Saturation and its effect on the resilient modulus of a pavement formation material

Abstract

This paper reports the effects of changing degree of saturation on the stiffness of a typical railway formation material. Material dynamically compacted to a target dry density over a range of water contents was cyclically loaded in triaxial and hollow cylinder apparatus. The results of both test types show the large effect of the degree of saturation on stiffness. In both the cyclic triaxial apparatus and the equivalent stress path in the cyclic hollow cylinder apparatus, the resilient modulus (MR) increased considerably (from ∼36 MPa to ∼467 MPa) as the degree of saturation fell. MR at a water content of 7% (optimum under the 2·5 kg rammer) was approximately 1·5 times the near-saturated value (at w = 8%). MR at the driest state tested (w = 4%) was approximately 6 times that measured for the near-saturated specimen. In the hollow cylinder apparatus, these trends were seen regardless of whether principal stress rotation was applied. The increase in MR associated with decreasing water content is thought to result from an increase in matric suction. Increased scatter in MR at higher suction may be the result of a more variable distribution of water within drier specimens. Comparison of suction stresses derived from the soil water retention curve with values back-calculated from cyclic triaxial testing suggests that useful estimates of railway formation resilient modulus, MR, may be made on the basis of measurements of matric suction.

The bounding effect of the water retention curve on the cyclic response of an unsaturated soil

“…The clay fraction of the tested soil is Hymod Prima [12], plastic Ball Clay consisting of disordered kaolinite, micaceous material, and quartz. The same soil has commonly been used in research studies, see for example Gra ¨be & Clayton [12], Mamou et al [23] and Blackmore et al [7]. The specimens were compacted in a compaction mould with a height of 200 mm and a diameter of 100 mm using a drop hammer following the standard Proctor test procedure [5].…”

“…Experimental results of cyclic testing showed that the response of unsaturated soils is dependent on soil water retention properties while information on both suction and water saturation levels are required to evaluate the accumulated permanent deformation and resilient modulus (e.g. [7,14,21,28,46]). Therefore, any interpretive framework developed for the cyclic response of unsaturated soils requires a water retention counterpart that recognises the evolution of soil suction and water saturation under cyclic loading conditions (e.g.…”

“…Therefore, any interpretive framework developed for the cyclic response of unsaturated soils requires a water retention counterpart that recognises the evolution of soil suction and water saturation under cyclic loading conditions (e.g. [2,7,34]).…”

Analysis of the resilience modulus of a subgrade soil front of humidity variations

“…However, seasonal variations in the degree of saturation are expected during the life of the pavement, since it goes through fluctuations in the water table level, water percolation, infiltration by surface cracks, lateral movements through the shoulder, among others [1]. The occurrence of excessive humidity produces a reduction in the pavement's support capacity, starting its degradation ( [2], [3], [4], [5]).…”

The role of clay content on the response of railway track foundations during free-to-drain cyclic changes in principal stress rotation

“…Laboratory studies suggest that the effects of principal stress rotation on the resilient stiffness of unsaturated sand / clay materials may be secondary (Blackmore et al 2019), but in saturated conditions, principal stress rotation may be significant (Xiao et al 2013;Cai et al 2015Cai et al , 2016Qian et al 2016;Guo et al 2017). Principal stress rotation affects both the axial strain and the resilient stiffness of sand clay mixes dominated by the sand fraction (Gräbe andClayton 2009, 2014).…”