人工冻土单轴抗拉,抗压强度的试验研究

简述了国内外冻土单轴抗拉、抗压强度的试验方法，分别在３个不同温度下（－７℃、－１２℃、－１７℃）进行了单轴抗拉、抗压强度测定。试验表明，采用劈裂法测定冻上抗拉强度是可行的。试验的结论对冻土工程的设计与施工有一定参考作用。     

Determination of Shear Strength and Three-dimensional Yield Strength for the Hoek-Brown Criterion

Summary. Most currently used techniques for analysing the stability of near surface structures, such as rock slopes, are based on the application of the effective Coulomb shear strength parameters cohesion c′, and the angle of friction φ′ on some known or anticipated shear surface subjected to an effective normal stress σ′_n. The most widely used of these techniques are the variants of the method of slices and related upper bound techniques. If the Hoek-Brown criterion is to be used to model the strength of near surface fractured rocks, it is necessary to determine equivalent Coulomb shear strength parameters for the specified level of effective normal stress. Calculation of the equivalent Coulomb parameters for the Hoek-Brown criterion for cases when a ≠ 0.5 is not a straightforward matter. A simple procedure for calculating instantaneous values of c′_i and φ′_i has been developed based on spreadsheet calculations and the application of a numerical optimisation routine. This procedure can also be applied to calculating the Hoek-Brown envelope plotted in shear stress/normal stress space. A simple closed form solution for c′_i and tan φ′_i has also been developed for the special case when a = 1. A three-dimensional version of the Hoek-Brown criterion has been developed by combining it with the Drucker-Prager criterion. This new yield criterion has been implemented by numerical solution of the governing equations. A simplification of this three-dimensional yield criterion has been developed by introducing an intermediate principal stress weighting factor. Comparison with published results demonstrates that this simplified criterion has the capacity to model the results of true triaxial tests for a range of different rock types over a wide range of stress levels. The new three-dimensional yield criterion has the advantage that its input parameters can be determined from routine uniaxial compression tests and mineralogical examination.     

煤矸石的强度特性

本文首先讨论煤矸石的应力-应变、抗剪强度二者与试样尺寸的关系;其次,研究二者的试验变形速率效应;其三,研究其应力-应变的归一化性态;最后,用松弛和蠕变相耦合的方法来研究煤矸石的强度变化现象,从另一侧面探讨土的长期强度降低机理。     

非饱和土的剪切强度

首先回顾了非饱和土剪切强度的研究现状,接着在控制吸力非饱和土三轴剪切试验的基础上提出了非饱和土剪切强度的双曲模型,它可预测不同吸力对强度的贡献———τｓ ,预测结果令人满意,具有很好的实用性。     

冻结粉土动强度的荷载效应及长期极限动强度

荷载效应包括速率效应和疲劳效应两部分．速率效应使冻土的动强度和退荷回弹动弹模随应变速率加快而提高;疲劳效应使冻土的动强度随振频增加而下降,但在低应变速率下却使动强度略有提高．在高应变速率下动强度大于静强度,在低应变速度下动强度小于静强度,其间存在一个临界应变速率．通过动强度－破坏振次关系,可确定长期极限动强度．     

岩体强度的各向异性研究

本文运用断裂力学理论推导了含节理岩体的初裂强度公式,定量地讨论了节理方向、长度对岩石强度的影响,阐明了节理岩体强度各向异性的实质。通过证实,本文所建立的公式具有很强的适用性和较高的可靠性,可用于实际的工程岩体稳定性评价。     

Basic Facts Concerning Strength of Sandstone

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冻结砂土的强度特性

本主要阐述在一定的加荷速率下，围压和温度对冻结兰州砂土应力－应变特性的影响。试验表明，围压的增大或温度的升高明显增强了冻结砂土的塑性及应变硬化性能。随着围压的增大，冻结砂土的极限偏应力强度和轴向破坏应变增大，随着温度的降低，极限偏应力强度增加，而轴向破坏应变减小，但是当围压为零时，轴向破坏应变不随温度变化，当平均法向应力σ≤６ＭＰａ时，冻结砂土抗剪强度近似服从库仓定律，此时粘聚力和内摩擦角随温度     

冻结黄土抗拉强度的试验研究

冻结饱水黄土的拉伸试验表明，拉伸破坏均属脆性破坏类型，拉断面上矿物颗粒剪移错粒，裂隙发育。拉伸的应力－应变过程，视荷载作用的快慢大致可分为粘弹－塑性、粘－弹性有脆性破坏三类，它们可用统一的方程形式加以描述，此外，对饱水冻结黄土的峰值应力、破坏应变和破坏时间等特性进行了分析，对抗拉、抗压强度作分析比较后指出，它们的比值为０．４４－０．６３，与负温和加载速率的关系不大。     

Shear Strength Criteria for Unsaturated Soils

Shear strength is one of the fundamental properties of unsaturated soils. It has been found to change with matric suction. Various shear strength equations have been proposed for predicting the shear strength versus suction relationship for unsaturated soils. Some of these equations are based on regression analysis of experimental data, while some are embodied in more complex stress–strain constitutive models. In this paper, a variety of shear strength equations are examined and compared with respect to their fit of experimental data. Data for specimens prepared from initially slurry conditions as well as data for initially compacted soil specimens are analysed. The advantages and limitations associated with various proposed shear strength equations are discussed in this paper.     

Strength characteristics of compacted pond ash

Strength properties of compacted ash layers depend to a great extent on the moulding conditions. This paper focuses on the effects of compaction energy and degree of saturation on strength characteristics of compacted pond ash. The pond ash sample, collected from the ash pond of Rourkela Steel Plant (RSP), was subjected to compactive energies varying from 357 kJ/m³ to 3488 kJ/m³. The optimum moisture content and maximum dry densities corresponding to different compactive energies were determined by conventional compaction tests. The shear strength parameters, unconfined compressive strengths (UCS) and California bearing ratio (CBR) values of specimens compacted to different dry densities and moisture content were assessed and reported. The effects of compaction energy and degree of saturation on shear strength parameters i.e. unit cohesion (c_u) and angle of internal friction (Ф) values and also the UCS values are evaluated and presented herein. The results indicate that the dry density and strength of the compacted pond ash can be suitably modified by controlling the compactive energy and moulding moisture content. The strength achieved in the present study is comparable to the good quality, similar graded conventional earth materials. Hence, it may be safely concluded that pond ash can replace the natural earth materials in geotechnical constructions.     

Strength of iron-ore agglomerates during reduction

The paper deals with the reduction strength of iron-ore agglomerates, especially under the conditions in the blast furnace. As an introduction, the reduction zones, temperature zones and pressures exerted on the charge are covered.Special attention has been paid to the reasons for the often very large decrease in strength during heating and reduction. The plasticity of the wüstite is, in this case, of special interest. A number of testing methods for investigation of stresses and strains of the agglomerates during reduction are introduced. The test methods cover different procedures in the blast furnace — isothermal as well as blast furnace simulating.A method of measuring the pressure strength during reduction has been worked out which comprises testing the agglomerates at high temperature during the reduction. It was originally developed in order to study the cold-bound balls during the reducing process. With the aid of this test method the necessary conditions were established for the development of perfect agglomerates according to the COBO method.A series of results from investigations made with these tests are given both for cold-bonded COBO balls of various compositions and for commercial types of burnt pellets.     

粉砂岩的强度特性和变形特性

本文通过实验,研究了一种介于岩石与土之间的软岩--粉砂岩在不同应力状态和应力路径下的基本力学性质、时间效应和交叉效应,提出了一维率相关型本构方程、三维体积应变本构方程以及破裂准则。     

泥岩强度特性的动力效应

本文通过对泥岩(粉质粘土)所进行的静、动强度试验结果的比较,验证了加荷速率效应和重复效应对泥岩强度的影响。试验发现:在快速加荷(升压时间10ms)的情况下,土的动强度都大于静强度。该泥岩无侧限抗压强度动力值为静力值的2.3-2.9倍;动强度指标C为静强度指标C.的2.8倍左右,它们的ф值相近。重复(3600次)荷载效应对泥岩强度的影响不太明显。在无侧限的条件下,其疲劳强度稍低于静力无侧限抗压强度值。     

Dynamic Effect of Mudstone Strength Properties

This paper, comparing the dynamic test results of mudstone (silty clay) with the static ones, verifies influence of cyclic loading and loading rates on the strength of mudstone. It is found that the dynamic strength is higher than the static strength. In the case of rapid loading (rising time of pressure is 10ms ), the unconfined compressive strength for this type of soil in dynamic test is 2.3 to 2.9 times as high as that in static tests, and the strength index, Cd , is about 2.8 times as great as Cs , but ∅ values are approximately equal to each other. Repeat loading (up to 3600 cycles) has no great influence on the strength of mudstone, and under the condition of unconfined loading, the fatigue strength of mudstone is somewhat lower than its statically strength.     

莫尔－库仑强度理论的修正

本文对莫尔－库仑（Ｍｏｈｒ－Ｃｏｕｌｏｍｂ）强度理论作了重要修正。指出静水应力不仅对材料固有强度，而且对剪切滑移也有影响，从而得到了一个计及中间主应力影响的剪切强度公式。根据断裂力学的分析，该公式可进一步用于材料的断裂强度的计算。     

Strength capacity evolution in thawing soils

The strength properties of the main types of thawing clayed soils, including loamy sand, loam, and clay have been studied. The factors controlling their evolution during freezing and thawing have been revealed as follows: grain-size composition, freezing and thawing conditions, physical properties such as unit weight and water content, and pore pressure. Using a special technique developed to account for these factors, we have revealed the geotechnical soil properties for the soil types under study.     

正常固结饱和粘性土的不排水强度

本文以有效应力强度理论和Henkel孔隙水压力公式为基础,建立了各种类三轴与平面应变试验条件下正常固结饱和粘土的不排水强度公式及相互关系;初步估计了粘土强度随固结增长的计算公式.     

Strength and Deformation Performances of Siltstone

The fundamental mechanical properties, time and crisscross effects of a kind of siltstone under different stress states and along different stress paths are studied with laboratory testing. A failure criterion, constitutive equations with one dimensional rate dependence and three dimensional volume deformation are proposed in this paper.     

In-situ Rock Spalling Strength near Excavation Boundaries

It is widely accepted that the in-situ strength of massive rocks is approximately 0.4 ± 0.1 UCS, where UCS is the uniaxial compressive strength obtained from unconfined tests using diamond drilling core samples with a diameter around 50 mm. In addition, it has been suggested that the in-situ rock spalling strength, i.e., the strength of the wall of an excavation when spalling initiates, can be set to the crack initiation stress determined from laboratory tests or field microseismic monitoring. These findings were supported by back-analysis of case histories where failure had been carefully documented, using either Kirsch’s solution (with approximated circular tunnel geometry and hence σ _max = 3σ ₁ ?σ ₃) or simplified numerical stress modeling (with a smooth tunnel wall boundary) to approximate the maximum tangential stress σ _max at the excavation boundary. The ratio of σ _max /UCS is related to the observed depth of failure and failure initiation occurs when σ _max is roughly equal to 0.4 ± 0.1 UCS. In this article, it is suggested that these approaches ignore one of the most important factors, the irregularity of the excavation boundary, when interpreting the in-situ rock strength. It is demonstrated that the “actual” in-situ spalling strength of massive rocks is not equal to 0.4 ± 0.1 UCS, but can be as high as 0.8 ± 0.05 UCS when surface irregularities are considered. It is demonstrated using the Mine-by tunnel notch breakout example that when the realistic “as-built” excavation boundary condition is honored, the “actual” in-situ rock strength, given by 0.8 UCS, can be applied to simulate progressive brittle rock failure process satisfactorily. The interpreted, reduced in-situ rock strength of 0.4 ± 0.1 UCS without considering geometry irregularity is therefore only an “apparent” rock strength.