These particles are not distinguishable by the naked eye. You need to look at an effective stress analysis for very stiff clay. Piles Driven into Stiff Clay through Overlying Soft Clay – When piles are driven through soft clay or silts into stiff to very stiff cohesive soils, a soft skin is carried down, again to a limited depth. If the clay dries out without having been frozen, it can become very stiff and difficult to work. Silt and clay are classified as “fines” and pass the No. The terms used to describe silty and clayey soils refer to their “consistency” or “cohesiveness”: very soft, soft, medium stiff, stiff, very stiff, and hard. A phi=0 analysis is fine for soft, contractive clay soils, but not for very stiff clay, particularly high plasticity clay. When dredging stiff clay with a backhoe dredger large lumps form. Chapter 5 Engineering Properties of Soil and Rock 5 .1 Overview The purpose of this chapter is to identify, either by reference or explicitly herein, appropriate methods of soil and rock property assessment, and how to use that soil and rock property data to establish the final soil and rock parameters to be used for geotechnical design. In the water-saturated state these soils can be sticky and very impermeable to water. Silt and Clay are considered to be smaller family members of soil group, Even small amounts of fines can have significant effects on the engineering properties of soils. The purpose of this chapter is to provide a background to the properties of natural clay materials used in the construction industry and other applications (see Table 4.1). Due to the high clay content, the nutrient content is very high. You can find this discussion in any good soil mechanics book-Holtz … Properties of Clay Soil. The remaining clay lumps will settle in t. If the clay has high plasticity, discharging the load from the hopper may be difficult because the material will stick to the walls of the hopper. If as little as 10 percent of the particles in sand and gravel are smaller than the No.200 sieve size, the soil can be virtually impervious, especially when the coarse grains are well graded. Cohesive soil is hard to break up when dry, and exhibits significant cohesion when submerged. "Cohesive soil" means clay (fine-grained soil), or soil with a high clay content, which has cohesive strength. Dredging Stiff Clays with a backhoe dredger. boulders and cobbles) cannot be reliably estimated from boreholes-trial pits or exposures must be used. Very stiff fissured dark grey CLAY (London clay) (a) (b) (c) (f) (h) Loose brown very sandy subangular coarse GRAVEL with pockets of soft grey clay ... noted that the properties of very coarse soils (i.e. Cohesive soil does not crumble, can be excavated with vertical sideslopes, and is plastic when moist. 200 sieve for a gradation analysis. There is a frequent need to evaluate clay materials for civil engineering projects, which has led to a bias in this chapter towards a consideration of their geotechnical properties. Reduction in friction angle through shearing Variable Stiff clays (progressive failure) Softening of fissured clay, loss of cohesion Decades Stiff, fissured clay Weeks to years Time frame Increase of pore-pressure through drainage clay, silt Process: Materials Loss of true cohesion due … Though different soils have a wide range of colors, textures and other distinguishing features, there are only three types of soil particles that geologists consider distinct. 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