EP0135478B1 - Method of stabilising soils so as to improve their bearing capacity - Google Patents

Description

The invention relates to a method for stabilizing soft, fine-grained soils in order to improve their load-bearing capacity, according to the preamble of claim 1.

It is known for certain types of loads to have insufficiently stable or load-bearing soils by admixing solidifying binders or the incorporation of so-called geotextiles made of non-rotting plastic materials or non-corrosive fabrics with a lattice or network structure, at least for a limited time, but also continuously to improve so that a sufficient stability or load-bearing capacity is achieved for the requirements. “Insufficiently stable soils” are to be understood in particular to mean those which are highly sensitive to water and are sensitive to environmental influences such as Water ingress, changes in load, but also freezing and thawing, react with changes in volume and / or strength. Stabilizations with cement or lime are known in particular, the cement or lime being added as evenly as possible before any compaction and setting or hardening undisturbed for a few days after compaction. Soils stabilized in this way are generally stable against water and frost due to sufficient resistance to water absorption after setting or hardening. However, it is disadvantageous that these methods can only be used if the processed soil has a water content well below that of the flow limit, which is not the case with soft and / or softened soils.

Cement- and / or lime-stabilized floors have a greater or lesser compressive strength, depending on the binder content and floor structure, but practically no tensile strength. In particular, when there is frequent or constant alternating stress, there is a risk that the cohesion of the stabilized layer will be lost due to mechanical stress and that the layer will dissolve into more or less large clods, provided the stabilized layer is not thick. Such clods can then sink into a soft surface, or with strong dynamic stress such as in the case of railway lines, ascend to the ballast or base course by pumping action. In both cases there is a progressive reduction in the size of the stabilized soil layer and the effect desired by the stabilization becomes increasingly less.

German Offenlegungsschrift 31 27 350 describes a method for ground stabilization, which, however, cannot be used for the recognized difficult stabilization of fine-grained soils, especially since the known method does not mention any reinforcing elements, so that the absorption of significant tensile forces is practically impossible. Also, the soil material is merely sprayed according to this laid-open document for the purpose of impregnation, whereas there is no question of the formation of a paste-like mass which is a prerequisite for the successful implementation of the method according to the invention.

The object of the present invention is to propose a method for stabilizing soft, fine-grained soils, such as clayey silt, silt, fine sands and organically contaminated soils, in order to improve the load-bearing capacity of an overlying soil layer, in order to absorb the load through the grown, underlying soil without material replacement to be as "fluid" as possible, to increase work capacity and flexibility by increasing the bending tensile and shear strength within the solidified floor area and to limit the formation of cracks caused by stress and shrinkage and to prevent the spreading of the giant. Another object is to achieve increased early strength properties, i.e. the ability of the stabilized soil layer to be able to absorb larger loads shortly after installation or construction.

The aim of the invention is a method for stabilizing soils, in which the disadvantages of previous soil stabilization methods can be effectively eliminated with relatively simple means. In particular, a method is to be created which is preferably used to improve the load-bearing capacity of the subsoil of traffic routes and other mechanically stressed areas by carrying out soil stabilization even under difficult weather conditions, e.g. Allows rain. It should be possible to achieve a stable soil layer between the grown soil and a wear or load-bearing layer shortly after completion of the work.

The inventive solution to the problem and the means to achieve the object of the invention are defined by the characterizing features of claim 1. Embodiments thereof emerge from the dependent claims.

• Fig. 1 a, b Querschnitte durch a) einen Bahngeleisekörper mit einer unter der Schotterauflage, und b) im gewachsenen Boden eines Strassen-oder Platzterrains unter der Verschleissschicht eingebauten stabilisierten Schicht nach der Erfindung;
• Fig. 2a, b, c drei Beispiele für nach dem Streuverfahren in eine zu stabilisierende Schicht eingebrachte Armierungselemente aus a) offenen, beliebig biegbaren, schnitzelartigen Materialien, b) in sich geschlossenen Gebilden aus federsteifen Ringgliedern, und c) aus nadel- oder stabförmigen länglichen Fasern oder Fasergebilden und

• Fig. 3 eine weitere Ausführungsform der erfindungsgemässen Bodenstabilisierung mit einer die Materialverzahnung und die Bruchfestigkeit im Übergangsbereich zum gewachsenen Boden mechanisch steigernden Gittereinlage im Bereich der zu stabilisierenden Schicht.

An exemplary embodiment of the method according to the invention or of the stabilized bottom layer to be achieved by the method are described below with reference to the drawing. In these shows:

• 1 a, b cross sections through a) a rail track body with a stabilized layer according to the invention installed under the ballast layer, and b) in the grown soil of a street or square terrace under the wear layer;
• 2a, b, c three examples of reinforcement elements introduced by the scattering process into a layer to be stabilized, made of a) open, freely bendable, chip-like materials, b) self-contained structures made of spring-stiff ring members, and c) of needle-shaped or rod-shaped elongated ones Fibers or fiber structures and

• Fig. 3 shows another embodiment of the inventions Ground stabilization according to the invention with a mesh insert mechanically increasing the material interlocking and breaking strength in the transition area to the grown soil in the area of the layer to be stabilized.

1a, b show two typical forms of application of the invention to existing civil engineering objects. The first example shown (FIG. 1 a) relates to an application that can be practiced specifically but not exclusively for track maintenance. A ballast bed 1, which has become inelastic due to years of driving, and into which building material (= grown soil or embankment fill) that has risen from the gravel case originally underneath as a result of pumping action should be replaced. In order to carry out the method according to the invention, the gravel and gravel case, which is permeated with earth, are first removed and the soil beneath it is then processed in a local mixing process, the soil being first brought to a pulpy state by adding a mixture of water and a silicate-containing binder. A large number of reinforcing particles are then added to this slurry, which should not be longer than the thickness of the soil layer and should be distributed as evenly as possible in the slurry of the soil. The grown soil is expediently prepared using a tiller. The solidified layer ensures good load transfer so that the entire gravel case can be omitted.

The usual admixture of the binders takes place in the liquid state, so that automatically a lowermost binder-free base layer 3 of 2 to 3 cm in height at a e.g. a total of 12 to 15 cm high layer 2 to be stabilized and solidified. However, it is also possible to add the binder together with the water.

The second example shown (FIG. 1 b) relates to an application of the method according to the invention in the construction or maintenance of low-stress roads, and in the creation of sidewalks and squares. The method can also be used for the construction of the substructure of main roads in areas with unsustainable subsoil. The preparation of the binder, liquid or water / earth mixture is also carried out here using the local mixing method as described above. Likewise, a lower-binder base layer is expediently provided. In the context of the present invention, binders are to be understood as meaning at least one silicate-containing binder which can be supplemented by cement or lime as required. The main layer 5 made of stabilized soil material then receives a cover layer 6 in the form of a wear layer. In the case of the local mixing method, the height of the base layer 4 can advantageously be determined, for example, by means of height-adjustable means of the mixing device.

• 1. Auffräsen . der zu stabilisierenden Bodenschicht;
• 2. Vorinfiltration von Bindemitteln bzw. Bindemitteln und Flüssigkeit bzw. Wasser;
• 3. Einstreuen von Armierungselementen;
• 4. Mischen des mit Bindemittel vorinfiltrierten Bodenmaterials, Wasser und Armierungselementen und allfälliger Beigabe von weiterem Wasser zur Erzielung des breiigen Zustandes;
• 5. Beigabe von allenfalls weiterem (weiteren) Bindemittel (Bindemitteln);
• 6. Einmischen der allenfalls nach 5) beigegebenen weiteren Bindemittelbeigabe.

According to the invention, reinforcement elements are added to the soft to viscous soil material-binder-water mixture, which are incorporated into the above-mentioned mixture and suspended therein in an essentially uniform distribution. The reinforcement elements are only worked in when the soil to be stabilized is in a mushy state and is expediently carried out by means of mobile distributing and introducing devices, for example by means of the tiller which is also used to prepare the soil. As an example of a typical workflow in soil stabilization according to the invention, the following process can be considered after the removal of any cover layers that cannot be described in more detail:

• 1. Milling. the soil layer to be stabilized;
• 2. pre-infiltration of binders or binders and liquid or water;
• 3. sprinkling of reinforcement elements;
• 4. Mixing the soil material, water and reinforcement elements pre-infiltrated with binding agent and any additional water to achieve the mushy state;
• 5. addition of any further (further) binder (binders);
• 6. Mix in any additional binder added after 5).

According to FIG. 2 a, the reinforcement elements can consist of any shape and any flexible, rod-like or schnitzel-like, about 4 to 20 cm long reinforcement elements 7 made of an elastic, stretchable material. In the case of reinforcement elements which are closed in a ring shape according to FIG. 2b, the elements - in an at least circular configuration - should have a diameter of 4 to 10 cm. Rod or needle-shaped elements according to Fig. 2c should be about 4-10 cm long. The element thickness in the soil material mixture to be stabilized is selected depending on the desired load-bearing capacity, so that a reinforcing element surface proportion of more than 2% is obtained for each cut surface unit - viewed in any direction.

The reinforcing elements 9 should be oriented in any direction in the material mixture in order to achieve an approximately uniform anchoring effect.

Fundamentally, the reinforcement elements shown in the examples according to FIGS. 2a-c have a length which at most corresponds approximately to the thickness of the bottom layer to be stabilized. The cross-section of the reinforcing elements is at most about 12 _m ² to maintain the flexibility described.

A further possibility of reinforcing a floor section that is to be stabilized and solidified for greater resilience is shown in FIG. 3. On a low-binder and essentially reinforcing element-free base layer 10, B. placed on a relatively wide-mesh spacing grate 11, which is shown here as a bar grate, a lattice or mesh-like sheet 12, for example a geotextile or steel wire mesh as basic reinforcement, which is penetrated by the stabilized layer. Connection The elemental reinforcement of the described type of mixture takes place.

A plurality of grids or net-like flat structures 12 can be embedded in the soft to viscous mixture at vertical intervals. In addition to the flat structures mentioned, reinforcement particles according to FIGS. 2a-c are sprinkled in in all cases.

Of course, it is possible to achieve such short setting times, particularly in the maintenance of the railway substructure, by means of quick-setting additives that the soil stabilization described can also be carried out in sections during the normally relatively short breaks in operation. The decisive factor, however, is the presence of the reinforcement elements described, which are able to increase the resting time which is usually also necessary in the case of quick ties by their internal stabilization. However, the method according to the invention brings advantages not only in those cases where rapid progress or completion of the work is important. The method offers advantages for all subsoil and slope stabilization where it is practically applicable.

Claims (5)

1. A method of stabilizing soft, fine-grained soils, such as silts, fine sands, etc., without weight densification to obtain enhanced rapid strength properties which allow the soil to be loaded only a few hours after stabilization, the soil to be stabilized being prepared by in situ mixing processes with the addition of at least one silicate-containing binder, characterized in that the soil layer to be stabilized is first brought into a slurry condition by the addition of a mixture of water and the silicate-containing binder, whereafter a plurality of individual reinforcing particles whose main dimension corresponds at most to the thickness of the soil layer to be stabilized are uniformly distributed in the resulting slurry.

2. A method according to Claim 1, characterized in that the reinforcing elements (7) are rod- like or chip-like elements.

3. A method according to Claim 1, characterized in that the reinforcing elements (8) are shapes closed in a ring.

4. A method according to Claim 1, characterized in that a low-binder base layer is produced in the same operation between the natural soil and the layer to be stabilized.

5. A method according to Claim 1, characterized in that a lattice-like web bearing against a spacing grid is incorporated in the layer to be stabilized.

Images