Silts and Loess

Dilatancy is characteristic of fine sands and silts. The environment is all important for the development of dilatancy since conditions must be such that expansion can take place. What is more, it has been suggested that the soil particles must be well wetted, and it appears that certain electrolytes exercise a dispersing effect, thereby aiding dilatancy. The moisture content at which a number of fine sands and silts from British formations become dilatant usually varies between 16 and 35%. 

Consolidation of silt is influenced by grain size, particularly the size of the clay fraction, porosity and natural moisture content. Primary consolidation may account for over 75% of total consolidation. In addition, settlement may continue for several months after construction is completed because the rate at which water can drain from the voids under the influence of applied stress is slow. 

The angle of shearing resistance decreases with increasing void ratio. It also is dependent on the plasticity index, grain interlocking and density. 

Loess may exhibit sub-vertical columnar jointing. In addition, pipe systems may be developed in loess soils. Extensive pipe systems and sinkholes are present in some loess and have been referred to a loess karst. Pipes tend to develop by weathering and widening that takes place along the joint systems in loess. The depths to which pipes develop may be inhibited by changes in permeability associated with the occurrence of palaeosols. 

as noted earlier, owes its engineering characteristics largely to the way in which it was deposited since this gives it a metastable structure, in that initially the particles are loosely packed. The porosity of the structure is enhanced by the presence of fossil root-holes. The latter are lined with carbonate cement, which helps bind the grains together. However, the chief binder is usually the clay matrix. On wetting, the clay bond in many loess soils becomes soft, which leads to the collapse of the metastable structure. The breakdown of the soil structure occurs under its own weight. 

---

Liquefaction Sand, silt and loess 1) Burial depth of soil Commonly Area of... 

---