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Home My WebLink About3466; OLIVENHAIN RD WIDENING & REALIGNMENT; SUPPLEMENTAL GEOTECHNICAL INVESTIGATION; 1996-07-010 G11 ETna. ginsers Engeejg pgts I 0• I 'I I. SUPPLEMENTAL I GEOTECHNICAL INVESTIGATION OLIVENHAIN ROAD IMPROVEMENTS CARLSBAD, CALIFORNIA I , 1 PREPARED FOR PROJECT DESIGN CONSULTANTS SAN DIEGO, CALIFORNIA I I JULY 1996 I 7 1 RECEIVED :1 JUL 12 1996 ENGiNEERING :1 DEPARTMENT I '- V I GEOCON I1h INCORPORATED Geotechnical Engineers and Engineering Geologists Project No. 05466-12-01 July 10, 1996 Project Design Consultants 7018 Street, Suite 800 San Diego, California 92101 Attention: Mr. Tom Tomlinson, PE Subject: OLIVENHA1N ROAD IMPROVEMENTS CARLSBAD, CALIFORNIA SUPPLEMENTAL GEOTECHNICAL INVESTIGATION Gentlemen: In accordance with your authorization dated June 19, 1996, we have performed a supplemental geotechnical investigation for the subject project. The purpose of the investigation was to provide additional information regarding the stability of the proposed cut slope along the northern portion of the Olivenhain Road, just east of El Camino Real. Specifically, the investigation was focused on verifying the need to buttress the cut slope to the west of the SDG&E easement. SCOPE OF. WORK As a part of this supplemental investigation, we have reviewed the following documents; Soil and Geologic Investigation for Olivenhain Road Improvements and Off-Site Dyke, Carlsbad, California, prepared by Geocon Incorporated, dated March 21, 1995. Consultation - Slojie Stability Evaluation, Olivenhain Road Improvements, Carlsbad, California, prepared by. Geocon Incorporated, dated July 21, 1995. Plans for Grading and Improvements of Olivenhain Road Widening and Realignment, prepared by Project Design Consultants, dated May 2, 1996. I . 6960 Flanders Drive San Diego, CA 92121-2974 619 558-6900 FAX 619 558-6159 I Project No. 05466-12-01 July 11, 1996 Page 2 The field phase of the investigation consisted of excavating and downhole logging of 2 large-diameter borings along the proposed cut slope' area. Approximate locations of the exploratory excavations are shown on Figure 1. The excavations were performed utilizing an Earthdrill E-120, truck-mounted drill rig equipped with a 30-inch-diameter bucket auger. The borings were excavated to depths of 35 and 41.5 feet below existing ground surface. Logs of the borings are presented in Appendix A. I . BACKGROUND The referenced project geotechnical investigation (March 21, 1995) report provided recommendations for grading the proposed Olivenhain Road improvements. These recommendations included the construction of a buttress fill to stabilize the cut slope along the northern right-of-way, west of the SDG&E easement crossing. The adverse geologic conditions requiring the remedial grading were based on soil conditions encountered in Boring No. LB-1 excavated as part of a previous study (1990) for this project. Subsequently, the cut slope area was further investigated by others. After review of the report from that study, Geocon Incorporated issued a revision (July 21, 1995) to the original report decreasing the slope buttressing requirement to the western 250 feet of the roadway cut. SOIL CONDITIONS The soils encountered in the new excavations consisted of a relatively thin layer of topsoil and formational soils of the Delmar Formation, predominately consisting of massive to thinly bedded claystone interbedded occasionally with layers of sandstone. A few concretionary, well-cemented, drill resistant beds or lenses were encountered mostly at the lower depths. The most common feature found in the borings was highly fractured zones of claystone with abundance of randomly oriented slickensided surfaces. A near- horizontal bedding plane shear was encountered at 'a depth of 9 feet in Boring No. LB-2. Slightly remolded, discontinuous clay seams were also encountered over the concretionary beds or lenses. Overall, no. significant adversely bedded bedding plane shear zones, correlating with those found in Boring No.. LB-1, were encountered. However, highly weathered clays were present near-surface along with highly fractured claystone, particularly interbedded with lenses or beds of sand. I I I I Ll I I I I I I I I I I I I I I I Fl p j vflol Ali Sadr CEG 177 I Project No. 05466-12-01 July 11, 1996 Page 3 CONCLUSIONS AND RECOMMENDATIONS No significant bedding plane shear zone was encountered in Boring Nos. LB-2 and LB-3, that correlate with those found in Boring No. LB-1. Therefore, it is our opinion that the adverse conditions will be limited to the very westernmost portion of the proposed cut slope. 'A buttress fill will be reql4ired .for an approximately 150-foot section, from El Camino Real to Station 3+00. This is a reduced length from that recommended in the referenced consultation letter (July 21, 1995). The buttress shear key should be. 30 feet wide and have a depth of at least 5 feet below finish subgrade. The backcut inclination should be no steeper than 1.5:1 (horizontal to vertical). A 'typical buttress configuration is presented in the referenced investigation report. The remaining cut slope will be stable against deep-seated failure; however, the presence of the highly fractured and weathered claystones, occasionally interbed with sandy layers, may cause surficial instability and sloughage' along the slope. While this sloughage condition is not desirable, we understand that this is may be considered a maintenance, issue. 'Construction of a stability fill as previously recommended is an alternative to mitigate this issue. This supplemental report should be considered as a revision to the referenced geotechnical correspondence. '. Should you have any questions regarding this report, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, LI I I RCE 225 - AS:DFL:dmc CA (2) Addressee (2) City-of Carlsbad Engineering Department Attention: Mr. Pat Entezari I 'I I or ai co 3" I - ---- •.. .. •.• L'----.. =Ar ciTT\1 .?1 -, LEGEND ...... APPROX. LOCATION OF LARGE - DIAMETER BORING ' I APPROX LOCATION OF BUTTRESS KEY Rwy 3, GRQCQN.° 9P GEOTECHNICAL. ENGINEERS AND ENGINEERING GEOLOGISTS 6960 &.NDERS DRiVE - SANDIEGO, CALIFORNIA 92121-2974 PHONE 619 558-6900 - FAX 619 558-6159 PROJECT NO. 05466-12-01 FIGURE I DATE 7-13-1996 APPENDIX A LOGS OF BORINGS FOR OLIVENHAIN ROAD IMPROVEMENTS CARLSBAD, CALIFORNIA Project No. 05466-12-01 / PROJECT NO. 05466-12-Ui BORING -LB 2 0U L_. Z. -. w SAMPLE ELEV. (MSL.) 112 DATE COMPLETED 6/26/96 F CD EQUIPMENT E-120 BUCKET RIG MATERIAL DESCRIPTION 0 - TOP SOIL SC Loose damp, light brown Clayey SAND with some 2 rootlets and desiccation cracks - - _______ DELMAR FORMATION Hard, moist, dark green, Silty waxy CLAYSTONE - moderately fractured - CL — HORIZONTAL DEPOSITIONAL CONTACT Very dense, damp, light green to tan Silty fine ____ ] ::~l I :• - S M SPSf(?rE with occasional well cemented zones -. - - - - :•: - 8 Hard dark grayish green Silty CLAYSTONE • SM-CL interbedded with light yellowish Silty SANDSTONE -Bedding plane shear, horizontal 1/16 inch thick at 9 - 10 \ feet - - Becomes dark green Claystone random orientation —CL-CH 'higilyfractured ---- 12 Dense, moist grayish tan, Silty fine SANDSTONE SM heavy staining - Hard dark grayish green, Claystone, abundant slicken- 14 sided surfaces, random orientation, - -Near vertical slicken sided surface at 14 feet 16 CL-CH 18 - - ____ - -Concretionary lense 8-inches thick at 18.5 feet - Grades in to light gray Clayey SILTSTONE to Silty - 20 SANDSTONE MIML 22 24 - Grades in to hard,dark gray CLAYSTONE, slicken- 26 sided, mostly dipping NE, heavy staining, lenses of - coal 1/2 inch thick - CH 28 -becomes sandier with depth Figure A-i Log of Boring Lii 2, page 1 012 ORW SAMPLE SYMBOLS D ... SAMPLING UNSUCCESSFUL 11... STANDARD PENETRATION TEST ... DRIVE SAMPLE (UNDISTURBED) DISTURBED OR BAG SAMPLE .. CHUNK SAMPLE ... WATER TABLE OR SEEPAGE NOTE: THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES. I PROJECT NO. 05466-12-01 BORING LB 2 DEPTH SOIL SAMPLE NO. = z CLASS ELEV. (MSL.) 112 DATE COMPLETED 6/26/96 u w FEET C CD EQUIPMENT E-120 BUCKET RIG MATERIAL DESCRIPTION 30• CH -Thin layer of slightly remolded Clay over the 32 - - concretionary bed. approximately 20 degrees eastward. -Concretionary bed 16 inches thick- near refusal -------------------------------------- - Very dense, moist tan to yellowish tan fine to - 34 - medium Silty SANDSTONE :SM BORING TERMINATED AT 35 FEET 'I Figure A-2 Log of Boring LB 2, page 2 of 2 ORW 0 ... SAMPLING UNSUCCESSFUL IL.. STANDARD.-PENETRATION TEST ... DRIVE SAMPLE (UNDISTURBED) SAMPLE SYMBOLS DISTURBED OR BAG SAMPLE ... CHUNK SAMPLE ... WATER TABLE OR SEEPAGE NOTE: THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES. I PROJECT NO. 6-12-01 - )- W V%i'fThTI' T .. BORING LB z,- DEPTH ( I- SOIL o. i-WX SAMPLE ELEV. (MSL.) 120 DATE COMPLETED 6/26/96 FEET EQUIPMENT E-120 BUCKET RIG MATERIAL DESCRIPTION / Sc TOP SOIL - / / Loose, to medium dense, dry to damp light brown 2 - - _____ Clayey fine to medium SAND with rootlets and \ desiccation cracks DELMAR FORMATION - 4 - Highly weathered- formational creep- Stiff, very moist, light green highly fractured clay with fractured - :L-CH filled with Silty SAND - - Very hard, moist, dark green CLAYSTONE, 8 - moderately fractured with shiny parting surfaces 10 - - - CL-CH 12 - 14 - - - - -Lens-of very dense, moist, light yellowish brown Silty fine to medium SAND, 2-6 inches thick, near - 16 - horizontal at 14.5 feet - 18 - SM Dense, moist, light grayish brown Silty fine - - SANDSTONE - - 20 - Hard, very moist, mediiiiñ brown, thinly bedded, CLAYSTONE with dark brown and yellow staining - - along bedding and fractures slightly remolded, CH discontinuous. - 22 - -becomes light grayish green with light yellow - stainng : SM -Very dense, wet, light green Silty Sandstone 23-24 24 - - fèet / - 26 CH 28 - • -Concretionary lens orange standing along fractures at - VIIIA! 28.5 feet Figure A-3 Log of Boring LB 3, page 1 of 2 ORW [El SAMPLING UNSUCCESSFUL El ... STANDARD PENETRATION TEST U ... DRIVE SAMPLE (UNDISTURBED) SAMPLE SBOLS ... DISTURBED OR BAG SAMPLE fil ... CHUNK SAMPLE ... WATER TABLE OR SEEPAGE I NOTE: THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES. I PROJECT NO. 05466-12-01 >- w B ORING LB 3 z DEPTH SOIL SAMPLE NO. ELEV. (MSL.) 120 DATE COMPLETED 6/26/96 FEET CD EQUIPMENT E-120 BUCKET RIG 0 C.) MATERIAL DESCRIPTION - - 30 ____ - . ------------------------------------ - - Very hard, 'moist dark gray to greenish gray - 32 - CLAYSTONE from 30 feet CH - 34 - -Gypsum veinlets from 32 to 36 feet - -Concretionary bed 12 to 14 inches thick at 35 feet - 36 ______ .c. - - Interbedding with light green Silty SANDSTONE at 38 - • H-SM 36.5 and 38.5 feet - p -40- 'CH - - Concretionary bed-near refusal - boring terminated at 41.5 feet Figure A-4 Log of Boring LB 3, page 2 of 2 ORW 0 ... SAMPLING UNSUCCESSFUL 111 .. STANDARD PENETRATION TEST ... DRIVE SAMPLE (UNDISTURBED) SAMPLE SYMBOLS ... DISTURBED OR BAG SAMPLE ... CHUNK SAMPLE ... WATER TABLE OR SEEPAGE I NOTE: THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.