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Mr. David A. Kidd, P.E. <br />29 September 1993 <br />.Page 5 <br />TEST RESULTS <br />For each test in the test series, sliding (i.e., shear failure) was <br />observed to occur at the interface between the wetted overliner and the <br />geomembrane specimen. Pinholes and surface deformations were also <br />observed in the geomembrane after each test. <br />The total- stress interface shearing resistance was evaluated for each <br />applied normal stress. The test data were potted on a graph of shear <br />force versus horizontal displacement. The resulting plots are presented <br />in Attachment 1 to this letter report. Tie peak value of shear force was <br />used to calculate the peak shear strength. For this report, the residual <br />shear strength was assumed to be equal tc the stabilized post -peak shear <br />force measured at the end of each test. <br />The total- stress peak and residual shear strengths derived from the <br />plotted test results are summarized in Table 3. These strengths were <br />plotted on a graph of shear stress versus normal stress to evaluate the <br />total- stress peak and residual shear strength envelopes. The plots of <br />shear stress versus normal stress for the test series are also presented <br />in Attachment 1. A best -fit straight line was drawn through the four <br />data points from the test series to obtain total- stress peak and residual <br />interface friction angles and adhesions. The coefficient of correlation <br />(R a standard statistical indicator of how well the best -fit line <br />matches the test data points, was obtained for each best -fit line. The <br />interface friction angles, adhesions, and R values derived from the <br />plotted test results are summarized in Table 4. <br />For the test series, it is noted that the reported adhesion is the <br />shear stress axis intercept of the best fit straight line drawn through <br />the test data on a plot of shear stress ve ^sus normal stress. This value <br />may not be the true adhesion of the interface and caution should be <br />exercised in using this adhesion value for applications involving normal <br />stresses outside the range of stresses covered by the test series. <br />GL3458/GEL93234 <br />GEOSYNTEC CONSULTANTS <br />