DRAFT GEOTECHNICAL INVESTIGATION REPORT

Transcription

1 DRAFT GEOTECHNICAL INVESTIGATION REPORT PROPOSED NEW SEWER INSTALLATION CITY OF CLARENCE-ROCKLAND, ONTARIO Prepared for: City of Clarence-Rockland Date: July 2015 WSP Canada Inc. 500 Greber Blvd, 3 rd Floor Gatineau (Quebec) J8T 7W3 Phone: Fax:

2 July 28, 2015 Mr. Yves Rouselle, CET Assistant Director Infrastructure and Engineering City of Clarence-Rockland 415 Lemay St. Clarence Creek, ON K0A 1N0 Subject: Geotechnical Investigation Report New Sewer Installation, Morris Street, City of Clarence-Rockland, Ontario Dear Mr. Rouselle: We are pleased to submit our geotechnical investigation report for the above-noted project. A field investigation and laboratory testing program was conducted to assess soil and groundwater conditions at the site as input to design of the proposed new sewer installation. This report includes our geotechnical recommendations for the proposed sewer installation, a site plan with borehole layout, and results from our field and laboratory investigation. We trust that the report is straightforward and meets your current requirements. Please contact us if you have any questions. Yours truly, Chris Hendry, M.Eng., P.Eng. Sr. Geotechnical Engineer Director Environment, Eastern Ontario WSP Canada Inc. 500, Greber Blvd, 3rd Floor Gatineau (Québec) J8T 7W3 Phone: Fax:

3 T A B L E O F C O N T E N T S 1 INTRODUCTION Context Site Description Objectives and Limitations 1 2 SITE INVESTIGATION Desktop Study Field Investigation Laboratory Testing Program 3 3 SUBSURFACE GEOTECHNICAL CONDITIONS Topsoil Fill Sand and Silty Sand Organic Soil Silty Clay DCPT Refusal Groundwater 6

4 ii 4 RECOMMENDATIONS General Excavation and Dewatering Excavation Dewatering Frost Penetration and Frost Protection Seismic Site Classification Grade Raise Bedding Cover and Backfill Bedding and Embedment Cover Backfill Corrosion and Cement Type 10 5 GEOTECHNICAL PROJECT TEAM 11 A P P E N D I C E S Appendix A Appendix B Appendix C Drawings Borehole Logs Laboratory Testing Results

5 1 1 INTRODUCTION 1.1 CONTEXT SPL Consultants Limited (SPL) was retained by the City of Clarence-Rockland to conduct a geotechnical investigation as part the design and construction of a new sewer system connecting nine (9) townhouses to the city s public sewer system on Morris Street, in Clarence-Rockland, Ontario. The Terms of Reference (TOR) for this investigation are outlined in WSP s Proposal No. P dated April 1, 2015 and subsequent project correspondence. The purpose of the geotechnical investigation was to obtain subsurface information at the site by means of exploratory boreholes. This report presents the findings of the investigation and provides comments and recommendations related to the geotechnical aspects of the project. 1.2 SITE DESCRIPTION The site is located on Morris Street, approximately 130 m east of Lawrence Street, in the City of Clarence-Rockland, ON (see Figure No. 1). The site is located within the previously developed portion of the City, with low-rise residential development being present in the surrounding area. The site is relatively flat and is a combination of Morris Street (residential road) as well as the landscaped front lawns and driveways of the existing townhouse development. 1.3 OBJECTIVES AND LIMITATIONS The current report was prepared at the request and for the sole use of the City of Clarence-Rockland according to the specific terms of the mandate given to WSP. The use of this report by a third party, as well as any decision based upon this report, is under this party s sole responsibility. WSP may not be held accountable for any possible damages resulting from third party decisions based on this report. Furthermore, any opinions regarding conformity with laws and regulations expressed in this report are technical in nature; the report is not and shall not, in any case, be considered as a legal opinion. Information in this report is only valid for the borehole locations as described. Geotechnical Investigation Proposed Sewer Installation, Morris Street

6 3 2 SITE INVESTIGATION 2.1 DESKTOP STUDY Surficial geology maps indicate the area is underlain by alluvial deposits consisting of clay, silt, sand, gravel and organic remains overlying offshore marine deposits consisting of sensitive silty clay with minor sand deposits which overlies glacial till. Bedrock geology maps indicate the bedrock in the general area includes limestone, sandstone and shale of the Rockcliffe Formation. 2.2 FIELD INVESTIGATION The field investigation was carried out on April 27, 2015 and included the drilling of two boreholes (BH15-1 and BH15-2) near the proposed sewer alignment. The boreholes were advanced using a track-mounted drill rig supplied and operated by Forage Geo Inc. of Grenville, Quebec. Boreholes BH15-1 and BH15-2 were advanced using hollow-stem auger drilling to a maximum depth of 6.1 m below the existing road surface and extended using Dynamic Cone Penetration Testing (DCPT) to a depth of up to 12.4 m below the existing road surface. The soil samples retrieved during drilling were logged and visually classified in the field by a member of SPL s geotechnical staff. In-situ tests including Standard Penetration Testing (SPT) and shear vane testing were carried out at regular intervals. A monitoring well was installed in borehole BH15-2 to allow for subsequent measurement of stabilized groundwater levels and long-term groundwater monitoring at the site. The approximate borehole locations are shown in Drawing No. 2. The borehole logs are included in Appendix I of this report. 2.3 LABORATORY TESTING PROGRAM Upon completion of drilling and in-situ testing, soil samples were returned to SPL s laboratory for further examination, classification and testing. A laboratory testing program, which was carried out on selected representative soil samples included the determination of natural water content, grain size distribution, Atterberg limits (Plasticity) and chemical analyses of soil corrosivity. The results of natural water content tests are included on the relevant borehole logs in Appendix I. The results of determination of grain size distribution are summarized on the individual borehole logs and are presented in Appendix C. The results of Atterberg limits (plasticity) testing are summarized on the individual borehole logs and presented in Appendix C. Chemical testing to determine sulphate Geotechnical Investigation Proposed Sewer Installation, Morris Street

7 4 content, chloride content, ph and resistivity was also carried out on selected soil samples obtained during drilling. The results of these tests are included in Appendix C. Geotechnical Investigation Proposed Sewer Installation, Morris Street

8 5 3 SUBSURFACE GEOTECHNICAL CONDITIONS The subsurface soil profile at the site generally consists of a layer of topsoil and fill material, overlying a layer of silty sand and sand, below which is sensitive silty clay. 3.1 TOPSOIL 3.2 FILL Specific descriptions of individual geological units are presented below. A surficial layer of topsoil 225 mm in thickness was encountered in both boreholes (which were drilled on the lawns of the existing townhomes). Underlying the topsoil in boreholes BH15-1 and BH15-2 is a layer of fill which ranged in consistency from silty sand to silty clay. This layer extended to a depth of 1.2 m below the existing surface elevation in borehole BH15-1 and to a depth of 0.8 m below the existing surface elevation in borehole BH15-2. One standard penetration test was carried out within this layer of upper fill gave an SPT N value of 6 blows per 305 mm of penetration indicating a loose state of packing. 3.3 SAND AND SILTY SAND Underlying the fill in both boreholes is a layer of native sand and silty sand. Standard penetration tests carried out within this layer gave SPT N values which ranged from 3 to 18 blows per 305 mm of penetration indicating a very loose to compact consistency. This layer extended to a depth of 2.1 m below the existing ground surface in borehole BH15-1 and to a depth of 4.1 m below the existing ground surface in borehole BH15-2. A grain size distribution analyses from this unit is summarized below. Table 1 Results of Particle Size Analysis - Sand Borehole Sample No. Depth Interval (m below grade) BH15-2 SS Grain Size Distribution 8% gravel, 84% sand; 8% fines Description Sandy Silt 3.4 ORGANIC SOIL Underlying the native sand in borehole BH15-1 is a layer of organic soil. Standard penetration tests carried out within this layer gave SPT N values which ranged from the weight of the SPT hammer to Geotechnical Investigation Proposed Sewer Installation, Morris Street

9 6 3 blows per 305 mm of penetration. This layer extended to a depth of 4.9 m below the existing surface elevation in borehole BH15-1. This layer was not encountered in borehole BH15-2. A selected sample of this material was submitted for testing to determine the percent organic matter by mass which was found to be 20.1 percent. The natural water content within the organic soil ranged from 140 to 215 percent. 3.5 SILTY CLAY Underlying the silty sand in both boreholes is a layer of sensitive silty clay. This deposit generally consists of interlayered clay, silty clay and silt. Sand lenses may also be present. For simplicity this deposit is referred to in this report as silty clay (as this is the predominant soil type). The silty clay was proven through a combination of SPT sampling and shear vane testing to a depth of 6.1 m below the existing ground surface in borehole BH15-1 and to a depth of 5.5 m below the existing road surface in borehole BH15-2. In-situ soil strength was measured during drilling through a combination of SPT testing and in-situ shear vane testing at regular intervals. Standard penetration tests carried out within the silty clay gave SPT N values ranging from 1 to 2 blows for 305 mm of penetration. Shear vane testing within the silty clay deposit yielded shear strengths between 50 kpa and 90 kpa indicating a stiff to very stiff consistency. Atterberg Limits (plasticity) testing was carried out on two samples of silty clay, the results of which are summarized below. Table 2 Plasticity Test Results Silty Clay Borehole No. Sample No. Depth Interval (m below grade) Moisture Content (%) Liquid Limit (%) BH15-1 SS BH15-2 SS Plastic Limit (%) 28 Description High Plasticity Silty Clay 30 High Plasticity Silty Clay 3.6 DCPT REFUSAL Upon completion of augering, both boreholes were extended through Dynamic Cone Penetration (DCPT) Testing. In borehole BH15-1 DCPT refusal was encountered at 10.6 m below the existing ground surface. In borehole BH15-2 DCPT refusal was encountered at 12.4 m below the existing ground surface. 3.7 GROUNDWATER A monitoring well was installed in borehole BH15-2 during the field investigation. Stabilized groundwater levels were read on May 8 th and May 20 th, 2015 (11 and 23 days after drilling, respectively). Groundwater levels were found to be at 2.1 m below the ground surface on both occasions. Geotechnical Investigation Proposed Sewer Installation, Morris Street

10 7 It should be noted that the groundwater levels can vary and are subject to seasonal fluctuations as well as fluctuations in response to major weather events. 4 RECOMMENDATIONS 4.1 GENERAL It is understood that a new section of sewer will be installed to connect the existing townhouses to the existing City sewer system. It is understood that no significant changes will be made to the site grading. Based upon the borehole results the following geotechnical recommendations are provided. 4.2 EXCAVATION AND DEWATERING EXCAVATION Temporary excavations for typical sewer installations can be carried out using conventional hydraulic excavating equipment. Fill material can have, by its nature, a highly variable composition and could contain obstructions not encountered in the boreholes drilled at the site. All excavations should be carried out in accordance with the most recent Occupation Health and Safety Act (OHSA). For preliminary planning purposes, the soils encountered at the borehole locations may be classified as Type 3 soils above the groundwater table (approximately 2 m depth). The organic soils, loose silts and sands and sensitive silty clays should be classified as Type 4 soils below the groundwater table. If sufficient space does not exist to accommodate sloped excavations in these materials (which is likely the case given the amount of development in the area) then a temporary support system may be used. Temporary support for this type of project would typically include specially designed and constructed trench boxes but could also include interlocking sheet piles or similar shoring. Temporary support should be designed and installed by a contractor to both retain the existing soils and provide a safe working space, as well as to limit deflection and soil movement outside the work area to an acceptable level which will not cause damage to the existing structures and utilities. The soils at the site are a combination of silty clay, organic soils, silts and sands, some of which should be expected to have virtually no stand-up time and may behave as flowing soils if left unsupported below the water table. Caution should therefore be taken when moving trench boxes to prevent the sides of the excavation from being in an unsupported condition for any significant length of time. Similarly, caution should be exercised when excavating to ensure that the trench box fits tightly in the limits of the excavation, if not, the sides of the excavation may slough in. Where the trenches pass under the existing road, and allowance should be made for reconstructing the pavement adjacent to the trench boxes where sloughing or loosening occurs. Geotechnical Investigation Proposed Sewer Installation, Morris Street

11 DEWATERING The existing groundwater levels were found to be at approximately 2.1 m below the ground surface. Assuming the base of the excavation will be approximately 3.5 m to 4 m below the ground surface to accommodate the frost cover, pipe, bedding, etc. the base of the excavation could be 1.5 m to 2 m below the water table in a combination of silty sands, sands and organic soils. It is likely that seepage can be managed using pumping from closely spaced and properly filtered sumps in the base of the excavation. In the event the groundwater is higher at the time of construction then an active dewatering system, such as pumping from well points, may be required to maintain a dry base and prevent heaving and disturbance of the excavation base. The soils present in the boreholes (silty sand, sand, organic soil and silty clay) are expected to be susceptible to disturbance due to construction activities and groundwater piping. If appropriate groundwater control is not in place during construction then disturbance of the excavation base may occur. In addition, construction activities in saturated soils can also loosen the trench base. Either condition could result in a requirement for removal and replacement of the subgrade with imported granular soil. A Permit to Take Water (PTTW), issued by the Ontario Ministry of the Environment (MOE) is required if the dewatering system results in a water taking of more than 50,000 l/day. The quantity of groundwater to be pumped will depend no only on soil types and groundwater levels, but on the size and depth of excavation which will remain open at a given time. If the excavation is kept very small and completed in sections, it is likely that the pumping will be less than 50,000 l/day. It should be noted, however, that the MOE requires 90 days to process and review a PTTW application. This process has the potential to cause major delays if unforeseen groundwater conditions are encountered, or if very large temporary excavations are used. For this reason it may be beneficial for the City to obtain a PTTW prior to construction so as to avoid major delays or constraining the contractor s activities once construction has started. The presence of the new utility trench has the potential to permanently lower the groundwater table (by providing a drainage path) which could result in long-term settlement of the silty clay. It is recommended that clay cut-offs extending the full depth and width of the trench be installed to prevent the new utility trench from acting as a drain. 4.3 FROST PENETRATION AND FROST PROTECTION Water bearing services should maintain a minimum burial depth of 2.4 m. If this depth of soil cover cannot be accommodated then the services may be insulated as an alternative to deep burial. 4.4 SEISMIC SITE CLASSIFICATION The site can be classified as Class D for seismic site response. 4.5 GRADE RAISE It is understood that no significant grade raise is anticipated for the site. Grade raises have the potential to cause settlement of the underlying clay and organic soils, and should they be required, WSP should provide additional review and consultation. Geotechnical Investigation Proposed Sewer Installation, Morris Street

12 9 4.6 BEDDING COVER AND BACKFILL BEDDING AND EMBEDMENT Flexible pie bedding and embedment material should include a minimum of 300 mm of OPSS Granular A sand and gravel. The bedding and embedment material should extend a minimum of 300 mm above the pipe as per OPSD Bedding for rigid pipes should include OPSS Granular A from a depth of 300 mm below the invert of the pipe to the springline of the pipe. Bedding and embedment material should be compacted to 95% of Standard Proctor Maximum Dry Density (SPMDD). All trench bases should be reviewed by WSP prior to placement of bedding material. Where loose, wet or disturbed soils are encountered in the base of the trench it may be necessary to excavate and replace the soil with additional granular fill or bedding COVER Pipe cover should extend to 300 mm above the top of pipe. Cover for rigid pipe may include either Granular A or B with a maximum grain size of 26.5 mm (as per OPSS 401). Cover material should be compacted to 95% SPMDD. Care should be taken when compacting overtop of the pipe so as to protect the pipe from damage due to equipment and compaction BACKFILL All backfill should consist of suitable portions of the existing soils or approved imported fill material. In paved areas, to the extent possible, backfill in the frost zone should be made to match the existing soils exposed in the excavation to minimise the potential for differential frost heave. Portions of the existing fill materials as well as the sandy soils may be salvageable for reuse as backfill. The organic soils encountered in BH15-1 are not considered suitable for reuse as trench backfill and should be discarded. It is important to note that soils present below the water table may require moisture conditioning (drying) prior to reuse. It is recommended that the soils be reviewed as excavated to confirm suitability for reuse as backfill. Both native and imported soils should be approved by the contract administrator prior to reuse. All backfill should be free from frozen lumps, cinders, ash, organic matter, rock and boulders over 150 mm in diameter or other deleterious material. Backfill should be placed in lifts not exceeding 300 mm loose thickness and compacted to 95% SPMDD. Failure to properly moisture condition the backfill material will likely lead to difficulty in achieving the required compaction. Geotechnical Investigation Proposed Sewer Installation, Morris Street

13 Corrosion and Cement Type Samples of the existing fill and native silt and silty clay were submitted to Exova Accutest for testing related to soil corrosivity and potential exposure of concrete elements to sulphate attack. The results of these tests are included in Appendix C and summarized below. Table 3 Results of Soil Corrosivity Testing Borehole Sample No. Soil Type Chloride (%) Electrical Conductivity (ms/cm) ph Resistivity (ohm-cm) Sulphate (%) BH15-1 SS3 Sand BH15-2 SS5 Silty Sand < 0.01 The soil resistivity values measured in the sand and silty sand suggest a moderately to severely corrosive environment for buried steel elements. The test results indicate low soluble sulphate content in the naïve soils. For these values, GU Portland cement is suitable. Geotechnical Investigation Proposed Sewer Installation, Morris Street

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15 Appendix A DRAWINGS

16 JEAN STREET Lac Dollard-des-Ormeaux COUNTY ROAD 17! CLARENCE-ROCKLAND LAURIER STREET ST CARON STREET LEGEND! APPROXIMATE SITE LOCATION SITE LOCATION MAP PROPOSED NEW SEWER - MORRIS STREET For the City of Clarence-Rockland. DATE: MAY 2015 PROJECT: SCALE: 1:20000 FILE. NO.: F1 Data Source: Ministry of Natural Resources, Ontario Base Mapping, March Metres FIGURE 1

17 BH15-1 APPROXIMATE BOREHOLE LOCATION AND DESIGNATION BOREHOLE LOCATION MAP PROPOSED NEW SEWER - MORRIS STREET For the City of Clarence-Rockland. DATE: MAY 2015 PROJECT: SCALE: 1:800 FILE. NO.: F2 Data Source: Ministry of Natural Resources, Ontario Base Mapping, March Imagery, BING Metres FIGURE 2

18 Appendix B BOREHOLE LOGS

19 PROJECT NAME: NEW SEWER SYSTEM INSTALLATION BOREHOLE NO. BH15-1 PROJECT NO.: PAGE 1 of 1 CLIENT: CITY OF CLARENCE-ROCKLAND BOREHOLE TYPE: 203 mm HOLLOW STEM AUGER DATE COMPLETED: Apr 27, 2015 SUPERVISOR: DW GROUND ELEVATION: NOT DETERMINED REVIEWER: CH 0.0 DEPTH (m) 0.2 STRATIGRAPHIC DESCRIPTION TOPSOIL mm SILTY SAND trace gravel, trace roots, dark brown, moist (FILL) STRATIGRAPHY MONITOR DETAILS TYPE SS1A SS1B N VALUE 7 SAMPLE % WATER % RECOVERY RQD (%) CONE PENETRATION "N" VALUE SHEAR STRENGTH WATER CONTENT % 25 W P WL REMARKS 1.0 SS SAND dark brown, trace gravel, trace silt, moist, loose Organic Soil with wood fragments, dark brown, damp SS3 SS GSA SS3: GRAVEL: 7.8% SAND: 84.1% SILT AND CLAY: 8.1% 3.0 SS5 3 SS SS some roots and trace gravel - light brown - fine fiberous SILTY CLAY grey, wet, stiff to very stiff - Augering ended at 6.1 m. Borehole continued by DCPT testing. SILTY CLAY (Infered by DCPT results) SS8 SS9 VANE VANE AL SS9B: LL: 80 PL: 28 PI: 52 S u = 86 kpa; S = 5.7 S u = 90 kpa; S = WSP GEOLOGIC (METRIC) DYNAMIC CONE MORRIS_STREET.GPJ WSP_ENV_V1.GDT 5/21/ End of Borehole Notes: 1) Borehole was dry upon completion of augering 2) DCPT refusal at 10.6 m below surface level 100

20 PROJECT NAME: NEW SEWER SYSTEM INSTALLATION BOREHOLE NO. BH15-2 PROJECT NO.: PAGE 1 of 1 CLIENT: CITY OF CLARENCE-ROCKLAND BOREHOLE TYPE: 203 mm HOLLOW STEM AUGER DATE COMPLETED: Apr 27, 2015 SUPERVISOR: DW GROUND ELEVATION: NOT DETERMINED REVIEWER: CH DEPTH (m) STRATIGRAPHIC DESCRIPTION TOPSOIL mm SILTY SAND TO SILTY CLAY with wood fragments, brown to grey, moist (FILL) SILTY SAND brown, moist, loose STRATIGRAPHY MONITOR DETAILS TYPE SS1A SS1B SS2 N VALUE 5 9 SAMPLE % WATER % RECOVERY RQD (%) CONE PENETRATION "N" VALUE SHEAR STRENGTH WATER CONTENT % 25 W P WL REMARKS 2.0 SS grey - wet - compact - loose SS4 SS SILTY CLAY grey, wet, stiff to very stiff SS6 VANE AL SS6B: LL: 73 PL: 30 PI: VANE Augering ended at 5.5 m. Borehole continued by DCPT testing. SILTY CLAY (Infered by DCPT results) 7.0 WSP GEOLOGIC (METRIC) DYNAMIC CONE MORRIS_STREET.GPJ WSP_ENV_V1.GDT 5/21/ GLACIAL TILL (Infered by DCPT results) End of Borehole Notes: 1) Water level was at 2.7 m below surface level upon completion of augering 2) DCPT refusal at 12.4 m below surface level 3) 50mm dia. monitoring well was installed at 3.8 m below surface level 4) Date Depth-groundwater May 8, m May 20, m 100

21 Appendix C LABORATORY TESTING RESULTS

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24 EXOVA ENVIRONMENTAL ONTARIO Certificate of Analysis Client: SPL Consultants Ltd. 146 Colonnade Rd., Unit 17 Ottawa, ON K2E 7Y1 Attention: Ms. Wendy McLaughlin PO#: Invoice to: SPL Consultants Ltd. Report Number: Date Submitted: Date Reported: Project: COC #: Lab I.D. Sample Matrix Sample Type Sampling Date Sample I.D Soil BH 15-1 SS Soil BH 15-2 SS Soil BH 15-1 SS8 Group Analyte MRL Units Guideline Agri. - Soil Organic Matter (@440C) 0.1 % ph 2.0 General Chemistry Cl % Electrical Conductivity 0.05 ms/cm Resistivity 1 ohm-cm SO % < Guideline = * = Guideline Exceedence MRL = Method Reporting Limit, AO = Aesthetic Objective, OG = Operational Guideline, MAC = All analysis completed in Ottawa, Ontario (unless otherwise indicated by ** which indicates analysis was completed in Mississauga, Ontario). Results relate only to the parameters tested on the samples submitted. Maximum Acceptable Concentration, IMAC = Interim Maximum Acceptable Concentration, STD = Standard, PWQO = Provincial Water Quality Guideline, IPWQO = Interim Provincial Water Quality Objective, TDR = Typical Desired Range Methods references and/or additional QA/QC information available on request. 146 Colonnade Rd. Unit 8, Ottawa, ON K2E 7Y1 Page 2 of 3

25 EXOVA ENVIRONMENTAL ONTARIO Certificate of Analysis Client: SPL Consultants Ltd. 146 Colonnade Rd., Unit 17 Ottawa, ON K2E 7Y1 Attention: Ms. Wendy McLaughlin PO#: Invoice to: SPL Consultants Ltd. Report Number: Date Submitted: Date Reported: Project: COC #: QC Summary Analyte Blank QC % Rec QC Limits Run No: Analysis Date: Method: C CSA A23.2-4B Cl <0.002 % Run No: Analysis Date: Method: Cond-Soil Electrical Conductivity ph Resistivity Run No: Analysis Date: Method: C SM4500-SO4--D SO4 <0.01 % Run No: Analysis Date: Method: Ag Soil Organic Matter (@440C) Guideline = * = Guideline Exceedence MRL = Method Reporting Limit, AO = Aesthetic Objective, OG = Operational Guideline, MAC = All analysis completed in Ottawa, Ontario (unless otherwise indicated by ** which indicates analysis was completed in Mississauga, Ontario). Results relate only to the parameters tested on the samples submitted. Maximum Acceptable Concentration, IMAC = Interim Maximum Acceptable Concentration, STD = Standard, PWQO = Provincial Water Quality Guideline, IPWQO = Interim Provincial Water Quality Objective, TDR = Typical Desired Range Methods references and/or additional QA/QC information available on request. 146 Colonnade Rd. Unit 8, Ottawa, ON K2E 7Y1 Page 3 of 3