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Compaction+-+Holtz-Kovacs - 108 Clay Mlnerals and Soll...

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108 Clay Mlnerals and Soll Stmct~m 4-4. Describe briefly the crystalline or atomic structure of the following ten minerals. Also list any important distinguishing characteristics. (a) Smectite (b) Brucite (c) Gibbsite (d) Attapulgite (e) Bentonite (f) Allophane (g) Halloysite (h) Ihte (i) Mica 6) Chlorite 4-5. Describe the following types of bondmg agents found with clay minerals. (a) Hydrogen bond (b) Covalent bond (c) van der Waals' forces (d) James bond 4-6. The wet density of a sand in an embankment was found to be 1.9 Mg/m3 and the field water content was 10%. In the laboratory, the density of the solids was found to be 2.66 ~ ~ / m ~ , and the maximum and minimum void ratios were 0.62 and 0.44, respectively. Calculate the relative density of the sand in the field. 4-7. Which sheet, silica or alumina, would you wear to a toga party? Why? 4-8. Given the particles in Fig. 4.26, is it realistic to show that all the particles are in contact with each other for this given plane? Any given plane? Why? five Compaction 5.1 INTRODUCTION In geotechnical engineering practice the soils at a given site are often less than ideal for the intended purpose. They may be weak, highly compressible, or have a higher permeability than desirable from an en- gineering or economic point of view. It would seem reasonable in such instances to simply relocate the structure or facility. However, considera- tions other than geotechnical often govern the location of a structure, and the engineer is forced to design for the site at hand. One possibility is to adapt the foundation to the geotechnical conditions at the site. Another possibility is to try to stabilize or improve the engineering properties of the soils at the site. Depending on the circumstances, this second approach may be the most economical solution to the problem. Stabilization is usually mechanical or chemical, but even thermal and electrical stabiliza- tion have occasionally been used or considered. In this chapter we are primarily concerned with mechanical stabiliza- tion or densification, also called compaction. Chemical stabilization in- cludes the mixing or injecting of chemical substances into the soil. Port- land cement, lime, asphalt, calcium chloride, sodium chloride, and paper mill wastes are common chemical stabilization agents. Other methods for stabilizing unsuitable foundation soils include dewatering, which is the removal or reduction of unwanted excess ground water pressures, andpreloading, in which the foundation soils are surcharged with a temporary overload so as to increase the strength and decrease anticipated settlement. The details of these and other methods are de- scribed in textbooks on foundation and highway engineering. A good state
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110 Compaction of the art discussion and reference to methods for improving the engineer- ing characteristics of soils is provided in the ASCE (1978) committee report "Soil Improvement-History, Capabilities, and Outlook." Compaction and stabilization are very important when soil is used as an engineering material; that is, the structure itself is made of soil. Earth
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Compaction+-+Holtz-Kovacs - 108 Clay Mlnerals and Soll...

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