When constructing over ground where the foundation material is unstable, there is the possibility of settlement of the ground and hence any construction above.
Differential settlement can be controlled by the construction of a basal platform to spread, span or dissipate the construction loads, downwards into the ground.
There is debate within the industry as to which design methodology is appropriate for the design of basal reinforcement. Maccaferri Ltd adopts the BS8006; Strengthened Earthworks and Reinforced Fills design code, and where appropriate 3 dimensional analytical procedures.
A basal platform reinforced with geogrids or geotextiles, make it perform better than in its unreinforced state including;
- Strengthens the platform construction
- Accommodates higher loads
- Reduces differential settlements
- Can reduce the platform thickness and thus saving on vehicle movements and quarrying
Constructing embankments upon piles is a common technique when building over poor ground, as it is often uneconomic to replace the poor material with a more competent one. By transferring the high embankment loads through piles and thus into more competent strata, the risk of settlement of the overall embankment is minimized.
As piles are expensive, any reduction in the number of piles can offer savings on the project. High strength geosynthetic reinforcement at the level of the pile cap may provide the answer.
The presence of soft or wet ground beneath an embankment can cause settlement problems. A platform of granular material, reinforced with geosynthetics, can limit differential settlement by providing a more competent foundation for the embankment. Geogrid and geotextile reinforcement can allow construction in areas previously considered out-of-bounds for building infrastructure upon due to soft ground.
Mining or naturally occurring voids within the ground can play havoc with infrastructure above. Sudden settlements of the ground are difficult to predict and are expensive to repair once they have occurred. The use of geogrids and geotextiles beneath infrastructure in these areas can provide reassurance that differential settlements would be controlled in the event that a void appeared.
NB: We do not advocate the use of basal reinforcement / platforms beneath buildings or structures sensitive to differential settlement. The differential settlement that can be accommodated by a road or railway embankment compared to a masonry wall or building is dramatically different.
We're presenting at GeoTex on May 25th 2011 at the Imperial War Museum, Duxford.
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