A Contribution to the Design of a Piled Embankment

The use of timber or concrete piles offers one solution to the problem of stability and settlement posed by construction of road or highway embankments on soft ground. The idea is to transfer most of the applied load on to a grid of piles, and for reasons of economy, the piles should be spaced as widely as possible and capped individually rather than by a continuous slab. However the mechanism of load transfer from ground to the top of the pile cap appears not to be fully understood. Design methods are empirical, based on the results of low stress level model tests on sand, and on field experiences. Using centrifugal and laboratory model tests the influences of parameters such as fill height, pile area ratios and fill properties on the load sharing between the pile and ground are examined and described in the paper

Performance Assessment of Screw Piles Embedded in Soft Clay

Screw piles are widely used in a variety engineering applications supplying stability against compression, overturning moment, uplift tension, and horizontal loads. Screw pile is a famous solution for support light structures, roads and rail signs which have relatively low-capacity foundation. In this study, the behavior of circular (10) mm solid screw pile models embedded in a bed of soft clay soil covering a layer of sandy soil has been studied. The 200 mm thick sand layer was compacted in a steel container with a diameter of 300 mm into four sublayers. The sandy soil layer was compacted at a relative density of 70%. The 300 mm thick soft clay soil bed with Cu (30) kPa was compacted in six sub-layers on the sandy bottom layer. Model tests are carried out with screw piles with a length of 300 mm, 350 mm and 400 mm and a helix diameter of 30 mm. Also, single and double helix and different S/Dh ratio were used for these piles and a comparative study between screw piles and ordinary piles (without helices) is accomplished. This study revealed that introducing screw pile of double helix increases its bearing capacity in soft clay soil by up to a (4-8) % as compared to a single helix screw pile. The results showed that the behavior of screw pile essentially depends on the geometric properties of the pile. According to the achievements, compressive load capacity of screw piles depends on embedded length, spacing ratio (S/Dh) and number of helical plates

Angle of Repose and Angle of Marginal Stability: Molecular Dyanmics of Granular Particles

We present an implementation of realistic static friction in molecular dynamics (MD) simulations of granular particles. In our model, to break contacts between two particles, one has to apply a finite amount of force, determined by the Coulomb criterion. Using a two dimensional model, we show that piles generated by avalanches have a {\it finite} angle of repose $\theta_R$ (finite slopes). Furthermore, these piles are stable under tilting by an angle smaller than a non-zero tilting angle $\theta_T$, showing that $\theta_R$ is different from the angle of marginal stability $\theta_{MS}$, which is the maximum angle of stable piles. These measured angles are compared to a theoretical approximation. We also measure $\theta_{MS}$ by continuously adding particles on the top of a stable pile.Comment: 14 pages, Plain Te

Stability of Monomer-Dimer Piles

We measure how strong, localized contact adhesion between grains affects the maximum static critical angle, theta_c, of a dry sand pile. By mixing dimer grains, each consisting of two spheres that have been rigidly bonded together, with simple spherical monomer grains, we create sandpiles that contain strong localized adhesion between a given particle and at most one of its neighbors. We find that tan(theta_c) increases from 0.45 to 1.1 and the grain packing fraction, Phi, decreases from 0.58 to 0.52 as we increase the relative number fraction of dimer particles in the pile, nu_d, from 0 to 1. We attribute the increase in tan(theta_c(nu_d)) to the enhanced stability of dimers on the surface, which reduces the density of monomers that need to be accomodated in the most stable surface traps. A full characterization and geometrical stability analysis of surface traps provides a good quantitative agreement between experiment and theory over a wide range of nu_d, without any fitting parameters.Comment: 11 pages, 12 figures consisting of 21 eps files, submitted to PR

Performance of shallow anchor in ice-rich silt

Thesis (M.S.) University of Alaska Fairbanks, 2014Shallow anchor systems have been widely used for decades due to their time and cost efficiency. Yet when it comes to cold regions like Alaska, new challenges caused by the harsh environment need to be resolved before they are used extensively in cold regions. One challenge associated with anchor installation could be the potential thawing of warm permafrost due to the grout mortar hydration, which might undermine the capacity of the anchor. Another challenge is that due to low temperature the grout may cure slower or not cure at all, which will also result in a significant decrease in the ultimate strength of the anchor. Field tests were conducted to evaluate the performance of shallow anchors including duckbill anchors and grouted anchors with three types of different grouting materials, including Microsil Anchor Grout, Bentonite Clay and a newly-developed Antifreeze Grout Mortar. Constant-load creep test and pullout test were conducted to evaluate the performance of the anchors. Test results indicated that the anchors grouted with Antifreeze Grout Mortar caused the least permafrost disturbance and degradation, gained the largest tensile strength, exhibited the least creep displacement, and showed relatively large pullout capacity, and thus achieved the best performance among all types of shallow anchors