This Chapter presents in-situ and laboratory experimental techniques used to describe mechanical behaviour of pavement materials (soils and aggregates) at different saturation stages. Repeated triaxial load testing can be applied to obtain both stiffness characteristics and assessments of the ability of the material to withstand accumulation of permanent deformation during cyclic loading. For unsaturated soils, in addition to mechanical variables, a moisture/suction control should be added, which can be imposed by several techniques as explained in the chapter. A brief presentation of the model parameters and tests needed for model calibration was introduced with particular reference to the modelling approaches described in Chapter 9. Evaluations of pavement structural capacity based on deflection measurements with non-destructive testing equipment have also been presented. Finally, some examples of laboratory and in-situ measurement are shown.
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Fig. 10.23 Soil suction measured with tensiometers and saturation measured with the mois — ture/density probe (Krarup, 1995). Reproduced by permission of the Danish Road Institute Note: Where measurements were carried out at different depths, the depths of the tensiometer are given in brackets (69 cm). The curves are time series beginning from the left (high suction). |
Based on experimental results presented above it can be concluded as follows:
i) Bearing capacity and unconfined compressive strength decrease with increase in moisture content.
ii) The permanent axial strain increases when water content approaches to wOPM.
iii) Resilient modulus decreases as the water content approaches to wOPM. The resilient modulus of soils decreases by a factor 4-5, for realistic (temperate) seasonal variation of moisture contents.
iv) Reduction in resilient modulus with suction depends also on the grading coefficient: lower grading parameters (i. e. more fine particles) yields larger modulus reductions as saturation is approached.
v) In-situ experimental data confirms that resilient moduli decrease with decrease in suction. The soil-water characteristic curve depends on the grading of tested material meaning that the modulus-suction relationship is likely to be very soil- specific.
