WHAT ARE THE ENGINEERING PROPERTIES OF SOIL?

Engineering Properties of Soil

在处理土壤作为建筑材料的同时考虑以下性质。

• Cohesion
• Angle of internal friction
• Capillarity
• 渗透性
• Elasticity
• 压缩系数

凝聚力

它是抵抗材料破裂或剪切的内部分子吸引力。凝聚力衍生在来自水膜的细粒土壤中，该薄膜与土壤质量中的个体颗粒一起结合在一起。内聚力是细粒土的性质，粒径低于0.002毫米。随着水分含量的增加，土壤的内聚力降低。在压实良好的粘土中的内聚力更大，它与施加的外部负荷无关。

2. Angle of internal friction

The resistance in sliding of grain particles of a soil mass depends upon the angle of internal friction. It is usually considered that the value of the angle of internal friction is almost independent of the normal pressure but varies with the degree of packing of the particles, i.e. with the density. The soils subjected to the higher normal stresses will have lower moisture contents and higher bulk densities at failure than those subjected to lower normal stresses and the angle of internal friction may thus change. The true angle of internal friction of clay is seldom zero and may be as much as 26⁰. The angle of internal friction fro granular soils may vary in between 28⁰到50.⁰.

3. Capillarity

It is the ability of soil to transmit moisture in all directions regardless of any gravitational force. Water rises up through soil pores due to capillary attraction. The maximum theoretical height of capillary rise depends upon the pressure which tends to force the water into the soil, and this force increases as the size of the soil particles decreases. The capillary rise in a soil when wet may equal as much as 4 to 5 times the height of capillary rise in the same soil when dry.

粗砾石没有毛细血管升高;粗砂高达30厘米;细砂和土壤具有毛细管升高至1.2米，但干燥的沙子具有很少的毛细血管。

Clays may have capillary rise up to 0.9 to 1.2 m but pure clays have very low value.

4.渗透率

渗透性of a soil is the rate at which water flows through it under action of hydraulic gradient. The passage of moisture through the inter-spaces or pores of the soil is called ‘渗滤'。具有足够多孔的土壤足够渗透发生的被称为“pervious’ or ‘permeable’, while those which do not permit the passage of water are termed ‘impervious’ or ‘不透水的'。The rate of flow is directly proportional to the head of water.

渗透性is a property of soil mass and not of individual particles. The permeability of cohesive soil is, in general, very small. Knowledge of permeability is required not only for seepage, drainage and ground water problems but also for the rate of settlement of structures on saturated soils.

5. Elasticity

当施加负荷时，据说土壤是弹性的，而在施加负荷时，它会受到体积（或改变的形状和体积），但是在移除负载时立即恢复其初始体积。土壤弹性行为的最重要特征是，无论施加多少载荷重复，都要提供在土壤中的应力不超过屈服应力，土壤不会永久变形。这种弹性行为是泥炭的特征。

6.可压缩性

砾石，砂和淤泥是不可压缩的，即，如果这些材料的湿质量受到压迫;新利客户他们没有大量的体积变化。粘土是可压缩的，即，如果粘土的湿质量受到压缩，则可以排出水分和空气，导致在压缩负荷撤回时不会立即回收的体积减小。每个单元的压力增加的减少被定义为土壤的可压缩性，并衡量“巩固所需的速率”共同合并'土壤。沙子和淤泥的可压缩性随着粘土的密度和压缩性而变化，含水量直接变化，与粘性强度成反比。