tailieunhanh - Soil and Environmental Analysis: Physical Methods - Chapter 11

Độ bền kéo và có thể tán Độ bền kéo được định nghĩa là căng thẳng, hoặc lực lượng trên một đơn vị diện tích, yêu cầu làm đất để thất bại trong sự căng thẳng, đó là, để kéo nó ra. Độ bền kéo là khá nhạy cảm với vi cấu trúc của đất, và điều này làm cho nó một tham số có giá trị để đo lường trong nghiên cứu cấu trúc và hành vi của đất. Độ bền kéo của đất là ít quan tâm đến kỹ thuật dân sự, nơi nó thường được giả định là. | 11 Tensile Strength and Friability A. R. Dexter and Chris W. Watts Silsoe Research Institute Silsoe Bedfordshire England I. INTRODUCTION Tensile strength is defined as the stress or force per unit area required to cause soil to fail in tension that is to pull it apart. Tensile strength is remarkably sensitive to the soil microstructure and this makes it a valuable parameter to measure in research into the structure and behavior of soil. The tensile strength of a soil is of little interest in civil engineering where it is usually assumed to be zero as soils are maintained under compressive loads and are not meant to fail anyway. However when soils are considered in agricultural and environmental contexts this is not the case and tensile strength is important. For example the cracking and crumbling of soil that occurs during soil wetting and drying or during tillage operations are strongly dependent on the tensile strength characteristics. Soil friability may be defined as the tendency of a mass of soil to crumble into a certain size range of smaller fragments under an applied stress. This property is crucial for the production of seedbeds during tillage operations. It is often observed that the results of tillage depend more on the soil conditions than on the details of the tillage implement. Intuitively one can imagine that this crumbling property depends on the pre-existing micro-structure of the soil. Later we show that it can be quantified through the variability of the tensile strength. II. TYPES OF TENSILE STRENGTH TESTS A. Indirect Tension Tests Indirect tests of tensile strength are so called because the stress is not applied directly. Instead a compressive force is applied across the diameter of a cylindri- Copyright 2000 Marcel Dekker Inc. Fig. 1 Contours of equal tensile stress in a cylindrical sample loaded across a diameter by a force P. Maximum tensile stress Y occurs at the center of the sample and is given by Eq. 1. The first two contours from the .