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Arching effect, which is a common phenomenon in any system involving soil-structure interaction, has been found to be inevitably affected by various factors, including loading conditions. This study investigated the evolution of arching effect induced by cyclic loading by conducting a series of tests using a trapdoor apparatus. The test box was instrumented to control the displacement of the moving gate and to record the variation of vertical stress distribution by using a set of dynamic load cells. Digital images were captured during tests and processed using particle image velocimetry (PIV) to determine the displacement field and hence to examine the variation of geometric features of arch and particle movements. The evolution process of arching effect, from the initial formation to the finial collapse, was identified. Depending on the analysis for the geometry appearance, displacement region, and variation of cyclic stresses, both stable and collapsed arches were observed. By increasing the amplitude of cyclic loading step by step, critical loading amplitude corresponding to the threshold of collapse of the arching effect was determined. Based on the results, the effects of trapdoor displacement, cyclic loading frequency, and filling height on arching effect are discussed. Key words: soil arching effect, trapdoor tests, cyclic loading, particle image velocimetry, arching evolution. L'effet de voute, qui est un phenomene courant dans tout systeme impliquant une interaction sol-structure, s'est avere inevitablement affecte par divers facteurs, dont les conditions de charge. Cette etude a examine l'evolution de l'effet de voute induit par une charge cyclique en effectuant une serie d'essais a l'aide d'un appareil de trappe. Le banc d'essai a ete instrumente pour controler le deplacement de la porte mobile et pour enregistrer la variation de la distribution verticale des contraintes a l'aide d'un ensemble de capteurs de force dynamiques. Des images numeriques ont ete capturees pendant les essais et traitees a l'aide de la velocimetrie de l'image des particules (PIV), afin de determiner le champ de deplacement et donc d'examiner la variation des caracteristiques geometriques des mouvements des arcs et des particules. Le processus d'evolution de l'effet de voute, depuis la formation initiale jusqu'a l'effondrement de l'epi, a ete identifie. Selon l'analyse de l'apparence geometrique, de la region de deplacement et de la variation des contraintes cycliques, on a observe des arcs a la fois stables et affaisses. En augmentant pas a pas l'amplitude de la charge cyclique, on a determine l'amplitude de charge critique correspondant au seuil d'effondrement de l'effet de voute. Sur la base des resultats, les effets du deplacement de la trappe, de la frequence de chargement cyclique et de la hauteur de remplissage sur l'effet de voute ont ete discutes. [Traduit par la Redaction] Mots-cles : effet de voute du sol, essais de trappe, charge cyclique, velocimetrie de l'image des particules, evolution de l'arche., Introduction Arching effect is a general phenomenon often observed in granular materials. It is induced by relative displacement between soil mass and adjoining structure in a system involving soil-structure interaction, [...]

Purpose: This study establishes a method for predicting ground vibrations caused by railway tunnels in unsaturated soils with spatial variability. Design/methodology/approach: First, an improved 2.5D finite-element-method-perfect-matching-layer (FEM-PML) model is proposed. The Galerkin method is used to derive the finite element expression in the ub-pl-pg format for unsaturated soil. Unlike the ub-v-w format, which has nine degrees of freedom per node, the ub-pl-pg format has only five degrees of freedom per node; this significantly enhances the calculation efficiency. The stretching function of the PML is adopted to handle the unlimited boundary domain. Additionally, the 2.5D FEM-PML model couples the tunnel, vehicle and track structures. Next, the spatial variability of the soil parameters is simulated by random fields using the Monte Carlo method. By incorporating random fields of soil parameters into the 2.5D FEM-PML model, the effect of soil spatial variability on ground vibrations is demonstrated using a case study. Findings: The spatial variability of the soil parameters primarily affected the vibration acceleration amplitude but had a minor effect on its spatial distribution and attenuation over time. In addition, ground vibration acceleration was more affected by the spatial variability of the soil bulk modulus of compressibility than by that of saturation. Originality/value: Using the 2.5D FEM-PML model in the ub-pl-pg format of unsaturated soil enhances the computational efficiency. On this basis, with the random fields established by Monte Carlo simulation, the model can calculate the reliability of soil dynamics, which was rarely considered by previous models. [ABSTRACT FROM AUTHOR]

In soft-soil areas, excessive transverse deformations have occurred in numerous shield tunnel linings accompanied by serious structural defects. However, to date, a method to effectively diagnose the health status of these poor-performing structures is unknown. This study focuses on health diagnosis for the typical stagger-joint-assembled shield tunnel linings in soft-soil areas of China. First, based on theoretical analyses, it is assumed that diametral deformation can be a significant indicator for the structural performance of a lining; subsequently, this is verified by abundant field data. In particular, a strong positive correlation between the diametral deformation and development of defects is observed. Subsequently, a full-scale test is performed to reveal further quantitative correlations. Besides the service limit values determined in the range of 0.24%–0.79% by specifications and prior studies, the test reveals detailed structural performance deterioration when the deformation is getting larger, where 1.5% is considered a threshold for the failure the entire structure. Additionally, the values of 0.5%, 0.8%, and 1.1% are observed to be key points indicating the gradual degradation of waterproofing, cracks, and overall mechanical performance of the lining. Based on these key points, a five-level health-degree model is constructed to determine the health status of a ring that can be regarded as a supplement of the previous limit values, which is more detailed and practical for the common large-deformed in-service linings in soft-soil areas. These findings can also serve as benchmarks for related studies on linings with different structural parameters in the future. [ABSTRACT FROM AUTHOR]