6.5.6 Settlement of Cohesive and Organic Soils Cohesive and organic soil can be susceptible to a large amount of settlement from structural loads. It is usually the direct weight of the structure that causes settlement of the cohesive or organic soil. The settlement of saturated clay or organic soil can have three different components: immediate (also known as initial settlement), primary consolidation, and secondary compression. Immediate Settlement. In most situations, surface loading causes both vertical and horizontal strains. This is referred to as two- or three-dimensional loading. Immediate settlement is due to undrained shear deformations, or in some cases contained plastic flow, caused by the two- or three-dimensional loading. Common examples of three-dimensional loading are from square footings and round storage tanks. Many different methods are available to determine the amount of immediate settlement for two- or three-dimensional loadings. Examples include field plate load tests, equations based on the theory of elasticity, and the stress path method (see R. W. Day, Geotechnical and Foundation Engineering: Design and Construction, Mc- Graw-Hill Publishing Co., New York). Primary Consolidation. The increase in vertical pressure due to the weight of the structure constructed on top of saturated soft clays and organic soil will initially be carried by the pore water in the soil. This increase in pore water pressure is known as an excess pore water pressure (ue). The excess pore water pressure will decrease with time as water slowly flows out of the cohesive soil. This flow of water from cohesive soil (which has a low permeability) as the excess pore water pressures slowly dissipate is known as primary consolidation, or simply consolidation. As the water slowly flows from the cohesive soil, the structure settles as the load is transferred to the soil particle skeleton, thereby increasing the effective stress of the soil. Consolidation is a time-dependent process that may take many years to

vo  initial vertical effective stress of the in-situ soil (see Art. 6.4.1)  v  for an underconsolidated soil (this represents the increase in vertical effective stress that will occur as the cohesive soil consolidates under its own weight) vm  maximum past pressure, also known as the preconsolidation pressure ( p), which is obtained from the consolidation curve using the Casagrande construction technique (see Fig. 6.22)  v  increase in load, typically due to the construction of a building or the construction of a fill layer at ground surface The value of  v (also known as z) can be obtained from stress distribution theory as discussed in Art. 6.4.2. Note that a drop in the groundwater table or a reduction in pore water pressure can also result in an increase in load on the cohesive soil. For overconsolidated soil, there are two possible cases that can be used to calculate the amount of settlement. The first case occurs when the existing vertical effective stress ( vo) plus the increase in vertical stress ( v) due to the proposed building weight does not exceed the maximum past pressure ( vm). For this first case, there will only be recompression of the cohesive soil. For the second case, the sum of the existing vertical effective stress (

Design Considerations Brick Technical Manual 61 5.2.2 Limiting dimensions for robustness The following charts show limiting heights and lengths The chart for walls supported only at the top and for single leaf and cavity walls constructed with clay bottom (chart 5) show the transition to limiting heights masonry units of common sizes. Support conditions for isolated piers when the length falls below five times and the applicable slenderness coefficients are the thickness at the left-hand side. indicated by an icon on each chart. For further information on Robustness, please refer to Where the icon shows hatching along an edge, the section 8 of the Think Brick Australia manual 7, Design corresponding edge of the wall is laterally supported. of Clay Masonry for Servicability. Chart 1 Wall is laterally supported from both ends and the top Design Considerations Brick Technical Manual 62 Chart 2 Wall is laterally supported from both ends only Chart 3 Wall is laterally supported from one end and the top