Construction may require slope soil reinforcement aiming at its protection against water, wind and other adverse impacts.
Contents
Slope reinforcement justification
Selection of reinforcement variant
Slope reinforcement techniques
Slope reinforcement justification
Slope reinforcement is justified in the following cases:
- When an area is susceptible to land slide and ground failure;
- To ensure construction safety and prevent embankment land slide;
- When embankment stability is compromised during construction;
- For erosion protection;
- For high-profile landscaping;
- When vertical load distribution is required.
Selection of reinforcement variant
Selection of reinforcement variant depends on:
- site and slope profile;
- presence of ground water under the site, its routes and depth;
- the level of seasonal precipitation at site;
- the scale of site reinforcement;
- the site application.
An optimal reinforcement method is selected based on analysis of all the site data collected and feasibility study.
The site acclivity measurement is an important factor. If it is less than 8%, the slope soil reinforcement can be achieved through plants i.e. soil conservation by afforestation.
Important! Plants is a viable way of slope reinforcement. It is applied, but not everywhere. Plant types with a powerful root system, such as perennial grass and biomats, are used for reinforcement. The plants can be set out over a geofabric layer. The plant root system will grow and strengthen the soil preventing its migration.
Plants of the most common use in slope reinforcement:
- tree peony;
- creeping briar;
- savin juniper;
- lilac;
- greenweed;
- deutzia.
As geosynthetic slope reinforcing materials, the widest application has been achieved by volumetric geogrids, geomats and geonets.
Geogrid use is recommended if the slope angle exceeds 70 degrees. Geonet, in its turn, enables maintaining fertile soil. The net cells preserve the slope ground to enable plant growth and prevent land sliding.
With geomat used, plant roots are intertwined with its fibers. A solid earth layer is thus formed to prevent the slope from erosion and land sliding.
Besides this, there is a geotextile that can perform, depending on type and brand, a function of reinforcement, separation and drainage. Geotextile is divided by manufacturing type into woven (made of polypropylene or polyester fibers) and nonwoven (needle punched, thermally bonded) geotextile. It does not allow weed growth and evenly distributes fill material loads. It is used in combination with geogrid in slope reinforcement.
Slope reinforcement techniques
Geogrid reinforced slopes
Geogrid-assisted slope reinforcement includes preparation of a base (slope surface) for installation, geogrid laying and cell filling with relevant materials.
1. The slope surface shall be leveled and compacted; the slope geometric parameters shall be checked, the conditions for fixing geogrid end parts at the slope foot and edges shall be ensured as set out by the project design documentation. If required, a protective layer (a backflow filter) of nonwoven geosynthetic material shall be installed. The boundaries of the sections laid shall be marked, and anchor rods shall be installed lengthwise near the slope edge, at least 0.5 m away from it.
2. For the purpose of geogrid installation, its outmost cells shall be placed over anchor rods, the geogrid shall be spread in direction A, with its opposite side fixed with anchor rods. The adjacent sections shall also be prefixed with anchor rods followed by final stapling of every cell at several points along its height (approximately every 30 mm) with special staples and stapler. The anchor rods can be jammed, depending on soil and hydraulic conditions, in the following manners:
— near the slope edge and foot only, if a water-impermeable cover (various reservoirs) shall be installed on the slope surface or the anchor rod jamming is complicated (the slope is formed by very coarse soils);
— following the standardized method strengthened by cable bracing, if the standardized method does not provide sufficient stability to the reinforcement arranged (normally, in cases of inundated slopes).
In the latter case, before the geogrid spreading and fixing, polymeric cables shall be pulled through the holes in the geogrid ribs and attached to the ground (in every 3 to 4 cells) also with anchor rods.
3. The aggregate shall be poured by an excavator or a loader, disallowing coarse fraction drop from a height of over 0.5 m in case of soil, and over 1 m, in case of sand-gravel mixture. The aggregate shall be leveled and compacted manually. The compacted aggregate layer height along the slope surface shall be approximately in line with the cell height, with a 2.5cm to 3 cm thick (5 cm in case of coarse filler) protective layer provided on a horizontal surface.
Geomat reinforced slopes
Stage 1. Site leveling: remove waste, level the ground. Compact the ground with a hand roller.
Stage 2. Dig a 30cm deep trench at the slope upper and lower edge. Make a channel across the slope to divert water.
Stage 3. Unroll the roll along the whole slope surface. In case the fabric is too large, cut it to size.
Stage 4. Lay geomats with the smooth side down so that they overlap, 20 cm crosswise and 15 cm lengthwise.
Stage 5. Fix the geomat upper edge in the trench with anchor rods, dowels, forked wooden sticks or bolts, with 2 anchors per 1 meter.
Stage 6. Fix the geomat lower edge in the same manner.
Stage 7. Fill all the trenches with soil and then compact it. If the risk of water impact is high, better use 2 to 5 mm graded macadam instead of soil.
Stage 8. Sow the ground with plants and grass.
Geonet reinforced slopes
Stage 1. Level and compact the ground surface.
Stage 2. Unroll the roll over the whole site area of the slope, end to end without overlapping.
Stage 3. Fix the joints with anchor rods 1 to 1.15 m away from each other.
Stage 4. Stretch the net along the slope ensuring its tight contact with the soil.
Stage 5. Cover the net with three layers i.e. macadam – stones – soil.
Stage 6. Put in plants and lay turf over the soil. In a month, the plants root system will grow through the material thus forming a solid structure.
Conclusions
Slope reinforcement with geosynthetic materials is a multipurpose solution towards prevention of slope and embankment soil from erosion, eolation and migration. A wide range of geosynthetics available allows selection of the type required for a specific solution based on the goals and the location conditions.
Geospan range includes materials proven successful in slope reinforcement in hundreds of federal and regional projects.
Geospan GC (GCP) is a volumetric geogrid of strong polyethylene strips. A perforated design is available for applications requiring enhanced drainage in the geogrid filling plane.
Geospan PM is a polyester geomat. This geosynthetic 3D material is made of thermally bonded fibers intertwined at random among each other.
