NL2010257C2 - Method and apparatus for stabilising a dike. - Google Patents

Description

Method and Apparatus for Stabilising a Dike Background of the Invention

The present invention relates to a method of stabilizing an earth body such as an embankment or dike and, in particular, to a ground anchor assembly for performing the method.

Dikes and embankments have been extensively used for millennia for various purposes, including water retention, road construction and the like. In the following, reference to dikes is intended to cover raised earth bodies in the broadest sense, including dikes, embankments, dams, levies and the like and is not intended to be limiting to sea and river defences. Depending on the local soil conditions, various techniques have been used to construct and stabilize such earth bodies. In particular, dikes made of sand and similar material are difficult to stabilize without additional support. Dikes, especially those comprising a core of turf-like material tend to compact and expand depending on the weather conditions. After elongated periods of rain or drought or in the case of raised water level in, under and behind the dike, migration of earth material can occur, resulting in weakening of the dike. A characteristic of most such constructions is the tendency for shear to occur within the dike body. Any weight on an upper portion of the dike tends to bear downwards, tending to subsidence if no action or provision is taken to prevent this. This is particularly problematic in the case that new construction is required on top of or against the dike or if the dike is to be increased in height.

Previous procedures for stabilizing existing dikes have involved the introduction of anchors through the dike and into the stable earth layers therebelow. These anchors have then been grouted into place using a cement or concrete construction. A disadvantage of such an approach is that the dike becomes more rigid and is unable to swell and contract with the climate without relative movement occurring between the concrete and the core of the dike. Other procedures have involved the formation of concrete and steel dam constructions, vertically into the ground beneath. Although this may lead to a strong and stable structure, it comes at significant expense and the result is to all intents and purposes a retaining wall rather than a traditional dike.

It would be desirable to provide a device that can be used for stabilizing of dikes in a cost effective manner.

BRIEF SUMMARY OF THE INVENTION

According to the invention there is provided a ground anchor assembly for stabilizing a dike, comprising a ground anchor, a counter member and an elongate tensile member connecting the ground anchor and the counter member. The tensile member is provided between the ground anchor and the counter member with a pressure distributing member, arranged to prevent earth flow in a direction perpendicular to a length direction of the tensile member. In this manner, by providing the tensile member with a pressure distributing member, flow of earth in a direction perpendicular to the tensile member may be reduced or prevented. Depending on the embodiment of the tensile member also flow in other directions is reduced or prevented.

In contrast to existing anchor arrangement that can only be subjected to tensile forces, according to the invention flow loading of the tensile member occurs, preventing lateral flow of earth material within the dike that could lead to subsidence. The pressure distributing member acts as a flow restricting means and distributes the forces acting in different earth layers. In dike bodies it has been observed that depending on the water level in, under or behind the dike and also the constitution of the dike material it is possible that on different levels different lateral forces may act. The same may apply in relation to changes in loading on the dike.

If an earth body such as a dike would only be stabilized by “clamping” the earth material between a ground anchor and a counter member, lateral migration of earth which can be promoted by water resulting in a flowable slurry, cannot be prevented. According to the invention such lateral flow can be considerably reduced.

It should also be understood that flow of earth material can be in a nonhorizontal plane. This depends on the build-up of the different layers of the dike and the way in which the dike is subjected to water and draining of such water.

It will also be appreciated that ground anchors are generally known in the art and used for many purposes. One particular use of such anchors is for applying tension to a sheet piling wall. In such situations however the action of the anchor is purely in tension and there is no requirement of any resistance against lateral forces or flows.

According to a preferred embodiment, the pressure distributing member is elongated and extends along the tensile member, preferably over at least 10 % of its length, more preferably over at least 30 % of its length. It may also extend over substantially the whole of its length. In general, it may be expected that the pressure distribution member extends over between 20% and 50% of the length of the tensile member but this may depend on the actual length of the tensile member compared to the length of the portion requiring stabilisation. For very long tensile member of e.g. 25 m in length the portion over which the pressure distribution member extends may be less than 10%. In general, the pressure distribution member cover at least 1 m. It will be understood that a plurality of pressure distribution members may be provided on a single tensile member e.g. spanning different zones of possible slip. The location of these zones may be determined by geotechnical surveys of the dike.

The pressure distributing member can be embodied in several ways in order to optimize its function to restrict displacement of earth material. Preferably the pressure distributing member has a relatively large surface to be as effective as possible. Preferably the pressure distribution member has a width or diameter of at least 7 cm, more preferably at least 10 cm and most preferably at least 15 cm. According to one preferred embodiment, the pressure distributing member is embodied as a bladed structure. Particularly such bladed structure may be centered around the elongated tensile member. According to another preferable embodiment the pressure distributing member may be integral with the tensile member. It is possible to use one and the same material for both the pressure distributing member and the tensile members. For the pressure distributing member, such materials may include metals, preferably corrosion resistant or treated metals, composite materials including fibre composites, ceramic materials, plastics and the like. A particularly suitable material is basalt epoxy composite, as this is not subject to corrosion.

The tensile member may be a rod, a cable a rope or any other suitable member capable of supporting the required loads. The tensile member may have any required length for insertion through the dike to the required anchor location. Most preferably it will have a minimum length of 3m. It may comprise any of the materials mentioned above, subject to adequate tensile strength. One particularly suitable material is based on a basalt fibre composite material. This can be provided on a reel and cut to length for the production of ground anchor assemblies in-situ. Other materials may also be used in this way. At the place of installation, parts of the tensile member/earth flow restricting means are taken from the reel and connected to the ground anchor. After that the ground anchor is introduced in the soil after which the other end of the tensile member/earth flow restricting means is connected to the counter member. It is also possible to effect separation of the tensile member/earth flow restricting means from the end on the reel only after the ground anchor together with the tensile member/earth flow restricting means have been entered in the dike.

The invention also relates to an dike comprising a number of adjacently arranged ground anchor assemblies, wherein each ground anchor assembly comprises a ground anchor to be introduced in an dike, a counter member and an elongate tensile member, connecting said ground anchor and said counter member, wherein said tensile member is provided between said ground anchor and said counter member with a pressure distributing member arranged to prevent earth flow in a direction perpendicular to the length direction of said tensile member wherein the pressure distributing member is arranged to restrict the flow. Through the use of a number of ground anchor assemblies having pressure distributing members a possible flow path for earth material can be effectively blocked. It will be appreciated that such ground anchor assemblies may be inserted in any direction through the dike, including vertically and horizontally and from any angle from a front side or rear side of the dike. It is also conceivable that the tensile member may extend right through the dike and in which case the ground anchor may be embodied as a second counter plate or another form of counter member.

The counter member can be arranged in any position, i.e. below ground level or at ground level. According to a preferred embodiment the counter member comprises a perforated plate which may be made of plastic material such as is used for parking spaces where grass growth through the plate is required. It is also possible to embody the counter member as a geonet, i.e. a net of geomaterial. Grass and vegetation on the dike is understood to be advantageous in reducing erosion. The counter member may also be made from concrete, metal, composite materials and the like. In particular, the above-mentioned basalt composite material is particularly suitable.

The invention also relates to a method for stabilizing a dike using a ground anchor assembly, the method comprising: connecting a ground anchor to a first end of a tensile member; introducing the ground anchor through the dike and into a stable layer; providing a pressure distributing member on or around the tensile member at a position within the dike where stabilisation against lateral earth movement is required; and connecting a second end of the tensile member to a counter member at an outer surface of the dike. In this context, a stable layer is intended to denote a layer that is not subject to lateral slip and that is adequate for providing the required tension force. This layer may be the underlying clay layer beneath the dike or a stable core, not subject to slip.

Although it is possible to install the ground anchor assembly in any possible way, according to a preferred embodiment of the invention the ground anchor is pivotable around the end of the tensile member. In this manner it may be positioned parallel to the tensile member during introduction and tilted by around 90° once located at the anchoring position. This can be realized by applying tension to the tensile member when the ground anchor is in the desired position. Relatively rigid tensile members can be inserted by pushing in the direction of introduction. If necessary an additional pusher rod could be used for inserting the tensile member to the desired position. The pusher rod can be vibrated using otherwise conventional equipment. The pressure distributing member may be introduced together with the ground anchor and tensile member or may be inserted over it at a later stage once the anchor is in position. The pressure distributing member may then be fixed to the tensile member to prevent further sliding or migration within the dike.

The invention will be further elucidated referring to preferred embodiments shown in the drawing in which:

Fig. 1 shows schematically a ground anchor assembly according to the invention;

Fig. la is a detail of Fig. 1;

Fig. 2 is partial cross section through a dike according to the invention;

Fig. 3 is an arrangement of a number of ground anchor assemblies according to the invention;

Fig. 4-6 show cross sectional views of several embodiments of the pressure distributing member; and

Fig. 7 shows a schematic view of a reel of tensile member attached to a ground anchor.

In Fig. 1 a ground anchor assembly according to the invention is generally shown at 1. It comprises a ground anchor 4 having a pivot 15 for connection to a tensile rod 3. A substantial part of tensile rod 3 is provided with a pressure distributing member 2. Remote from the ground anchor 4 a counter plate 5 is provided. In Fig. la connection of the counter plate 5 and the tensile rod 3 is shown. A clamping sleeve 7 is provided over tensile rod 3 and crimped thereto. Thereafter an epoxy sealing material 6 is introduced in the cavity in which clamping sleeve 7 is arranged to make the assembly vandal proof. It will be understood that alternative fixations may be provided instead of the clamping sleeve, including screw fixation and adhesives, depending on the material of the tensile member. Other materials may be used for encasing the fixation member. Such clamping action can be effected after inserting the ground anchor 4 to the desired position and tensioning the tensile rod 3 to the desired value.

In Fig. 2 an example is given wherein the final condition after mounting a ground anchor assembly is shown. Fig. 2 shows that the counter member 5 is embodied as a plate having perforations. It should be understood that counter member 5 can have any configuration according to the related requirements. It is also clear from Fig. 2 that counter plate 5 is at the surface of the dike 8. It should be understood that it can also be provided below the surface thereof. Dike 8 is arranged above the original soil layer 10 and comprises an earth core 9. One side of the dike 8 is subjected to pressure from water 11 whilst the other side thereof should remain dry. By placing a number of ground anchor assemblies 1 as shown in Fig. 2 adjacent to each other in length direction and having the ground anchor 4 extending into the original soil the position of the earth core 9 is fixed in normal conditions.

However due to rain or other particular circumstances it might be possible that the moisture content in the dike becomes so high that flow of earth material is possible resulting in removal of earth material between ground anchor 4 and counter plate 5.

This results in lowering of the stabilization force from counter plate 5 on the body of earth such that the effectiveness of such an anchor assembly is greatly reduced. According to the invention by using pressure distributing member 2 movement of earth is substantially prevented. By placing a number of ground anchor assemblies adjacent to each other occurrence of a flow of earth material is blocked.

In Fig. 2, arrow a shows a flow direction perpendicular to the tensile rod 3. It should be understood that other flows, for example horizontal flows, are also prevented.

In Fig. 2 the pressure distributing member 2 is shown as having a cross shape in cross-section. This is further shown in Fig. 5. Fig. 4 shows the pressure distributing member 2 embodied in the form of a strip. Figure 6 shows the pressure distributing member 2 in the form of a three bladed shape. It will be understood that these shapes are merely exemplary and that any other suitable cross-section may be provided that increases the surface area for the prevention of lateral flow. The pressure distributing member 2 may also be spiralled along the length of the tensile member and that other shapes are possible. It is also possible that the shape thereof is not the same over the length thereof but might vary according to the requirements set which depend from the constitution of the several ground layers and the probability of lateral movement.

Fig. 3 shows a further example of a dike 8 having a top surface 13 and earth core 9. In this embodiment 14 shows possible slip lines. Portions of the dike can slide with respect to each other under unfavourable circumstances in the direction of arrows d along these slip lines 14. The location of these slip lines 14 or planes can be determined through geotechnical surveying of the dike. Through the presence of the ground anchor assemblies 1 according to the invention and more particular the pressure distributing members 2 such migration can be effectively prevented. In the Fig. 3 embodiment the ground anchor assemblies 1 are placed at numerous elevations within the dike 8 and each tensile member 3 carries two pressure distribution members 2 located such as to span a respective slip line 14.

Fig. 7 shows a reel 16 on which a length of material is provided comprising a flexible tensile member 3 formed of basalt based material. In use, the tensile member 3 can be threaded through the pressure distributing member 2 and connected by a crimped connecting sleeve (not shown) to a ground anchor 4. The ground anchor 4 is then inserted into the dike to the required depth using a conventional push rod and vibratory driver which drive both the ground anchor 4 and the pressure distributing member 2 into the dike. Once the required depth is reached, the ground anchor 4 is pivoted to its anchoring position by applying a pulling force on the tensile member 3. This can then be cut to the required length after which counter member 5 can be connected using the clamping sleeve 7 shown in Fig la.

In an alternative embodiment it is possible to first insert the ground anchor together with the tensile member and subsequently slide flow restrictor 2 over the tensile member 3 to the required depth. It is also possible to introduce a hardening or non-hardening stabilizing material into the body of earth before, during or after introduction of tensile member 3, in particular to fill any voids created during insertion and prevent channel forming along the tensile member.

It should be realized that the above are only examples of the invention. Furthermore it should be clear that combinations can be made with other techniques resulting in further effectiveness of stabilization. For example it is possible that the counter plate is embodied as geonet, such as a geotextile.

Starting from this disclosure, many more embodiments will be evident to a skilled person, which are within the scope of protection and the essence of this invention and which are obvious combinations of prior art techniques and disclosure of this invention.

Claims (17)

A ground anchor assembly (1) for stabilizing a dike, comprising a ground anchor (4), a counterpart (5) and an elongated tension member (3) connecting the ground anchor (4) and the counterpart, characterized in that tension member between the ground anchor and the counter part (5) is provided with a pressure distribution member (2) which is positioned to prevent a flow of earth in a direction (a) perpendicular to the longitudinal direction of the tension member (3). An assembly according to claim 1, wherein the pressure distribution member is elongated and extends along the pulling member, preferably over at least 10% of its length, more preferably over at least 30% of its length. Assembly as claimed in any of the foregoing claims, wherein the pressure distribution member comprises a blade structure, which preferably has a cross or a star in cross-section. Assembly as claimed in any of the foregoing claims, wherein the pressure-distributing member is slidably arranged around the pulling member. Assembly as claimed in any of the foregoing claims, wherein the pressure distribution member is integral with the pulling member. An assembly according to any preceding claim, wherein the pressure distribution member comprises a composite material, preferably basaltic epoxy composite. Assembly as claimed in any of the foregoing claims, wherein the ground anchor is a hinged ground anchor that can be inserted into the dike by an insertion rod and can be pivoted to the correct position by applying tension to the tension member. An assembly according to any preceding claim, wherein the tension member is a flexible rod of composite, preferably a basalt fiber composite, firmly connected to the ground anchor and to the opposite. Assembly according to a preceding claim, wherein the opposite part is a perforated plate, preferably from basalt composite. 10. Assembly as claimed in claims 1-9, wherein the opposite part comprises a net. A dike (9) comprising a plurality of adjacent ground anchor assemblies according to any preceding claim, arranged to prevent a flow of soil in a direction (a) perpendicular to the longitudinal direction of the tension member. The dike of claim 11, wherein the opposite is provided near an outer surface of the dike. A method for stabilizing a dyke using an anchor assembly comprising: - connecting a ground anchor to a first end of a tension member; - introduction of the ground anchor through the dike and in a stable layer below the dike; - providing a pressure distribution member on or around the tension member at a position within the dike where stabilization against lateral displacement is required; and - connecting a second end of the tension member to an opposite part at an outer surface of the dike. The method of claim 13, wherein the pressure distribution member is introduced together with the ground anchor and tension member. The method of claim 13 or 14, wherein introducing the ground anchor comprises hinging the ground anchor relative to the tension member to engage the stable layer. A method according to claim 13 to 15, wherein the opposite part is connected to the tension member under a bias. The method of claims 13 to 16, further comprising performing a geotechnical survey of the dike and positioning the pressure distribution member in a position corresponding to a slip zone in the dike.