Equivalent Density Method Research Articles

Experimental study on the strength and deformation characteristics of sandy pebble soil foundation based on the equivalent density method

With the rapid development of urban construction, many bridges and subways are built on sandy pebble soil foundation. As a special kind of soil, sandy pebble soil has the characteristics of large particle size, low compressibility, low cohesion, poor self-stability, large permeability coefficient, large friction coefficient, etc. The strength and deformation characteristics of the sandy pebble soil are one of the key concerns in engineering field. Due to the size limitation of the laboratory test equipment, scaling is necessary for sandy pebble soil. The equivalent density of coarse-grained material could be obtained by equivalent density method; large-scale triaxial and interface shear tests were performed to study the comprehensive mechanical characteristics. Furthermore, appropriate models were investigated to describe the stress-strain relationships of sandy pebble soil, and the corresponding model parameters were summarized. The tests results reveal that the saturated sand pebble soil show shear shrinkage characteristics under low confining pressure, conversely unsaturated samples show shear dilatancy characteristics under low confining pressure. Under high confining pressure, obvious shear shrinkage characteristics could be observed. The shear strength parameters of unsaturated samples are obviously larger than those of saturated samples. It shows a good hyperbolic relationship between shear stress and displacement on the interface of sandy pebble soil and concrete slab, and the shear strength and normal stress are in a good linear relationship. The research could provide strong support for engineering design in sandy pebble soil.

Research progresses in key technologies for construction and long-term safety protection of extra high earth-rock dams under complicated conditions

China has the largest amount of extra-high earth-rock dams over 200 m in the world. Complicated construction and severe operation conditions pose great difficulties and huge challenges in their construction and long-term safety. This paper introduces main research progresses in the areas of Key Technologies for Construction and Long-term Safety Protection of Extra High Earth-rock Dams under Complex Conditions. The particle-size effect, mesoscopic and deterioration mechanism of dam materials were studied throughly. The calculation model of rheological behavior of rockfill materials considering loading and creep coupling effect was established. The numerical simulation method for complex contacting problems in high earth-rock dams was developed using computational contact mechanics, and was used in studying the damage mechanism of concrete slabs and galleries. Testing apparatus conducting deformation-seepage coupling experiments were fabricated, and were used to investigate the permeability characteristics of core materials, the performance of anti-seepage systems in dam body and foundation. An equivalent density method was proposed to evaluate the in-situ density of overburden materials based on pressuremeter tests both in laboratory and field. New compound structure, modulus increasing technology, slab design method and water-stop materials for extra-high concrete face rockfill dams were studied, and safety evaluation and control standards were proposed for the demonstrating Dashixia project. The relevant results have provided technological supports for the two demonstrating projects, i.e. Rumei and Dashixia extra-high earth-rock dams, improving considerably the construction level and long-term safety of extra-high earth-rock dams.

Experiment Analysis and Modelling of Compaction Behaviour of Ag60Cu30Sn10 Mixed Metal Powders

A novel process method combines powder compaction and sintering was employed to fabricate thin sheets of cadmium-free silver based filler metals, the compaction densification behaviour of Ag60Cu30Sn10 mixed metal powders was investigated experimentally. Based on the equivalent density method, the density-dependent Drucker-Prager Cap (DPC) model was introduced to model the powder compaction behaviour. Various experiment procedures were completed to determine the model parameters. The friction coefficients in lubricated and unlubricated die were experimentally determined. The determined material parameters were validated by experiments and numerical simulation of powder compaction process using a user subroutine (USDFLD) in ABAQUS/Standard. The good agreement between the simulated and experimental results indicates that the determined model parameters are able to describe the compaction behaviour of the multicomponent mixed metal powders, which can be further used for process optimization simulations.

A density-dependent modified Drucker-Prager Cap model for die compaction of Ag57.6-Cu22.4-Sn10-In10 mixed metal powders

Due to the bad plastic workability, silver based brazing filler metals with high proportions of additional elements such as Zn, Sn, In, Ga, are very brittle and difficult to be made into thin sheets using conventional manufacturing processes. A novel process method that combine powder compaction and sintering, can fabricate thin sheets of the fragile silver based filler metals. In this work, the densification mechanism of Ag57.6-Cu22.4-Sn10-In10 (wt.%) mixed metal powders was investigated, and a modified density-dependent Drucker-Prager Cap (DPC) model was introduced to describe its compaction behavior based on the equivalent density method. The powder compact was considered as a continuum, and a linear elasticity law as a function of relative density was then used to express the elastic behavior of the powders. An instrumented die with force transducers has been designed to determine the material parameters of the modified DPC model. The elastic and plastic material parameters such as E, υ, β, d, pa, R and pb were then determined experimentally. The friction coefficient between the powders and the die wall with a lubricated die was determined based on the Janssen–Walker theory in the instrumented die experiments. Furthermore, the modified DPC model with the linear elasticity law was validated using finite element simulation method in ABAQUS with a user subroutine (USDFLD). A good agreement between the simulations and experimental results was obtained, indicating the feasibility and applicability of the introduced modified models to describe the die compaction behavior of the mixed metal powders.