drawn as two straight line segments which appear to best approximate 

 the data. The upper portion of the failure envelope, if extended, 

 passes through the origin while the lower portion does not. A failure 

 envelope which passes through the origin is characteristic of a normally 

 consolidated soil and a non-zero intercept is characteristic of an over- 

 consolidated soil. Once again it may be seen that the soil behaves in 

 an overconsolidated manner at low consolidation stresses and in a nor- 

 mally consolidated manner at higher stresses. These results are similar 

 to those obtained from the one-dimensional consolidation tests. 



The strength parameters expressed in effective stresses needed to 

 evaluate long-term anchor holding capacity and footing bearing capacity 

 are defined by the Mohr-Coulomb failure law (Lambe and Whitman, 1969, 

 p. 139) 



t,.,- = c + b,, tan <J> (2) 



ff ff 



where t = shear strength 



a ff = normal effective stress on failure plane 



c,<j> = cohesion intercept and friction angle, respectively, 

 expressed in terms of effective stresses 



The parameters c and <J> can be readily obtained from the failure 

 envelope of a stress path diagram such as Figure 8 (Lambe and Whitman, 

 1969, p. 141). The parameters obtained were: 



°l + 5 3 , , . °l + °3 , , . 

 r <3.5 psi >3.5 psx 



c .46 psi psi 



♦ 30° 37° 



Each of the five triaxial tests was performed to satisfy a partic- 

 ular need; a discussion of these needs follows: 



Test 1. The test was performed at very low strain rate (3 percent 

 per day) . 



Test 2. The test was performed at a more rapid strain rate (4 

 percent per hour). The results of Tests 1 and 2 were compared, and it 

 was decided that the differences were not sufficient to warrant per- 

 forming tests at the slower rate. The remaining tests were performed 

 at about 4 percent per hour. 



Test 3. The test was performed to define the failure envelope in 

 the zone of slight apparent overconsolidation. 



18 



