Question

Question 1 Consolidated undrained triaxial laboratory tests yielded the following results: Additional axial stress at Cell pressure Pore water failure (kN/m2) pressure at failure (kN/m²) (kN/m²) 200 650 400 770 880 350 50 600 a. Draw the Mohr circles representing: i. Total stresses ii. Effective stresses b. From the Mohr circles, determine the cohesion and angle of internal friction for the two scenarios in a) above c. Briefly differentiate between consolidated drained (CD) and unconsolidated undrained (UU) triaxial tests. Indicate the civil engineering situations where parameters obtained from each of these two tests will be useful. 116 + 3 + 6 Marks

Answer 1

on Consolidated Dhammed Test Drainage is allowed in both stages. Effective stress analysis Dů used. 0 DO Unconsolidated Undtrained Pest (UO) • Drainage is not permitted during got & and stage ( sample is iwiti ally corturated Identical specimen tested under various confining pressure will fail by equas increment of deviator streu o ac Sail NC Soil failure envelope Horizontal for NC soil, Mour's, circle pass through origin. Dc coil Mohr's circle curve does not pass through origin. • Total stress analysis is Derformed • Application : • Analysis of gradual loading colldition • To check long term Totability has l. It is a very quick a long term test. It takes only 15 minuta d e mbankment Application: It has been in to Used in sudden loading such istence since long ago. as Rapid construction short term stability under A construction Pore weater Pressure. been long ago. Jas which short from Pore u

(Page 1) Ans, JJz to co-u ceu Pressure (3 kN/m²) (KNM) (KN/m?) (+Nime) (kN/m2) (kning 200 50 800 850 150 650 200 1190 970 400 200 770 880 350 3480 1130 600 250 a.) (). Total stresses: iztan" (45+6) + 2C -tan (45+8/2) | 850 = 200 tan² x + 2C tand 1170 = 400 ton²a + 2c tank. Subtracting (2) - (1) 320 = 200 tanta tanax = 3200 1.6 IX - 1+26 99 Tx = tan" (102649) > 51.67° ; 850 = 200x (16) + 2C Hoe (12649) C => 209.50 kN/m2 45+,- 51.67 • using Total stress $ 13:34 Parametery 51.67

(Page 2) 5 thing effective strese Parameters for a) 1 - 800 l 6) ' 970 Tg = 150 T = 200 9': 1130 g = 250 T = Ttan't + 26 taux 1800 = 150 tau? x + 20 taux f e [970 = 200 tau? x + ac taux. On Subtracting - C 170 = 50 tau? K taux = 170% = 3.4. taux = 1.843 x=tan' (1.843) 61.52° ; Putting values 800 + 150 (3.4) + 20' (1843) C'78.67 KN me using effective 45+ & 61052 stress Parameters = 33.04 and

RI.. Page 3 a) Mohr's circles are : U Total stresses 13.34 = 209.5kW/m2 36) 200 3(b) 400 3L) 850 1170 1980 KN/m2

Effective stress (Page 4) Jo = 35.04° (c =78067 (a) 50 & Gul b) c) 200 250 970 1130 800 m2 b.) from Molio's i for Total stress; circle ; c = 209.5 kN/m² 0 - 13.34 c) for effective straces; c'= 0 78.67 kN/m 33.04