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Home My WebLink AboutHDP 2017-0001; DR. MANEA PROPERTY LOT 52; GEOTECHNICAL ASSESSMENT OF REAR YARD RETAINING WALLS; 2017-01-10-· ------------------------------------- s . T SDVOSB.DVBE SCST, Inc. Corporate ~eadquarten 6280 Riverdale Street San Diego, CA 92120 619.280.4321 • 877.215.4321 , 619.280.4717 ,,. www.scst.com January 10, 2017 Joanne Tyler, PE SCST No. 170106N Report No.1 O'Day Consultants, Inc. 2710 Loker Avenue West, Suite 100 Carlsbad, CA 92010 Subject: GEOTECHNICAL ASSESSMENT OF REAR YARD RETAINING WALLS MANEA RESIDENCE, LOT 52 7298 SITIO LIMA CARLSBAD, CALIFORNIA O'DAY PROJECT NO. HOP 2017-0001 DWG NO. 507-7A PERMIT NO. GR2017-0059 References: 1.) GoogleEarth, (2016), Aerial Photographs dated October 2012, November 2012, November 2013, May 2014, December 2014, April 2015, and March 2016. 2.) Hunsaker and Associates (2015), As-Built Drawings 475-2D: "La Costa Town Square Residential, Sheet 6 of 22," dated January 8, originally prepared by O'Day Consultants, dated October 1 O, 2012. 3.) Southern California Soil & Testing, Inc. (2013), "Final As-Graded Geotechnical Report, La Costa Towne Square -Residential Development, La Costa Avenue, Carlsbad, California, Project No. C.T. 08-03", Report No. 1211179-37, dated September 5. 4.) O'Day Consultants (2016), Drawings: "Hillside Development Permit for La Costa Town Square Residential Lot 52 of Map 15918," dated December. Dear Ms. Tyler: In accordance with your request, SCST, Inc. performed an assessment of the retaining walls in the rear yard of the subject property. The assessment was performed to provide an opinion whether the retaining walls are adequately constructed, and whether the preexisting slope should be reconstructed to restore the stability of the slope. To prepare our assessment, we performed a site reconnaissance on December 7, 2016 to observe the exposures at the retaining walls and document the conditions, reviewed referenced development plans, aerial photographs, and geotechnical reports for the property, and reviewed engineering design manuals from the retaining wall block manufacturer. BACKGROUND The site's rectangular lot was mass graded in early 2013 (References 1 and 2). The site consisted of a rear cut slope ascending approximately 35 feet to a drainage and access easement adjacent to Geotechn1cal E::ngineenng E::nvironmental Science & E::ngineering Special lnspec!1on & Materials Testing i=ac1l1!ies Consulting -· -------------------- ---------------- O'Day Consultants 7298 Sitio Lima Carlsbad, California January 10, 2017 SCST No. 170106N-1 Page2 Rancho Santa Fe Road. A relatively small masonry retaining wall was constructed as part of the original residential construction in 2014. Recently the homeowner solicited the construction of a pair of subject, tiered segmental retaining walls {Keystone Country Manor block) above the masonry wall. The two walls are about 4 feet in exposed height and offset about the same. The construction was not completed and remains partially exposed. AS-GRADED GEOLOGIC CONDITIONS The slope is documented to be partially fill {in the mid, upper portion), and cut {in the lower and peripheral portion), as the slope originally hosted a drainage {References 2 and 3). The lower portion of the fill was placed upon a documented keyway, at elevation 385 feet above mean sea level, which coincides with the elevation of the excavations needed for the segmental retaining wall construction. Based on our referenced as-graded report and site observations, the geologic conditions observed at the site were similar to those described in the project geotechnical report. These conditions consist of exposures of both cut slope of moderately soft to hard metavolcanic rock and previous fill materials associated with the mass grading. With the construction of the retaining walls, some of this rock {cut conditions) has been excavated and replaced as fill associated with the walls. SITE RECONNAISSANCE On December 7, 2016, a representative of SCST visited the site to observe the exposures at the retaining walls and document the conditions. The findings in part included the following: • The segmental wall blocks are connected by adhesive rather than shear pins. • The segmental wall backfill includes some geog rid reinforcement, but not at the frequency specified by the manufacturer. • The segmental wall backfill utilized onsite fill material, which contains angular gravel and cobble, as well as clayey soils. • The segmental wall offset and separation is not in accordance with standard manufacturer recommendations. • The foundation materials, preparation, and backfill were not documented. • Although the foundation materials were not observed, the site generally offers favorable conditions. DISCUSSION AND CONCLUSIONS Based on the observations and background review, we provide two conclusions: -• ------------.. -.... ---------------------- O'Day Consultants 7298 Sitio Lima Carlsbad, California January 10, 2017 SCST No. 170106N-1 Page3 1. The retaining walls do not meet engineering standards. Therefore, we would recommend the walls be designed by an engineer familiar with the manufacturer and reconstructed in accordance with the design. The construction should include observations and testing by the geotechnical representative. 2. In our opinion, the finish grade documented prior to the retaining wall construction was in a stable condition. The excavation and construction of the retaining walls has changed that condition and reduced the stability. Removing the construction and replacing the slope will not provide the previous stability conditions, as the inherent stability of the cut conditions cannot be restored. However, a properly designed and constructed retaining wall configuration similar to that existing would provide a condition considered similar or more favorable than the as-graded slope . LIMITATIONS Our opinions are based on our observations and are limited by the scope of the work that we agreed to perform. Our work was performed in accordance with the currently accepted standard of practice and in such a manner as to provide a reasonable measure of the compliance of the grading and backfill operations with good engineering and construction practice. No warranty, express or implied, is made or intended with respect to the work that we have performed, and neither the performance of this work nor the submittal of this report should be construed as relieving the contractor of their responsibility to conform with good engineering and construction practice. We appreciate this opportunity to be of professional service. If you have any questions, please call us at (619) 280-4321. Respectfully submitted, SCST, INC. ' .,.',\ ~ ~ TH:ER: (1) Addressee via e-mail: Joannet@odayconsultants.com