Numerical stress-deformation analysis of cut-off wall in clay-core rockfill dam on thick overburden

The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden layer, the frictional force induced by the differential settlement between the cut-off wall and surrounding soils, and the water pressure. Thus, reduction of the stress of the cut-off wall has become one of the main problems for consideration in engineering design. In this paper, numerical analysis of a core rockfill dam built on a thick overburden layer was conducted and some factors influencing the stress-strain behaviors of the cut-off wall were investigated. The factors include the improvement of the overburden layer, the modeling approach for interfacial contact between the cut-off wall and surrounding soils, the modulus of the cut-off wall concrete, and the connected pattern between the cut-off wall and the clay core. The result shows that improving the overburden layer,selecting plastic concrete with a low modulus and high strength, and optimizing the connection between the cut-off wall and the clay core of the dam are effective measures of reducing the deformations and compressive stresses of the cut-off wall. In addition, both the Goodman element and the mud-layer element are suitable for simulating the interfacial contact between the cut-off wall and surrounding soils.

Application of in situ direct shear device to shear strength measurement of rockfill materials

A simplified in situ direct shear test （DST） was developed for measuring the shear strength of soils in fields. In this test, a latticed sheafing frame replaces the upper half of the shear box used in the conventional direct shear box test. The latticed shearing frame is directly embedded in the ground to be tested after a construction process and is pulled with a flexible chain while a constant dead load is applied to the sample in the sheafing frame. This simplified in situ DST has been validated by comparing its results with those of triaxial tests on samples with parallel gradations under normal stresses less than 100 kPa. In this study, the DST was further validated by carrying out tests on samples with the same gradations, rather than on samples with parallel gradations, under normal stresses up to 880 kPa. In addition, the DST was performed inside fills in two applications.

Packing,compressibility,and crushability of rockfill materials with polydisperse particle size distributions and implications for dam engineering

In rockfill dam engineering,particle breakage of rockfill materials is one of the major factors resulting in dam settlement.In this study,one-dimensional compression tests on a series of coarse granular materials with artificially-graded particle size distributions(PSDs)were carried out.The tests focused on understanding the role of initial PSDs in the dense packing density,compressibility and crushability of coarse granular materials.The effects of fractal dimension(D)and size polydispersity(θ)of PSDs were quantitatively analyzed.Two different loading stages were identified from the logarithms of the stress-strain relationships,with the turning point marked as the yield stress.A similar effect of initial PSDs was observed on the packing density and low-pressure modulus of coarse granular materials.The packing density and low-pressure modulus increased monotonically withθ,and their peak values were attained at a D value of approximately 2.2.However,there was no unique correspondence between the dense packing density and low-pressure modulus.The particle breakage was influenced differently by the initial PSDs,and it decreased with the values of D andθ.The emergence of the unique ultimate state was also identified from both the compression curves and PSDs of the samples after the tests.The potential implications of the test results in the design of both low and high rockfill dams were also demonstrated.

Calibration and performance of two different constitutive models for rockfill materials

In this paper, two different concepts for the constitutive modeling of the mechanical behavior of creep-sensitive rockfill materials are presented. Specifically, the performance of an extended generalized plasticity model proposed by Wang is compared with a simplified version of the hypoplastic constitutive model for weathered rockfill materials proposed by Bauer. Both models can reflect the influence of the mean stress on the incremental stiffness, the peak friction angle, and the dilatancy angle. The so-called solid hardness defined for a continuum description and originally introduced by Bauer is embedded in both models. Hydrochemical, thermal, and mechanical weathering are usually caused by environmental changes and are taken into account in a phenomenological description with an irreversible and time-dependent degradation of the solid hardness. A degradation of the solid hardness is usually accompanied by creep deformation of the stressed rockfill material. It is shown that appropriate modeling of creep deformation requires at least a unified description of the interaction between the time-dependent process of degradation of the solid hardness and the stress state. In this context, the solid hardness can be understood as a key parameter for describing the evolution of the state of weathering of the rockfill material. Particular attention is also paid to the necessary procedure for determining the constitutive constants of the two different constitutive models. Finally, the performance of the two different constitutive models is demonstrated by comparing the results obtained from numerical simulations with experimental data from the creep-sensitive rockfill material.

Preface for special section on long-term behavior of dams

When it comes to the long-term operation of hydropowerplants, the service life of mechanical and electrical equipmentand the reliability of hydraulic engineering structures areboth crucial. The loading history and interaction of theconstruction with ground settlements, earthquake activities andflooding, chemical reactions with water, overtopping, and thestate of weathering and aging of the construction material mayplay an important role in the safe operation of hydraulicstructures such as earth, rockfill, and concrete dams, as wellas novel reinforced soil structures. A critical reduction ofthe safety of dams can be caused by the evolution of internalerosion, cracks in the sealing, earthquake-induced deformations,reduction of the slope stability of earth and rockfilldams triggered by heavy rainwater infiltration, or rapid reductionof the water level in the reservoir.