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Applegate <br />Group, <br />Water Resource Advisors for the West <br />Memorandum <br />Date: August 21, 2015 AG Job No.: 10-116 <br />To: <br />From: Carrie R. Herbolsheimer, PE; Tyler J. Desiderio, EIT <br />Subject: Brannan Sand and Gravel Co. Pit #29 Trench Slope Stability Analysis <br />A slope stability analysis was performed for proposed construction at Brannan Sand and Gravel Co. <br />Pit #29. The construction entails a 10 foot deep trench to install a French Drain on the southern <br />side of the North Cell of Pit 29 and a solid drain pipe on the western side of the North Cell of Pit 29. <br />The analysis modeled the construction condition of the trench comprised of one material, during <br />which the excavation slope will be no steeper than 1.5HAV grade and ground water is expected 4 <br />feet from the surface. The analysis was performed using Rocscience Slide6 software. <br />In absence of soil strength testing data, strength values were assumed from gradation curves for <br />the pit obtained from the client. The curves indicate that the soil expected during excavation is a <br />well -graded sand (USCS SW) with cohesive elements (USCS CL - ML). Typical values for granular <br />materials were referenced from Design of Small Dams and Soil Strength and Slope Stability. The <br />first reference lists SC and SM cohesion values ranging from 30 psf to 3000 psf and phi angles <br />ranging from 23 deg to 45 deg. The second reference lists SC -SM and SW cohesion values ranging <br />from 0 psf to 1700 psf and phi angles ranging from 34 deg to 55 deg. <br />Ultimately engineering judgment and experience on previous submittals were exercised to develop <br />conservative yet reasonable soil property values based on the discussion above. The embankment <br />material properties furthered in the analysis can be seen below. <br />Moist Density <br />(p CD <br />Saturated Density <br />(p CD <br />Cohesion <br />(PSD <br />Phi Angle <br />(deg) <br />120 <br />130 <br />100 <br />33 <br />A model in Slide6 was developed based on the above discussion. The model of the excavation slope <br />produced a FOS of 1.411, which is above the DWR Dam Safety Branch's construction minimum FOS <br />of 1.3. The results of the analysis can be seen on the following page. <br />