Soft soil, basal reinforcement

Geosynthetics with high tensile strength and stiffness such as geogrids, woven tapes/strips are used in reinforcement applications. Examples are reinforced soil walls, reinforced steep slopes, slope repair by reinforced soil, basal reinforcement at the base of embankments on soft ground or embankments over piled foundations, as illustrated in Figure 5.6. 

For cases in which the available construction time is limited or serviceabiUty criteria are high, methods other than basal-reinforced embankments need to be chosen. Most commonly, ground improvement using stone or gravel columns is chosen. However if the foundation soil is extremely soft, the use of conventional stone columns can lead to unacceptable deformation or even failure. This is because the soft soil... 

The use of geotextiles to reinforce soft foundation soils has progressed from the earliest applications some 40 years ago to the current status of widespread use and success. This chapter presents three major application areas (1) basal reinforcement, (2) geotextile-encased granular columns, and (3) geosynthetic piled foundations. In addition to the descriptions, elements of design, and information on performance, a specific project example was given for each topic. Further advances can and should be made, but we beheve that the current state of the practice in the selected applications is properly reflected here. 

One technique to improve the stability of breakwaters and containment dykes con-stmcted on soft foundations is to use geotextile reinforcement across the base of the stmcture (Fig. 20.19). This basal reinforcement technique has been used successfully for many years in the onshore construction of embankments on soft foundation soils, and is discussed in detail in chapter Geotextiles used in reinforcing foundations. Because of its cost—benefits, this technique has also been used in marine engineering structures over the past 20 years. 

The reinforced soil technique, such as basal-reinforced breakwater constmction, is an example of a land-based technique employed in a marine engineering environment to provide a cost-effective solution to improve the stability of stmctures constmcted on soft marine foundation soils. The presence of soft marine foundation soils close to coastlines in bays, harbours, estuaries and deltas makes for difficult conditions on which to constmct stable marine stmctures. Reinforced soil is one technique along with other associated foundation consolidation and strengthening technologies that is expected to be used more often in these locations. 

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