{"id":2952,"date":"2023-02-15T18:50:27","date_gmt":"2023-02-15T18:50:27","guid":{"rendered":"https:\/\/evertekengineering.com\/?p=2952"},"modified":"2023-02-15T19:20:29","modified_gmt":"2023-02-15T19:20:29","slug":"clay-deposits","status":"publish","type":"post","link":"https:\/\/evertekconsultants.com\/punjabi\/clay-deposits\/","title":{"rendered":"Clay Deposits"},"content":{"rendered":"\t\t
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Clay Deposits<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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The principal minerals in a deposit of clay tend to influence its engineering behaviour. For example, the plasticity of a clay soil is influenced by the amount <\/span>of its clay fraction and the type of clay minerals present since clay minerals <\/span>greatly influence the amount of attracted water held in a soil. The undrained shear <\/span>strength is related to the amount and type of clay minerals present in a clay <\/span>deposit together with the presence of cementing agents. In particular, strength is <\/span>reduced with increasing content of mixed-layer clay and montmorillonite in the <\/span>clay fraction. The increasing presence of cementing agents, especially calcite, <\/span>enhances the strength of the clay. <\/span>Geological age also has an influence on the engineering behaviour of a clay <\/span>deposit. The porosity, water content and plasticity normally decrease in value <\/span>with increasing depth, whereas the strength and elastic modulus increase. <\/span>The engineering performance of clay deposits is also affected by the total <\/span>moisture content and by the energy with which this moisture is held. For <\/span>instance, the moisture content influences their consistency and strength, and the <\/span>energy with which moisture is held influences their volume change <\/span>characteristics. <\/span>One of the most notable characteristics of clays from the engineering point of <\/span>view is their susceptibility to slow volume changes that can occur independent of <\/span>loading due to swelling or shrinkage. Differences in the period and magnitude of <\/span>precipitation and evapotransportation are the major factors influencing the swell-shrink <\/span>response of a clay beneath a structure. Generally kaolinite has the smallest <\/span>swelling capacity of the clay minerals. Illite may swell by up to 15% but <\/span>intermixed illite and montmorillonite may swell some 60\u2013100%. Swelling in Ca <\/span>montmorillonite is very much less than in the Na variety; it ranges from about 50 <\/span>to 100%. Swelling in Na montmorillonite occasionally can amount to 2000% of <\/span>the original volume. One of the most widely used soil properties to predict swell <\/span>potential is the activity of a clay. <\/span>Volume changes in clays also occur as a result of loading and unloading which <\/span>bring about consolidation and heave, respectively. When a load is applied to a <\/span>clay soil its volume is reduced, this being due principally to a reduction in the pressures are induced, the effective strength is increased, and the undrained <\/span>strength is much higher than the drained strength\u2014the exact opposite to a <\/span>normally consolidated clay. When the negative pore-water pressure gradually <\/span>dissipates the strength falls as much as 60 or 80% to the drained strength. <\/span>Skempton (1964) observed that when clay is strained it develops an increasing <\/span>resistance (strength), but that under a given effective pressure the resistance <\/span>offered is limited, the maximum value corresponding to the peak strength. If <\/span>testing is continued beyond the peak strength, then, as displacement increases, <\/span>the resistance decreases, again to a limiting value which is termed the residual <\/span>strength. In moving from peak to residual strength, cohesion falls to almost, or <\/span>actually, zero and the angle of shearing resistance is reduced to a few degrees (it <\/span>may be as much as 10\u00b0 in some clays). Under a given effective pressure, the <\/span>residual strength of a clay is virtually the same whether it is normally <\/span>consolidated or overconsolidated (Figure 1.4). Furthermore, the value of residual <\/span>shear strength (_\u2019r) decreases as the amount of clay fraction increases in a <\/span>deposit. Not only is the proportion of detrital minerals important but so is that of <\/span>the diagenetic minerals. The latter influence the degree of induration of a deposit <\/span>of clay and the value of _\u2019r can fall significantly as the ratio of clay minerals to <\/span>detrital and diagenetic minerals increases.<\/span><\/p>\n

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\u00a0<\/span>The shear strength of an undisturbed clay is frequently found to be greater than\u00a0<\/span>that obtained when it is remoulded and tested under the same conditions and at\u00a0<\/span>the same water content. The ratio of the undisturbed to the remoulded strength at\u00a0<\/span>the same moisture content is termed the sensitivity of a clay. Clays with high\u00a0<\/span>sensitivity values have little or no strength after being disturbed. Sensitive clays\u00a0<\/span>generally possess high moisture contents, frequently with liquidity indices well\u00a0<\/span>in excess of unity. A sharp increase in moisture content may cause a great\u00a0<\/span>increase in sensitivity, sometimes with disastrous results. Heavily\u00a0<\/span>overconsolidated clays are insensitive.\u00a0<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Clay Deposits The principal minerals in a deposit of clay tend to influence its engineering behaviour. For example, the plasticity of a clay soil is influenced by the amount of its clay fraction and the type of clay minerals present since clay minerals greatly influence the amount of attracted water held in a soil. The undrained shear strength is … <\/p>\n

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