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Slope Rehabilitation |
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Many effective and cost-effective methods of slope rehabilitation are available today. The engineering practice has adopted a categorization according to the protection types, as follows:
Most common is the slope protection with rockfall netting (TYPE-1). This is a protection measure applicable after thorough survey of the site. Other types of protection require elaboration of designs, including the development of surveying support data, geostatic calculations and structural designs.
Protection TYPE-1 – rockfall net
Slope protection in rock material, preventing small rock fragments from falling on the road. As the netting is made of double twist wire, it is strong enough to resist the impact of falling rocks and – as opposed to single twist mesh – suffers no breaks or deformations. In cases where a stronger protection against corrosion is required, the Zn-coated wire may be additionally coated with PVC of nominal thickness 0.5 mm. Technical characteristics and resistance of the netting comply with applicable standards.
Protection TYPE-1A – rockfall net and anchors
This type includes the cut slope protection with netting, steel wire cables and bar anchors. Bar anchors are 3, 6 or 9 m long, depending on the quality and state of rock mass, on the size of instable rock mass blocks and on the width of the zone to be protected. In the zones where the rock mass is significantly crushed and weathered, self-drilling anchors are installed, and in other zones standard bar anchors are applied. Slope protection with wire fabric, steel wire cables and bar anchors is applied on the locations where it is anticipated that falling out of instable blocks could disturb the slope geometry. The criterion for the installation of protective wire fabric is the anticipated rock mass fragmentation: if the rock mass fragmentation exceeds the mesh size, the protective netting may be applied. If the fragments of rock mass are smaller, the MACMAT® mat is applied. Depending on the size of instable blocks and on the width of fault zones, the TYPE-1A protection is divided into three subtypes:
TYPE-1Aa includes slope protection with protective netting and bar anchors of 25 mm diameter and 3 m length, on the 3 x 3 m grid. This protection type is applied in wide fault zones, for consolidation of instable blocks.
TYPE-1Ab includes slope protection with protective netting, bar anchors of 25 mm diameter and 6 m length, on the 3 x 3 m grid and steel wire cables of 12 mm diameter. This protection type is applied in very wide fault zones, for consolidation of instable blocks.
TYPE-1Ac includes slope protection with protective netting, bar anchors of 32-36 mm diameter and 9 m length, on the 3 x 3 m grid and steel wire cables of 12 mm diameter. This type of protection is used in extremely difficult soil conditions.
Protection TYPE-2 – rockfall net and shotcrete
This protection type includes the wire fabric as in TYPE-1 and the application of 3-5 cm thick protective shotcrete layer over the wire fabric
This protection type is applied instead of the protection TYPE-1 on the locations where the anticipated fragmentation of material is too small to be retained by the protective wire fabric with concrete weights. In order to prevent that the hydrostatic pressure is generated between the rock and the shotcrete, short drains (up to 2.0 m) are executed on the 4 x 4 m grid.
Protection TYPE-3 – shotcrete and anchors
This protection type includes slope protection with shotcrete, fabric reinforcement and bar anchors and is applied on the locations of anticipated falling out of instable blocks, which would disturb the slope geometry. Bar anchors are 3, 6 or 9 m long, depending on rock mass quality, size of instable rock blocks and on the width of the zone to be protected. In the areas of significantly crushed and weathered rock mass self-drilling anchors are installed. Depending on the size of instable blocks and on the width of fault zones, protection TYPE-3 is subdivided into three subtypes:
TYPE-3a includes the slope protection with 10 cm thick shotcrete, 3 m long bar anchors of 25 mm diameter on the 3 x 3 m grid and fabric reinforcement Q131. This protection type is applied in wide fault zones for stabilization of instable blocks.
TYPE-3b - includes the slope protection with 10 cm thick shotcrete, 6 m long bar anchors of 25 mm diameter on the 3 x 3 m grid and fabric reinforcement Q131. This protection type is applied in very wide fault zones for stabilization of instable blocks
TYPE-3c – includes the slope protection with 15 cm thick shotcrete, 9 m long bar anchors of 32 mm diameter on the 3 x 3 m grid and fabric reinforcement Q131, if necessary Q188. This protection type is applied in extremely severe soil conditions.
Protection TYPE-3 modified – MACMAT® with steel wire cables and anchors
Cut slope protection with MACMAT® net, steel wire cables and bar anchors. The bar anchors are 3, 6 or 9 m long, depending on the quality of
rock mass, size of instable rock mass blocks and the width of the zone to be protected. In the zones of extremely crushed and weathered rock mass the self-drilling bar anchors are installed, and in other zones the standard bar anchors are applied. MACMAT® is a composite material consisting of zinc coated or plasticized hexagonal fabric as a bearing section and of fill of three-dimensional polypropylene fibre structure MAT. It is used for protection against erosion and for stabilisation of slopes and embankments, as well as for reinforcement of topsoil and provision for vegetation development.
The use of this protection type is significantly faster, simpler and more acceptable in terms of landscape. The protection TYPE-3 modified is also applied on locations where it is anticipated that the instable blocks could fall out and disturb the slope geometry. Depending on the size of instable blocks and on the width of the fault zones, the TYPE-3 modified protection is divided into three subtypes:
TYPE-3a modified includes slope protection with MACMAT® netting and 3 m long bar anchors of 25 mm diameter, on 3 x 3m grid. This protection type is applied in wide fault zones for stabilization of instable blocks.
TYPE-3b modified includes slope protection with MACMAT® netting and 6 m long bar anchors of 25 mm diameter, on 3 x 3m grid and steel wire cables of 12 mm diameter. This protection type is applied in very wide fault zones for stabilization of instable blocks.
TYPE-3c modified includes slope protection with MACMAT® netting and 9 m long bar anchors of 32 mm diameter, on 3 x 3m grid and steel wire cables of 12 mm diameter. This protection type is applied in extremely severe soil conditions.
Protection TYPE-4 – stone
This is the slope protection with the wall of stone revetment. This protection type is applied in the zones where larger cavern systems or clayey zones in the cut side are observed.
Protection TYPE-5 – gabion
This is the slope protection with gabion wall. This protection type is applied in the zones of excavation in deeper clay and/or mix of clay with rock mass fragments and/or in sinkhole zones. Gabions are baskets made of hexagonal wire fabric made of heavy zinc coated wire or wire galvanized with Galfan® with PVC-U coating. The wire has double twist as to enable the localisation of the damage and to prevent further ripping of the wire fabric. The height of the wall is determined by the height of the cut and by the depth of the clay material; however, it is recommended that the height of gabion wall does not exceed 6.0 m. The retaining structure needs not be executed over the entire cut height. The clay material behind the retaining structure should be shaped as a slope with inclination 1:2 or 1:1.5, depending on the height of the overburden of clay material. The slope may also be designed with inclination 1:1, but in this case the clay material needs to be additionally protected against erosion by installation of MAT protective netting.
Protection TYPE-6 - MAT
Protection of cut slope against erosion by application of MAT netting. This protection type is applied in clayey cuts and in the cuts consisting of coherent material. MAT netting is applied on mild slopes (1:1 and milder), where the global stability of the slope is not compromised, but due to the danger of erosion the slope needs to be grassed. MAT is a three-dimensional polypropylene mesh of fibrous structure. MAT must be placed from the embankment crown downwards. The mat rolls are positioned along the cut top, fixed on the embankment crown, rolled down towards embankment toe and fixed on the slope and at the embankment toe. Subsequently the mat is covered with topsoil material mixed with grass seed.
Protection TYPE-7 – MACMAT®
This protection type includes cut slope protection against erosion by installation of MACMAT®. This protection is designed for cuts composed of mixed materials or cuts in extremely weathered rock material subject erosion. MACMAT® is a composite material consisting of zinc coated or plasticized hexagonal fabric as a bearing section and of fill of three-dimensional polypropylene fibre structure MAT. Placing of MACMAT® is executed from the cut crown towards the cut toe. The rolls of MACMAT® are placed along the cut crown and fixed on the crown, rolled down towards the cut toe and fixed on the slope and in the cut toe. Subsequently the mat is covered with topsoil material mixed with grass seed.
Protection TYPE-8 – anchors
This protection type includes the stabilisation of potentially instable rock blocks with bar anchors. The stabilization of larger rock blocks is provided by installation of standard bar anchors of 3, 6 or 9 m length, depending on the stretching of the crack system and on the size of the potentially instable rock mass block. |
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Technical guidelines (PDF)
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It is used on slopes where the rock mass fragmentation exceeds the mesh size thus generating the erosion danger. It can be combined with geotechnical anchors on the locations where instable blocks were observed during construction, if such blocks could disturb the slope geometry and compromise the traffic safety.
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3D polymer netting for greening and slope protection against erosion. It is a combined system of materials and hydroseeding.
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Applied on slopes consisting of mixed material, where there is a danger of rockfall and washing away of small material particles. This material is used exclusively in combination with hydroseeding.
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Honeycomb 3D structure used for slope surface stabilization and greening.
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