The URL can be used to link to this page

Home My WebLink About3957; EL CAMINO REAL ROAD WIDENING; GEOTECHNICAL RECONNAISSANCE; 2015-09-09z w w z z w 1€c '1 07/0 Corporate Headquarters 6280 Riverdale Street San Diego, CA 92120 P 619.280.4321 T 877.215.4321 F 619.280.4717 W www.scst.com SDV0SB.DVB.S8 September 9, 2015 SCST Project No. 150105P3 Report No. 3 Mr. Casey Arndt City of Carlsbad Construction Inspection Division 5950 El Camino Real Carlsbad, California 92008 Subject: GEOTECHNICAL RECONNAISSANCE DISTRESSED PAVEMENT, CURB, GUTTER AND SIDEWALKS - EL CAMINO REAL STATION 495+00 TO STATION 532+00 CARLSBAD, CALIFORNIA Dear Mr. Arndt: In accordance with your request, Southern California Soil & Testing, Inc. (SCST) conducted a reconnaissance of the site on July 23, 2015 to review distress to the eastern most lane and sidewalk on El Camino Real between approximately Stations 495+00 to 532+00, in Carlsbad, California. We understand that the concern is that the observed distress may be an indication of ongoing slope movement or loss of strength in the soil between the street and the adjacent drainage. The purpose of the reconnaissance was to identify possible causes of the distress and to provide recommendations for interim protection, monitoring and future investigations. SITE DESCRIPTION In the area observed, the paved street is bound to the east by a curb and gutter, sidewalk, soil parkway and a drainage that ranges from 5 to 40 feet below street grade. The slope to the drainage ranges from near vertical to flatter than 2:1 (horizontal:vertical). The unimproved parkway ranges in width (between the sidewalk and the drainage slope) from approximately 5 to 20 feet. Buried utilities in the roadway parallel the curb. Storm drainage drop structures are being reconstructed as part of a roadway widening project. We understand that modification of the drainage channel is not practical. The subsurface conditions exposed in open excavations consist of poorly to moderately compacted sandy fill over predominantly sandy alluvium and claystone and sandstone Santiago Formation. Geotechnical borings performed across the street for the roadway widening project (Ninyo & Moore, 2009) indicate that the alluvium consists of moist to wet, stiff to very stiff sandy clay with relatively weak shear strength. Seepage has been observed the subsurface materials, particularly in the aggregate base section of pavements observed in open trenches. San Diego • Los Angeles • Inland Empire 4 Central Valley City of Carlsbad September 9, 2015 El Camino Real NB Widening SCST No. 150105P3-3 Carlsbad, California Page 2 DISTRESS FEATURES Distress consists of longitudinal open cracks paralleling the road (up to approximately 2-inches wide), local settlement of the concrete gutter (up to approximately 2-inches), open expansion joints between the curb and sidewalk (up to %-inch), and local settlement of the sidewalk (up to approximately 114-inch). Piping, in the form of small sinkholes were observed locally in the parkway east of the sidewalk. Voids could be probed locally sideways beneath the sidewalk. The distress is discussed in more detail below. The cracks in the pavement parallel saw cuts, cold joints in overlays, utility trench backfill or other construction related joints. Some of the cracks appear to be in the overlay and appear to terminate on underlying pavement. Other cracks penetrate through the pavement into the underlying subgrade. The gutter has settled or portions have uplifted to create a wavy appearance. The concrete is not severely cracked and movement appears to have been taken up on the expansion joints. The distress is the result of soil movement, but without further study, it is difficult to assess whether the movement is the result of expansion or settlement. Overall the gutter flows to the south without impediments. The sidewalk is not severely cracked. There is localized settlement of approximately inch but the movement has been accommodated along expansion joints. There are open expansion joints between the curb and sidewalk that expose subgrade indicating local horizontal movement. Most, but not all, of the distress is occurring where the adjacent drainage slope is highest, steepest and closest to the roadway improvements. CONCLUSIONS Based on our reconnaissance and knowledge of the site soils, some of the distress may be caused by lateral creep or loss of strength in soils near the drainage, especially where the highest and steepest slopes are near the improvements. The lateral creep may extend into the paved street as well. However, some of the cracking in the pavements may be caused by other factors such as settlement of trench backfill, expansive subgrade soil, pavement fatigue or shrinkage. Furthermore, there appears to be only minor vertical movement across the cracks. All cracks are not necessarily indicative of slope movement but do offer an avenue for water to infiltrate the subgrade soil. Water infiltration will accelerate soil movement and reduce slope stability, particularly if these cracks are tension cracks. Tension cracks that collect surface or subsurface water are common causes for slope failures. Overall the observations do not suggest imminent slope failure, but do indicate that features are present that could significantly reduce the stability of the slope with infiltration of surface or subsurface water. City of Carlsbad September 9, 2015 El Camino Real NB Widening SCST No. 150105P3-3 Carlsbad, California Page 3 RECOMMENDATIONS Based on our reconnaissance, we recommend maintenance, monitoring, and further assessment prior to the storm season. Monitoring may reduce the potential for catastrophic failure of the slope, sidewalk and portions of the roadway, as well as provide information for assisting in recommendations for emergency measures to be implemented in a timely fashion. Specifically, we recommend the following: Crack Filling - We recommend that the cracks be filled or sealed with impermeable material to reduce the potential for water to infiltrate the subgrade soil. A semi-flexible sealant such as asphalt emulsion or similar may be utilized. Monitoring of Monuments - We recommend that the site be monitored to evaluate the magnitude, pattern, and rate of movement. Monitoring can be performed by installing monuments in the hardscape such as screws and nails. Periodic measuring distances between monuments to an accuracy of approximately 1 mm is recommended every two weeks until further recommended. This time interval can be adjusted depending on the results of the monitoring. Visual Monitoring - We recommend that this portion of El Camino Real be visually monitored following and/or during prolonged periods of rainfall to see if assess erosion in the drainage walls adjacent to the slope. Further, our office should observe excavations for planned improvements. Further Investigation - We recommend that a subsurface geotechnical investigation be conducted following the establishment of distress rates and magnitudes to provide recommendations for long-term repair and stabilization of pavement subgrade and slopes. The investigation may include soil borings, laboratory testing, and slope stability modeling. If you have any questions, please call us at (619) 280-4321. Respectfully Subm SOUTHERN CAk W.LEE Qf VANDERHURST No. 1125 1— CERTIFIED X (\J ENGINEERING GEOLOGIST W. Lee VanderhuI Principal Geologist WLV: ER:rt & TESTING, INC. (1) Addressee by email: casey.arndt@carlsbadca.gov (1) Mr. Dave Carlin: DCarlin@kleinfelder.com