisting of a pipe and a porous sheath partially surrounding it is then inserted into each borehole. A suspension supplied via the pipe reaches the soil in the vicinity of the borehole via outlet openings in its wall and via the porous casing in order to solidify it. Because the known method is based on the fact that reinforcing elements are inserted into boreholes, it is not suitable for use for stabilizing bulk material.

It is therefore the object of the present invention to propose a method for stabilizing soil material which permits the use of the soil present on the spot, also gives the treated soil sufficient tensile strength and, moreover, with a relatively small amount of binder, in particular cement, gets along and is characterized by modest production costs.

This method is defined in claim 1. Preferred embodiments for the method result from the dependent claims.

A geotextile, which has proven itself very well as a reinforcing material for soil stabilization, is preferably used for the production of the reinforcing elements. Descriptions of geotextiles can be found in the SN standard 640 550 "Geotextiles, terms and product descriptions" as well as in "Geotextile manual of the Swiss Association of Geotextile Experts", publisher Vogt and Schild, Solothurn.

Embodiments of the invention are described below with reference to the accompanying drawings.

1 is a simplified sectional view of a reinforcement element laid in the floor,
2 shows a slope covered with reinforcement elements before filling up the slipped soil,
3 to 5 show further embodiments of reinforcing elements in section,
6 illustrates, also in section, the arrangement of reinforcement elements for the purpose of stabilizing deeper soil layers,
7 uses a sectional view to illustrate the use of the method according to the invention in the stabilization of forest and field paths,
8 is a vertical section through a dam created according to the method according to the invention,
9 is a sectional view along the line IX-IX in FIG. 8,
10 and 11 illustrate the application of the method according to the invention in the anchoring of retaining walls,
12 is a top view of the arrangement shown in section in FIG. 11;
13 shows a further variant of the reinforcement elements,
14 shows the prepared slope surface before laying the reinforcement hoses,
FIG. 15 is a plan view of a slope area remaining after a landslide after the installation of reinforcement hoses, and
16 is a sectional view of the slope section renovated according to the invention.

Fig. 1 shows a simplified section of a reinforcement element 1 laid in the ground E. The latter has a flexible reinforcement hose 2 made of an unsustainable, alkali-resistant and tear-resistant material, preferably of a geotextile, the mesh size of which is selected so that it is the largest grain of water Binder suspension contained still lets through. A supply hose 3, which consists of a relatively stiff material and is accordingly not collapsible and therefore cannot be compressed by the soil on it, is arranged within the reinforcement hose 2. The supply hose 3 provided with outlet openings 3a serves to supply the aqueous binder suspension and can, at its free end, which preferably protrudes from the reinforcement hose 2, with the aqueous binder suspension be loaded. The end section of the feed hose opposite this free end is generally tightly closed, so that the aqueous binder suspension can only exit through the outlet openings 3 a, that is to say inside the reinforcement hose 2.

When stabilizing poured soil, a number of reinforcement elements 1 are first laid at mutual intervals on the soil remaining after the slide or excavation (FIG. 2) and then covered with the existing soil Ea, so that the reinforcement elements 1 are surrounded on all sides by the soil are. Now the reinforcement hoses 2 are fed via the feed hoses 3 with the aqueous binder suspension, which e.g. Lime, cement, silicate, mortar, concrete, synthetic resins, etc. may be present and, depending on the prevailing conditions (inclination of the ground, strength of the soil, etc.), is supplied without pressure or under low pressure. As indicated in FIG. 1 by arrows, the suspension flows from the supply hose 3 on both sides into the reinforcement hose 2 and through it into the surrounding soil E. After the binder has solidified or set or hardened, the entire environment of the reinforcement hose 2 is solidified, since the suspension fills up all gaps in the soil, with the reinforcement hose 2 naturally also being firmly embedded in the stabilized soil.

The reinforcement hose 2 fulfills a double function: on the one hand, it serves as an infiltration element which ensures the all-round distribution of the binder suspension; on the other hand, it gives the ground an increased resistance to tensile stress, which is particularly important when it comes to slope stabilization, wall anchoring, etc.

Thus, while the reinforcement hose 2 absorbs the tensile forces that occur, the floor material is glued by the described binder injection and thus solidified or stabilized so that it can also absorb larger pressure loads.

FIG. 2 shows the reinforcement elements 1 after they have been laid and before filling up the slipped or removed soil Ea. Since the existing soil Ea is reused, it is no longer necessary to remove it and, on the other hand, there is no need to purchase the material previously required (sand, gravel, etc.). After the reinforcement elements are covered by the soil Ea, the binder suspension is introduced from a cistern wagon L via a hose S into the free openings 3B of the supply hoses 3 until the latter has sufficiently penetrated the soil.

The method described also offers the possibility of solidifying only certain zones of a slope by providing the supply hose with outlet openings only over the partial lengths corresponding to these zones.

According to the method described, a reinforcing element is thus used for the first time in soil stabilization not only to improve tensile stress, but also to transport and infiltrate the binder suspension. These two functions can also be taken over by the variant according to FIG. 3, in which only one reinforcement hose 3 is provided, in the central region of which a spacer 4 is arranged. This spacer 4 can be, for example, a rigid plastic profile, that is to say that it cannot be compressed by earth pressure, the lateral openings for passage has the binder suspension.

The basic idea of the present invention can be varied in various ways by the person skilled in the art. 4, the central region 2a of the reinforcing hose 2 is reinforced and rigid, while smaller spacers 5 are formed on the inner wall of the hose, which in turn have openings for the binder suspension.

The infiltration reinforcement need not necessarily be in the form of a hose. 5, two webs 6, 7 of a relatively thick (for example 5 to 15 mm) geotextile are placed on top of one another, between which in turn there is a supply hose 3 provided with lateral outlet openings. This sandwich form also fulfills the intended purpose: the binder suspension flowing into the supply hose 3 is distributed in the direction of the arrow and, taking into account the surrounding soil material, forms a stabilized soil zone that can absorb compressive and tensile forces.

In all the embodiments described so far, it is also possible to increase the tensile strength of the infiltration armature by laying a wire rope or other element that can be subjected to tensile strength.

When stabilizing deeper soil layers, as shown in FIG. 6, a plurality of reinforcement elements 1 are preferably arranged offset in different planes.

Fig. 7 illustrates the renovation of the washed and extended ruts of forest and field paths. According to one embodiment of the method according to the invention, the ruts F1 and F2 are first milled out to depth T, whereupon the reinforcement elements 1 are inserted and covered with the milled bottom material. Now the binder suspension is injected, which spreads in the direction of the arrow and forms the stabilized ruts, while the vegetation remains undisturbed on the other parts of the path.

When building new dams and dikes, e.g. in coastal and bank protection created by pouring can be done according to FIGS. 8 and 9. The reinforcing elements 1 are rolled out at different levels when the soil is poured out and, after the dam has been completed, are filled with the binder suspension, which is supplied via a line S (see FIG. 2). It goes without saying that the reinforcing elements in all the described embodiments can also be laid, for example, in a U-shape, in a spiral shape or in any other shape.

In the case of levees or bank walls stabilized in this way, the dreaded washing out of the fine parts of the bulk material is excluded, since these are bound by the bonding of the binder.

For the purpose of anchoring a retaining wall M, according to FIG. 10, for example, reinforcement elements according to FIG. 1 can be used, the feed hoses 3 of which can be passed through the wall M so that they can be loaded from outside the wall. When this stabilization is created, a further floor layer is poured on after the reinforcement elements have been rolled out and anchored to the wall M. To improve the tensile load steel reinforcements such as steel cables or tapes can also be installed with the reinforcement elements. Basically, depending on the conditions, it would also be expedient to attach the reinforcing elements only to the inner wall of the wall M and to feed the supply hoses 3 with suspension from the other end.

In the embodiment according to FIGS. 11 and 12, a wall M was securely anchored in that first several trenches opening against the wall were milled out to depth T, in which the reinforcement elements 1 were then rolled out, covered with soil and then as in the variant Fig. 10 from outside the wall or from the other end of the feed hoses 3 were loaded with the binder suspension. In comparison to the usual anchoring methods, there is also no need to drill and create the ground anchors.

The infiltration reinforcements could also be designed in the form of cushions 9 (FIG. 13), which can consist, for example, of two geotextile mats lying one above the other and attached to one another. The end of the supply hoses 9 lie between the two geotextile mats and are preferably provided with outlet openings only in the area of the geotextile cushions 8. The shape of the supply hoses 9 can be adapted to the requirements in the pillow area, for example as shown at point 9a, so that there is more or less strong infiltration.

A further embodiment of the method according to the invention is shown in FIGS. 14 to 16. According to FIG. 14, the slope surface H 1 remaining after a landslide is processed by means of an excavator in such a way that a wave or step-shaped surface H₂ arises. Should the slope H 1 be wave-shaped from the beginning or have a large number of depressions, this first machining step according to FIG. 14 can be omitted.

On the undulating or uneven slope surface H₂, a first geotextile web G₁ is now placed with a mesh size of, for example, 0.5 to 2.0 mm, which can have, for example, a width of 2 m and a mesh size of 1.5 mm. For reasons to be explained below, this laying takes place at an angle α to the fall line FL. Now a first provided with outlet openings hose 10 is meandered on the first geotextile web G 1, fixed by means of steel nails 11 and covered with a second geotextile web G 2, whereupon the whole is covered with the existing, slipped soil E. Now the aqueous suspension is introduced from above and penetrates through the openings of the hose 10 and the meshes of the geotextile tracks G 1 and G 2 into the surrounding earth.

Due to the meandering laying of the hoses 10, the desired effect is achieved that the aqueous suspension, as soon as there is no replenishment from above, remains in the sections a (Fig. 15) that extend downwards and thus has time to gradually emerge laterally and infiltrate the surrounding soil. This effect is reinforced by the step-like preprocessing of the slope area according to FIG. 14.

As further shown in FIG. 15, there is an untreated strip of earth E _u between two rehabilitation lanes, which must be left free in order not to disturb the natural water balance. Thanks to the sloping, these untreated earth stiffeners E _u can be kept wide without a risk of slipping to the fall line FL at an angle α running the rehabilitation tracks or reinforcement hoses 10. Arrows in Fig. 15 indicate how the untreated soil is supported on the rehabilitated sections and is held by them.

). Sobald die Förderpumpe abgestellt wurde, baut sich dieser Staudruck langsam wieder ab, wobei das Erdreich nach und nach absinkt und sich dabei mit der wässrigen Suspension durchtränkt.Another valuable effect is obtained when the reinforcing hoses 10 (FIG. 16) pump so much aqueous suspension per unit of time that it does not have enough time to exit the adjacent soil E through the geotextile tracks G 1 and G 2. Due to the dynamic pressure building up between the reinforcement hose 10 and the upper geotextile web G₂, the geotextile web G₂ is raised with the soil which is on the same, as indicated by dotted lines in FIG. 16 (G $\genfrac{}{}{0ex}{}{\text{'}}{\text{2nd}}$

). As soon as the feed pump has been switched off, this dynamic pressure slowly decreases again, the soil gradually sinking and soaking itself in the aqueous suspension.

When carrying out this method, the mesh size of the geotextile webs G 1 and G 2, the outlet openings 3a (FIG. 5) of the hose and the delivery capacity of the pump can be coordinated with one another in such a way that the desired dynamic pressure results.

Thanks to the method described, the existing, inferior soil can be reinforced on site at the same time with little effort in terms of working time and material in order to absorb the tensile forces and solidify with a view to absorbing compressive forces by means of binder infiltration. Because the reinforcement elements the binder supply and take over its distribution, there is no need for the usual mixing and compacting of the material, which is otherwise only possible with a special soil composition and could only be carried out under certain moisture conditions.

The geotextiles have proven to be particularly useful for use as reinforcing elements, but could also be replaced by other alkali-resistant and tear-resistant materials.

The described method can of course be combined with known methods. Thus, it may be expedient to attach the reinforcement elements rolled out on the slope according to FIG. 2 at their upper ends to an injection nailing device, as a result of which lower-lying sliding circles can also be secured.

The aqueous suspension can e.g. also in several successive phases, if necessary with the inclusion of waiting times. For example, it would also be possible to first add silicate gel pH 12 to 13 and then infiltrate the soil with cement milk W / Z 0.8 to 1.0.

• a) der Wiederverwendbarkeit des abgerutschten Erdmaterials,
• b) der Ueberführung von Bodenzonen in den alkalischen Bereich,
• c) der Bodenstabilisierung durch den Einbau einer Armierung, welche Zugkräfte aufnehmen kann und
• d) der Verbesserung der gestörten Bodenstruktur durch Bindemittel.

The decisive advantages realized by the present invention lie in

• a) the reusability of the slipped earth material,
• b) the conversion of soil zones into the alkaline range,
• c) soil stabilization by installing reinforcement which can absorb tensile forces and
• d) the improvement of the disturbed soil structure by means of binders.

Claims (8)

1. Method of stabilising fill material while adding a hydrous suspension of a binding agent, characterised in that a row of reinforcing elements (1, 2) is laid out on the soil remaining after slippage or excavation, which reinforcing elements (1, 2) are made of a flexible, alkali-resistant and tear-proof material, enclose a channel serving to introduce a hydrous suspension and are at least partly provided with openings which are larger than the largest grain of the suspended binding agent, in that, furthermore, the laid-out reinforcing elements are covered with the slipped or excavated soil material so that they are enclosed on all sides by the soil material except for an open end section, and in that the hydrous suspension is introduced through the open end sections of the reinforcing elements so that this hydrous suspension comes out through the openings of the reinforcing elements into the earth surrounding the latter and solidifies there.
2. Method according to Claim 1, characterised in that the reinforcing elements are elongated tubular webs which are laid offset relative to one another at different depths of the soil material to be stabilised.
3. Method according to either of Claims 1 or 2, characterised in that a first geotextile web having a mesh width of between 0.5 and 2.0 millimetres is laid onto the soil surface remaining after slippage or excavation, facultatively after finishing the soil surface in a terraced shape, a tube serving as reinforcing element and provided with outlet holes is laid in a meander shape onto this first geotextile web and this tube is covered with a second geotextile web, whereupon the whole is covered with the slipped or excavated earth and then the hydrous suspension is introduced from above into the tube.
4. Method according to Claim 3, characterised in that a silicate gel is introduced as hydrous suspension into the tube in a first phase and cement slurry is introduced into the tube in a second phase.
5. Method according to Claim 3, characterised in that the mesh width of the two geotextile webs, the outlet openings of the tube and the delivery capacity of a pump feeding the tube with the hydrous suspension are matched to one another in such a way that more suspension comes out of the outlet openings of the tube than can pass at the same time through the mesh of the geotextile webs into the surrounding earth in such a way that initially, i.e. just after introduction of the hydrous suspension starts, a pressure builds up below the upper geotextile web, which pressure slightly lifts the upper geotextile web together with the earth adjacent to the same, whereupon, after introduction of the hydrous suspension is complete, the earth presses the upper geotextile web down again and as a result is gradually impregnated with the hydrous suspension.
6. Method according to one of Claims 1 to 5, characterised in that the tubular reinforcing elements are anchored in the underlying earth by means of steel spikes in order thus to prevent at the same time the formation of a deeper lying sliding joint.
7. Method according to one of Claims 1 to 6, characterised in that the reinforcing elements are laid at an angle to the line of dip of the slope in order thus to prevent the untreated earth strips lying between the reinforcing elements from slipping.
8. Method according to Claim 1 for stabilising the soil material in the area of a retaining wall, characterised in that one or more trenches are dug in the soil material adjacent to the retaining wall and reinforcing elements are laid in these trenches in such a way that their end sections on the wall side are anchored in the retaining wall, whereupon the reinforcing elements are covered with earth and the hydrous suspension of the binding agent is introduced via the open end sections.

Images