A large number of C_c - w_n (C_c is the compression index and w_n is the natural water content) correlations have been proposed by researchers for different soft clays around the world, but comparisons of these correlations and reasons for differences between them are rarely reported. In this paper the C_c - w_n relationships of marine soft clays from eight China’s coastal cities are presented. It is found that the north coast clays have larger slope of the C_c - w_n relationships (about 0.02) than the south coast clays (about 0.008). Comparisons with C_c - w_n relationships for remoulded clays and structured natural clays reported by other researchers show the importance of accounting for soil structure, and the higher compressibility and higher apparent preconsolidation stresses of the north coast clays, in comparison to the south coast clays, are believed to be associated with chemical bonding and other post-depositional changes. Most of the reported C_c - w_n correlations for natural soft clays from around the world have slopes of about 0.011, which are applicable to weakly structured clays. To develop a more widely applicable C_c - w_n correlation, the effects of soil structure need to be incorporated.

High-energy impact rollers (IR) have been increasingly used for earthworks by compacting on-site soils. The IR applies high energy to the ground and densifies deeper soils than conventional rollers and plate-type compactors. A trial program was implemented on the third runway of the Shanghai Pudong International Airport in China to validate the performance of the IR technology. Field monitoring and in-situ testing were undertaken during or after the IR compaction. The cone penetration data indicated that significant improvement in soil properties was measured up to a depth of 4 m after 20 to 25 passes of compaction. However, the improvement of the properties of the very soft silty clay at the depth of 1–2 m was limited. The vibration monitoring data suggested that the IR compaction with 12-t impact module would not cause damage to buildings at a distance of 9.5 m away from the boundary of the compaction path.

The presence of fissures poses significant threats to tunnel-lining structures, and the interaction between tunnels and linings under complex stress conditions remains poorly understood. This study investigated the failure modes of tunnel-lining structures with prefabricated fissures via 3D-printed samples, uniaxial compression experiments using DIC technology for full-field strain monitoring, and a particle-based meshless (SPH) numerical method to simulate tunnel–fissure interactions. The results show that under uniaxial compression, three crack types (main, upper/lower side cracks) initiate from the tunnel, while only wing cracks form at pre-existing fissures; wing crack initiation suppresses upper-side cracks, whereas more lining cracks (upper, middle, lower, corner, bottom) emerge without fissure-induced propagation. Fissure orientation (β) and inclination (α) significantly affect crack distributions: β = 90° induces maximum stress concentration and asymmetric deformation, while α ≥ 45° promotes wing crack initiation and reduces lining crack density. Along with our findings, we offer design recommendations to prioritize fissure orientation in tunnel engineering and expand SPH applications for predicting crack propagation in underground structures with complex fissures.

A laboratory investigation of the influence of different factors - including weight, size and towing speed of impact modules - on the effectiveness of impact roller (IR) compaction was carried out. An impact roller simulation device was developed to do the investigation and air pluviation technique was used to prepare loose, dry, sand specimens. The Chinese cone penetration tests in the position of impact craters in sand specimens with different passes of IR compaction were used to verify the effectiveness of IR compaction. Results of the laboratory tests show that the weight and towing speed of a module significantly affects the effectiveness of IR compaction, but the size of the module has little influence on effectiveness. It is mainly observed that better improvement can be achieved when heavier impact modules are used and towing speeds close to the optimum towing speed are adopted during IR compaction.