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HomeMy WebLinkAbout; Monroe St Extension Woodridge; Soils Report; 1981-04-07GEOTECHNICAL INVESTIGATION MONROE STREET EXTENSION WOODRIDGE SUBDIVISION CARLSBAD, CALIFORNIA Prepared For Broadmoor Homes, Inc. 3911 Sorrento Valley Boulevard Suite B San Diego, California 92111 WMERING DfP7: ll8AARY City of Carlsbad 2075 Las Palms Drive CaWa4 CA 92009-4859 -_ 3467 Kurtr Streel San DIego, Calllornia 92110 714-224~2!311 Telex 697-84, Woodward=Clyde Consultants April 7, 1981 Project No. 592073-SI02 Broadmoor Homes, Inc. 3911 Sorrento' Valley Boulevard Suite B San Diego, California 92111 Attention: Mr. James Carter GEOTECHNICAL INVESTIGATION MONROE STREET EXTENSION WOODRIDGE SUBDIVISION CARLSBAD, CALIFORNIA Gentlemen: We are pleased to present the results of our geotechnical investigation for the subject project. This report presents our conclusions and recommendations pertaining to the project as well as the results of our field explorations and laboratory tests. Our geologist assigned to this project is Mr. Robert J. Dowlen. If you have any questions, or if we can be of further service please call. Very truly yours, WOODWARD-CLYDE CONSULTANTS Richard P. While R.E. 21992 RPW/RJD/kb/pr Attachments (6) Broadmoor Homes, Inc. (3) Roy L. Klema Engineering Consulting Engineers. Geclog~sts and Environmenral Scienr~srs onices I” Other Principal c,tes Project No. 592073-SI02 WoodwardGyde Consultants TABLE OF CONTENTS DESCRIPTION OF TI-IE PROJECT FIELD AND LABORATORY INVESTIGATION SITE, SOIL AND GEOLOGIC CONDITIONS Topography and Surface Conditions Subsurface Conditions Fill Soils Alluvium Bay Deposits Fornational Soils STRUCUTRE AND FAULTING LANDSLIDES GROUND WATER DISCUSSIONS, CONCLUSIONS AND RECOMMENDATIONS Faulting and Ground Breakage Landslides Ground Water Slopes .Excavation and Soil Characteristics Grading RISK AND OTHER CONSIDERATIONS 10 APPENDIX A - FIELD INVESTIGATION A-l APPENDIX B - Cut and Fill Slopes B-l Page 2 2 5 5 6 6 ii Woodward-Clyde Consultants GEOTECHNICAL INVESTIGATION MONROE STREET EXTENSION WOODRIDGE SUBDIVISION, CARLSBAD, CALIFORNIA This report presents the results of our geotechnical investigation for the proposed improvement of Monroe Street between Marron Road and the existing end of Monroe Street within the Woodridge Unit 5 subdivision in the City of Carlsbad, California. The purpose of our study is to assist Broadmoor Homes, Inc. and their consultants in evaluating the project and in project design. This report presents our conclusions and/or recommendations regarding: 0 General subsurface soils and geologic conditions, 0 Potential geologic hazards, 0 Conditions of areas to receive fill, 0 Suitability of existing fill soils, 0 Suitability of proposed fill material, and 0 General grading recommendations. Project No. 592073-SI02 Woodward43yde Consultants DESCRIPTION OF THE PROJECT For our study, we have discussed the project with Mr. James Carter of Broadmoor Homes, Inc., and we have reviewed the following plans and reports. 0 "Soil Investigation for the Proposed Hosp Grove Development, Carlsbad, California," prepared by Woodward-Clyde &Associates, dated April 13, 1968. 0 lVSoil and Geologic Investigation for the Proposed Carlsbad Tract No. CT 77-2, Planned Unit Development No. 8, Hosp Grove, Carlsbad, California," prepared by Woodward-Clyde Consultants, dated July 19, 1979. 0 "Plans and Profiles for Street, Sewer, Water and Drainage Improvements in Monroe Street," prepared by Roy L. Klema Engineering, dated February 14, 1980. Grading plans are not available to date, however, improvement plans indicate that grading will be minor with cuts and fills on the order of 10 feet maximum and cut and fill slopes having maximum heights of less than 10 feet and maximum slope inclinations of 2 to 1. FIELD AND LABORATORY INVESTIGATION The current field investigation was performed on March 24, 1981 and included, making a visual geologic recon- naissance of existing surface.conditions, making five backhoe test pits and obtaining representative soil samples. The backhoe test pits were advanced to depths ranging from 7-S/2 to 11 feet below existing ground surface. The .locations of 2 Project No. 592073-SI02 Woodward-Clyde Consultants the test pits are 'referenced to station numbers on the proposed Monroe Street as presented in the aforementioned improvement plans. A Key to Logs is presented in Appendix A as Fig. A-l. Simplified logs of the test pits are presented in Appendix A as Figs. A-2 through A-4. Descriptions on the logs are based on field logs and sample inspection. The field investigation program is discussed in Appendix A. SITE, SOIL AND GEOLOGIC CONDITIONS Topography and Surface Conditions The proposed roadway alignment is in a north trending drainage in the Woodridge area of Carlsbad, California. The alignment is relatively flat, sloping gently toward the north. Elevations at the site range from approxi- mately 90 feet (MSLD) at the southern end of the alignment to a low of approximately 21 feet at the northern end of the alignment. Small groves of eucalyptus trees are present at various locations along the alignment. An existing stream channel is present along the western border of the proposed alignment. The northern ap- proximately 300 feet of this channel has been rock lined for erosion protection. An existing siltation basin is present westerly of the proposed alignment in the extreme'northern end of the project. 3 Project No. 592073-SI02 WoodwarxbClyde Consultants The improvement plans indicate that an existing &inch diameter ESVCP sewer line and an existing 12-inch diameter ACP water line are present within the alignment and extend the full length of the alignment. At the extreme southern end of the roadway there is a concrete headwall and rock riprap. The improvement plans indicate these structures will be removed. Subsurface Conditions The proposed street alignment is underlain by fill soils, alluvial soils, bay deposit soils and formational soils. These units are described below in general order of increasing age. Fill Soils - Undocumented fill soils, composed of silty and clayey sands and sandy clays, are present over the entire length of the proposed roadway alignment. The test pits indicate that the fill has maximum observed thicknesses on the order of 7 feet with an average on the order of 3 feet. Alluvium - The alluvial soils consist of loose to medium dense, silty to clayey sand. Test Pits 1, 2 and 3 did not extend through the alluvial soils. In the area of Test Pits 1 through 3, an examination of the existing channel westerly of the proposed roadway indicates that the alluvial soils are in excess of 20 feetin depth. 4 Project No. 592073-SI02 Woodward-Clyde Consultants Bay Deposits - The field work performed for the 1968 soil investigation indicates that loose silty to clayey sands and soft sandy clays are present in the extreme northern end of the proposed roadway alignment and extend out to the old bay area north of Marron Road. Based on our review of the 1968 report, we estimate that the bay deposit materials extend to approximate Station 41 on the proposed roadway alignment. Formational Soils - Dense to very dense silty to clayey sand characteristic of the materials of the Eocene age Santiago Formation were encountered beneath the fill soils in Test Pits 4 and 5 in the southern portion of the proposed roadway alignment. STRUCTURE AND FAULTING The formational soils are essentially horizontally stratified, dipping slightly to the west-southwest in general accordance with the regional dip. No faulting was identified on the site during the current field reconnaissance. LANDSLIDES Our field reconnaissance did not indicate the presence of landslides within the proposed roadway alignment. However, ancient landslide planes are present in the hillsides southwest of the proposed roadway extension. 'A weak clay 5 Project No. 592073-SI02 Woodward-Clyde Consultants seam, indicative of ancient landsliding, was noted in the existing road cut for Marron Road immediately east of the proposed alignment. GROUND WATER No ground water was encountered in any of the test excavations. A minor amount of surface flow was present in the drainage bottom at the time of the investigation. DISCUSSIONS, CONCLUSIONS AND RECOMMENDATIONS The discussions, conclusions and recommendations presented in this report are based on the results of our field studies, analyses and professional judgment. Faulting and Ground Breakage Our review of the July 19, 1979 field investigation report indicates that a northeast-southwest trending fault was identified in a natural erosional exposure in the northwestern part of the subdivision and crosses the southern part of the proposed roadway. The fault was observed to offset the Santiago Formation materials, several feet and offset of a few inches was observed in the Pleistocene age terrace deposits. In our opinion, the fault should not be a constraint to the construction of the roadway. 6 Project No. 592073-s102 Woodward-Clyde Consultants The fault closest to the site that has historically generated earthquakes greater than magnitude 4 is the Elsinore Fault Zone located approximately 23 miles northeasterly of the site. The major faulting closest to the site is within the offshore zone of deformation located about 4 miles offshore from Carlsbad. Faulting in general is not considered a con- straint to the proposed project. Landslides No landslides or features that can be construed as landslides were observed or are known to exist within the proposed alignment. Mass slumping has been defined within the terrace deposits in the hillsides southwesterly of the site. Weak clay seams were noted in the roads cut for Marron Road immediately east of the intersection of Monroe Street and Marron Road. We understand that up to 8 feet of fill will be placed in the northern part of the alignment. We do not anticipate that the weak clay seams will have a detrimental effect on the proposed construction. Ground Water No ground water wasencountered in any of the test excavations nor were any water seeps noted. There is, however, a minor flow of surface water within the drainage bottom. This flow is expected to increase in',, the winter 7 Project No. 592073-SI02 Woodward-Clyde Consultants season and ground water may be present in the alluvial soils during the wet season. We recommend that drainage waters on the roadway be directed off the street away from slopes and into storm drains. Slopes We have performed stability analyses for the antici- pated fill slopes by the Jar&u Method using soil parameters developed during the field investigation for the Woodridge subdivison. The results of our analysis indicate that the proposed cut and fill slopes will have calculated factors of safety in excess of 1.5 for static conditions. Calculations are attached (Appendix B). Stability analyses require the use of parameters selected from a range of possible values. Thus, there is a finite possibility that slopes having calculated factors of safety as indicated could become unstable. In our opinion, the probability of the slopes becoming unstable is low and it is our professional judgment that the slopes can be constructed. We recommend that fill slopes be backrolled at maximum 4-foot fill height intervals. Additionally, we recom- mend that all fill slopes be trackwalked upon completion so that a dozer track covers all surfaces at least twice. _~ 8 Project No. 592073-SI02 Woodward-Clyde Consultants We recommend that an engineering geologist from our firm inspect all cut slopes during grading to evaluate actual geologic conditions. We also recommend that the geologist inspect the road cut for Marron Road immediately east of the site. - Excavation and Soil Characteristics The soils on the site range from the highly ex- pansive clays within the existing fill soils and alluvial soils to the nonexpansive silty sands of the alluvial soils, fill and formational soils. Based on the results of our field investigation, in our opinion, all materials on the site can be excavated with light to moderate effort with heavy duty excavation equipment. Grading We recommend that all earthwork be done in accor- dance with the attached Specifications for Controlled Fill (Appendix B). We further recommend that all grading be observed by and the compacted fills be tested by Woodward- Clyde Consultants. We recommend that, a preconstruction conference be held at the site with the owner or developer, civil engineer, contractor and geotechnical engineer in attendance. Questions regarding special soil handling or the grading plans can be discussed at that time. I_ 9 Project No. 592073-SI02 Woodward-Clyde Consultants We recommend that the grading plans be submitted to Woodward-Clyde Consultants for review prior to final&zing. We recommend that all loose fill soils in the pro- posed roadway alignment be excavated, any perishable materials removed, and then the soil compacted at the proper water content. We also recommend that-the upper 5 feet of the allu- vial soil be excavated, the material be watered and dried as required, and then properly compacted prior to placing addi- tional fill. We recommend that the actual depth of excavation be evaluated in the field by the geotechnical engineers' representative at the time of grading. We anticipate that some settlement of the roadway will occur where the roadway is underlain by alluvial and bay deposit soils. We anticipate that maximum settlements will be on the order of 6 to 12 inches. RISK AND OTHER CONSIDERATIONS We have only observed a small portion of the per- tinent soil conditions. The recommendations made herein are based on the assumption that soil conditions do not deviate appreciably from those found during our field investigation. If the plans for site development are changed, or if varia- tions or undesirable geotechnical conditions are encountered during construction, the geotechnical consultant should_ be consulted for further recommendations. '_ 10 Project No. 592073-s102 Woodward-Clyde Consultants We recommend that the geotechnical consultant review the grading plans to verify that the intent of the recommen- dations presented herein has been properly interpreted and incorporated into the contract documents. We further recom- mend that the geotechnical consultant observe the site grading and subgrade preparation under paved areas. It should also be understood that California, including San Diego, is an area of high seismic risk. It is generally considered economically unfeasible to build totally earthquake resistant structures; therefore, it is possible that a large or nearby earthquake could cause damage at the site. Professional judgments presented herein are based partly on our evaluations of the : technical information gathered, partly on our understanding of the proposed con- struction, and partly on our general experience in the geo- technical field. Our engineering work and judgments rendered meet current professional standards. We do not guarantee the performance of the project in any respect. This firm does not practice or consult in the field of safety engineering. We. do not direct the contractor's operations, and we cannot be.. responsible for the safety of other than our own personnel on the site; therefore, the safety of others is the responsibility of the contractor. The contractor should notify the owner if he considers any of the recommended actions presented herein to be unsafe. 11 Project No. 592073-SI02 Woodward-Clyde Consultants APPENDIX A FIELD INVESTIGATION Five exploratory pits were advanced at the approxi- mate locations indicated by the Station numbers on the logs. The excavations were performed by personnel from our firm on March 24, 1981 using a 24-inch wide tractor mounted backhoe. Samples of the subsurface materials were obtained from the excavations, sealed to preserve the natural moisture content of the sample, and returned to the laboratory for examination and testing. The location of each excavation and the elevation of the ground surface at each location were estimated -from the improvement plans. A-l Location Boring Number Elevation SAMPLE IUMBER I SOIL DESCRIPTION -d I Very dense, damp, brown silty sand (SM) 1 65 1 2 WATER LEVEL J At time Of drilling or as inclicared. SOIL CLASSIFICATION - soil Clerrificationr are bared an the ““i‘ied soil Clarrlflcation S”lmn an-3 include cdor. moill”W and conrirtancy. Field dercrlptionl have been mcdified to ret,ect re.“lt* 0‘ kboratcwy ana,yrrr where Ipp,Op,iste. DISTURBED SAMPLE LOCATION Obtained by collecting the auger cut,iNJs in a pl.lfiE or Cloth bag. - DRIVE SAMPLE LOCATION MODIFIED CALIPDRNIA SAMPLER SamPls with recorded blow per toot was obtsine.3 With * Modi‘led California *rive Ylmpler 12” inside diamte,. 2.5” rJ”,lide chmter~ lined with sample tuber. The rampIer was driven into the IDi, *t the bottom 01 the hole v&l a 140 PO”nd hammer f*lhng 30 indler. INDICATES SAMPLE TESTED FOR OTHER PROPERTIES GS- Grain size Dirtribution CT - Conrolidatlo” TR, LC - l.aborator” COmpaction “cs - “nconflned comprcrllo” -rest Tert PI - Atterberg Limits Tea ST - Loaded Swell Test cc - Confined Comprerrion Test DS - Direct Shear Test TX- Trmrial Compre.lio” TN NOTE: I” this col”rn” the rew,ts 0‘ these tells may be recorded where applicable. BLOW COUNT Number cd tmrrr needed to advance sampler one ‘0.X or as i”dKaed. DRY DENSITY Pounds per Cubic Foot .MOlSTURE CONTENT Percent Of Dry Weight NOTESON FIELD INVESTIGATION 1. REFUSAL indiutn th* inability to sxtmd excav*tion. practically, with eqq~ipmnt being usad in th* invertigation. I KEY TO LOGS I MONROE STREET EXTENSION DRAW,,W:ch 1 C”ECKEDElY:,A~~,RD.,ECTNO: 592073-SIO2 1 DATE: 4-6-81 I WGURE NO: A-1 WOODWARD-CLYDE CONSULTANTS Test Pit 1 STATION 39+00 West Of Centerline - TDE - ‘DD - - OTHER rESlS iAMPLE IUMBER .-l c .-2 c STATION 36+50 West of Centerline 1 DE Plw TES IN FEET l MC ’ TO1 LTA - -r ‘DD - - 5- 10 1 15 -I r L ‘BC -I- 0, 1 f 3THER SAMPLE rESTS N-ER 2-l 2-3 [ I 2-2 t 2-4 C SOIL DESCRIPTION Damp, brown, silty to clayey sand FILL Medium dense, moist, brown to dark broth, silty medium sand (SM) ALLUVIUM Bottom of Hole Test Pit 2 SOIL DESCRIPTION Damp, brown, silty to clayey sand \ FILL Medium dense, moist, yellowish brown, silty \ sand (SM) with gravels ALLWIUM Medium dense, moist, dark brown, silty sand (SM); porous ALLUVIUM Bottom of Hole *FW c~srription of rymbo,,. SW ~ipur. A-1 DRAWNSY: ch LOG OF TEST PITS 1 AND 2 MONROE STREET EXTENSION PRDJECTND: 592073-SIO2 DATE: 4-6-81 FlDURE No:~,-2 WOODWARD-CLYDE CONSULTANTS Test Pit 3 STATION 34+40 East of Centerline DEPTH IN - 5: lo- 157 iAMPLE IUMBER 3-l C 3-2 c 3-3 c SOIL DESCRIPTION Damp, brown, silty to clayey sand FILL Medium dense, moist, light reddish brown, clayey sand (SC) ALLWIUM Loose, dark brown, silty sand (SM) ALLWIUM Medium dense, moist, light reddish brown, silty to clayey sand (SM-SC) ALLUVIUM Bottom Of Hole -~ord.wiption o‘r,mbok.se, ~&w. A-l LOG OF TEST PIT 3 MONROE STREET EXTENSION DRAWNBY: ch C"ECIED sv:mc PROJECTNO: 5920~73-SI02 DATE: 4-b-81 F,D”RE 110: A-3 WOOOWARO-CLYOE CONSULTANTS STATION 32+00 Centerline 10 1 15 STATION 5: 10 - 15 1 TDP Gr - - t80 - iT Dd - ‘DD - - h - WC - - 3st - BC - - - DTHEI rE!SlS - - ,f ce DT”Ef 7Esr.s T R s N 4 iAMPLE IVMBEF terlin SAMFtE NUMBER 5-1 c 5-2 1 Test Pit 4 SOIL DESCRIPTION lamp, brown, silty to clayey sand FILL dense, moist, light reddish brown, clayey to silty sand (SM-SC) SANTIAGO FORMATION Bottom Of Hole Test Pit.5 SOIL DESCRIPTION 1 Damp, brown, silty to clayey sand FILL Dense.to very dense, moikt, yellowish brown, silty. sand (SM) SANTIAGO FORMATION .~ Bottom Of Hole *For delcfiption 0‘ l”mboll, L. Figure A-l T LOG OF TEST PITS 4 AND 5 MONROE STREET EXTENSION DRAWN BY: ch C”ECKED BY: rJ\ PRDJECTNO: 592073-SIO2 FIGURE ND: A-4 WOOOWARO-CLYDE CONSULTANTS Project No. 592073-SI02 Appendix B cut and Fill Slopes AssumptiOnS: (1) Maximum height of slopes (2) Maximum slope inc+lnatlOn (3) Unit weight of sol1 (4) Apparent angle of internal fr+r.tion LA1 (5) Apparent cohesion H= 10 ft. 2 to 1 Y = 120 pcf 4= 30" c = 300 psf (6) No seepage forces References: (1) Janbu, N., "Stability Analysis of Slopes with Dimensionless Parameters," Harvard Soil Mechanics Series No. 46, 1954. (2) Janbu, N., "Dimensionless Parameters for Homogeneous Earth Slopes," JSMFD, NO. SM6, November 1967. Analyses: Safety Factor, F.S. = Ncf c Where 'N - cf is the stability YH number for slopes with both c and@. ‘I A cf = yH z;"" 4 =2.3 bxvn Fig. P.S. = 3.2 10 of Reference (2) Ncf = 13