GEOTECHNICAL EXPLORATION FOR PROPOSED PAVEMENT IMPROVEMENTS, SIERRA MIDDLE SCHOOL, 4950 CENTRAL AVENUE, CITY OF RIVERSIDE, CALIFORNIA.

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1 GEOTECHNICAL EXPLORATION FOR PROPOSED PAVEMENT IMPROVEMENTS, SIERRA MIDDLE SCHOOL, 4950 CENTRAL AVENUE, CITY OF RIVERSIDE, CALIFORNIA Prepared for: RIVERSIDE UNIFIED SCHOOL DISTRICT 3070 Washington Street Riverside, California Project No September 6, 2018

2 September 6, 2018 Project No To: Attention: Subject: Riverside Unified School District 3070 Washington Street Riverside, California Mr. Daniel Rodriguez Geotechnical Exploration for Proposed Pavement Improvements, Sierra Middle School, 4950 Central Avenue, City of Riverside, California In response to your request, Leighton Consulting, Inc. (Leighton) is pleased to present this report of geotechnical exploration for proposed pavement improvements at Sierra Middle School, located at 4950 Central Avenue in the city of Riverside, California. The purpose of this exploration has been to evaluate the general geotechnical conditions in the area of the improvements and to provide geotechnical recommendations for design and construction. Project Description According to the overall revised site plan sheet no. AS-1 and overall demolition plan sheet no. AS-2 prepared by tbp Architecture dated July 9, 2018, the improvements at Sierra Middle School will include demolishing an approximate 22,000 SF grass area and walkway located on the north side of the property and replacing it with an asphalt parking lot. The existing pavement and planters between buildings 200 and 300A (approximately 6,200 SF) are also planned to be removed and replaced with new asphalt pavement.

3 Purpose and Scope of Work The purpose of this exploration has been to evaluate the general geotechnical conditions in the area of the improvements and provide geotechnical recommendations for design and construction. Our work included the following tasks: Document Review - We reviewed readily available geotechnical literature, maps, and historical aerial photographs relevant to the planned improvements. Utility Clearance - We coordinated with Underground Service Alert (USA) to have existing underground utilities located and marked prior to our subsurface investigation. Field Exploration Two hand auger borings were excavated to depths ranging from 5 to 6 feet below the ground surface. Representative bulk soil samples were collected from existing subgrade within the upper 3 feet. The borings were backfilled with soil cuttings. Approximate test locations are shown on the accompanying Test Location Map (Figure 1). Laboratory Tests - Laboratory tests were conducted on selected bulk soil samples obtained during our field investigation. The laboratory testing program was designed to evaluate engineering characteristics of the onsite soil. Laboratory tests conducted during this investigation include: - In-situ moisture content - Atterberg Limit - Sieve analyses for grain-size distribution Results of the laboratory tests are provided in Appendix B. Engineering Analysis - Data obtained from our background review and field exploration was evaluated and analyzed to provide geotechnical conclusions and preliminary recommendations presented in the following sections. Report Preparation - Results of our study have been summarized in this report, presenting our findings, conclusions and preliminary recommendations. 2

4 Subsurface Soil Conditions Based upon our subsurface exploration, the site is underlain by artificial fill and alluvial soil. Alluvial soils was observed at the surface in boring LB-1, while artificial fill extending to a depth of about 4 feet was observed in Boring LB-2. Soil in the upper 1 to 2 feet of both borings mostly consisted of silty sand and sandy silt. The lower 3 to 6 feet mostly consisted of sandy silt, silt with clay and silt with sand. According to the laboratory test results, soil moisture content was in the range of 5 to 7 percent by weight. More detailed descriptions of the subsurface conditions are presented on the boring logs in Appendix B. CONCLUSIONS AND RECOMMENDATIONS Fill Placement and Compaction Prior to placement of new pavement sections, the exposed subgrade soil should be scarified a minimum depth of 12 inches and recompacted to a minimum of 90 percent relative compaction. Aggregate base should be placed in thin lifts, moisture conditioned, as necessary, and compacted to a minimum of 95 percent relative compaction. The onsite soil is generally suitable for use as compacted structural fill. All fill materials should be free of clay lumps, organic material, and debris and should not contain rocks larger than 6 inches in greatest dimension. Any soil to be placed as fill, whether onsite or import material, should be accepted by the geotechnical consultant. All fill soil should be placed in thin, loose lifts, moisture conditioned (moistened or dried) to, or slightly above, optimum moisture content, and compacted to 90 percent relative compaction as determined by ASTM Test Method D1557. Aggregate base should be compacted to a minimum of 95 percent relative compaction. Asphalt Pavement Section Design Based on the design procedures outlined in the current Caltrans Highway Design Manual, and using an assumed design R-value of 45 for compacted subgrade soils, preliminary flexible pavement sections may consist of the following for the Traffic Indices (TI) indicated. 3

5 Table 1 - Asphalt Pavement Section Thickness Traffic Index Asphaltic Concrete (AC) Thickness (inches) Class 2 Aggregate Base (AB) Thickness (inches) 5 or less (auto access) (bus/truck access) 4 6 Paving Materials Asphalt concrete, PCC and aggregate base should conform to Caltrans Standard Specifications (2015 Edition) or the Standard Specifications for Public Works Construction (Green Book), 2015 Edition, as listed below: Asphalt Concrete (AC): AC, or more specifically, Hot Mix Asphalt Concrete (HMAC) pavement should be Type B and should conform to Section 39 of the Caltrans Standard Specifications. As an alternative, asphalt concrete can conform to Section of the Standard Specifications for Public Works Construction (Greenbook), 2015 Edition. Aggregate Base (AB): Aggregate base should conform to Section A of the Caltrans Standard Specifications for Class 2 aggregate base. As an alternative, crushed aggregate base or crushed miscellaneous base should conform to Sections and of the Standard Specifications for Public Works Construction (Greenbook), 2015 Edition, respectively. Field observations and periodic testing, as needed during placement of the base course materials, should be undertaken to ensure that the requirements of the standard specifications are fulfilled. Prior to placement of base, the subgrade soil should be processed to a minimum depth of 12 inches, moisture-conditioned as necessary, and compacted to a minimum of 90 percent relative compaction. Base should be moisture conditioned as necessary and compacted to a minimum of 95 percent relative compaction. If full depth AC on subgrade (no aggregate base) pavement option is chosen, the subgrade soils should be compacted to a minimum of 95 percent relative compaction to a minimum depth of 12 inches. 4

6 Surface Drainage Irrigation of landscaping should be controlled to maintain, as much as possible, consistent moisture content sufficient to provide healthy plant growth without overwatering. Irrigation should not be allowed to drain onto the pavement, as this can significantly reduce the service life of the pavement. 5

7 LIMITATIONS This report was based in part on data obtained from a limited number of observations, site visits, soil excavations, samples, and tests. Such information is, by necessity, incomplete. The nature of many sites is such that differing soil or geologic conditions can be present within small distances and under varying climatic conditions. Changes in subsurface conditions can and do occur over time. Therefore, our findings, conclusions, and recommendations presented in this report are based on the assumption that Leighton Consulting, Inc. will provide geotechnical observation and testing during construction. This report was prepared for the sole use of the Riverside Unified School District for application to the design of the proposed parking lot improvements project in accordance with generally accepted geotechnical engineering practices at this time in California. We appreciate the opportunity to work with you on this project. If you have any questions, or if we can be of further service, please call us at your convenience at (909) Respectfully submitted, LEIGHTON CONSULTING, INC. SD/LP/JDH/rsm Distribution: (1) Addressee Figure 1 Site Location Map Figure 2 Test Location Map Appendix A References Appendix B Field Explorations Appendix C Geotechnical Laboratory Test Results Jason D. Hertzberg, GE 2711 Principal Engineer 6

8 Approximate Site Boundary ³ 0 2,000 4,000 Feet Project: Scale: 1 " = 2,000 ' Base Map: ESRI ArcGIS Online 2018 Thematic Information: Leighton Author: Leighton Geomatics (btran) Eng/Geol: JDH Date: August 2018 SITE LOCATION MAP Sierra Middle School 4950 Central Avenue City of Riverside, California Figure 1 Leighton Map Saved as V:\Drafting\11988\006\Maps\ _F01_SLM_ mxd on 8/6/2018 8:56:56 AM

9 Legend &< Approximate Boring Location Approximate Site Boundary ³ Feet Project: Scale: 1 " = 200 ' Base Map: ESRI ArcGIS Online 2018 Thematic Information: Leighton Author: Leighton Geomatics (btran) Eng/Geol: JDH Date: August 2018 Map Saved as V:\Drafting\11988\006\Maps\ _F02_GM_ mxd on 8/6/2018 9:05:50 AM GEOTECHNICAL MAP Sierra Middle School 4950 Central Avenue City of Riverside, California Figure 2 Leighton

10 APPENDIX A References

11 References Asphalt Institute, 2000, Asphalt Overlays for Highway and Street Rehabilitation, Manual Series No. 17 (MS-17). Caltrans, 2001, Flexible Pavement Rehabilitation Manual, revised June 6, Caltrans, 2015, Highway Design Manual, Chapters Caltrans, 2015, Standard Specifications, Division IV and V, Chapters Morton, D.M., Miller, F.K., 2006, Geologic Map of the San Bernardino and Santa Ana 30 X60 Quadrangles, California: U.S. Geological Survey, Open File Report , scale 1:100,000. Public Works Standard, Inc., 2015, Greenbook, Standard Specifications for Public Works Construction: BNI Building News, Anaheim, California.

12 APPENDIX B Field Exploration

13 APPENDIX B FIELD EXPLORATION The field investigation was conducted on July 26, 2018, and consisted of surface reconnaissance and subsurface exploration. Encountered soils were logged in the field by our representative and described in accordance with the Unified Soil Classification System (ASTM D 2488). A total of two borings were conducted at representative locations. Bulk samples of representative soil types were obtained from existing subgrade. These samples were transported to our geotechnical laboratory for evaluation and appropriate testing. Borings were backfilled with the excavated earth materials after logging and sampling were completed. The attached subsurface logs and related information depict subsurface conditions only at the locations indicated and at the particular date designated on the logs. Subsurface conditions at other locations may differ from conditions occurring at these locations. The passage of time may result in altered subsurface conditions due to environmental changes. In addition, any stratification lines on the logs represent the approximate boundary between soil types and the transition may be gradual. B-1

14 BORING LOG LB-1 Project No. Project Drilling Co RUSD Sierra MS Leighton Date Drilled Logged By Hole Diameter BER 3" Drilling Method Hand Auger Ground Elevation 796' Location Grass area north side of school against central avenue Sampled By BER Elevation Feet 795 Depth Feet 0 N Graphic Log S Attitudes Sample No. B1 Blows Per 6 Inches Dry Density pcf Moisture Content, % Soil Class. (U.S.C.S.) CL-ML SOIL DESCRIPTION This Soil Description applies only to a location of the exploration at the time of sampling. Subsurface conditions may differ at other locations and may change with time. The description is a simplification of the actual conditions encountered. Transitions between soil types may be grass Alluvium SILTY CLAY, medium, dark brown, moist, low plasticity, 57% fines, fine grained sand, trace SANDY SILT, dense, reddish brown, moist Type of Tests -200, AL SANDY SILT, dense, brown, slightly moist, nonplastic, 25% fine to medium sand (field estimate) 790 Same, increase in sand content, 35-40% fines (field estimate), becomes moist with trace clay Total depth of 6 feet No groundwater encountered Backfilled with spoils and sand, tamped, capped with grass patch on SAMPLE TYPES: TYPE OF TESTS: B BULK SAMPLE -200 % FINES PASSING DS DIRECT SHEAR C CORE SAMPLE AL ATTERBERG LIMITS EI EXPANSION INDEX G GRAB SAMPLE CN CONSOLIDATION H HYDROMETER R RING SAMPLE CO COLLAPSE MD MAXIMUM DENSITY S SPLIT SPOON SAMPLE CR CORROSION PP POCKET PENETROMETER T TUBE SAMPLE CU UNDRAINED TRIAXIAL RV R VALUE SA SIEVE ANALYSIS SE SAND EQUIVALENT SG SPECIFIC GRAVITY UC UNCONFINED COMPRESSIVE STRENGTH * * * This log is a part of a report by Leighton and should not be used as a stand-alone document. * * * Page 1 of 1

15 BORING LOG LB-2 Project No. Project Drilling Co RUSD Sierra MS Leighton Date Drilled Logged By Hole Diameter BER 3" Drilling Method Hand Auger Ground Elevation 799' Location Between building 200 and 300A Sampled By BER Elevation Feet Depth Feet 0 N Graphic Log S Attitudes Sample No. B1 Blows Per 6 Inches Dry Density pcf Moisture Content, % Soil Class. (U.S.C.S.) CL-ML SM SOIL DESCRIPTION This Soil Description applies only to a location of the exploration at the time of sampling. Subsurface conditions may differ at other locations and may change with time. The description is a simplification of the actual conditions encountered. Transitions between soil types may be grass Artificial Fill SILTY CLAY, moderately dense, dark brown, moist, nonplastic, 20% sand, medium SILTY SAND, dense, brown, moist, medium to coarse grained, 1/4" average gravel size Type of Tests Sieve ' Same, trace fines added to soil, more cohesive Alluvium SILTY SAND with clay, moderately dense, dark brown, moist, low plasticity, 20% sand (field estimate), 5-10% clay (field SILT with sand, dense, reddish brown, moist, nonplastic, 5-10% sand Total Depth of 5.3 feet No groundwater encountered Backfilled with spoils and tamped on SAMPLE TYPES: TYPE OF TESTS: B BULK SAMPLE -200 % FINES PASSING DS DIRECT SHEAR C CORE SAMPLE AL ATTERBERG LIMITS EI EXPANSION INDEX G GRAB SAMPLE CN CONSOLIDATION H HYDROMETER R RING SAMPLE CO COLLAPSE MD MAXIMUM DENSITY S SPLIT SPOON SAMPLE CR CORROSION PP POCKET PENETROMETER T TUBE SAMPLE CU UNDRAINED TRIAXIAL RV R VALUE SA SIEVE ANALYSIS SE SAND EQUIVALENT SG SPECIFIC GRAVITY UC UNCONFINED COMPRESSIVE STRENGTH * * * This log is a part of a report by Leighton and should not be used as a stand-alone document. * * * Page 1 of 1

16 APPENDIX C Geotechnical Laboratory Test Results

17 Moisture Content ASTM D 2216 Project Name: RUSD/Sierra MS Geo Tested By: M. Vinet Project No. : Date: 7/30/2018 Container Number: 123 SR-71 Sample Type: Boring No.: BULK LB-1 BULK LB-2 Sample No.: Depth: (ft.) B-1 B Soil Type: s(cl-ml) SM Moisture Content (%) Wt. Wet Soil+Container (g) Wt. Dry Soil+Container (g) Weight Container (g)

18 PARTICLE-SIZE DISTRIBUTION (GRADATION) of SOILS USING SIEVE ANALYSIS ASTM D 6913 Project Name: RUSD/Sierra MS Geo Tested By: MRV Date: 08/01/18 Project No.: Checked By: MRV Date: 08/02/18 Boring No.: LB-2 Depth (feet): Sample No.: B-1 Soil Identification: Silty Sand (SM), Brown Container No.: Wt. of Air-Dried Soil + Cont.(g) Wt. of Container (g) Dry Wt. of Soil (g) Moisture Content of Total Air - Dry Soil SR Wt. of Air-Dry Soil + Cont. (g) Wt. of Dry Soil + Cont. (g) Wt. of Container No. (g) Moisture Content (%) 5.3 After Wet Sieve Container No. Wt. of Dry Soil + Container (g) Wt. of Container (g) Dry Wt. of Soil Retained on # 200 Sieve (g) SR U. S. Sieve Size Cumulative Weight (in.) (mm.) Dry Soil Retained (g) Percent Passing (%) 3" " /4" /2" /8" # # # # # # # PAN GRAVEL: 7 % SAND: 73 % FINES: 20 % GROUP SYMBOL: SM Cu = D60/D10 = Cc = (D30)²/(D60*D10) = N/A N/A Remarks:

19 Boring No. Sample No. Depth (ft.) Sample Type LB-1 B BULK Visual Soil Classification s(cl-ml) Moisture Correction Wet Weight of Soil + Container Dry Weight of Soil + Container (gm.) (gm.) Weight of Container Moisture Content (%) Container No.: (gm) Sample Dry Weight Determination Weight of Sample + Container (gm.) Weight of Container (gm.) Weight of Dry Sample (gm.) Container No.: After Wash Dry Weight of Sample + Container (gm) Weight of Container (gm) Dry Weight of Sample (gm) % Passing No. 200 Sieve % Retained No. 200 Sieve PERCENT PASSING No. 200 SIEVE ASTM D Project Name: RUSD/Sierra MS Geo Project No.: Client Name: Riverside Unified School District Tested By: M. Vinet Date: 8/1/18 Rev Wash; LB-1, B-1 ( )

20 Moisture Content (%) Plasticity Index (PI) ATTERBERG LIMITS ASTM D 4318 Project Name: RUSD/Sierra MS Geo Tested By: M. Vinet Date: 8/2/18 Project No. : Input By: M. Vinet Date: 8/2/18 Boring No.: LB-1 Checked By: M. Vinet Date: 8/2/18 Sample No.: B-1 Depth (ft.) Sample Description: Sandy Silty Clay s(clml), Brown. TEST NO. Number of Blows [N] Wet Wt. of Soil + Cont. (gm) Dry Wt. of Soil + Cont. (gm) Wt. of Container (gm) Moisture Content (%) [Wn] PLASTIC LIMIT LIQUID LIMIT **IN-SITU MOISTURE Liquid Limit 25 Plastic Limit 19 Plasticity Index 6 Classification CL-ML PI at "A" - Line = 0.73(LL-20) = 3.65 One - Point Liquid Limit Calculation LL =Wn(N/25) For classification of finegrained soils and finegrained fraction of coarse-grained soils CL-ML CL or OL ML or OL CH or OH "A" Line MH or OH PROCEDURES USED Wet Preparation Multipoint - Wet X Dry Preparation Multipoint - Dry X Procedure A Multipoint Test Procedure B One-point Test Liquid Limit (LL) Number of Blows Rev