铁路隧道混凝土理论消耗量分析及计算

混凝土超耗是隧道工程施工面临的难题,如何有效减小隧道混凝土超耗是项目成本管控的重点,也是难点。为有效降低施工成本,合理确定隧道混凝土消耗标准,做好施工管控,立足于隧道施工特点,从混凝土超耗原因、消耗组成、消耗量化分析及二次衬砌模板台车轮廓外放影响等方面,针对混凝土施工前后工序进行混凝土消耗量化计算及评估,得出:1)初期支护喷混凝土消耗量主要与设计量、回弹量及平均线性超挖量相关,喷混凝土理论消耗量是设计量的1.6~3.8倍;2)二次衬砌模筑混凝土消耗量主要与设计量及预留变形量相关,在实际预留变形量是设计预留量1/3的情况下,二次衬砌模筑混凝土理论消耗量是设计量的1.04~1.12倍;3)一般的二次衬砌模板台车结构强度及刚度较大,满足二次衬砌混凝土浇筑施工至初凝时的自重或冲击压力,定位时不需要将台车轮廓外放大,以防变形回落。

Mechanical response and dilatancy characteristics of deep marble under different stress paths:A sight from energy dissipation

Dilatancy is a fundamental volumetric growth behavior observed during loading and serves as a key index to comprehending the intricate nonlinear behavior and constitutive equation structure of rock.This study focuses on Jinping marble obtained from the Jinping Underground Laboratory in China at a depth of 2400 m.Various uniaxial and triaxial tests at different strain rates,along with constant confining pressure tests and reduced confining pressure tests under different confining pressures were conducted to analyze the mechanical response and dilatancy characteristics of the marble under four stress paths.Subsequently,a new empirical dilatancy coefficient is proposed based on the energy dissipation method.The results show that brittle failure characteristics of marble under uniaxial compression are more obvious with the strain rate increasing,and plastic failure characteristics of marble under triaxial compression are gradually strengthened.Furthermore,compared to the constant confining pressure,the volume expansion is relatively lower under unloading condition.The energy dissipation is closely linked to the process of dilatancy,with a rapid increase of dissipated energy coinciding with the beginning of dilatancy.A new empirical dilatancy coefficient is defined according to the change trend of energy dissipation rate curve,of which change trend is consistent with the actual dilatancy response in marble under different stress paths.The existing empirical and theoretical dilatancy models are analyzed,which shows that the empirical dilatancy coefficient based on the energy background is more universal.

Load-bearing characteristics and energy evolution of fractured rock masses after granite and sandstone grouting

Experiments on grouting-reinforced rock mass specimens with different particle sizes and features were carried out in this study to examine the effects of grouting reinforcement on the load-bearing characteristics of fractured rock mass.The strength and deformation features of grouting-reinforced rock mass were analyzed under different loading manners;the energy evolution mechanism of grouting-reinforced rock mass specimens with different particle sizes and features was investigated;the energy dissipation ratio and post-peak stress decreasing rate were employed to evaluate the bearing stability of grouting-reinforced rock mass.The results show that the strength and ductility of granite-reinforced rock mass(GRM)under biaxial loading are higher than that of sandstone-reinforced rock mass(SRM)under uniaxial loading.Besides,the energy evolution characteristics of grouting-reinforced rock mass under uniaxial and biaxial loading mainly could be divided into early,middle,and late stages.In the early stage,total,elastic,and dissipation energies were quite small with flatter curves;in the middle stage,elastic energy increased rapidly,whereas dissipation energy increased slowly;in the late stage,dissipation energy increased sharply.The energy dissipation ratio was used to represent the pre-peak plastic deformation.Under uniaxial loading,this ratio increased as the particle size increased and the pre-peak plastic deformation of grouting-reinforced rock mass became larger;under biaxial loading,it dropped as the particle size increased,and the pre-peak plastic deformation of grouting-reinforced rock mass became smaller.The post-peak stress decline rate A_(v) was used to assess the post-peak bearing performance of grouting-reinforced rock mass.Under uniaxial loading,parameter A_(v) exhibited reduction as the particle size kept increasing,and the ability of post-peak of grouting-reinforced rock mass to allow deformation development was greater,and the bearing capacity was greater;under biaxial loading,A_(v) increased with the particle size,and the ability of post-peak of grouting-reinforced rock mass to allow deformation development was low and the bearing capacity was reduced.The findings are considered instrumental in improving the stability of the roadway-surrounding rock by granite and sandstone grouting.

Mechanical and energy dissipation characteristics of granite under cyclic impact loading

This study investigated the effect of repeated blasting on the stability of surrounding rock during the construction of a tunnel or city underground engineering.The split Hopkinson pressure bar(SHPB)was used to carry out cyclic impact tests on granite samples,each having a circular hole,under different axial pressures,and the cumulative specific energy was proposed to characterize the damage characteristics of the rock during the cyclic impact.The mechanical properties and the energy absorbed by the granite samples under cyclic impact loads were analyzed.The results showed that under different axial pressures,the reflected waveform from the samples was characterized by“double-peak”phenomenon,which gradually changed to“single-peak”wi th the increase in damage value.The dynamic peak stress of the sample first increased and then decreased with an increase in impact times.The damage value criterion established based on the energy dissipation could well characterize the relationship between the damage and the number of impacts,which showed a slow increase,steady increase,and high-speed increase,and the damage value depended mainly on the last impact.Under the action of different axial pressures,all the failure modes of the samples were axial splitting failures.As the strain rate increased,with an increase in the dimension of the block,the sizes of the rock fragments decreased,and the fragmentation became more severe.

Effect of specimen size on energy dissipation characteristics of red sandstone under high strain rate

In this experiment, red sandstone specimens, having slenderness ratios of 0.5, 0.7, 0.9 and 1.1 respectively, were subjected to blow tests using a Split Hopkinson Pressure Bar(SHPB) system at a pressure of 0.4 atmospheres. In this paper, we have analyzed the effect of slenderness ratio on the mechanical properties and energy dissipation characteristics of red sandstone under high strain rates. The processes of compaction, elastic deformation and stress softening deformation of specimens contract with an increase in slenderness ratio, whilst the nonlinear deformation process extends correspondingly. In addition, degrees of damage of specimens reduced gradually and the type of destruction showed a transformation trend from stretching failure towards shear failure when the slenderness ratio increased. A model of dynamic damage evolution in red sandstone was established and the parameters of the constitutive model at different ratios of length to diameter were determined. By comparison with the experimental curve, the accuracy of the model, which could reflect the stress–strain dynamic characteristics of red sandstone, was verified. From the view of energy dissipation, an increase in slenderness ratio of a specimen decreased the proportion of energy dissipation and caused a gradual fall in the capability of energy dissipation during the specimen failure process. To some extent, the study indicated the effects of slenderness ratios on the mechanical properties and energy dissipation characteristics of red sandstone under the high strain rate, which provides valuable references to related engineering designs and academic researches.

Energy dissipation of cavity expansion based on generalized non-linear failure criterion under high stresses

Based on the compression mechanism for analyzing the cavity expansion problem in soil under high stresses,generalized non-linear failure criterion and large strain and energy conservation in plastic region during the cavity expanding were adopted.The energy conservation equation was established and the limited pressure of cavity expansion under high stresses was given based on the energy dissipation analysis method,in which the energy generated from cavity expansion is absorbed by the volume change and shear strain caused in soil.The factors of large strain and dilatation were considered by the proposed method.The analysis shows that the limited pressure is determined by failure criterion,stress state,large deformation characteristic,dilatation and strength of soil.It is shown from the comparison that the results with the proposed method approximate to those of the in-situ method.The cavity expansion pressure first decreases and then increases nonlinearly with both of shear modulus and dilatation increasing.

Practical elasto-plastic damage model for dynamic loading and nonlinear analysis of Koyna concrete dam

The elasto-plastic damage model for concrete under static loading,previously proposed,was extended to account for the concrete strain-rate through viscous regularization of the evolution of the damage variables.In order to describe the energy dissipation by the motion of the structure under dynamic loading,a damping model which only includes stiffness damp stress was proposed and incorporated into the proposed rate dependent model to consider the energy dissipation at the material scale.The proposed model was developed in ABAQUS via UMAT and was verified by the simulations of concrete specimens under both tension and compression uniaxial loading at different strain rates.The nonlinear analysis of Koyna concrete dam under earthquake motions indicates that adding stiffness damp into the constitutive model can significantly enhance the calculation efficiency of the dynamic implicit analysis for greatly improving the numerical stability of the model.Considering strain rate effect in the model can affect the displacement reflection of this structure for slightly enhancing the displacement of the top,and can improve the calculation efficiency for greatly reducing the cost time.

Comparison on Commercial Application of Two Types of C_8 Aromatics Isomerization Catalysts

The results of commercial application of two types of C_8 aromatics isomerization catalysts under different feed conditions were compared to gain an insight in the techno-economical basis for selecting proper technological route at the plant.The comparison reveals differences in every aspect of feed consumption,unit capacity,product output,product distribution,and unit process parameters depending upon which catalyst type is adopted by the integrated PX complex.The type of aromatics isomerization catalyst has its influence on the plant scale,the construction cost,the process unit capacity and the product cost,with the magnitude of its impact varying with changing feed conditions.

Fusion Reactor and Fusion Reactor Materials— Target Fuel Depletion Fraction and Energy Gain of Inertial Confinement Fusion with D-^3He Advanced Fuel

The target fuel depletion and energy gain of inertial confinement fusion （ICF） for uniform spherical target of D-SHe advanced fuel compressed by high power laser-beam have been derived and calculated in this article. Our numerical calculations show that if only the approximation of small internal energy of central spark and high inertial confinement parameter Hr = ρRF is valid for typical efficiency parameters of reactor system, the net fusion energy output can be possible for ICF of D-3He target. Inversely, under the approxi- mation of large internal energy of central spark and low HF it will not be possible to get net fusion energy output for ICF of D-^3He target. Hereby, an indirect proof of the scientific basis of fast ignition（FI） philosophy has been provided as a matter of fact.

Apply of Low-Carbon Technology in Building Energy Conservation in Hot Summer and Cold Winter Area

Building energy conservation is the basis for carbon emission reduction, through elaborating the relationship between low carbon and energy efficient building. It points out that the construction of energy-saving emission reduction is an effective means to solve the problems of high energy consumption of the building, and it is also an important measure for China＇s carbon emission reduction. According to the climate characteristics in hot summer and cold winter area, low carbon technology suitable for the construction of energy-efficient hot summer and cold winter area is proposed which is based on the analysis of the current main building energy-saving technical measures.

Determining method,conditional factors,traits and applications of nonlinear chemical fingerprint by using dissipative components in samples

The thermodynamic systems and dynamic model suitable for determining the nonlinear chemical fingerprints of samples were analyzed.The results indicated that the damp nonlinear chemical reactions in close systems away from the equilibrium and open systems without the complementarity of the dissipation substances have important significance for the throng characterization and whole content analysis of chemical components in samples.Various factors influencing on nonlinear chemical fingerprint,such as reactant species and their concentrations,electrode types,temperature,stir rate,the sort,dosage and granularity of the sample,etc.were amply researched by a nonlinear chemistry reaction,namely,damp B-Z oscillation which used acetone and glucose as the main dissipative substances.In addition,the quantitative information on the whole of chemical components in samples and the traits and applications of the fingerprint were investigated.The method and its important conditions for determining nonlinear chemistry fingerprint used in distinguishing and evaluating complex samples were successfully put forward.

Review of research and measurement for application properties of HTS tapes

Research and development of high-temperature superconducting(HTS)apparatus are ongoing in the world with the great progress on the HTS tapes in recent years.The most attractive applications require the HTS tapes to perform well upon the application of an alternative current(AC)and/or an AC magnetic field.The electromagnetic properties of the HTS tapes including anisotropy,uniformity,alternative current(AC losses)and stability as well as mechanical characteristics are important fundamental parameters for these applications.This paper summarizes and focuses on several typical measurement principles and methods as well as apparatuses of those characteristic parameters except for their stability developed in past several years in China.