Abstract:
A landslide activated during heavy precipitation in the winter of 2017 on the campus of California Polytechnic State University – San Luis Obispo. The landslide deposited saturated soil against the eastern wall of the Fremont Hall dormitory. Students were evacuated and the 3-story dormitory building was closed. The landslide continued to move and reactivated again in the winter of 2019.
The University procured a design-build team in 2019 to complete a geotechnical investigation and design a stabilization project. The investigation involved exploratory drilling, test pits, bucket augers, slope inclinometers, vibrating wire piezometers, and laboratory testing. The landslide that activated in 2017 had a length of approximately 900 feet extending upslope and a width of approximately 200 to 350 feet. The estimated depth of the slide plane varied from 15 to 50 feet below the ground surface which generally corresponded with the contact between landslide deposits and underlying greywacke sandstone.
The stabilization design consisted of a series of ground anchor galleries and an anchored soldier pile wall at the toe of the slope directly behind the dormitory. Horizontal drains and subdrains were also installed to collect and lower groundwater elevations. Anchor galleries were constructed by notching into the hillside, placing a 2-foot thick and 8- to 10-foot-high reinforced shotcrete waler. Anchors with lengths of 35 to 124 feet were drilled, installed, and grouted and tensioned to lock-off loads of approximately 264 kips. A sculpted reinforced shotcrete anchored soldier pile wall was constructed along the toe of the slope behind Fremont Hall. Beams were installed and embedded into the underlying greywacke sandstone and one to two rows of anchors installed. The project was completed in the summer of 2022 allowing students to reoccupy the building in September. A long-term instrumentation monitoring program has been implemented by the University.