Environmetal Soil Properties and Behaviour
DisciplinaControle e Remediação da Poluição dos Solos5 materiais • 18 seguidores
Steady population Growth stage Decay stage FIguRE 2.19 Schematic diagram of the survival mode of bacteria with reproduction for the long term. Process A: an event reproduced at an interval. Process B: an event with reproduction overlap- ping with decay. The solid lines represent the growth stage, and the dashed lines represent the decay stage. 75Nature of Soils Group II \u2022 Impact of \u201cfailure to perform design functions\u201d on safety, health, and economic welfare of the public and environment \u2022 Expertise of parties\u2014owners, regulators, contractors, consultants, and others involved. 2.9.2 Soil Type and Mineral Analysis 22.214.171.124 Soil Type Some of the tests conducted by experienced soil engineers and practitioners for determination of soil type do not classify as rigorous or quantitative tests. Upon first encounter with a sample of a particular soil for consider- ation for an engineering application, the experienced practitioner uses sight (colour), smell, feel, and in some instances, taste. With these preliminary sight- smell-feel-taste observations, one can deduce whether (a) the particular soil is granular or clayey or somewhere in between, (b) some organic material is present in the soil, and (c) the soil is plastic or nonplastic. Whilst these preliminary observations are essentially qualitative in nature, they are nev- ertheless very useful since they provide one with an initial appraisal of the soil under consideration. With the basic laboratory tests for soil type, this initial appraisal can be tested and confirmed or denied. The basic laboratory tests generally used to identify soil type include \u2022 Sieve analyses and hydrometer tests for determination of grain-size distribution and soil texture, and to classify soil type. The important point to be made here is to ensure that the grab samples used for these tests are representative of the soil under consideration, espe- cially if reduction of sample size is necessary. Pulverization of aggre- gate groups, quartering procedures, and preparation and allocation of samples are some of the procedures that are partly qualitative in nature and also sensitive to operator technique. The top portion of the protocols shown in Figure 2.20 contains some of the principal elements pertaining to sieve analyses for particle- size distribution analyses and also for separation of the grab sam- ples into sand, silt, and clay. Sieve separation into sand, silt, and clay is necessary if one needs information on the types of minerals in the soil under consideration. \u2022 Consistency tests to determine liquid limit, plastic limit, shrinkage limit, and plasticity index. It is important to note that since sample preparation and operator technique are significant factors in labora- tory testing for consistency limits, the results obtained should be considered as operationally defined. 76 Environmental Soil Properties and Behaviour \u2022 Tests to determine the physical properties such as density, water content, degree of (water) saturation, porosity, void ratio, and spe- cific gravity of solids. Other tests to determine such properties as soil rheology, compactibility, transmissivity, and others do not clas- sify physical properties. These will be discussed in the next few chapters. 126.96.36.199 Mineral Analysis The various types of tests for mineral analysis are shown in Figure 2.20. There is no single method that can be considered to be fully satisfactory for identification of the kinds of minerals in soils. In part, this is because (a) soil is composed of a variety of minerals and (b) there will always be a range in composition of the crystal structure of clay minerals from different sources. Techniques for determination of a single mineral will be complicated because of interference between the various different minerals and the less than pure crystal structures of the minerals. Accordingly, several methods are required X-ray diffraction (XRD) On air-dry sample and with C3H5(OH)3 Differential thermal analysis (DTA) On air-dry sample Transmission & scanning electron microscopy (TEM & SEM) Infra-red spectra On pellet of dry clay and KBr Selective chemical dissolution (SCD) Other\u2026.. Test Sample Sieve For particle-size distribution data or to separate sand, silt and clay for mineral analyses Sand Identify minerals by light microscope Silt Light microscope and/or XRD Clay Wash with MgCl2 solution and wash to remove excess salts M in er al An aly se s Consistency tests Liquid, plastic and shrinkage limits (LL, PL, SL)Sieve to separate gravel and larger sizes Remove organic matter, carbonates and free iron. Disperse mechanically or by ultrasonic vibration FIguRE 2.20 Test techniques and procedures for initial identification of soil type, consistency, and minerals. For detailed information on clay mineralogy (right-hand panel), one begins with the top tech- nique (XRD) and proceeds downward with other supplementing techniques for more clarity in mineral identification. 77Nature of Soils to seek identification of the different minerals in soils, especially if quantifi- cation of these minerals is required. X-ray diffraction (XRD) is the most useful method of identification. This is especially true if the samples are treated. Glycerol (C3H5(OH)3) treatment for detection of montmorillonite and K-saturation and heating to collapse ver- miculite are the most common treatment methods. A comparison of the x-ray diffraction spacings d obtained from the  planes of Mg-saturated air- dried, Mg-saturated glycerol-solvated, K-saturated air-dried, and K-saturated heated at 500°C samples of montmorillonite, vermiculite, and chlorite shows: Mg-saturated, air-dried: Montmorillonite, vermiculite, chlorite d = 1.4\u20131.5 nm Mg-saturated, glycerol solvated: Montmorillonite d = 1.77\u20131.8 nm Vermiculite, chlorite d = 1.4\u20131.5 nm K-saturated, air-dried Chlorite, vermiculite (with interlayer aluminium) d = 1.4\u20131.5 nm Montmorillonite d = 1.24\u20131.28 nm K-saturated, heated (500°C) Chlorite d = 1.4 nm Vermiculite (contracted), montmorillonite (contracted) d = 0.99\u20131.01 nm X-ray diffractograms combine with differential thermal analysis (DTA) and measurements of infrared absorption spectrum (IR spectra) to provide a use- ful grouping of tools for mineral identification. Clay minerals have absorption bands in the infrared region of the energy spectrum in the range of molecular bond vibration frequencies. Many of these bonds are not specific to one mineral because they are due to interatomic bonds common to many minerals. However, this should not limit the use of information from IR spectra since other support- ing techniques such as the use of DTA can assist in sorting mineral identification. Clay minerals lose water or undergo phase changes that give off or require heat at specific temperatures. The loss of water molecules causes an endo- thermic reaction in which heat is taken up by the sample. In contrast, an exothermic reaction is the result of heat given off by the sample, occurring because of a phase change in the structure of the mineral. The tempera- tures at which these reactions occur are characteristic of the mineral. The use of differential thermal analysis as a tool utilizes these thermal change characteristics. In essence, DTA provides information on the temperature at which changes occurs in a mineral when it is heated continuously to a 78 Environmental Soil Properties and Behaviour high temperature. The intensity of the change is directly proportional to the amount of the mineral in the sample being tested. 188.8.131.52 Soil Fabric and Microstructural Features The traditional methods for viewing soil fabric include light microscopy and electron microscopy.