隧道围岩位移的弹塑粘性解析解

建立了一种简单的隧道围岩位移的弹塑粘性解析解，它既能反映围岩的应变软化和塑性剪胀特性，又能体现围岩的流变规律。通过对Ｋｉｅｌｄｅｒ试验隧道围岩位移的理论计算结果与实测值的比较。

岩体弹塑粘损伤力学模型及其工程应用

由于岩体受开挖卸荷作用，导致岩体损伤以及质量的进一步裂化，因此，有必要考虑岩体的损伤蠕变。将岩体损伤作为一种元件来考虑，将其和弹性元件、塑性元件和粘性元件串并联建立一种岩体弹塑粘性损伤力学模型。根据建立的力学模型，推导模型的本构方程，分析其蠕变特性，并得到该模型的等效蠕变模量的计算式。将其应用于工程实际中；并将所得结果与实测数据进行比较，其变形趋势相近。

Viscoplastic friction and microstructural evolution behavior of laser-clad Co-Cr-Ni-Mo coating

The viscoplastic friction and nanostructure formation mechanism of laser-clad Co-based coating were studied by rotary friction between laser-clad Co-Cr-Ni-Mo coating and WC-Co rod.The friction coefficient,friction interface temperature and axial displacement—time curves during rotary friction process were measured.The results showed that all the curves firstly experienced rising stage and then steady stage.The rising stage corresponded to sliding friction while the steady stage corresponded to viscoplastic friction.After viscoplastic friction processing,three typical zones of viscoplastic deformation zone,thermo-mechanically affected zone,and original laser-clad zone can be observed successively from the friction surface to the interior.The viscoplastic deformation significantly crushed the network M23C7 phase in original laser-clad zone and made it dispersively distributed with equiaxial shape and in nano-scale.The viscoplastic zone,in width of 37-131 μm,is mainly characterized by refined M23C7 and α-Co phase with grain size bellow 50 nm,and even a small quantity of amorphous.Thus,the hardness of viscoplastic zone about HV997 was improved compared with the hardness of original laser-clad zone about HV600.

High temperature oxidation behavior of magnetically sputtered Ni-0.5Y micro-crystal coating

The isothermal and cyclic oxidation behaviors of bulk pure nickel and its magnetically sputtered Ni 0 5Y micro crystal coating were studied at 1?000?℃ in air. Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine structures of the coating and the NiO oxide films. Laser Raman spectrum was also used to measure the stress level in NiO films formed on bulk nickel and the coating. It was found that Ni 0 5Y micro crystal coating had lower oxidation rate, and the grain size of NiO formed on Ni 0 5Y coating was also relatively smaller than that formed on bulk nickel. Meanwhile, the compressive stress level of oxide film formed on Ni 0 5Y coating was lower than that formed on bulk nickel, and the oxide film’s high temperature plasticity was improved in the coating case. The improvements of anti oxidation properties of the sputtered Ni 0 5Y coating were due to the micro crystal structure and the rare earth element Y.

±1100kV直流输电线路基础选型设计

针对特高压输电线路工程"点多线长、地质复杂多变"的特点,介绍了我国输电线路杆塔基础工程的选型原则,并结合某±1 100 k V特高压直流工程的实际情况,介绍了硬塑粘性土与岩石地基两种地质条件的铁塔基础选型设计方法,为今后各种地质条件的基础设计积累了经验。

RESEARCH ON COMPLICATED DAM FOUNDATION DURING EXCAVATION WITH THREE DIMENSION VISCO ELASTIC PLASTIC CONDENSED FEM

On the basis of the two geological factors rock structure and ground stress environment,a visco elastic plastic model is established to analyze the rock stability of dam foundation and dam abutment during excavation by a kind of FE condensed method.Rock mechanics is applied in analysing the dynamic process of displacements,stresses,yielding destruction of construction base level,soft interface of dam foundation.Results of the FE analysis indicate that theories and methods in this paper are reasonable and reliable.

用土层换算法编制钻孔桩的钻孔定额

钻孔灌注桩定额中工作内容包括钢护筒制造、下沉、拆除,钻孔、清孔,灌注砼桩身,钢筋笼制造、安装,此外还包括一系列辅助工作项目。现在,就反循环转盘钻孔机钻孔定额的编制,作一简要介绍。 钻孔的施工工艺系采用反循环、全断面一次钻进,用膨润土造浆护壁,并按表9配备主要施工机械。钻孔穿过的地层按三级划分,即:①Ⅰ～Ⅱ级为可塑粘性土、中细砂;

Influence of features of natural soft clay on behaviour of embankment

The influence of different features of natural soft clays,namely anisotropy,destructuration and viscosity,on modelling the time-dependent behaviour of Murro embankment was investigated.The newly developed elasto-viscoplastic models were enhanced for determining viscosity parameters in a straightforward way and adopted for the finite element analysis.The same set of common parameters determined from conventional triaxial and oedometer tests was employed for all models,with additional parameters required for representing different soil features.The finite element predictions by using models coupled with BIOT's consolidation theory were compared with each other and with field data for settlement,horizontal displacement and excess pore pressures.In addition,the stress paths under the embankment loading were also compared with each other to improve the understanding of the effect of different soil features.All simulations demonstrate that all three features significantly influence the predictions.As a consequence,accounting for soil features needs to be carefully considered when they are applied to a construction site.

Consolidation Properties of Highly Plastic Clay During Osmotic Pressure Consolidation Test

For the very soft clay with high water content, its void ratio, compressibility coefficient and permeability varied with stress during consolidation. It is necessary to use large strain consolidation based on the permeability-void ratio relationship and effective stress-void ratio relationship to analyze these properties. To overcome the disadvantages of conventional oedometer test, and determine the effective stress-void relations of this kind of soil, osmotic pressure consolidation test for highly plastic clay study and the expression of permeability-void ratio are performed. Therefore, the decided properties will be reasonably used for solving the large strain consolidation equation.

Hydro-mechanical coupling mechanism on joint of clay core-wall and concrete cut-off wall

The joint of clay core-wall and concrete cut-off wall is one of the weakest parts in high earth and rockftll dams.A kind of highly plastic clay is always fixed on the joint to fit the large shear deformation between clay core-wall and concrete cut-offwall,so the hydro-mechanical coupling mechanisms on the joint under high stress,high hydraulic gradient,and large shear deformation are of great importance for the evaluation of dam safety.The hydro-mechanical coupling characteristics of the joint of the highly plastic clay and the concrete cut-off wall in a high earth and rockfill dam in China were studied by using a newly designed soil-structure contact erosion apparatus.The experimental results indicate that：1） Shear failure on the joint is due to the hydro-mechanical coupling effect of stress and seepage failure.The seepage failure will induce the final shear failure when the ratio of deviatoric stress to confining pressure is within 1.0-1.2; 2） A negative exponential permeability empirical model for the joint denoted by a newly defined principal stress function,which considers the coupling effect of confining pressure and axial pressure on the permeability,is established based on hydro-mechanical coupling experiments.3） The variation of the settlement before and after seepage failure is very different.The settlement before seepage failure changes very slowly,while it increases significantly after the seepage failure.4） The stress-strain relationship is of a strain softening type.5） Flow along the joint still follows Darcian flow rule.The results will provide an important theoretical basis for the further evaluation on the safety of the high earth and rockfill dam.

Micro-seismic wave's propagation law and its numerical simulation

Deduced the propagation rule of longitudinal and transverse wave. On the basis of this, propagation rules in attenuated visco-elastic media and varied Lame coefficient were put forward as well. The subsequent numerical analysis found that in a small scope longitudinal and transverse wave could be considered as homogeneously propagating when faultages and joints were not taken into account. The existence of lane hindered the wave＇s propagation, and it made the velocity gradient change in a local vicinity area. Therefore velocity varied in different direction.

pH Value Effects in Shear Rheology of Concentrated Alumina Suspensions

The influence of pH on the rheological properties of concentrated alumina suspensions was investigated. At various pH values, the alumina exhibited pseudoplastic, near Bingham flow behaviors. The fully-deflocculated suspensions exhibited Newtonian flow behaviors, while the fully-flocculated suspensions demonstrated very high viscosity and shear yield stress.

Model Test and Numerical Analysis on Long-Term Mechanical Properties of Stepped Reinforced Retaining Wall

Model tests and numerical analyses of stepped reinforced retaining wall were performed to investigate the effects of rheology of backfill and creep of geogrids on the long-term performance of the structure.The geogrid tensions,soil pressures,wall deformations and foundation pressure were measured during model construction and loading.A visco-elasto-plastic model and an empirical nonlinear visco-elastic model were utilized to simulate the stresses and deformations of geogrid-reinforced earth-retaining wall under long-term loads.By comparing test data with numerical results,it is shown that the foundation pressure distribution is nonlinear,and the lateral constraint of geogrids for backfill can cause a redistribution of foundation pressure.The curve of soil pressure is outside convex at each step initially,and it is close to the distribution for the case of vertical wall subsequently.The variation trend of geogrid tensions at different heights is obtained.Moreover,the failure mechanism and development mode of potential slip surface in retaining wall are proposed.

A triaxial creep model for coal containing gas and its stability analysis

Triaxial creep tests on CCG specimens were systematically performed using aself-made creep seepage experimental apparatus for determining the creep law of CCG.An improved triaxial creep model of CCG was established on the basis of a Nishiharamodel and another visco-elasto-plastic model,parameters of which were fitted on test data.Furthermore,the creep model is validated according to the result of triaxial creep experiments,and the outcome shows that the proposed triaxial creep model can properly characterizethe properties of various creep deformation phases of CCG,especially the acceleratingcreep phase.At the same time,the instability conditions of CCG were presentedbased on the discussion of the improved model's stability in terms of stability theories ofdifferential equation solution.

Uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays

This work focuses on the uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays under one-dimensional condition. An elasto-viscoplastic model is briefly introduced based on the rate-dependency of preconsolidation pressure. By comparing the rate-dependency formulation with the creep based formulation, the relationship between rate-dependency and creep behaviors is firstly described. The rate-dependency based formulation is then extended to derive an analytical solution for the stress relaxation behavior with defining a stress relaxation coefficient. Based on this, the relationship between the rate-dependency coefficient and the stress relaxation coefficient is derived. Therefore, the uniqueness between behaviors of rate-dependency, creep and stress relaxation with their key parameters is obtained. The uniqueness is finally validated by comparing the simulated rate-dependency of preconsolidation pressure, the estimated values of secondary compression coefficient and simulations of stress relaxation tests with test results on both reconstituted Illite and Berthierville clay.

Visco-elastoplastic damage constitutive model for compressed asphalt mastic

In order to describe the three-stage creep behavior of compressed asphalt mastic, a visco-elastoplastic damage constitutive model is proposed in this work. The model parameters are treated as quadratic polynomial functions with respect to stress and temperature. A series of uniaxial compressive creep experiments are performed at various stress and temperature conditions in order to determine these parameter functions, and then the proposed model is validated by comparison between the predictions and experiments at the other loading conditions. It is shown that very small permanent deformation at low stress and temperature increases rapidly with elevated stress or temperature and the damage may initiate in the stationary stage but mainly develops in the accelerated stage. Compared with the visco-elastoplastic models without damage, the predictions from the proposed model is in better agreement with the experiments, and can better capture the rate-dependency in creep responses of asphalt mastic especially below its softening point of 47 ℃

Modeling and Numerical Simulation of Yield Viscoplastic Fluid Flow in Concentric and Eccentric Annuli

Numerical solution of yield viscoplastic fluid flow is hindered by the singularity inherent to the Herschel-Bulkley model. A finite difference method over the boundary-fitted orthogonal coordinate system is util- ized to investigate numerically the fully developed steady flow of non-Newtonian yield viscoplastic fluid through concentric and eccentric annuli. The fluid rheology is described with the Herschel-Bulkley model. The numerical simulation based on a continuous viscoplastic approach to the Herschel-Bulkley model is found in poor accordance with the experimental data on volumetric flow rate of a bentonite suspension. A strict mathematical model for Herschel-Bulkley fluid flow is established and the corresponding numerical procedures are proposed. However, only the case of flow of a Herschel-Bulkley fluid in a concentric annulus is resolved based on the presumed flow stnicture by using the common optimization technique. Possible flow structures in an eccentric afinulus are presumed, and further challenges in numerical simulation of the Herschel-Bulkley fluid flow are suggested.

A Phenomenological Constitutive Law for the Description of Nonlinear Post-yield Behaviour of Glassy Polymers under Different Strain Rate

In this study, a modelization of the viscoplastic behaviour of amorphous polymers is proposed, from an approach originally developed for metals behaviour at high temperature, in which state variable constitutive equations have been modified. The model includes the effect of strain rate sensitivity, strain softening and strain hardening. A procedure for the identification of model parameters is developed through the use of experimental data from uniaxial tests extracted from the literature, across a variety of strain rates and below the glass transition temperature ( Tg). The numerical algorithm shows that the predictions of this model well describe the intrinsic softening upon yield threshold and the subsequent progressive orientational hardening typical for amorphous glassy polymers.

Effects of Limestone Powder on Rheological Properties of Cement - Fly Ash Mortar

This article studies the effects of limestone powder on rheological properties of cement - fly ash mortar with RHEOLAB QC type rotation viscometer. The Bingham fluid model is introduced to fit the yielding stress and plastic viscosity of the mortar. The POWER LAW fluid model is introduced to fit the rheological index of the mortar. The results show that, adding limestone powder and fly ash to the cement mortar significantly decreases the yield stress of the mortar, changes the plastic viscosity of the mortar, increases the rheological index, decreases the degree of shear thinning of the mortar, and thereby improves the mortar＇ s workability. In the case of cement - fly ash mortar, with the increase of limestone powder content, both the yield stress and plastic viscosity of the mortar increase. When the limestone powder content is not higher than 14%, the increase of yield stress is not significant. When the limestone powder content is lower than 8%, the increase of plastic viscosity is not significant. When the content of limestone powder is higher than 22%, the rheological index of the mortar decreases and the degree of shear thinning increases. The effects of limestone powder＇ s packing density, shape and size, specific surface area, and fluid volume, are found to be the four major factors responsible for the changes ofrheological properties of the mortar.

An elastic-viscous-plastic model for overconsolidated clays

The influences of time on clays are discussed first,and the concept of the instant normal compression line is proposed by analyzing the existing theories and experimental results.Based on the creep law,the relationship between the aging time and the overconsolidation parameter is built.With the reloading equation of the UH model(unified hardening model for overconsolidated clays) used to calculate the instant compression deformation,a one-dimensional stress-strain-time relationship is proposed.Furthermore,the evolution of this relationship is analyzed,and the characteristic rate that is a function of the overconsolidation parameter is defined.Then a three-dimensional elastic-viscous-plastic constitutive model is suggested by incorporating equivalent time into the current yield function of the UH model.The new model can describe not only creep,rate effect and other viscous phenomena,but also shear dilatancy,strain softening and other behaviors of overconsolidated clays.Besides,compared with the modified Cam-clay model it requires only one additional parameter(the coefficient of secondary compression) to consider the creep law.Finally,because the proposed model can be changed into the UH model under instantaneous loading,the elastic-plastic and elastic-viscous-plastic frameworks are unified.