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Consistency and Plasticity

<div class="clearfix layout-row columns-2"><div class="layout-column first column-1"><p>Cohesive soils change their state depending on the water content. When the water content is very high, these soils become liquid. When the water content decreases, they transition from a liquid to a plastic condition, then to semi-solid and finally to a solid condition.</p><p>Thus, with a decreasing water content, cohesive types of soil become less mouldable, while their strength increases.</p><p/></div><div class="layout-column last column-2"><p>The water contents at which the soil consistency is transformed &#8230;</p></div></div>

Determining the Consistency of Cohesive Soil

<p>The determination of the <strong>consistency</strong> (condition) can be done both in situ and in the laboratory. In the case of the in-situ test, the condition of a cohesive type of soil is to be determined as follows:</p><ol><li> <p>A type of soil is called &#8220;<strong>very soft</strong>, if it runs through the fingers while being pressed together in a fist;</p></li> <li> <p><strong>Soft</strong>, if it can be kneaded easily;</p></li> <li> <p><strong>Firm</strong>, if, although it is hard to be kneaded, it can be rolled out to 0.12 in (3 mm) thick rolls in the &#8230;</p></li></ol>

Soil Consistency

<div class="clearfix layout-row columns-2"><div class="layout-column first column-1"><p>Using the soil samples' water content at the <strong>liquid</strong> and <strong>plastic</strong> limits, w_L and w_P (Atterberg consistency limit), according to&#160;[[ASTM D4318-10]]&#160;and/or&#160;[DIN18122], and the natural water content w, the consistency index I<span>C </span>(or CI) can be calculated&#160;:</p><p>(Formula: Consistency index)</p><p>The consistency index is a numerical representation of the consistency of a soil.</p></div><div class="layout-column last column-2"><p>(Table: Consistency index IC and designation of the soil state of cohesive soils in accordance &#8230;</p></div></div>

Soil Plasticity

<p>Soil plasticity is the &#8220;Property of a cohesive soil, which changes its mechanical behaviour with change in the water content&#8221;&#160;[DINENISO14688:2001].</p><p>The plasticity is the range between the liquid- and the plastic limit. This range is classified into very soft, soft and firm [DIN18122].</p><p>(Image: Consistency band [Trian00])</p>

Consistency and Plasticity

<p>The state conditions of the plastic range are shown as numerical values &#8203;&#8203;in the table. The liquidity index I_L = 1 - I_C is also listed.</p><p>(Table: Conditions in the plastic range [DIN18122])</p>

Plasticity Index

<div class="clearfix layout-row columns-2"><div class="layout-column first column-1"><p>The degree of plasticity is obtained from the water content of the soil at the liquid limit w_L [[ASTM D4318-10]], and is as per [DIN18196:1988] and [DINENISO14688:2001], divided into:</p><table><tbody><tr><td> <p>Low plasticity</p></td> <td> <p>w_L &lt; 35 % by weight</p></td> </tr><tr><td> <p>Medium plasticity</p></td> <td> <p>35 &lt; w_L &lt; 50 % by weight</p></td> </tr><tr><td> <p>High plasticity</p></td> <td> <p>w_L &gt; 50 % by weight</p></td> </tr></tbody></table></div><div class="layout-column last column-2"><p>The plasticity index, I_P, is used in order to achieve a clear distinction of the cohesive soil type into silt or clay, as well as in silty or clayey &#8230;</p></div></div>

Classification of Fine Soils Subject to the Liquid Limit

<div class="clearfix layout-row columns-2"><div class="layout-column first column-1"><p>Special classifications and designations for fine soils (silt and clay) subject to the liquid limit w_L can be found in EN ISO 14688-2.</p><p>[DINENISO14688:2001]</p></div><div class="layout-column last column-2"><p>(Table: Classification of fine soils subject to the liquid limit wL or plasticity index IP as per EN ISO 14688-2)</p></div></div><p/>

Parameters for Liquid Limit, Plastic Limit and Plasticity Index

<table><tbody><tr><td> <p>Typical parameters for liquid limit (w_L), plastic limit (w_P) and plasticity index (I_P) of several soil types, can be found in the table.</p><p>The plasticity index I_P is illustrated in the plasticity diagram subject to the liquid limit w_L<span>.</span></p></td> <td> <div>(Table: Typical parameters for wL, wP and IP of selected types of soil)</div><div>(Image: Plasticity diagram according to Casagrande with soil groups to DIN 18196)</div></td> </tr></tbody></table><p/>