Meysam Imani

Despite the advantages of combined vertical, moment, and horizontal (VMH) failure envelopes, serviceability was not adequately considered in previous studies, leading to the introduction of serviceability-based "design envelopes" in current research, as a complement to conventional failure envelopes. This study employs three-dimensional finite element analysis to develop design and failure envelopes for square raft and cubic embedded block foundations under VMH loading. The numerical investigation, validated against well-documented benchmarks, uses the Hardening Soil model with small-strain stiffness (HSS). The envelopes were developed using probe tests associated with the dominant system parameters: breadth (2.5 to 25 m), embedment depth to breadth ratio (1, 2, and 3), and c-ϕ subsoil relative density (loose, medium, and dense). The results demonstrate that serviceability limits often govern foundation design, since the design envelopes are significantly smaller than the associated failure envelopes. Embedment depth is identified as a significant parameter that influences the transition from base-bearing to three-dimensional resistance mechanisms and enhances moment and horizontal capacities. The study examines the relationship among foundation geometry, embedment ratio, and subsoil strength in shaping failure and design envelopes. Multivariate regression analysis was used to derive mathematical equations for ellipsoidal failure and design envelopes. Overall, the findings challenge the traditional safety-factor paradigm and highlight the need for displacement-based design methodologies in modern foundation systems.

The failure of concrete and rock is primarily governed by the initiation and propagation of cracks under different loading conditions. Despite extensive studies, the failure mechanisms remain partially understood. This paper presents an integrated numerical and experimental investigation into concrete and rock failure mechanisms using the Discrete Element Method (DEM), Digital Image Correlation (DIC), and ultrasonic compressional wave velocity (UCWV) test. Uniaxial compressive strength (UCS) and Brazilian disk splitting (BDS) tests were first conducted on concrete and rock samples. The obtained stress–strain curves and the observed failure patterns were used to validate the DEM-based numerical models. Moreover, compressional wave velocity (V_p) was measured by some UCWV tests before and after performing each UCS test to support the DEM results. Additionally, BDS tests were performed on both concrete and rock samples while high-speed imaging captured the fracture process. The results of numerical modeling indicate that the DEM model effectively reproduces the mechanical behavior and failure pattern of the samples. Microcrack initiation typically occurred near the loading boundaries and propagated toward the specimen center, eventually forming a major macrocrack along the loading axis. The BDS results also showed that crack propagation was predominantly aligned with the loading direction. Additionally, high-speed imaging captured the fracture process, revealing tensile and shear mode.

Determining a reliable value of the support pressure is necessary to prevent tunnel instability during excavation in weak rock masses. There are a few appropriate analytical solutions, most focused on tunnels excavated in soils. The present study proposes a method for determining the support pressure required to stabilize tunnels excavated in weak rock masses. The upper bound limit analysis method was applied for a rock mass obeying the Hoek–Brown failure criterion. Based on the findings, improving the strength of the rock masses results in decreasing the required support pressure. Increasing the Hoek–Brown parameters m_i from 5 to 20, GSI from 10 to 25, and σ_ci from 1 to 10 MPa, results in a maximum reduction of the tunnel support pressure by 62%, 56%, and 70%, respectively. In addition, increasing the ratio of horizontal to vertical insitu stresses from 0.4 to 1.2 reduces the maximum support pressure by about 59%. Moreover, increasing the disturbance factor from zero to 1 results in an increase of about 135% in the support pressure, while by increasing the tunnel width and the unit weight of the rock mass surrounding the tunnel, the maximum increase of 181% and 93% were observed in the support pressure.

Conventionally, foundations have been classified as shallow or deep in routine civil engineering practice. However, due to recent developments, two other approaches, semi‐deep and ground modification foundations, are now available, complicating foundation categorization. Accordingly, a new concept for foundation categorization is introduced in this paper based on insights into the theory of structure analysis. Based on the form aspect, foundation systems can be categorized as one‐dimensional (linear), two‐dimensional (planar), and three‐dimensional (volumetric). Based on the load transfer aspect, foundations can also be categorized as vector‐acting (piles), section or surface‐acting (rafts and shells), and block‐acting (piled rafts). As a step toward implementing this new categorization scheme, a database of 22 cases has been compiled, symbolizing novel introduced foundation systems. This compilation involves structures such as offshore jackets, high‐rise buildings, towers and storages, and diverse geomaterials. Among them, a few have been selected for detailed evaluation, emphasizing influential factors in foundation selection, comprising superstructure, subsoil condition, foundation system, circumferential conditions, and supplementary considerations, that is, constructional and sustainability‐based issues. Lessons learned from experience and these knowledge‐based cases have described for foundation selection and implementation. Geotechnical and practical aspects with critical components have been realized as major performance assessment and comparison factors. Foundation systems have been compared and ranked using the improved analytic hierarchy process approach. Finally, four categories of buildings, from low‐rise to towers and four prevailing levels of soil strength, from soft to very hard, have been considered to propose a perspective for building substructure implementation, adapted via relevant cases. Overall, the introduced categorization is recognized as an efficient algorithm for the experimentation of appropriate foundations for specific structures and subsoil conditions.