foundations, excavation & shoring specialists€¦ · relatively linear resulting in a...

July 28, 2017

Reference: 17-7254

Via email: [email protected]

McElhanney Consulting Services Ltd. Suite 2300 Central City Tower 13450 – 102nd Avenue Surrey, BC V3T 5X3 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 24, 2017 (our reference No. P17-5470).

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.

2.0 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 2017 exploration, the eastern tennis court area had experienced settlement up to 0.4m. 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 2m court widening to the west as well as construction of an asphalt pathway to service the facility.

Foundations, Excavation & Shoring Specialists Braun Geotechnical 106A-9785 192 St. Surrey, BC V4N 4X8 Tel: 604-513-4190 Fax: 604-513-4195 [email protected] www.braungeo.com Foundations Excavation & Shoring Slope Stability Natural Hazards Pavement Design and Management Reinforced Soil Walls and Slopes Rev. Sept 15, 2006

Tennis Court Rehabilitation July 28,2017 Queensborough Community Center, New Westminster, BC Project: 17-7254

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3.0 EXPLORATION

Geotechnical exploration was conducted on May 31, 2017 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 -02 were advanced to a depth of 6.1m north of the existing courts. Four pavement cores with hand augers designated as HA17-01 to -04 were completed to depths of 1.0 to 1.2m 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 17-7254-01).

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.

4.0 SOIL AND GROUNDWATER CONDITIONS

Based on published surficial geology information from the Geological Survey of Canada and in-house 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 60 to 70mm thick (single lift)

FILL 0.3m thick crushed SAND & GRAVEL fill (BASE) immediately below asphalt pavement

0.45 to 0.8m thick compact SAND fill encountered below

Biaxial reinforcement encountered at the base of the crushed gravel layer.

SUBGRADE PEAT subgrade at HA17-01 & -04 (east court area)

SAND / SILT subgrade, possibly fill encountered at HA17-02 & -03 (west court area)

NORTH OF COURTS

FILL Granular FILL encountered at TH17-01 to a depth of 0.9m underlain by silt FILL to a depth of 1.5m. Near surface silt FILL encountered TH17-02 to 0.45m depth.

PEAT Natural PEAT encountered below at each of the drilled test holes to depths of 3.2m at TH17-01 and 2.6m at TH17-02.

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 1.5m 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.


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5.0 DISCUSSION AND RECOMMENDATIONS

5.1 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:

5.2 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 0.4m 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 1.5m below finished tennis court grade as to provide for the proposed 0.4m raise in grade completed on a 1.0m thick LWG layer overlain by 0.45m 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 25 to 50mm uniformly graded materials with less than 3% passing the 4.75mm sieve. The LWG should be wrapped with a non-woven geotextile, comprised of M288 Class 2 Survivability non-woven filter fabric (Nilex 4551 or approved equivalent).


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The lightweight fill should be placed in maximum 300mm thick lifts, with each lift compacted using a three passes with a 500lb 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.

5.3 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 Material

35mm Hot Mix Asphalt - Surface Fine Mix

40mm Hot Mix Asphalt - LC #2 (MMCD Hot Mix Asphalt, HMA)

150mm Import MMCD crushed Granular Base

300mm 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)

9.5 100

6.7 80-100

4.75 70-90

2.36 45-65

1.18 34-55

0.600 22-45

0.300 14-33

0.150 8-18

0.075 5-8

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.

17-7254

920 Ewen Avenue, New Westminster, BC

DD

McElhanney Consulting Services Ltd.Tennis Court Rehabilitation

SH JW June 2, 2017 1:400

LOCATION PLAN

17-7254-01

BASE IMAGE OBTAINED FROM NEW WESTMINSTER WEBMAP

2017 TEST HOLEAPPROXIMATE LOCATION

TH17-01

LEGEND

2017 HAND AUGERAPPROXIMATE LOCATION

HA17-01

TH17-01

TH17-02

HA17-01

HA17-02

HA17-03

HA17-04

Hand Auger Log: HA17-01

Soil Description

Depth

Sam

ple #

Datum:

Water Depth:

Ground Surface Logged By:

Exploration Date:

Dwg No.:

Page: 1 of 1

Equipment:

Sampling Method:

Coring Rig, Hand Auger

Sam

ple

m

ft

15

10

5

20

1

2

3

4

5

6

Wa

te

r C

on

t.

DD

Seepage at 0.6mN/A May 31, 2017

17-7254-HA01

End of Hand Auger @ 1.2m

Remarks

brown, damp, compact, 19mm minus SAND &GRAVEL, trace silt (BASE)grey-brown, moist, compact SAND, tracegravel, trace silt (FILL)

dark-brown, moist, firm, amorphous PEAT

-water seepage @ 0.6m

70mm ASPHALT over

- biaxial geogrid layer at 0.3m

Soil Description

Depth

Sam

ple #

Sam

ple

m

ft

15

10

5

20

1

2

3

4

5

6


Remarks

brown, damp, compact, 19mm minus SAND &GRAVEL, trace silt (BASE)brown, damp, compact SAND, trace silt (FILL)

grey, rust-mottled, damp, firm, fine sandy SILT,trace clay, occasional gravel, trace rootlets

70mm ASPHALT over


Soil Description

Depth

Sam

ple #

Sam

ple

m

ft

15

10

5

20

1

2

3

4

5

6


Remarks

brown, damp, compact, 19mm minus SAND &GRAVEL, trace silt (BASE)grey-brown, damp, compact SAND, trace silt(FILL)

grey, moist, compact SAND, some gravel, trace silt

60mm ASPHALT over



Hand Auger Log: HA17-04

Soil Description

Depth

Sam

ple #

Datum:

Water Depth:


Exploration Date:

Dwg No.:

Page: 1 of 1

Equipment:

Sampling Method:

Coring Rig, Hand Auger

Sam

ple

m

ft

15

10

5

20

1

2

3

4

5

6

Wa

te

r C

on

t.

DD

Seepage at 1.0mN/A May 31, 2017

17-7254-HA04


Remarks

brown, damp, compact, 19mm minus SAND &GRAVEL, trace silt (BASE)

grey-brown to grey, damp to moist, compactSAND, trace silt (FILL)

dark-brown, moist, firm, amorphous PEAT -water seepage @ 1.0m

70mm ASPHALT over


Test Hole Log: TH17-01

Soil Description

Depth

Sam

ple #

Datum:

Water Depth:


Exploration Date:

Dwg No.:

Page: 1 of 1

Equipment:

Sampling Method:

Truck Drill

Sam

ple

m

ft

15

10

5

20

1

2

3

4

5

6

Wa

te

r C

on

t.

DC

Not EstablishedLump Sample May 31, 2017

17-7254-TH01

S1

S2

End of Test Hole @ 6.1m

Remarks

brown, damp, loose, silty SAND and GRAVEL(FILL)

25%

S3 34%

grey, damp, loose SAND, some organics (FILL)

grey, brown-mottled, moist, firm SILT, somesand, trace organics (FILL)

dark-brown, moist, firm, amorphous PEAT,trace wood fibers


sod & turf over

grey, moist, firm ORGANIC SILT, trace sand

- trace organics, trace clay below 5.5m

S5 460%

S6 385%

S7 94%

S8 115%

S9 134%

S10 74%

S4 28%

Moist below 1.5m

Test Hole Log: TH17-02

Soil Description

Depth

Sam

ple #

Datum:

Water Depth:


Exploration Date:

Dwg No.:

Page: 1 of 1

Equipment:

Sampling Method:

Truck Drill

Sam

ple

m

ft

15

10

5

20

1

2

3

4

5

6

Wa

te

r C

on

t.

DC

Lump Sample May 31, 2017

17-7254-TH02

S2

End of Test Hole @ 6.1m

Remarks

24%

grey-brown, damp, firm, sandy SILT, somegravel (FILL)

S3

brown, damp, soft, fibrous PEAT

dark-brown, moist, firm, amorphous PEAT


sod & turf over

- trace organics, trace clay below 5.5m

S5 780%

S6 137%

S7 123%

S8 178%

S9 160%

S10 76%

S4 583%

grey, moist, firm ORGANIC SILT, trace sand

Not Established

Moist below 1.5m

foundations, excavation & shoring specialists€¦ · relatively linear resulting in a...

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