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Aggregates are the principal materials of railway ballast, which for the most part contain huge, angular particles with a normal size of roughly 40 mm. Well-designed ballast is attractive to resist the pressures from the sleeper and after that to pass a satisfactory pressure level at the top surface of the subgrade soil. Though the functions of ballast by and large break down when subjected to Repeated traffic loading and in the end come into non-shakedown, (for the sample, ratcheting or incremental failure) reactions. In this work, a progression of expansive scale cyclic triaxial Experiments on aggregate did distinguish diverse cyclic degradation reactions. The permanent axial and volumetric strains are seen under various cyclic stress ratios. Three distinct cyclic reactions, shakedown, cyclic creep and incremental failure, are found. Shakedown happens at a moderately low cyclic stress ratio, under which the IPC (increase per cycle) of fixed axial strain and the IPC (area of hysteretic loop per cycle) of energy, dissipation will, in general, become negligible in the wake of cycling, and the fixed volumetric strains show compacting. Incremental failure happens at a generally high cyclic stress ratio, under which the IPCs of axial strain and energy dissipation increment after a set number of cycles, and the fixed volumetric strains show dilatancy. For cyclic creep, the IPCs of axial and volumetric strain and energy dissipation become about constant after an extensive number of cycles.

In this paper, the shakedown behavior of flexible pavement on saturated subsoil subjected to moving vehicle loading is studied. Based on Biot’s dynamic theory of saturated porous media, dynamic stresses of layered saturated subgrade are derived by the transfer matrix method. Then, the lower limit shakedown theory is introduced to estimate the shakedown state of the pavement system. The study focuses on the effects of vehicle’s velocity, saturated soil’s permeability, pavement and subsoil’s strength and modulus ratios on the shakedown behavior. Theoretical results show that for the pavement system on the saturated subgrade, the growth of stiffness ratio or strength ratio leads to the transition of the critical shakedown state from the upper to the lower layers. It is also found that there exists a set of optimal modulus and strength ratios so that the upper and lower layers can reach the critical shakedown state simultaneously.

The grouting induced enlarged-base pile is an uplift pile combining conventional enlarged-base pile with post-grouting technique. This type of uplift pile has great value in engineering practice for its higher uplift bearing capacity and less material used. This paper will discuss the uplift bearing capacity and failure mechanism in depth from two aspects, including the model experiment and finite element modelling (FEM). Considering the grouting induced enlarged- base pile, experimental model was developed to investigate the uplift capacity of the enlarged base. The load-displacement curves for enlarged bases of different sizes were obtained under the overburden pressure corresponding to a certain depth. Meanwhile, the experiment was numerically investigated via FEM and the results are consistent with the experimental data. It is found that the degree of increase of uplift bearing capacity becomes greater as the length ratio of the enlarged base to the pile or the diameter ratio of enlarged base to pile increase.

To satisfy the increasing power demands, lots of transmission lines are constructed in the middle-west of China. Expansive soil widely distributes in these areas, and the safety of foundation for transmission line tower needs to be evaluated. Based on consolidated drained triaxial tests, the cohesion and internal friction angle of unsaturated expansive soil were obtained. The compressive and uplift bearing capacities of the plate foundation for transmission line tower foundation were analyzed by 3D finite element modeling. The failure mode of the plate foundation under compressive load shows a local shear mode. For the uplift bearing capacity, the failure mode shows an annular apophysis mode around the plate foundation at the surface. The influence of the saturation of soil on the bearing capacity is more obvious than the uplift bearing capacity of a plate foundation.

Sand is the most widely existing granular material for the foundations of extensive constructions which bear various complex cyclic loading such as traffic loading, ocean wave loading and earthquakes. The road pavements and the offshore foundations subjected to cyclic loads tend to produce excessive permanent deformation, which affects the constructions’ normal operation and safety. Nowadays, many engineering projects change from strength controlled criterion to deformation controlled criterion, such as the high-speed railway in China. Therefore, accurately prediction of the settlement due to cyclic loading is essential. Over the years many explicit models have been established to predict the permanent deformation of sand under cyclic loading. Most of these models are more or less empirical and lack of essential analysis of permanent deformation. There are many parameters obtained by fitting the test results in these models which cannot be easily determined in practical engineering use. In this paper, the concept of shear strain amplitude during cyclic loading is put forward to predict the permanent deformation. By introducing the shear strain amplitude, a unified explicit model is established to predict the cyclic permanent deformation of sand, which only contains four empirical parameters. The result shows that the model can successfully predict the permanent deformation under cyclic loading.

Shakedown solution is widely used to analyze elastic-plastic behaviors of structures in pavement design. It is an effective way to predict the maximum admissible load (termed ‘shakedown limit’) against excessive rutting in flexible pavements. However, previous research is concerned with shakedown theorem under traffic loads without the influences of anisotropy. This paper has firstly proposed numerical analysis for anisotropic material under traffic moving load, based on Melan’s lower bound shakedown theory. An anisotropic Finite Element–Infinite Element (FE–IE) model with a user subroutine in ABAQUS is proposed to calculate the dynamic response of elastic stress against load moving speeds. Shakedown limits for an anisotropic half-space pavement system under traffic moving loads at various speeds are investigated. It is found that the shakedown limit decreases when the load moving speed increases towards the Rayleigh wave speed of the pavement for isotropic half-space system. For cross-anisotropic half-space system, Poisson’s ratio only leads to negligible effect on shakedown limit. Furthermore, the shakedown limit rises with the increasing cohesion ratio c v /c h , but it reaches maximum value when cohesion ratio is larger than a specific value. And the maximum shakedown limit rises slightly with the increase of moving speed below Rayleigh wave speed.

The discrete element method was adopted in this paper to numerically investigate the macroscopic behaviors of granular material with initial anisotropic fabric in simple shear tests. The evolutions of the stress-strain relationship, the non-coaxiality referring to the difference of principle directions between the strain rate and the stress increment, and the fabric anisotropy were analyzed during the tests. The results indicated that inherent anisotropy affects the shear strength. The directions of principal strain rate and principal stress are non-coaxial at the start of the shear loading and they become coaxial gradually as the shear strain increases. Both the principle directions of particle orientation and contact normal change towards 45°, but the later is much faster than the other.