Laserfiche WebLink
1 <br />4.0 GEOTECHNICAL TESTING AND ANALYSIS <br />' Geotechnical tests were conducted on representative soil and tailings samples collected during [he <br />field investigation for the proposed embankment raise, to evaluate [he existing foundation conditions and <br />the suitability of on-site materials for construction purposes. The focused field investigation is described <br />' in Section 2.6 of this Design Report. The design of the proposed works reflects the findings and conclusions <br />of the tests and analyses. Details of the laboratory testing programs are outlined in Appendices A and C. <br />4.1 Existing Foundation Conditions <br />' The existing tailings were sampled and tested to evaluate the suitability of the materials as a <br />foundation for construction the proposed embankment raise. Time consolidation tests were conducted on <br />representative undisturbed samples of the tailings to estimate expected consolidation and surface settlement <br />' under the influence of the load imposed by the proposed embankment raise. Triaxial shear and permeability <br />testing of the tailings were not performed, although undisturbed samples were collected for future evaluation, <br />if deemed necessary. <br />Time consolidation and swell consolidation tesu were performed on portions of undisturbed samples <br />samples SH-1 and SH-2. These samples were collected using Shelby tubes that were pushed by hand into <br />the existing beach tailings, just below the surface of the ponded water. The samples consisted of nearly <br />saturated alternating sequences of silty sand and poorly graded sand with silt. The fraction of the material <br />' passing the No. 200 sieve ranged from 7% to 33%. <br />Estimates ofexpected primary consolidation were made for the fine and course fractions encountered <br />' in each of the beach tailings samples collected. It was not practical, at the time of the focused investigation, <br />`~to conduct an exhaustive investigation of the impounded tailings in the existing facility. Therefore, <br />(1 calculations ofexpected overall settlement were based upon an assumed maximumHail ni gs thickness of 10 <br />t eet, which is believed to be conservative, based on anecdotal information. The settlement estimates also <br />assume that the existing tailings would be under-consolidated, since they have been recently deposited and <br />' .no surcharge loads have ever been applied. Analysis of the consolidation behavior of the hvo samples <br />representing the fine fraction and the coarse fraction from the north delta beach indicates minor differences <br />in the results for the various fractions and locations. Results of settlement analysis of these hvo samples <br />' indicate that expected settlement of the tailings beneath the embankment raise at the north sampling location <br />will be between 2.4 and 2.9 inches. Analysis of the consolidation behavior of the two samples representing <br />' the fine fraction and the coarse fraction from the south delta beach indicates that expected settlement of the <br />tailings in response to the load imposed by the embankment raise at this location will be between 1,5 and <br />3.3 inches. <br />' Settlement for these conditions was calculated using a 12 ft-high tailing embankment causing a <br />surcharge load of approximately 1.64 ksf . The subgrade pressure distribution procedure used to determine <br />' the foundation stress increments at various depths and location beneath the embankment is that <br />recommended in the Soil Mechanics Design Manual published by the Naval Facilities Engineering <br />Command (US Navy, 1982). Based upon these analyses, it is estimated that approximately one month will <br />' 12 <br />