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l <br />Pa ae 3 <br />Fred Hanta <br />• Dean Ma slay <br />February 6, 1980 <br />5. The corsultcrt assumed an anele o_r internal friction for the spoil <br />material equivalent *_o observed angles of repose. The author observes; <br />"The research :/nich has been performed, indicates the assumption that is <br />approximately equal *_o the angle of repose is essentially valid, if not <br />conservative." Examination of the selected references listed by the <br />consultant in 3peerdi:c D did not discern any supportive presentation. In <br />addition, references specifically solicited from the author verbally <br />(Marsai, hlarachi) did not appear to support the consultant's assumption. <br />hiy experience and iiterautre research causes me to be skeptical concerning <br />the validity of this assumption of ecuivalence of angles of repose and internal <br />friction. 2 believe that the assumption is valid for strictlu cohesioniess <br />granular materials. However, overburden derived from formations containing <br />coal will typically be comprised of a mixture of shale, siltstone, sandstone, <br />limestone and their assxiated debris. Because many of these materials are <br />cohesive in nature, it seems unliiceiy that spell material so derived will be <br />truly cohesionless in character. <br />Besear,_^ =n~c rcafcfi77 material shear strancth has been performed <br />• specifically co increase knowledge concerning fill performance to allow <br />better ca_cslation of factors of safety to improve the validity of embankment <br />design. As referenced abovE, this research has de*_ermired that.the angle of <br />internal friction for such fills decreases with increasing confining pressure. <br />Several of to involved researchers have observed that the most important <br />factor affecting shear strengh is particle breakdown under increasing load. <br />/Marsla, Leps, Fusagalli, Leslie) Leslie stated: "There is a trend indicated <br />for a1i soil t,9at the angle of internal friction is reduced in proportion to <br />the increase in aarticle breakdo:m, but this cannot be confirmed until the <br />influence of increasing lateral pressure is known" He fprther observed; "The <br />degree of brew=:do:/n is dependent upon such characteristics as mineral <br />composition, structure, texture, friability, weathering, brittleness, hardness, <br />and particle shape, to name a few." In addition, research has determined <br />that the presence of oversize material is not as beneficial to shear strength <br />as originally theorized. In fact, several researchers have reported that <br />observed apples of internal friction derived from large sample size tests <br />actually decrease with increasing particle size. (Marsai, Marachi) <br />If t:e character of the spoil material was cohesienless, the research <br />performed to date suggests that as depth of the fill (loading) increases the <br />angle of internal friction of progressively deeper materials will decrease. <br />If this were the case the consultant's assumption :/ould be increasingly <br />inappropriate for successively deeper fill horizons. <br />• (cont'd) <br />