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Approximately 25% of China's 120 000 km of expressway, as well as many new metro lines and airports, rest on soft clay deposits. However, service settlements are proving larger than expected, especially in southeast China. This note describes laboratory experiments on K 0 -consolidated intact samples of soft clay taken near Wenzhou, south-east China, that explore whether cyclic traffic wheel loading contributes significantly to the observed settlement trends. Cyclic triaxial (CT) tests are reported together with cyclic hollow cylinder (CHCA) experiments that imposed cardioid-shaped 2τ zθ À (Δσ z À Δσ θ ) stress paths. Cyclic principal stress axis rotation is shown to have an important influence on vertical straining. Once a certain threshold has been exceeded, the resilient and permanent strains developed in the CHCA tests become progressively larger than their counterparts in CT tests conducted at the same vertical cyclic stress ratio, with trends that diverge progressively as vertical cyclic stress ratio increases. Critical cyclic stress ratios can be defined that divide the response into (a) stable, (b) metastable and (c) unstable cyclic ranges. The novel experimental approach and high-quality data reported should aid practitioners and modellers in developing new analyses to address this economically significant geotechnical problem.

The understanding of cyclic and post-cyclic behaviours of the soil–geosynthetic interface is essential for the design of geosynthetic- reinforced soil structures under repeated loads, such as those induced by traffic, earthquakes and compaction. In this paper, a series of monotonic direct shear tests and cyclic direct shear integrating monotonic direct shear tests were conducted by using a large-scale direct shear testing device. The effect of normal stresses, cyclic shear amplitude and cycle number on the post-cyclic behaviour of the interface are investigated. In addition, the influence of cyclic shear on interface direct shear behaviour was discussed in detail. The test results indicated that both the peak and residual shear stresses of the interface during the post-cyclic shear phase increased linearly with normal stress and the number of cycles. The volume contraction, which was induced by the direct shear, decreased with the increase in normal stress. The interface apparent adhesion and friction angle increased with the cyclic shear.

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