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HomeMy WebLinkAboutPIP 98-03; Cornerstone Corporate Centre Lot 7; Planned Industrial Permit (PIP) (15)GEOCON INCORPORATED Project No. 05724- 12-01 October 2 1, 1997 Newport National Corporation 5050 Avenida Encinas, Suite 350 Carlsbad, California 92008 Attention: Subject: Mr. John Couvillion CORNERSTONE CORPORATE CENTER PALOMAR AIRPORT ROAD CARLSBAD, CALIFORNIA GRADING PLAN REVIEW Gentlemen: In accordance with your request, we have reviewed the grading plans entitled Grading Plans for Cornerstone Corporate Center prepared by Latitude 33 (no date) to address the stability of the proposed variable fill slope adjacent to Palomar Airport road along the southern property boundary. The inclination of the proposed fill slope varies between 3: 1 (horizonta1:vertical) and 1.5: 1. Portions of the slope steeper than 2:1 do not conform to the requirements of the City of Carlsbad's grading ordinance. In addition, our preliminary calculations indicate that the portions of the slope steeper than about 1.75:l will not possess a factor of safety of at least 1.5 against deep-seated failure if constructed of the prevailing on-site clayey soils. For this reason, we recommend that one of two alternative mitigative measures be used to increase the factor of safety of the slope to at least 1.5. The first alternative would be to reinforce portions of the slope steeper than 1.75:l with a geogrid reinforcement system. Our firm has performed calculations that indicate that the desired factor of safety of 1.5 could be achieved by incorporating layers of geogrid such as Miragrid 10T at vertical intervals of approximately 4 feet into the fill mass. The length of the geogrid would be approximately 35 feet measuring horizontally from the face of the slope. We are in the process of completing sketches depicting the appropriate configuration of the geogrid reinforcement. A second method to achieve the necessary factor of safety would be to import granular fill material meeting minimum shear strength requirements to use in construction of the outer 25 to 35 feet of the proposed slope. It would be necessary for our firm to perform parametric calculations using various strength parameters to develop the actual geometry and soil types to be used in the slope. 6960 Fbnden Wie San Diego, California 92121-2974 Telephone (619) 558-6900 Fax (619) 558-6159 It is our opinion that either of these approaches would satisfactorily mitigate the oversteep configuration of the slopes as designed. If you have any questions regarding this review, or if we may be of further service, please call. Very truly yours, GEOCON MCORP( Michael S. Chapin 1 CEG 1 149 GE 2248 MSC:dmc (4) Addressee Project No. 05724- 12-0 1 -2- October 2 1, 1997