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HomeMy WebLinkAboutX2011-1893 - Soils+-le.I f Pkick Engineering and Construction July 25, 2011 Phillip Mitchell All -American Traditions, Inc. 1921 Wilson Avenue Upland, CA 91784 SUBJECT: GEOTECHNICAL EVALUATIO Foundation Repairs Raili Clasen Property 401 E. 15111 Street Newport Beach, CA 92663 Project No. 110715 ,loll- ibq3 1 I1� S�- :u ;n T� 2 fn9 O Oq' 00 O tt1 C:. iT-rlmg9l� n�l:W r Z ^S ,pomp (L'�Agg��NyCW in 1'4Z mva r Or i;0: mzm� 0 The following report presents an evaluation of the geotechnical issues that have contributed to the foundation movement at the above property. Foundation repair plans for the property have been prepared by Holcomb Structural Engineering, dated July 7, 2011. SCOPE OF SERVICES The following services were performed to address the pertinent geotechnical issues for the property: 1) Site observations (on July 18, 2011) 2) Review of floor level survey data for the home 3) Review of soils data provided by you 4) Review of test pier installed on July 18, 2011. 5) Review and approval of the structural repair plans dated July 7, 2011. 30640 Kristin Court, Redlands, CA 92373 — 909-389-7316 — fax 909-389-7326 — www,helfrich-associates.com GEOTECHNICAL EVALUATION Foundation Repairs Raili Clasen Property Page No. 2 FLOOR LEVEL SURVEY The southwest corner of the home has settled about 3 inches since the home was built in the early 1950's, based on the recent floor level survey. Maximum floor inclination is in the living room, where the floor tilt is about 2.5 inches over a horizontal distance of about 10 feet. SLOPE CREEP The affected part of the house is about 34 feet from the top of a descending slope down to Cliff Drive. The slope is about 20 feet tall, and is at an inclination of about 1.5:1 (horizontal: vertical). Tree trunks on the slope and slope surface conditions suggest that the slope has experienced slope creep in the past, and may still be subject to ongoing slope movement. The portion of the house that is being underpinned, however, is founded on soils that are not subject to the effects of slope creep. No signs were observed of extension features or separations in the foundations below the walls of the home that are perpendicular to the top of the slope. SUBSURFACE DATA Surface soils ronsist of clayey silt, which are expected to be moderately expansive. These soils are also susceptible to water -induced compression. The foundations are likely founded on shallow fills (on the south side of the home), and native soils on the north side of the home. A test pier (near the southeast corner of the home) was installed to a maximum depth of about 15 feet, where firm bearing soil was encountered. CAUSE OF THE FOUNDATION MOVEMENT The most likely cause of the foundation movement is water -induced settlement of the fill and native soils that support the affected corner of the home. The source of the water is roof drainage, surface water (from irrigation and rainfall sources), and plumbing leaks. Leaking irrigation valves were observed near the southeast corner of the home during my site observations on July 18, 2011. OLVIID►�.�/ The attached plans were reviewed and analyzed to determine the appropriateness of the repairs for the conditions encountered. These plans show resistance (push) piers installed at nine locations around the southeast corner of the home. The proposed repair is consistent with the conditions encountered at the home, and is appropriate for stabilizing and leveling the affected foundations. In addition, I recommend that exposed cracks in the foundations be filled with structural epoxy. I have reviewed and signed the attached plans as the geotechnical engineer for the project. >. GEOTECHNICAL EVALUATION Foundation Repairs Raili Clasen Property Page No. 3 SURFACE DRAINAGE RECOMMENDATIONS Surface drainage and slope maintenance recommendations are presented in the attached Appendix A. These recommendations are intended to minimize future foundation movement caused by poor surface drainage around the home. I appreciate the opportunity to assist you in this matter. Please call if you have any questions. Very truly yours, Helfrich -Associates, Inc. Steven C. Helfrich, G.E. Enclosed: Appendix A - Slope Maintenance Recommendations Repair Plans (5 sheets) APPENDIX A - SLOPE MAINTENANCE RECOMMENDATIONS The most important aspect of slope maintenance is proper control of surface drainage. Uncontrolled water from.broken pipes, improperly maintained irrigation systems, and rainfall are the most prevalent causes of slope instability in Southern California. The following recommended procedures should be followed by the property owner to minimize slope instability: 1) Homes should be provided with roof drains, gutters, and downspouts, and these facilities should be checked at least twice per year. 2) All drainage devices should be checked at least twice per year to ensure that they are not blocked. All blockages should be cleared. 3) Drains at the top of slopes should not allow water to overflow onto the slope. 4) Terrace drains and brow ditches on slopes or at the tops of slopes are designed to carry runoff water to an appropriate discharge point. These drains should be checked at least twice per year, and cleaned of any accumulation of dirt and other debris. Water that backs up in surface drains will overflow and seep into the slope, creating instability. 5) Water should not be permitted to collect or pond in yard areas. This water will either seep into the ground (loosening the soils) or will overflow onto the slope. Once erosion is started, it is difficult to control and severe damage can occur quickly. 6) Loose soil or debris should not be left on slopes. Loose soils soak up water more readily than compacted fill, and will often slide downslope. This material may clog terrace drains, and may cause additional slope damage. 7) Slopes should not be over -irrigated. Naturally, ground cover will require some moisture during the hot summer months, but during the wet season, irrigation can cause heavy ground cover to move, which not only destroys the cover, but also may begin slope surface erosion. Heavy ground cover can cause surface sloughing when saturated due to the increased weight and weakening of the near surface soil. 8) Water should not be allowed to collect against foundations, retaining walls, or basement walls. These walls are typically built to withstand the effects of normal soil moisture, and may require subsurface drains to collect and transfer excessive water away from the structures. 9) Irrigation systems should not be left running on or near a slope, particularly during the rainy season. 10) Swales that have been graded around the home or on the lot should not be blocked. These swales are typically constructed to provide drainage toward the driveways, street or other positive outlet. 11) Building pad and slope surfaces should be periodically inspected for rodent activity. Burrowing rodents will reduce slope stability by allowing additional water infiltration and channeling of surface runoff into the slope soils.