Retention criteria

In many cases, the retention criteria will result in opening sizes that are above or below the sizes that are manufactured. If the retention criterion requires an opening size below the available size, tests are recommended. If the retention criterion requires an opening size larger than the available size, often a fabric with a smaller opening size can be used, provided that the permeability criterion is met (Section 12.6). 

particle size distribution d, grain diameter at the lower size of the dxx grain diameter for which xx% of the particles is finer O90, size of opening whidi corresponds to the grain diameter fen which 90% of the soil passing through the geotextile is finer. 

Data from CFEM, 2006. Canadian Foundation Engineering Manual, fourth ed. Canadian Geotechrucal Society, pp. 343—356. 

The findings of Lafleur (1999) and the recommendations of Holtz et al. (1997) were combined in the design approach pubUshed by the Canadian Geotechnical Society (CFEM, 2006). The threshold value for the application of the approach by Lafleur for widely graded soils was taken to Cu = 8 (instead of Cu = 6 in the original proposal) and for coefficients of uniformity 4 Cu 8 opening sizes O90 I dgS re allowed (Table 12.1). 

The Goman approach (DVWK, 1992), which is recommended only for soils with d40 0.06 mm, is to take the uniformity into consideration. For soils with 

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The third area is sanple retention. The industry is having seme difficulty with this, particularly with respect to the retention of crop and tissue sanples which have been analyzed for residues. A "forever" retention criteria creates enormous practical problems. We would hope that the regulations will provide sane flexibility in this area. A fixed time limit seems reasonable. The NACA GLP guideline document dealt with sanple retention as follows ... 

Initially these results show that three of the four stationary phases are similar in terms of average k with values between 1.9 and 2.0. The best phase, at least using retention criteria, is the Platinum EPS Cl8 with an average k of 2.88. However, one... 

Product rule only applies if the retention criteria in both dimensions are orthogonal Highly optimized 2D-LC can achieve four to sixfold higher Hq in the same analysis as ID-LC... 

Soil zones Flow conditions Retention criteria... 

When accounting for particulate clogging in the retention criteria, consideration must be given to the total % of open area and the faction of open area that has small pore space. For the total open area, the principle is that a geotextile should always be more porous than the equivalent soil filter. However, because non-woven structures are more susceptible to clogging than woven structures, it is recommended that non-woven geotextiles used for filtration should have a porosity of 40-60% whereas woven geo-... 

Generally, the dry sieving method yields a relatively larger value of pore size than that obtained from either wet sieving or hydrodynamic sieving (Faure et al., 1986 Van der Sluys and Dierickx, 1991 Bhatia et al., 1994). This circumstance must be taken into account when design retention criteria are used. 

Figure 12.2 Normalized retention criteria O dso versus coefficient of uniformity Cu including...

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