Stress response function of a two-dimensional ordered packing of frictional beads

We study the stress profile of an ordered two-dimensional packing of beads in response to the application of a vertical overload localized at its top surface. Disorder is introduced through the Coulombic friction between the grains which gives some indeterminacy and allows the choice of one constrained random number per grain in the calculation of the contact forces. The so-called `multi-agent' technique we use, lets us deal with systems as large as $1000\times1000$ grains. We show that the average response profile has a double peaked structure. At large depth $z$, the position of these peaks grows with $cz$, while their widths scales like $\sqrt{Dz}$. $c$ and $D$ are analogous to `propagation' and `diffusion' coefficients. Their values depend on that of the friction coefficient $\mu$. At small $\mu$, we get $c_0-c \propto \mu$ and $D \propto \mu^\beta$, with $\beta \sim 2.5$, which means that the peaks get closer and wider as the disorder gets larger. This behavior is qualitatively what was predicted in a model where a stochastic relation between the stress components is assumed.Comment: 7 pages, 7 figures, accepted version to Europhys. Let

Order out of Randomness : Self-Organization Processes in Astrophysics

Self-organization is a property of dissipative nonlinear processes that are governed by an internal driver and a positive feedback mechanism, which creates regular geometric and/or temporal patterns and decreases the entropy, in contrast to random processes. Here we investigate for the first time a comprehensive number of 16 self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous {\sl order out of chaos}, during the evolution from an initially disordered system to an ordered stationary system, via quasi-periodic limit-cycle dynamics, harmonic mechanical resonances, or gyromagnetic resonances. The internal driver can be gravity, rotation, thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational instability, the Rayleigh-B\'enard convection instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or loss-cone instability. Physical models of astrophysical self-organization processes involve hydrodynamic, MHD, and N-body formulations of Lotka-Volterra equation systems.Comment: 61 pages, 38 Figure

General Report - Session 3

This General Report summarizes the 84 papers accepted for the Session 3 focused on: - 3a. Case Histories on Failure and Remediation of Slopes, Dams, Embankments and Landfills (53 papers), - 3b. Case Histories on Failure and Remediation of Retaining Structures, Slurry Walls, and Deep Excavations, Dewatering, Stability (27 papers), - 3c. Improving the Stability and Maintenance of Monuments (4 papers). The papers originate from 26 countries (11 European countries, 3 American countries, 11 Asian countries and 1 African country). The papers cover a number of relevant topics divided into three different sub - sessions. As for the two papers included in Session 3c, only one deals with maintenance and retrofit of historical monuments. Indeed paper 3.03c is more pertinent to session 3b. On the other hand some papers included in Session 3a could also be considered in Session 3b and vice versa

Proceedings of the 8th International Conference on Civil Engineering

This open access book is a collection of accepted papers from the 8th International Conference on Civil Engineering (ICCE2021). Researchers and engineers have discussed and presented around three major topics, i.e., construction and structural mechanics, building materials, and transportation and traffic. The content provide new ideas and practical experiences for both scientists and professionals

Proceedings of the 8th International Conference on Civil Engineering

This open access book is a collection of accepted papers from the 8th International Conference on Civil Engineering (ICCE2021). Researchers and engineers have discussed and presented around three major topics, i.e., construction and structural mechanics, building materials, and transportation and traffic. The content provide new ideas and practical experiences for both scientists and professionals

Monotonic and Cyclic Performance of Spun-Cast Ductile Iron Helical Tapered Piles

The performance of a novel piling system is investigated, which involves a spun-cast ductile iron (SCDI) tapered shaft fitted with a lower helical plate. It combines the efficiency of the tapered section, the competitive cost, effectiveness and durability of spun cast ductile iron with a rough surface and the construction advantages of helical piles. The system is installed using a fast, low vibration and reduced noise process. Seven instrumented piles including five SCDI tapered and two steel straight pipes were installed in sand using mechanical torque. The piles were subjected to cyclic and monotonic compression, uplift and lateral load tests. Different loading sequences were adopted to assess the effect of prior cyclic/monotonic loading on the piles’ performance. The installation torque was monitored and the resulting capacity-to-torque ratio was compared to the literature reported values. The compaction of the previously disturbed sand from the helix penetration due to the pile taper resulted in superior compressive behavior of the proposed system compared to the straight shaft piles. The tapered piles exhibited higher stiffness at lower displacements compared to the straight shafted piles and the helix increased their uplift resistance. In addition, tapered shafts enhanced the lateral stiffness and the helix provided fixation due to the passive bearing pressures on the helix surfaces, which further improved the lateral performance of the short helical piles. A three dimensional finite element model was established and calibrated using the experimental data. The model was then used to simulate the response of SCDI piles with different configurations when subjected to different loading conditions including axial and lateral as well as combined moment-horizontal loads. Under cyclic loading, the tapered helical piles exhibited better compressive performance while the straight shaft helical piles performed better in uplift loading. The proposed system stiffness remained practically unchanged through the cyclic lateral loading applied in the current study. The monotonic performance of the tapered helical piles in clay was numerically simulated. The results showed an increase in axial and lateral capacity and stiffness of the tapered piles over the straight shaft ones, with greater uplift-to-compressive capacity ratio than in sand

INVESTIGATION OF SOIL ARCHING UNDER DIFFERENT MODES OF SOIL MOVEMENT AND SURFACE LOADING

Soil arching exists in many geotechnical applications, including tunnels, buried pipes and culverts, and Geosynthetic-Reinforced Pile-Supported (GRPS) embankments. The existence of these buried structures or structural elements within soil masses causes redistribution of stresses, which is referred to as soil arching. The relative stiffness and differential settlement between these buried structures and their surrounding soils affect the magnitude and distribution of vertical stresses. Soil arching has been mostly investigated using trapdoor tests under soil self-weight and/or uniform surcharge. In real applications, localized surface loading, such as traffic loading, may be applied onto soil and affect or degrade soil arching. Also, additional stresses caused by traffic loading on a buried structure may cause excessive deformations and even failure of the buried structure. Geosynthetics have been used in GRPS embankments or over buried pipes and may have effects on soil arching mobilization and degradation under localized surface loading. Expanded Polystyrene (EPS) geofoam, a lightweight material, has been increasingly used above buried structures as a compressible inclusion to reduce vertical stresses acting on the buried structures. The effects of surface traffic loading and geosynthetics on soil arching have not yet been well investigated. Therefore, the main objective of this study was to investigate soil arching under different modes of soil movement and surface loading. To fulfill the above research objective, a comprehensive experimental study and numerical analysis were conducted. The experimental study included two experimental series. The first experimental series consisted of reduced-scale models of a buried box culvert that were constructed in a test box under a plane-strain condition. This study adopted the Induced Trench Installation (ITI) method to place the concrete culvert overlaid with an EPS geofoam and investigated the effects of EPS geofoam, including geofoam stiffness and thickness, on the distribution of vertical stresses above a rectangular concrete culvert under surface footing loading. The second experimental series utilized the trapdoor test setup to investigate the effects of localized surface loading on soil arching mobilization and degradation in geosynthetic-reinforced and unreinforced embankments under a plane-strain condition. The trapdoor was supported by compressible springs of a known stiffness and could move under fill self-weight and surface loading to simulate soil subsidence and/or consolidation of foundation (soft) soil between rigid supports. In both experimental series, the backfill material was a dry, poorly-graded Kansas River sand. The footing load was applied parallelly to the culvert or the trapdoor axes. Earth pressure cells were used to monitor the vertical stress distributions above the culvert, the trapdoor, and the surrounding soil. To comprehensively assess the effects of localized surface loading with different configurations, numerical models simulating trapdoor tests were built and validated against the results of the experimental tests. A series of parametric studies were conducted to investigate: the effects of fill height, the most critical condition of the surface loading (as for the footing width and location), and the effects of non-uniform trapdoor displacements by multi-segment trapdoors on soil arching mobilization. The experimental results of the buried box culvert show that the EPS geofoam reduced the vertical stresses on the buried structure due to the mobilization of soil arching. However, soil arching was found to be partially mobilized based on the measured soil arching ratio due to the low modulus ratio of soil to geofoam that caused limited compression of the geofoam. The lower stiffness and thin geofoam had more effect on the vertical stress reduction. Cyclic loading minimized the soil arching effect induced by the compressible geofoam. This study also examines the test results with available analytical solutions. The effects of soil arching and the induced vertical stresses above the rigid structure under static footing loading were considered separately. The analytical solutions were found to match well with the experimental results. The trapdoor test results show that the displacement of the trapdoor during the fill placement induced progressive mobilization of soil arching and geosynthetic reinforcement minimized soil arching mobilization due to the change of the soil deformation. Localized surface loading increased the degree of soil arching at low applied pressure (approximately 50 kPa); however, under higher footing loading, soil arching degraded or stress recovered due to larger trapdoor displacement. Single and double layers of geosynthetic reinforcement helped maintain soil arching under localized surface loading. Geosynthetic reinforcement increased the applied surface load required to fully degrade soil arching and eliminate the benefit of the geosynthetic. Soil arching exhibited arching degradation and even collapse under static loading; however, arching degradation was less pronounced under cyclic loading as the applied pressure increased beyond 80 kPa due to larger differential settlement within the fill. The results of the numerical simulations show that the degree of soil arching increased as the fill height (H) increased due to the additional shear forces mobilized throughout the fill material. Consequently, less pressure was applied on the trapdoor and more pressure transferred to the supports as the fill height increased from H/B of 1 to 3 (B is the trapdoor width). The model with a footing width of 0.5B was the most critical width and had the highest vertical pressure on the trapdoor for H/B of 2; however, the model with a footing width of 1B had the highest pressure on the trapdoor for both H/B of 1 and 3. The model with a footing offset of 0.0B from the centerline of the trapdoor had the highest vertical pressure on the centerline of the trapdoor. Also, as the footing offset increased to 1B, less pressure reached the trapdoor and more pressure transferred onto the support. In this study, an analytical solution was proposed based on Terzaghi’s theory but for localized footing loading along the centerline of the trapdoor. This solution well predicted the measured vertical pressures on the trapdoor under localized footing loading as compared with the trapdoor test results obtained in this study. In addition to the experimental tests, eight numerical models with different fill height to trapdoor width ratios (H/B = 1, 2, and 3) and different footing widths (0.25B, 0.5B, 1B, 1.5B, 2B, and 5B (uniform)) were selected and their numerical results were compared well with the proposed solution. The numerical results further validated the proposed solution for soil arching over a trapdoor or a yielding soil zone under localized footing loading

Cone Penetration Testing 2022

This volume contains the proceedings of the 5th International Symposium on Cone Penetration Testing (CPT’22), held in Bologna, Italy, 8-10 June 2022. More than 500 authors - academics, researchers, practitioners and manufacturers – contributed to the peer-reviewed papers included in this book, which includes three keynote lectures, four invited lectures and 169 technical papers. The contributions provide a full picture of the current knowledge and major trends in CPT research and development, with respect to innovations in instrumentation, latest advances in data interpretation, and emerging fields of CPT application. The paper topics encompass three well-established topic categories typically addressed in CPT events: - Equipment and Procedures - Data Interpretation - Applications. Emphasis is placed on the use of statistical approaches and innovative numerical strategies for CPT data interpretation, liquefaction studies, application of CPT to offshore engineering, comparative studies between CPT and other in-situ tests. Cone Penetration Testing 2022 contains a wealth of information that could be useful for researchers, practitioners and all those working in the broad and dynamic field of cone penetration testing

Visual modeling and simulation of multiscale phenomena

Many large-scale systems seen in real life, such as human crowds, fluids, and granular materials, exhibit complicated motion at many different scales, from a characteristic global behavior to important small-scale detail. Such multiscale systems are computationally expensive for traditional simulation techniques to capture over the full range of scales. In this dissertation, I present novel techniques for scalable and efficient simulation of these large, complex phenomena for visual computing applications. These techniques are based on a new approach of representing a complex system by coupling together separate models for its large-scale and fine-scale dynamics. In fluid simulation, it remains a challenge to efficiently simulate fine local detail such as foam, ripples, and turbulence without compromising the accuracy of the large-scale flow. I present two techniques for this problem that combine physically-based numerical simulation for the global flow with efficient local models for detail. For surface features, I propose the use of texture synthesis, guided by the physical characteristics of the macroscopic flow. For turbulence in the fluid motion itself, I present a technique that tracks the transfer of energy from the mean flow to the turbulent fluctuations and synthesizes these fluctuations procedurally, allowing extremely efficient visual simulation of turbulent fluids. Another large class of problems which are not easily handled by traditional approaches is the simulation of very large aggregates of discrete entities, such as dense pedestrian crowds and granular materials. I present a technique for crowd simulation that couples a discrete per-agent model of individual navigation with a novel continuum formulation for the collective motion of pedestrians. This approach allows simulation of dense crowds of a hundred thousand agents at near-real-time rates on desktop computers. I also present a technique for simulating granular materials, which generalizes this model and introduces a novel computational scheme for friction. This method efficiently reproduces a wide range of granular behavior and allows two-way interaction with simulated solid bodies. In all of these cases, the proposed techniques are typically an order of magnitude faster than comparable existing methods. Through these applications to a diverse set of challenging simulation problems, I demonstrate the benefits of the proposed approach, showing that it is a powerful and versatile technique for the simulation of a broad range of large and complex systems