Migration of fines in 0–20 mm crushed base during placement, compaction, and seepage under laboratory conditions

Abstract

The rate of deterioration of gravel base course materials may influence the durability of flexible pavements. In particular, selected gradation curves usually satisfy filter criteria thus avoiding migration of fines from one layer (subgrade, base, and subbase) into adjacent one. This paper shows that even if filter criteria are met between successive layers, some 0–20 mm materals do not satisfy the fines mobility criteria that presently are not considered in gradation criteria. This means that fines (<80 μm) can move within the pores of the layer. Three gradations of two 0–20 mm crushed stones were tested in the laboratory. Experiemrnts were designed to avoid degradation (breakage of particles), in order to study segregation only. One of the tested materials (No. 2) satisfies the gradation criteria but does not satisfy the fines mobility criteria. The experimental results confirmed that material No. 2 is subject to marked segregation during dry placement and compaction. When palced moist, it has a negligible initial segregation, but cyclic loading produces segregation. This internal instability was predictable from fines mobility (suffossion) criteria. It produces layers with different fines contents, which would reduce vertical drainage, increase pore pressures produced by traffic loading, and increase both capillary retention and frost damage. Key words: road, gravel base course, segregation, suffossion, seepage, gradation.

On the distinct phenomena of suffusion and suffosion

“…den Adel et al, 1988;Å berg, 1993;Bendahmane et al, 2008), or indirectly from a change in gradation of the test specimen (e.g. Chapuis et al, 1996;Wan & Fell, 2004;Moffat et al, 2011). On occasion, both methods have been used (Lafleur et al, 1989;Honjo et al, 1996;Li, 2008).…”

“…Although measurements of hydraulic gradient and flow rate are commonly recorded (Skempton & Brogan, 1994;Chapuis et al, 1996;Garner & Sobkowicz, 2002;Wan & Fell, 2004;Li, 2008;Moffat et al, 2011), it appears that changes in hydraulic conductivity are seldom reported in a systematic manner. Notably, Skempton & Brogan (1994), and later Li (2008), respectively, used measurements of hydraulic gradient and seepage and discharge velocity to quantify the onset of instability.…”

Modelling the impact of particle removal on granular material behaviour

“…The mechanism of suffusion has been widely studied, mainly with the purpose of defining the criteria for soils likely to develop internal erosion (e.g. Kenney & Lau, 1985;Lafleur et al, 1989;Chapuis et al, 1996;Foster & Fell, 2001;Wan & Fell, 2004;Bendahmane et al, 2008). Several studies have also proposed various numerical approaches to model the erosion process (e.g.…”

Experimental identification of mobile particles in suffusible non cohesive soils

“…The phenomenon of suffusion of sand-gravel soils has been studied by a number of researchers (including (Kenney and Lau, 1984, 1985, 1986Sun, 1989;Burenkova, 1993;Lafleur et al, 1989 andChapuis et al, 1996)). The soils investigated by most of these authors are sand gravels free of silty fines.…”