Creep of granular soils is frequently accompanied by grain breakage. Stress corrosion-driven grain breakage offers a micromechanically based explanation for granular creep. This study incorporates that concept into a new model based on the discrete-element method (DEM) to simulate creep in sands. The model aims for conceptual simplicity, computational efficiency and ease of calibration. To this end a new form of normalised Charles power law is incorporated into a DEM model for rough-crushable sands based on the particle splitting technique. The model is implemented using a controlled on–off computational strategy. The model is validated by simulating creep in quartz sands in oedometric and triaxial conditions. Model predictions are shown to compare favourably with experimental results in terms of creep strain, creep strain rates and particle breakage. The model proposed would facilitate the calibration of phenomenological continuum models, but may also be useful to directly investigate structural scale phenomena, such as pile ageing.@en

Stress relaxation of quartz sands is simulated using a recently proposed physically based time-to-fracture discrete element method framework. The framework incorporates time-dependency through stress-corrosion-induced grain fracture. This feature is embedded into a pre-existing particle-splitting-based rough-contact crushable model. The model is calibrated to represent Fontainebleau sand, a quartz sand. A controlled on–off computational strategy is adopted to advance the simulation efficiently. Model predictions are shown to compare favourably with laboratory results in oedometric and triaxial conditions in terms of stress relaxation and relaxation rate. Grain size distribution evolution is also tracked and shown to compare well with available laboratory results. The influence of initial mobilized strength q/qmax on stress relaxation is recovered by the model, and explained through increased grain breakage. The simulated relaxation results are examined at the microscale and compared with those from creep experiments. The model displays the nonisochronous behaviour characteristic of sands. The relaxation tests display a state shift towards higher dilatancy conditions that may offer a possible explanation for some observations of pile set-up.@en

In situ soil characterization often involves penetration tests. The response to both static and dynamic penetration in volcanic sands is known to be controlled by particle crushing, obscuring the effect of density and confinement on the response. This severely limits the use of penetration tests for soil characterization. In this work a virtual calibration chamber (VCC) built using the discrete element method (DEM) is employed to explore the relationship between cone penetration tests CPTs (static) and standard penetration tests SPTs (dynamic) results on a volcanic sand. The simulated CPT results are shown to capture well experiments from the literature over a range of density and confining stress. The comparison between the simulated CPT and SPT results shows good agreement with empirical expressions based on particle size. It was found that energy-based equivalent dynamic tip resistance obtained from the SPT is a good match for static cone tip resistance if shaft resistance effects are discounted. The results presented confirm the potential of DEM based VCC to examine the performance of in-situ tests in complex soil conditions.@en

The time-dependent pile settlement under sustained service load has been reported in the literature and defined as pile creep. Particle breakage has been found as the main mechanism for pile creep in sand by Leung et al. [1]. Based on the time-to-fracture Fontainebleau sand DEM model proposed by Lei et al. [2], particle breakage induced pile creep is first investigated in a centrifuge virtual chamber using the particle refined method. The creep settlement is highly similar to the results reported by Leung et al. [1]. The model shows great potential for investigating the pile creep in a microscopic view and the relevant pile ageing (set-up) phenomenon.@en

Stress relaxation of quartz sand is simulated using a recently proposed physically based time-to-fracture discrete element method (DEM) framework. The relaxation of stress on sands under high confining pressure is modelled using stress-corrosion induced grain fracture. This feature is embedded into a pre-existing particle-splitting based rough crushable model for Fontainebleau sand. A controlled on-off computational strategy is adopted to advance the simulation. The computed oedometer stress relaxation curve compares favourably with previous experimental results. Triaxial stress relaxation results indicate that stress relaxation increases linearly with time. Contact forces become more homogenous during stress relaxation; as a result, the sample becomes more stable. These microscopic behaviours agree with some observations in pile ageing, suggesting that the model may be adopted directly to investigate such engineering scale phenomena due to its conceptual simplicity, computational efficiency and ease of calibration. @en

Belled and multi-belled piles are cast-in-place piles with one or several bell-shaped enlargements. In this study, centrifuge model tests were conducted to explore the bearing mechanism of belled and multi-belled piles in loess area. It was found that both the bell shape forming and pile loading procedure lead to the compaction effect of soil adjacent to the pile which was shown intuitively as the mutation of axial force and side friction resistance at certain positions of pile shaft. The compaction effect due to the bell-shape enlargement transformed to the squeeze out behavior when the bell is oversize, with negative effects on the bearing capacity of piles. The com-paction effect due to bell tip stress together with the bell tip resistance strengthens the attenuation rate of pile ax-ial force. A stable relationship in the percentages of bell tip resistance, pile tip resistance and the upper load was also found at the later load stage of multi-belled piles. A settlement calculation formula for multi-belled piles was proposed based on Mindlin solution. Finally, the accuracy of the formula was verified by model test results. The method for predicting the ultimate bearing capacity of multi-belled piles was proposed, and it was verified by an in-situ worked-out example.@en

A contact model able to capture creep of crushable sands within a discrete element method (DEM) framework is presented. Time dependency is established through stress-corrosion induced grain fracture. This is grafted onto a pre-existing particle-splitting model developed to simulate rough-crushable sands. The model is calibrated for Fontainebleau sand and applied to simulate soil creep at high-confining pressures. Creep simulation is advanced using the off-DEM ageing technique. The crackvelocity evolution in particle scale and laboratory oedometer creep curve were successfully captured. Moreover, the onset of creep failure during triaxial creep curve under high deviatoric stress can also be simulated using this model. The results obtained indicate significant potential of this model for micromechanically based investigation of time-dependent soil behaviour.@en

A recently proposed DEM model for materials with rough crushable grains (Zhang et al. 2021; Ciantia et al. 2015; Otsubo et al. 2017) is here employed to examine the effect of contact roughness on the critical state line, a property of granular materials which is a) fundamental for the evaluation of liquefaction risk and liquefied responses and b) easily accessible through DEM simulation (Ciantia et al. 2019).@en

This paper studies the bearing characteristics of different types of cast-in-place piles, with or without grouting, based on a bridge construction in Wuqi-Dingbian Expressway. Manual digging piles (MDPs), rotary drilling piles (RDPs), and impact drilling piles (IDPs) are investigated, and an in-situ static load test is carried out on each type of hole-forming method. The post-grouting results show that the grouting quantity of RDP is the largest, which is 3.15 t, and the IDP is the smallest, which is 1.5 t. According to the static load test, the ultimate bearing capacity of IDP is the largest and increases the most after grouting, while MDP has the smallest increase in ultimate bearing capacity. The IDP also displays the most significant increase of pile side resistance and largest proportion of pile end resistance to the total load, showing obvious characteristics of the end bearing friction pile. The calculation method of ultimate bearing capacity of the post-grouting pile recommended by Chinese code is also verified in this work, illustrating that it is necessary to study the upper return height of slurry in post-grouting. The obtained research results provide an increased understanding of the post-grouting mechanism and reference for the rational calculation of the bearing capacity of post-grouting pile and hole-forming method selection.@en