Predictions of thermal cracking were made based on these Level 1 material inputs as well as on Level 3 default material properties. Montmorillonite smectite exhibits a high degree of swell potential, illite has negligible to moderate swell characteristics, and kaolinite exhibits almost none. The comparison of these two figures clearly shows that the higher quality Level 1 material inputs dramatically reduce the variability between predicted and observed cracking. Other combinations of weight and volume units may be used in computations where consistent units are needed. Of particular note is the void ratio e, which is a general indicator of the relative strength and compressibility of a soil sample; i. Field testing is covered in Chapter 4, and appropriate links to the Chapter 4 material are included here where appropriate. University of Anbar College of Engineering Civil Engineering Department Iraq-Ramadi Asst.
A simple way to determine whether sieves should be replaced is the periodic examination of the stretch of the sieve fabric on its frame. They are- 1- Liquid Limit L. It has a low relative density, a low unit weight, and a high void ratio. Grain size distribution of coarse particles mechanical sieve analysis. The vertical stress necessary to maintain zero volume change is the swelling pressure. Openings of fine mesh or fabric are easily distorted as a result of normal handling and use. A one-dimensional swell potential test is used to estimate the percent swell and swelling pressures developed by the swelling soils Table 5-23.
Although it is intuitively clear that higher level i. Collapsible soils are found most commonly in loess deposits, which are composed of windblown silts. Collapsible soils exhibit abrupt changes in strength at moisture contents approaching saturation. One consequence of all of the above is that this chapter is quite long; this is necessary to give sufficient coverage to all of the diverse geotechnical inputs required by the two design procedures. The geotechnical inputs required for flexible pavement design using the 1993 Guide are summarized in Table 5-1. Figure 5-7 shows example grain size distributions for sand, silt, and clay soils as obtained from mechanical sieve and hydrometer Table 5-20 tests.
This is especially true for material properties. This lecture introduces the concepts of weight volume relationships and phase diagrams. The reversibility and essentially isothermal nature of the of the gel-sol-gel transformation distinguish thixotropic materials from those that liquefy upon heating--for example gelatin. The material settling over the sieve during washing should be constantly stirred to avoid plugging. Exceptions include wave propagation problems earthquakes, pile dynamics,……. How would that help us to visualize the contribution of the voids to the behavior of the soil? For a gel system, agitation disrupts the three-dimensional structure that binds the system into a gel.
A sample of soil is a multi-phase material composed of solid soil grains, water, and air Figure 5-3. Loess, unlike other non-cohesive soils, will stand on almost a vertical slope until saturated. Property Description Level Section 1 2 3 General Material type 3. They probably have two main causes : Orientation of the adsorbed water and Cementation Factors that affect the soil structure are- The shape, size, and mineralogical composition of soil particles, The nature and composition of soil water. When the gel is agitated, the molecules can align in the direction of flow, reducing the resistance to flow. Gradation is occasionally expressed alternatively in terms of the percent coarser than a given grain size. The unit weight, y, can be computed using one of the following relationships: This expression for unit weight makes no assumption about the amount of water present in a sample of soil or rock, and is based simply on the weight and volume of the soil or rock.
Low-volume secondary road pavements do not require-and most agencies do not have the resources to provide-the same level of design effort as high-volume urban primary roads. A dilatant substance is one that develops increasing resistance to flow as the rate of shear increases. Porosity , n %100x Vt Vv n Expressed as percentage 0-100% Prove that e e n 1 or n n e 1 3. This appears to be a free-flowing liquid when poured, but when it is stirred, it becomes very firm. Again, these inputs are identical to those for the 1986 Guide.
In cases where some intermediate analysis is required to determine the design input e. Common terms associated with weight-volume relationships are shown in Table 5-7. Then, the geotechnical inputs are described in detail by category. Shape and size of grains. Level 1 inputs would typically be used for designing heavily trafficked pavements or wherever there are serious safety or economic consequences of early failure.
Swell potential also depends on the mineralogical composition of fine-grained soils. Some tricks for developing a phase diagram are discussed, and a practice problem is provided. Estimation of swell potential Holtz and Gibbs, 1956. The potential for volumetric swell of a soil depends on the amount of clay, its relative density, the compaction moisture and density, permeability, location of the water table, presence of vegetation and trees, and overburden stress. Note that the thicknesses D i for the unbound layers are included as flexible pavement geotechnical inputs in Table 5-1; although these would typically be considered outputs from the design i. The first five properties in Table 5-2 are used to determine the effective modulus of subgrade reaction k in the 1993 Guide procedure.