The stiffened deep cement mixing (SDCM) pile is a composite pile composed of the deep cement mixing (DCM) pile and an inner precast core pile. The excellent bearing performance of the SDCM pile that has been successfully witnessed in engineering practice is attributed to the double-layer load transfer mechanism, which effectively transfer the load from the stiffened core to the cemented soil and further to the adjacent soil. The mechanical properties of SDCM piles with stiffened cores that using large-size prestressed high-strength concrete (PHC) piles are rarely studied. This study aims to explore the bearing performance and failure behavior of the SDCM pile with a large-size PHC pile as stiffened core. The relationship between load and settlement as well as the distribution and development of axial force and lateral resistance was studied through field full-scale tests. The effects of the volume ratio, size, and concrete stiffness of the core pile, and the strength of cemented soil on the axial bearing capacity of SDCM piles were explored through the verified three-dimensional numerical model. The load transfer and failure modes at the internal and external interfaces of SDCM piles with different pile lengths were analyzed. Results show that the length of the core pile (Lcore) is a key factor for the bearing capacity of the SDCM pile. The bearing capacity of SDCM pile increases by 57.90% and 46.67% with Lcore increasing by 45% when cemented soil strength (qu, DCM) is 150 MPa and 300 MPa, respectively. The influence of qu, DCM and concrete stiffness on the bearing capacity of the SDCM pile is gradually significant with the increase of Lcore. The ultimate bearing capacity increases by 4.3% for every 100% increase in cemented soil strength at the optimal pile length. With the increase of Lcore, the investigated pile exhibits three failure modes, including the failure of pile end soil and cemented soil, the failure of pile top soil and core pile end soil, and the failure of pile top soil. The results of this study provide reference for the application of SDCM piles with large-size PHC piles as stiffened cores in the engineering field.

Layered rock formations are frequently encountered during the excavation of underground structures. The stability of such structures is influenced not only by the stress concentration caused by the cavities in the strata but also by the anisotropy of the layered rock mass. The interaction between them can lead to critical structural failure, such as rupture, collapse, or significant deformation within the adjacent rock mass, thereby jeopardizing operational safety. However, the coupling law and mechanism between the stress concentration resulting from the cavities and the anisotropy of a layered rock mass remain unclear. In this study, a uniaxial compression test was performed on shale specimens containing a circular hole to investigate the effects of layer inclination and circular holes on the mechanical properties, elastic energy storage, and failure behaviors of these specimens. The failure mechanism of the rock surrounding the hole was analyzed on the basis of the single plane of weakness theory and the Kirsch solution. The test results indicated pronounced anisotropy in the compressive strength, elastic modulus, and elastic strain energy of the specimens, with distinct V, M and U-shaped patterns correlated with varying layer inclination angles. In addition, the combined effect of stress concentration and layer inclination resulted in different failure types, which were classified into four groups according to their failure behavior. Theoretical analysis revealed that failure around circular holes in layered rock is affected by a range of variables, such as layer inclination, layer strength, lateral pressure coefficient, azimuth, and loading stress. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The constraining effect of soilbags inhibits soil dilatancy, enhancing the strength and stiffness of the wrapped soil, and resulting in a considerable increase in bearing capacity. This study numerically investigated the macromeso geotextile failure behavior, stress state, fabric anisotropies of wrapped soil and interlocking reinforcement mechanisms of three-layer soilbags under unconfined compression using the three-dimensional discrete element method (DEM). Macroscopically, the failure modes of wrapping geosynthetic depended on the friction between soilbags. With zero friction, failure initiated at the edges of the wrapping geosynthetic; whereas with a friction coefficient of 0.5, failure began in the middle and extended to the edges, showing a progressive failure pattern. Microscopically, the reinforcement of soilbag changed the contact pattern of the particle system from peanut-like to uniformly distributed ellipse. The load transfer to the boundaries caused the occurrence of wrapped soil expansion and geotextile rupture. Additionally, geosynthetic wrapping created an interlocking effect with the surrounding soils, forming a positive feedback to reinforce the wrapped soil before geotextile failure. New understanding on failure modes, stress states, interlocking effect and fabric anisotropies provides a solid foundation for designing reliable and stable soilbag geotechnical permanent protective structures.

A series of numerical true triaxial compression tests were carried out on rubber-sand mixtures (RSMs) by means of the 3D discrete element method to study the effect of the intermediate principal stress ratio b on the failure properties of RSMs with different rubber contents (RCs), and to explore the effect mechanism from a microscopic point of view. The numerical simulation results show that as the intermediate principal stress ratio b increases and the peak deviator stress qpeak gradually increases, while the peak internal friction angle phi b first increases and then decreases. The numerical simulation results were compared with four common strength criteria, including the modified Lade-Duncan criterion, the SMP criterion, the FKZ criterion and the DP criterion. The comparative analysis showed that the existing common criteria cannot accurately predict the damage state of RSMs, suggesting the necessity for further research. At the micro level, the combined effects of the intermediate principal stress ratio b values and RC on the micro-parameters, such as the coordination number, average normal stress between particles, probability density and anisotropy, were investigated.