Laserfiche WebLink
51 <br />9-19 CIVIL ENGINEERING REFERENCE MANUAL <br />_ For the auger-hole method (i.e., in-field, falling-head I. CONSOLIDATION TESTS <br />},tests), the combination of azea and length variables may Consolidation tests (also known as confined compression <br />be known as the shape factor or conductivity coe,~cien(, and oedometer tests) start with a disc of cohesive soil <br />F. For example, Eor a cased hole below the water ta- <br />ble of length L and radius r whose impervious casing (usually clay) confined by a metal ring. The faces of the <br />extends all the way to the hole bottom and whose liq- disc are covered with porous plates. The disc sandwich <br />is loaded i^ a water tank. The testing time is very <br />uid level rises from h; to h7 in time ((approaching the long, since the water out-seepage is very slow. The load <br />water table levelj, the shape factor and permeability <br />are. versus the void ratio is plotted as an e•log p curve. <br />llr <br />. F = 2 9.28 <br />z <br />k Ft In (ht) lltln (h' / 9.29 <br />. 7 \ 7 <br />. Other in-field tests can use cased holes with constant <br />head, or uncased holes with constant and variable head. <br />The shape factors for these tests are not the same as <br />. that in equation 9.28. <br />porous plate <br />confining ring <br /> Ezample 9.6 Figure 9.8 Consolidation Test <br /> The permeability of asemi-impervious soil was evalu- <br /> ated in a falling head permeator whose head decreased Figure 9.9 shows an e-log p curve for a soil sample from <br /> from 100 to 90 cm in 5 minutes. The body diameter which the load has been removed at. m allowing the clay <br /> was 13 cm; the standpipe diameter was 0.3 cm; and the to recover. <br /> sample length was 8 cm. What was the permeability of <br />The line segment m-r is known as the virgin Branch <br /> the soil? or virgin consolidation line. This type of behavior is <br /> From equation 9.27: typical of norm¢lly consolidated clay. Normally consol- I <br /> idated clay can either be virgin, previously lmloaded <br /> la(0.3)~(8) <br />k = ' !n(100/40) = 1.3 EE-5 cm/sec cla7, or it can be day carrying a load which has never <br /> 4x(13)2(5)(60) been removed or exceeded. <br /> <br /> <br /> <br /> <br />e k <br />reloading curve (from previous preconsolitlation) <br />J <br />) reloading curve <br />` <br />l <br /> <br />eo m 'a <br />m path taken if <br />/ loetl is not <br /> <br /> <br />) <br />rebound curve ` <br />removed at po I <br />\ <br />1 <br />\ <br />J virgin branch <br /> <br />l r <br /> p po9 scale) <br /> peq po <br /> <br /> Figure 9.9 a-log p Curve <br /> <br /> PROFESSIONAL PUBLICATIONS INC. • P.O. Box 199, San Carlos, CA 94070 <br /> <br />