Foundations, Excavation & Shoring Specialists

Transcription

1 Foundations, Excavation & Shoring Specialists July 8, 017 Reference: 17-7 McElhanney Consulting Services Ltd. Suite 00 Central City Tower nd Avenue Surrey, BC VT X Via mflorendo@mcelhanney.com Braun Geotechnical 106A St. Surrey, BC VN X8 Tel: Fax: info@braungeo.com Foundations Excavation & Shoring Slope Stability Natural Hazards Pavement Design and Management Reinforced Soil Walls and Slopes Attn: Michael Florendo, M.S., P.Eng. Re: Geotechnical Exploration Report Queensborough Community Center Tennis Court Rehabilitation City of New Westminster, BC 1.0 INTRODUCTION As requested, Braun Geotechnical Ltd. has carried out a geotechnical assessment for the above referenced project. The geotechnical work has been performed in general accordance with the terms and conditions of the Braun Geotechnical proposal dated May, 017 (our reference No. P17-70). The geotechnical work included completion of a geotechnical exploration and provision of this geotechnical report with comments and recommendations pertaining to rehabilitation of the existing tennis court facility. The scope of services was limited to the evaluation of the geotechnical characteristics of the site and no consideration has been given to any environmental aspects. Should any changes be made to the proposed layout, elevations, or general nature of the project, Braun Geotechnical should be notified to review and modify the recommendations to reflect those changes, as appropriate..0 SITE DESCRIPTION The subject tennis courts are located southeast of the existing Queensborough Community Center building, northwest of Salter Street, in New Westminster, BC (refer to enclosed location plan for details). At the time of the Braun Geotechnical 017 exploration, the eastern tennis court area had experienced settlement up to 0.m. The observed settlement trend was relatively linear resulting in a northeast to southwest orientated depression within the east court area. Excessive differential settlement of the west court area was not observed. It is understood the project includes rehabilitation of the existing court surfaces including a m court widening to the west as well as construction of an asphalt pathway to service the facility. Rev. Sept 1, 006

2 Tennis Court Rehabilitation July 8,017 Queensborough Community Center, New Westminster, BC Project: EXPLORATION Geotechnical exploration was conducted on May 1, 017 and included auger drilled test holes completed using a truck mounted drill rig, and pavement cores with hand excavation and augers completed below. Two drilled test holes designated TH17-01 to -0 were advanced to a depth of 6.1m north of the existing courts. Four pavement cores with hand augers designated as HA17-01 to -0 were completed to depths of 1.0 to 1.m within the existing court playing surface. The existing court fence precluded drill equipment access to the court area. Test hole locations are shown on the attached Location Plan (Ref ). Subsurface conditions were logged in the field and representative disturbed samples were collected from the augers for routine geotechnical laboratory moisture content testing and further visual classification purposes..0 SOIL AND GROUNDWATER CONDITIONS Based on published surficial geology information from the Geological Survey of Canada and inhouse experience in the project area we expect the site would be underlain by lowland peat overlaying silt loam. Results of the geotechnical exploration were reasonably consistent with the published information. A generalized subsoil profile based on the test holes has been summarized below. Please refer to the test hole logs for detailed subsurface conditions encountered at each test location. TENNIS COURTS ASPHALT FILL SUBGRADE NORTH OF COURTS FILL 60 to 70mm thick (single lift) 0.m thick crushed SAND & GRAVEL fill (BASE) immediately below asphalt pavement 0. to 0.8m thick compact SAND fill encountered below Biaxial reinforcement encountered at the base of the crushed gravel layer. PEAT subgrade at HA17-01 & -0 (east court area) SAND / SILT subgrade, possibly fill encountered at HA17-0 & -0 (west court area) Granular FILL encountered at TH17-01 to a depth of 0.9m underlain by silt FILL to a depth of 1.m. Near surface silt FILL encountered TH17-0 to 0.m depth. PEAT Natural PEAT encountered below at each of the drilled test holes to depths of.m at TH17-01 and.6m at TH17-0. SILT Firm condition ORGANIC SILT to SILT with increased depth was encountered below extending to the depth of exploration at 6.1m. Groundwater seepage was encountered within the open test holes below 1.m depth. Groundwater levels and near surface seepage flows are expected to fluctuate seasonally, and with drainage conditions. The subsurface conditions described above and presented on the test hole logs were encountered at the test hole location only. It should be noted that subsurface conditions at other locations could vary.

3 Tennis Court Rehabilitation July 8,017 Queensborough Community Center, New Westminster, BC Project: DISCUSSION AND RECOMMENDATIONS.1 General The geotechnical exploration encountered existing fills, near surface organic/peat soils over soft to firm condition organic silt/silt. The underlying peat and organic silt would be expected to consolidate and compress when subjected to vertical loading from placement of embankment fills which is the likely cause for the observed settlement within the east court area. Peat is highly compressible subject to substantial long term settlement with increased vertical loading. Review of available historical air photos was carried out to evaluate obvious sources for the existing settlement observed within the east court area relative to the west. It was considered that historical ditch infills and or utility services backfilled with granular fills may result in the linear settlement trend observed at the site. No obvious indicators to suggest historical ditch infills were observed during the historical air photo review. The observed settlement could be attributed to a historical fill sequence whereby an increased net vertical load was applied within the east court relative to the west during court construction. To reduce potential for future settlement resulting within the east court it is recommended that the use of a lightweight fill embankment be completed. Placement of granular fills within the settled east court area for grade restoration without a preload treatment would result in ongoing and substantial post-construction settlement and is not recommended. Benefit of the lightweight fill approach is the ability to rehabilitate the courts in a single construction sequence. An extensive preload treatment requiring substantial time delay could also be considered with specific details provided if requested. A simple mill+inlay or overlay treatment is considered appropriate for rehabilitation of the west court area and could be completed using the proposed surface mix material and minimum thickness. A net grade increase to accommodate the west court widening (which can lead to settlement) is generally not required and it is considered feasible to construct the court extension using conventional granular fills. Braun Geotechnical should be provided the opportunity to field review actual soil conditions during excavation of the west court widening at the time of construction for confirmatory purposes. Specific geotechnical recommendations for rehabilitation of the courts are provided as follows:. Lightweight Fill Embankment East Court A lightweight fill embankment would include sub-excavation for replacement with lightweight granular fill material (LWG) followed by application of the granular court fills and asphalt pavement/court surfacing. As identified grade restoration fills up to 0.m are expected within the east court area. The existing granular fills could be salvaged for onsite-reuse within the pavement subbase gravels on completion of the lightweight fill embankment. The proposed lightweight fill embankment would include excavation of the existing granular fills (and peat as required) up to 1.m below finished tennis court grade as to provide for the proposed 0.m raise in grade completed on a 1.0m thick LWG layer overlain by 0.m of granular fill. No construction traffic should be allowed on the prepared subgrade and final trimming should typically be completed using an excavator equipped with a smooth edged bucket. Lightweight granular fill should be comprised of vesicular basalt ( Red Pumice ), nominal to 0mm uniformly graded materials with less than % passing the.7mm sieve. The LWG should be wrapped with a non-woven geotextile, comprised of M88 Class Survivability nonwoven filter fabric (Nilex 1 or approved equivalent).

4 Tennis Court Rehabilitation July 8,017 Queensborough Community Center, New Westminster, BC Project: 17-7 The lightweight fill should be placed in maximum 00mm thick lifts, with each lift compacted using a three passes with a 00lb plate compactor. Compactive effort that results in material breakdown with oversized equipment (e.g. heavy drum roller) should be avoided. It is expected that settlements for an asphalt grade increase completed using a properly designed and constructed LWG fill embankment could reduce settlement of the tennis court to within tolerable limits. It is noted that increased court surface maintenance should be expected when compared to new court construction on a site underlain by more favourable soil conditions.. Pavement Design Sections The recommended pavement structure for the courts completed on the LWG embankment or existing granular fills (west widening area) is outlined below. Thickness mm 0mm 10mm 00mm Material Hot Mix Asphalt - Surface Fine Mix Hot Mix Asphalt - LC # (MMCD Hot Mix Asphalt, HMA) Import MMCD crushed Granular Base MMCD SGSB equivalent Sand & Gravel The gradation of the above materials should comply with the appropriate Master Municipal Specifications. Road construction materials should be placed and compacted in compliance with the current MMCD specifications. Surface mix to conform to the following grading standard (or alternate approved fine-mix blend) and be comprised of quarried materials only. Gradation Limits Surface Fine Mix Sieve Size Aggregate Size mm Limits of Grading (% Passing) Marshall mix-design for proposed asphalt pavement to be submitted Braun Geotechnical for review prior to construction. On completion, it is expected that the asphalt paved courts would receive a proprietary sport surface provided by a qualified supplier.

5

6 HA17-0 HA17-01 TH17-0 HA17-0 TH17-01 HA17-0 LEGEND TH17-01 HA TEST HOLE APPROXIMATE LOCATION 017 HAND AUGER APPROXIMATE LOCATION BASE IMAGE OBTAINED FROM NEW WESTMINSTER WEBMAP McElhanney Consulting Services Ltd. Tennis Court Rehabilitation 90 Ewen Avenue, New Westminster, BC LOCATION PLAN 17-7 DD SH JW June, 017 1:

7 Hand Auger Log: HA17-01 ft Depth m Sample Soil Description 70mm ASPHALT over brown, damp, compact, 19mm minus SAND & GRAVEL, trace silt (BASE) grey-brown, moist, compact SAND, trace gravel, trace silt (FILL) Sample # Water Cont. Remarks - biaxial geogrid layer at 0.m -water 0.6m 1 dark-brown, moist, firm, amorphous PEAT End of Hand 1.m Equipment: Sampling Method: Coring Rig, Hand Auger N/A Datum: Water Depth: Ground Surface Seepage at 0.6m Logged By: Exploration Date: Dwg No.: Page: DD May 1, HA01 1 of 1

8 ft Depth m Sample Soil Description 70mm ASPHALT over brown, damp, compact, 19mm minus SAND & GRAVEL, trace silt (BASE) brown, damp, compact SAND, trace silt (FILL) Sample # Remarks - biaxial geogrid layer at 0.m 1 grey, rust-mottled, damp, firm, fine sandy SILT, trace clay, occasional gravel, trace rootlets End of Hand 1.0m

9 ft Depth m Sample Soil Description 60mm ASPHALT over brown, damp, compact, 19mm minus SAND & GRAVEL, trace silt (BASE) grey-brown, damp, compact SAND, trace silt (FILL) Sample # Remarks - biaxial geogrid layer at 0.m 1 grey, moist, compact SAND, some gravel, trace silt End of Hand 1.0m -water 0.9m

10 Hand Auger Log: HA17-0 ft Depth m Sample Soil Description 70mm ASPHALT over brown, damp, compact, 19mm minus SAND & GRAVEL, trace silt (BASE) grey-brown to grey, damp to moist, compact SAND, trace silt (FILL) Sample # Water Cont. Remarks - biaxial geogrid layer at 0.m 1 dark-brown, moist, firm, amorphous PEAT -water 1.0m End of Hand 1.m Equipment: Sampling Method: Coring Rig, Hand Auger N/A Datum: Water Depth: Ground Surface Seepage at 1.0m Logged By: Exploration Date: Dwg No.: Page: DD May 1, HA0 1 of 1

11 Test Hole Log: TH17-01 ft Depth m Sample Sample # Water Cont. Soil Description sod & turf over brown, damp, loose, silty SAND and GRAVEL (FILL) S1 % Remarks grey, damp, loose SAND, some organics (FILL) S 1 grey, brown-mottled, moist, firm SILT, some sand, trace organics (FILL) S % S 8% dark-brown, moist, firm, amorphous PEAT, trace wood fibers S 60% -water 1.m S6 8% 10 grey, moist, firm ORGANIC SILT, trace sand S7 9% S8 11% 1 S9 1% - trace organics, trace clay below.m S10 7% 0 6 End of Test 6.1m Equipment: Sampling Method: Truck Drill Lump Sample Datum: Water Depth: Ground Surface Not Established Moist below 1.m Logged By: Exploration Date: Dwg No.: Page: DC May 1, TH01 1 of 1

12 Test Hole Log: TH17-0 ft Depth m Sample Soil Description sod & turf over grey-brown, damp, firm, sandy SILT, some gravel (FILL) Sample # S Water Cont. % Remarks brown, damp, soft, fibrous PEAT 1 dark-brown, moist, firm, amorphous PEAT S S 8% -water 1.m S 780% grey, moist, firm ORGANIC SILT, trace sand S6 17% 10 S7 1% S8 178% 1 S9 160% - trace organics, trace clay below.m S10 76% 0 6 End of Test 6.1m Equipment: Sampling Method: Truck Drill Lump Sample Datum: Water Depth: Ground Surface Not Established Moist below 1.m Logged By: Exploration Date: Dwg No.: Page: DC May 1, TH0 1 of 1