Attachment C - Thurber Report

COUNCIL REPORT

Executive Committee Report No. ENG 037-2019 Date: November 21, 2019 File No: 5330-30 To: Mayor and Council From: Stella Chiu, Senior Engineer, Drainage and Wastewater Tony Seibert, Project Engineer Subject: Geotechnical Seismic Assessment of Abbotsford Dykes - Final Report

RECOMMENDATION 1. THAT the future Drainage Master Plan and Long-term Financial Plan be updated to

reflect the recommendations contained in the Geotechnical Seismic Assessment of Abbotsford Dykes, Final Report, dated March 18, 2019; and

2. THAT staff be authorized to write a letter the Province with the updated information

contained in the Geotechnical Seismic Assessment of Abbotsford Dykes, Final Report, dated March 18, 2019.

REPORT CONCURRENCE

General Manager

The General Manager concurs with the recommendation of this report.

City Manager

The City Manager concurs with the recommendation of this report.

SUMMARY OF THE ISSUE

In 2017, the City received approval from the National Disaster Mitigation Program for full funding for the Geotechnical Seismic Assessment of Abbotsford Dykes, in the amount of up to $200,000. A geotechnical engineering firm was engaged and completed soil testing at key locations along Matsqui Dyke, Sumas Dyke and Vedder Dyke, to confirm soil conditions, seismically assess the dykes in their current location and provide a high-level cost estimates for future upgrades to address seismic risks.

BACKGROUND

A significant portion of the City is protected by the three dykes, namely the Matsqui Dyke, Sumas Dyke and the Vedder Dyke. The 2015 Lower Mainland Dyke Assessment report, prepared by the Province, deemed the dykes to be high consequence dykes and the assessment included geotechnical stability seismic as one of the nine evaluation criteria. The

Report No. ENG 037-2019 Page 2 of 5

three Abbotsford dykes were rated as unacceptable and poor due to potential liquefaction of sands that could affect dyke stability and cause lateral spreading. In 2016, a funding application was submitted to the Provincial/Federal National Disaster Mitigation Program (NDMP) for completing geotechnical (seismic) assessments of the Abbotsford Dykes. The scope was to confirm the findings, determine risks associated with the current location and provide high level cost estimates for future upgrades to address the seismic risk. In 2017, the City received approval for full funding of this study, up to the amount of $200,000. In late 2017, the City engaged the services of Thurber Engineering for the Geotechnical (Seismic) Assessment of Abbotsford Dykes, through a public BC Bid process. The work began in February 2018 and was completed by March 2019. This report summarizes the findings.

DISCUSSION

1) Assessment Findings The Geotechnical (Seismic) Assessment of the three Abbotsford Dykes included a liquefaction assessment and a numerical deformation analysis at ten borehole locations and dyke cross-sections. The 2014 Seismic Guidelines were used to provide guidance. The key findings are summarized below, with a summary of results in Attachment A. Attachment C includes the full report, without the appendices. a) Liquefaction Assessment Results (1D Model): There is insignificant liquefaction for all three dykes at a seismic event with 1:100 year return period. The liquefaction increases to none/mild with a bigger event (1:475 year return period) and further to moderate/high at a 1:2475 year return period. b) Numerical Deformation Analysis (2D Model): Out of the ten dyke sections, only two would meet the performance requirements of the 2014 Seismic Guidelines for all return periods. Two would not meet the requirement for any return periods as they have minimal setbacks. The remaining six generally meet the seismic design criteria for the 1:475 year and lower return periods. 2) Seismic Mitigation Measures Two options for seismic mitigation measures are shown below as independent solutions, with Class C cost estimates. These cost estimates include constructing the dykes to an elevation as per the 2018 Drainage Master Plan. A final solution could also include a combination of ground improvements and setback dykes. A summary of cost estimates is included in Attachment B. a) Ground Improvements (soil densification): Existing dyke fill would be removed before improvement works are completed and then the fill re-installed over the ground improvement zone. The total estimated costs for all three dykes to meet the performance criteria for 1:2475 year event is estimated at $333M. b) Setback (move away from the river) for Matsqui Dyke only:


As a potential alternative to ground improvement, the Matsqui Dyke could be set back from the river bank. The setback required to meet the performance criteria for the 1:2475 year event is 250m, which includes a relocation of 10.4km of dyke. Setting back the dyke for this distance would leave major regional infrastructure (e.g. JAMES Plant) at risk.

The estimated cost for relocating Matsqui Dyke, excluding real estate costs, is $69M. The total cost for this option, including seismic improvements to the Sumas Dyke and Vedder Dyke, is estimated at $274M.

Other considerations include 2014 Seismic guidelines, which are under review by the Province, as part of work undertaken by the Fraser Basin Council. Any updates could have implications for Abbotsford Dykes. Once Council receives this report, staff will share the findings with the Fraser Basin Council.

3) Comparison with 2018 Drainage Master Plan

The 2018 Drainage Master Plan includes dyke improvements, with a phasing of the capital program to 2050, at $415M. The cost estimates assumed ground improvements can be undertaken on either side of the dykes, without dyke reconstruction. New findings from the geotechnical seismic assessment indicate that dyke reconstruction is required.

The table below provides a comparison of the costs:

2018 Drainage Master Plan (DMP)

2018 DMP + 2019 Findings from Seismic study

Dyke Improvement Costs ($)

$415M (Including $302M ground improvements to meet 1:2475 even, and dyke raising costs (Class D))

$446M (Including Class C $333M ground improvements to meet 1:2475 event and dyke raising costs (Class C)

Additional work is planned in future years to refine the overall cost of the dyke improvements. It is recommended that the future Drainage Master Plan and long-term financial plan be updated with the new findings.

FINANCIAL PLAN IMPLICATION

The City will be seeking 100% funding from senior levels of governments for dyke improvements. It is recommended that a letter be written to the Province with the updated information.

Rajat Sharma General Manager, Finance and Corporate Services Signed 11/15/2019 11:57 AM

IMPACTS ON COUNCIL POLICIES, STRATEGIC PLAN AND/OR COUNCIL DIRECTION

Addressing the City Dykes Geotechnical (Seismic) stability supports the four Cornerstones of Council’s Strategic Plan by:


Vibrant Economy: reducing the risk of dyke failure, which protects diverse agriculture, historic sites, First Nations and major regional infrastructure, such as highways, railways, National Defense communications, BC Hydro towers, gas mains, watermains, Barrowtown and the JAMES Wastewater Treatment Plant.

Complete Community: upholding public safety by ensuring the dykes are not undermined due to seismic issues, public health by ensuring critical infrastructure, such as the water and sewer systems, are not compromised and the environment by protecting the fish habitat and sensitive ecosystems.

Fiscal Discipline: reducing the risk of dyke failure and loss of the City’s critical infrastructure that supports economic vitality and social well-being of the community. This issue can be managed in a fiscally responsible way.

Organizational Alignment: upholding public trust by addressing a critical infrastructure matter in a proactive, responsive fashion and fiscally responsible way.

SUBSTANTIATION OF RECOMMENDATION

The three Abbotsford Dykes, Matsqui Dyke, Sumas Dyke and Vedder Dyke, were rated as “unacceptable” and “poor” in the 2015 Lower Mainland Dyke Assessment, published by the Province. Provincial funding has allowed the City to retain Thurber Engineering to complete further geotechnical testing and seismic modelling to confirm soil conditions, seismically assess the dykes in their current location and provide high-level cost estimates for future upgrades to address seismic risks. Thurber Engineering noted that the three dykes have variable underlying soils and site geometry that contribute to a rating (for high consequence dykes) of poor/unacceptable. Two options for seismic mitigation measures are proposed as independent solutions, but a final solution could also include a combination of ground improvements and setback dykes. The cost to seismically upgrade the three dykes, to meet 1:2475yr event, ranges from $247M to $333M. The 2018 Drainage Master Plan includes a cost estimate of $415M for dyke improvements and would be updated to $446M with the new findings. It is recommended that the future Drainage Master Plan and long term financial plan be updated. As the City will be looking for 100% funding from senior levels of governments for dyke improvements, it is recommended that a letter be written to the Province with the updated information. Stella Chiu Senior Engineer, Drainage and Wastewater Signed 11/14/2019 4:22 PM

Rob Isaac GM, Engineering & Regional Utiities Signed 11/15/2019 2:44 PM


ATTACHMENTS:

Attachment A - Liquefaction Assessment Attachment B - Summary of Cost Estimates Attachment C - Thurber Report

COUNCIL REPORT

Attachment A Liquefaction assessment and numerical deformation analysis – results summary a) Liquefaction Assessment Results (1D Model):

Return Period

Matsqui Dyke Liquefaction

Sumas Dyke Liquefaction

Vedder Dyke Liquefaction

1:100 Year

None None None

1:475 Year None - Upstream half Mild - Downstream half

None to Mild None to Mild

1:2475 Year Moderate - Upstream half Moderate to high – Downstream half

Moderate to high Moderate to High

b) Numerical Deformation Analysis (2D Model): The 2014 Provincial Seismic Guidelines were followed. Recommends high-consequence dykes be designed to control seismic deformation within prescribed limits for each return period (i.e. 1:100yr event - horizontal and vertical displacement <30mm, 1:475yr event – horizontal 300mm, vertical 150mm displacement and 1:2475yr event – horizontal 900mm, vertical 500mm displacement allowed. Numerical Deformation Analysis Results (Minimum Criteria Met)

Section Dyke

Return Period (Year)

1

Matsqui

1:475 2 None 3 1:475 4 1:2475 5 1:475 6 1:100 7 Vedder 1:475 8 1:475 9 Sumas None 10 1:2475

COUNCIL REPORT

Attachment B Summary of cost estimates for seismic mitigation measures

1) Ground Improvements (soil densification) – requires the dyke fill to be removed before improvement works are done and then the fill re-installed over the ground improvement zone.

Dyke

1:2475 Year Event 1:475 Year

Event Matsqui $128M $66M Sumas $68M $68M Vedder $137M $26M Total

$333M

$160M

2) Setback (move away from the River) for Matsqui Dyke:

Dyke

1:2475 Year Event 1:475 Year Event

Matsqui* (250m setback) $69M (80m setback) $57M Sumas (as above) (0m setback) $68M (0m setback) $68M Vedder (as above) (0m setback) $137M (0m setback) $26M Total

$274M

$151M

*excluding land purchase costs

March 18, 2019 File: 21847 City of Abbotsford 32315 South Fraser Way Abbotsford, BC V2T 1W7 Attention: Tony Seibert, P.Eng.

GEOTECHNICAL SEISMIC ASSESSMENT OF ABBOTSFORD DIKES SEISMIC NUMERICAL DEFORMATION ANALYSIS

FINAL REPORT Dear Tony: As requested, Thurber Engineering Ltd. (Thurber) has carried out numerical seismic deformation analyses for the above project. This report presents the results of the deformation analysis and an assessment of the performance of flood control measures, including possible seismic mitigation measures (i.e. ground improvement), in the context of provincial design requirements for high-consequence dikes. It is a condition of this report that Thurber’s performance of its professional services is subject to the attached Statement of Limitations and Conditions.

1. BACKGROUND

The City of Abbotsford (the City) requires a geotechnical seismic assessment of their three dikes to better understand their anticipated performance in the event of an earthquake. The Matsqui Dike is about 11.5 km long and protects the Matsqui Prairie from flooding from the Fraser River. The Vedder Dike is about 4.5 km long and protects the Sumas Prairie from flooding from the Vedder Canal and Fraser River. The Sumas Dike is about 17 km long and protects the Sumas Prairie from flooding from the Sumas River. In 2015 Ministry of Forests, Lands and Natural Resource Operations (MFLNRO) released a report “Lower Mainland Dike Assessment” that rated the seismic vulnerability of these three dikes as poor and unacceptable. The 2015 Lower Mainland Dike Assessment evaluated the seismic performance on a subjective basis. This subjective seismic assessment was evaluated based on required performance criteria for high-consequence dikes described in the MFLNRO’s 2014 document “Seismic Design Guidelines for Dikes” (2014 Seismic Guidelines). The purpose of this geotechnical seismic assessment is to provide the City with a more detailed understanding of the seismic performance of their dikes in the context of the 2014 Seismic Guidelines. The scope of work required for the assessment is provided in the City’s RFP No. 1220-2017-2093 and is repeated verbatim as follows:

Review of all available background material, including but not limited to relevant reports, drawings and all available geotechnical (soil, borehole, etc.) information. The information

900, 1281 West Georgia Street, Vancouver, BC V6E 3J7 T: 604 684 4384 F: 604 684 5124thurber.ca

dparmar

Text Box

Attachment C

Client: City of Abbotsford Date: March 18, 2019 File No.: 21847 E-File: 20190318_final report siesmic dike assessment_21847 Page 2 of 15

to be reviewed should be in accordance with the requirements of the Seismic Design Guidelines for Dikes, Current Edition, as published by MFLNRO, Flood Safety Section.

Recommend locations for geotechnical investigations and testing methods along the dykes and specify the type(s) of tests to be performed at each location. The work program shall be sufficient to characterize the seismic site response to a level that is adequate for the purpose of an overview level study. Investigations and testing are to be completed in accordance with the relevant current ASTM standards, or where no standard exists, in accordance with industry established and accepted procedures.

Provide drawings to show proposed investigation locations and access plans, submit plans and any reports or details of investigation work to be used for approvals, access agreements, and work by sub-consultants / sub-contractor or others on the team.

Approvals from agencies, including but not limited to a Dyke Maintenance Act approval for exploratory drilling within a dyke as required, but excluding access agreements with private property owners (access agreements to be provided by City as determined necessary).

Coordinate and conduct all investigation and testing / drilling work to be completed as part of the scope of work (in-house or by sub-consultant / sub-contractor).

Inspection / monitoring during geotechnical investigations or other investigative work. Review results of geotechnical investigations and all other results. Conduct geotechnical

assessments in accordance with the Seismic Design Guidelines for Dikes, Current Edition, as published by MFLNRO, Flood Safety Section to:

o Evaluate the liquefaction potential of soil and associated consequences that could cause damage to the existing dykes.

o Evaluate seismic hazards associated with moving back the Matsqui Dyke, as discussed in the Fraser River at Matsqui – Erosion Study and Development of Mitigation Concepts report.

Propose appropriate dyke remediation solutions to address dyke sections determined to be susceptible to seismically-induced damage.

Provide conceptual drawings and Class C cost estimates on remediation / mitigation measures to address seismic risk, including an update to the cost estimates provided for the Matsqui Dyke Relocation.

Draft and final report summarizing project findings. This geotechnical seismic assessment is funded by the National Disaster Mitigation Program. 2. SEISMIC ASSESSMENT BASIS

Seismic assessments comprising liquefaction and numerical deformation analyses were carried for ten dike sections at the locations provided in the table below. The dike section names correspond to the test holes of the same number (i.e. TH/CPT 18-01 was carried out at the location of Section 1). The dike stations are based on as-built drawings from past dike upgrades (Matsqui in 1968, Vedder 1978, Sumas 1983).


Dike section Dike Station

(CPT/TH) 1 Matsqui 44+50 Line A 2 Matsqui 7+80 Line B 3 Matsqui 46+40 Line B 4 Matsqui 92+30 Line B 5 Matsqui 134+60 Line B 6 Matsqui 196+50 Line B 7 Vedder 40+65 8 Vedder 80+90 9 Sumas 6+770

10 Sumas 3+250 The assessments were carried out using cone penetration test (CPT) data obtained from a geotechnical investigation completed for this project. The locations of the dike sections analysed were selected by Thurber in consultation with the City. Profile drawings showing the dike sections are included in Appendix A. Our analyses followed the analytical methods described in the 2014 Seismic Guidelines. The 2014 Seismic Guidelines recommend designing high-consequence dikes and appurtenant structures to control seismic deformations within prescribed limits. The seismic deformation limits vary depending on the seismic hazard return period as shown in the table below.

Seismic hazard return Maximum allowable displacement (mm)

period (year) Horizontal Vertical

1 in 100 <30 <30 1 in 475 300 150

1 in 2,475 900 500 The analyses were carried out for the crustal, inslab, and interface (i.e. Cascadia subduction event) scenario earthquakes. Three earthquake time histories for each scenario earthquake were developed for each of the 1 in 100, 475 and 2475-year return period seismic hazards. The seismic hazard for the project was based on seismic hazard data from Natural Resource Canada’s (NRC’s) fifth generation seismic hazard model. This data is available on-line from NRC’s 2015 seismic hazard calculator and NRC Open File 8090. The time histories were based on seed time histories for the scenario earthquakes that were scaled and matched to the relevant part of the 2015 NRC uniform hazard response spectra (UHRS) for each return period seismic hazard. The crustal seed time histories were obtained from NGA West2 PEER ground motion database and the inslab and interface seed time histories were obtained from the USGS and CGS’s Center for Engineering Strong Motions Data. The seed time histories were scaled and matched to the site-specific target UHRS using the software program


SeismoMatch published by Seismosoft, which uses the wavelet addition algorithm RSPMATCH developed by N. Abramson. Three time-histories were developed for each scenario earthquake. We carried out 1-dimensional site-specific response analyses (SSRAs) using each of the time histories. The SSRAs were carried out using the software program DEEPSOIL published by the University of Illinois. The SSRAs were completed using three crustal, three in-slab and three interface earthquake time-histories for each of the 1 in 100, 475 and 2475-year return period seismic hazards, for a total of 27 SSRAs per dike section. The results of the SSRAs were used in both the liquefaction assessment and numerical deformation analysis. The SSRAs used the shear wave velocity data from the CPTs to estimate the site-specific seismic accelerations and seismically induced shear stresses and strains. The analysis included numerical seismic deformation analyses using the software program Plaxis 2D. The analyses were carried out to assess the seismic performance of the existing dikes and seismic mitigation measures, such as ground improvement or providing setback dikes, that could be required to meet the performance criteria of the 2014 Seismic Guidelines. 3. GEOTECHNICAL INVESTIGATION

3.1 Program of work

The field investigation was carried out from February 27 to March 1, 2018 and comprised a combination of auger drilling and CPT profiling. Ten CPTs were completed, including three seismic CPTs (i.e. SCPTs), which are CPTs with the addition of shear wave velocity profiling. The CPT profiles, test hole logs and a test hole location plans (Drawings 21847-1 to 21847-4) are attached in Appendix B. The CPTs were advanced to depths of 30 m. SCPTs 18-03, 18-06 and 18-10 included shear wave velocity measurements. The CPT provides a continuous trace of cone tip resistance, sleeve friction and pore pressure. This data was used to interpret the soil stratigraphy and estimate soil properties (e.g. strength and density). The shear wave velocity measurements were used to estimate the small-strain shear modulus of the soil, which has been used in the SSRAs and numerical deformation analyses. The CPTs were drilled out to depths of nominally 7.5 m with a solid-stem auger to confirm the soil profile and collect disturbed samples. The soil and groundwater conditions in the test holes were logged in the field by an experienced geotechnical engineer and representative disturbed samples were collected for routine moisture content testing and visual classification in our laboratory. Fines content analyses (% passing 75 µm sieve) and Atterberg limit testing were carried out on select representative samples. All test holes were located on dikes or within the dike right-of-way and were grouted in general accordance with B.C. groundwater protection regulations and MFLNRO requirements.


3.2 Results of the Investigation

The results of the investigation and laboratory testing are summarized on the attached test hole and CPT logs. The logs provide a complete, detailed description of the conditions encountered and should be used in preference to the generalized descriptions given below. The soil descriptions provided on the CPT logs are Gregg Drilling and Testing Canada’s interpretations of the CPT data using generally accepted correlations and should be considered approximate. CPT/THs 18-01 to 18-06 were carried out on the Matsqui Dike between Sumas Mountain and the tip of the Matsqui Prairie. The soil profile encountered in CPT/THs 18-01 to 18-05 generally comprised dike fill overlying silt that varied from sandy to clayey silt and extended to depths of about 6 m to 8 m. Below the silt, uniform sand was encountered to the maximum depth investigated. CPT/TH 18-06 was closest to Sumas Mountain. At this location the soil profile generally comprised dike fill overlaying clayey silt extending to a depth of about 14 m. Below the clayey silt, uniform sand was encountered to the maximum depth investigated. CPT/THs 18-07 and 18-08 were carried out on the Vedder Dike. CPT/TH 18-07 was located on the Vedder Canal and CPT/TH 18-08 was near the Barrowtown Pump Station. The soil profile encountered at these test holes generally comprised dike fill overlying and silt extending to a depth of about 3 m. Below the silt there was sand with some silt layers. The amount of silt layers increased with depth, and the sand eventually transitioned to silt at a depth of about 15 to 20 m. The silt has some sand layers, becoming siltier with depth. In CPT/TH 18-08 sand was encountered at a depth of about 26 m and extended to the maximum depth investigated. CPT/TH 18-09 was completed on the Sumas Dike on the Sumas River beside Sumas Mountain. The soil profile generally comprised dike fill overlying sandy to clayey silt to the maximum depth investigated. Sand layers were encountered in this silt deposit from depths of about 6 m to 8 m and 11 m to 13 m. CPT/TH 18-10 was carried out on the Sumas Dike on Saar Creek in Sumas Prairie. The soil profile encountered at this location comprised dike fill underlain by silt extending to a depth of about 4 m. Below the silt, interlayered sand and silty sand, becoming siltier with depth, was encountered to the maximum depth investigated. There were some silt layers in the interlayered sand and silty sand deposit. These subsurface conditions encountered during the investigation are consistent with the conditions described in the following documents:

Golder Associates’ December 13, 2007 report “Completion Report for Matsqui and Vedder Dike Upgrades – Abbottsford, B.C.”

Crippen Engineering Ltd.’s 1977 report “Subsurface Investigation – Dikes” for the west side of the Vedder Canal.

Thurber Engineering Ltd.’s September 11, 2015 report “Vedder Canal West Dike (Right Bank) Upgrades – Preliminary Design”

B.C. Surficial Geology Map 1485A

March 18, 2019 File: 21847 City of Abbotsford 32315 South Fraser Way Abbotsford, BC V2T 1W7 Attention: Tony Seibert, P.Eng.

GEOTECHNICAL SEISMIC ASSESSMENT OF ABBOTSFORD DIKES SEISMIC NUMERICAL DEFORMATION ANALYSIS

FINAL REPORT Dear Tony: As requested, Thurber Engineering Ltd. (Thurber) has carried out numerical seismic deformation analyses for the above project. This report presents the results of the deformation analysis and an assessment of the performance of flood control measures, including possible seismic mitigation measures (i.e. ground improvement), in the context of provincial design requirements for high-consequence dikes. It is a condition of this report that Thurber’s performance of its professional services is subject to the attached Statement of Limitations and Conditions.

1. BACKGROUND

The City of Abbotsford (the City) requires a geotechnical seismic assessment of their three dikes to better understand their anticipated performance in the event of an earthquake. The Matsqui Dike is about 11.5 km long and protects the Matsqui Prairie from flooding from the Fraser River. The Vedder Dike is about 4.5 km long and protects the Sumas Prairie from flooding from the Vedder Canal and Fraser River. The Sumas Dike is about 17 km long and protects the Sumas Prairie from flooding from the Sumas River. In 2015 Ministry of Forests, Lands and Natural Resource Operations (MFLNRO) released a report “Lower Mainland Dike Assessment” that rated the seismic vulnerability of these three dikes as poor and unacceptable. The 2015 Lower Mainland Dike Assessment evaluated the seismic performance on a subjective basis. This subjective seismic assessment was evaluated based on required performance criteria for high-consequence dikes described in the MFLNRO’s 2014 document “Seismic Design Guidelines for Dikes” (2014 Seismic Guidelines). The purpose of this geotechnical seismic assessment is to provide the City with a more detailed understanding of the seismic performance of their dikes in the context of the 2014 Seismic Guidelines. The scope of work required for the assessment is provided in the City’s RFP No. 1220-2017-2093 and is repeated verbatim as follows:

Review of all available background material, including but not limited to relevant reports, drawings and all available geotechnical (soil, borehole, etc.) information. The information

900, 1281 West Georgia Street, Vancouver, BC V6E 3J7 T: 604 684 4384 F: 604 684 5124thurber.ca


to be reviewed should be in accordance with the requirements of the Seismic Design Guidelines for Dikes, Current Edition, as published by MFLNRO, Flood Safety Section.

Recommend locations for geotechnical investigations and testing methods along the dykes and specify the type(s) of tests to be performed at each location. The work program shall be sufficient to characterize the seismic site response to a level that is adequate for the purpose of an overview level study. Investigations and testing are to be completed in accordance with the relevant current ASTM standards, or where no standard exists, in accordance with industry established and accepted procedures.

Provide drawings to show proposed investigation locations and access plans, submit plans and any reports or details of investigation work to be used for approvals, access agreements, and work by sub-consultants / sub-contractor or others on the team.

Approvals from agencies, including but not limited to a Dyke Maintenance Act approval for exploratory drilling within a dyke as required, but excluding access agreements with private property owners (access agreements to be provided by City as determined necessary).

Coordinate and conduct all investigation and testing / drilling work to be completed as part of the scope of work (in-house or by sub-consultant / sub-contractor).

Inspection / monitoring during geotechnical investigations or other investigative work. Review results of geotechnical investigations and all other results. Conduct geotechnical

assessments in accordance with the Seismic Design Guidelines for Dikes, Current Edition, as published by MFLNRO, Flood Safety Section to:

o Evaluate the liquefaction potential of soil and associated consequences that could cause damage to the existing dykes.

o Evaluate seismic hazards associated with moving back the Matsqui Dyke, as discussed in the Fraser River at Matsqui – Erosion Study and Development of Mitigation Concepts report.

Propose appropriate dyke remediation solutions to address dyke sections determined to be susceptible to seismically-induced damage.

Provide conceptual drawings and Class C cost estimates on remediation / mitigation measures to address seismic risk, including an update to the cost estimates provided for the Matsqui Dyke Relocation.

Draft and final report summarizing project findings. This geotechnical seismic assessment is funded by the National Disaster Mitigation Program. 2. SEISMIC ASSESSMENT BASIS

Seismic assessments comprising liquefaction and numerical deformation analyses were carried for ten dike sections at the locations provided in the table below. The dike section names correspond to the test holes of the same number (i.e. TH/CPT 18-01 was carried out at the location of Section 1). The dike stations are based on as-built drawings from past dike upgrades (Matsqui in 1968, Vedder 1978, Sumas 1983).


Dike section Dike Station

(CPT/TH) 1 Matsqui 44+50 Line A 2 Matsqui 7+80 Line B 3 Matsqui 46+40 Line B 4 Matsqui 92+30 Line B 5 Matsqui 134+60 Line B 6 Matsqui 196+50 Line B 7 Vedder 40+65 8 Vedder 80+90 9 Sumas 6+770

10 Sumas 3+250 The assessments were carried out using cone penetration test (CPT) data obtained from a geotechnical investigation completed for this project. The locations of the dike sections analysed were selected by Thurber in consultation with the City. Profile drawings showing the dike sections are included in Appendix A. Our analyses followed the analytical methods described in the 2014 Seismic Guidelines. The 2014 Seismic Guidelines recommend designing high-consequence dikes and appurtenant structures to control seismic deformations within prescribed limits. The seismic deformation limits vary depending on the seismic hazard return period as shown in the table below.

Seismic hazard return Maximum allowable displacement (mm)

period (year) Horizontal Vertical

1 in 100 <30 <30 1 in 475 300 150

1 in 2,475 900 500 The analyses were carried out for the crustal, inslab, and interface (i.e. Cascadia subduction event) scenario earthquakes. Three earthquake time histories for each scenario earthquake were developed for each of the 1 in 100, 475 and 2475-year return period seismic hazards. The seismic hazard for the project was based on seismic hazard data from Natural Resource Canada’s (NRC’s) fifth generation seismic hazard model. This data is available on-line from NRC’s 2015 seismic hazard calculator and NRC Open File 8090. The time histories were based on seed time histories for the scenario earthquakes that were scaled and matched to the relevant part of the 2015 NRC uniform hazard response spectra (UHRS) for each return period seismic hazard. The crustal seed time histories were obtained from NGA West2 PEER ground motion database and the inslab and interface seed time histories were obtained from the USGS and CGS’s Center for Engineering Strong Motions Data. The seed time histories were scaled and matched to the site-specific target UHRS using the software program


SeismoMatch published by Seismosoft, which uses the wavelet addition algorithm RSPMATCH developed by N. Abramson. Three time-histories were developed for each scenario earthquake. We carried out 1-dimensional site-specific response analyses (SSRAs) using each of the time histories. The SSRAs were carried out using the software program DEEPSOIL published by the University of Illinois. The SSRAs were completed using three crustal, three in-slab and three interface earthquake time-histories for each of the 1 in 100, 475 and 2475-year return period seismic hazards, for a total of 27 SSRAs per dike section. The results of the SSRAs were used in both the liquefaction assessment and numerical deformation analysis. The SSRAs used the shear wave velocity data from the CPTs to estimate the site-specific seismic accelerations and seismically induced shear stresses and strains. The analysis included numerical seismic deformation analyses using the software program Plaxis 2D. The analyses were carried out to assess the seismic performance of the existing dikes and seismic mitigation measures, such as ground improvement or providing setback dikes, that could be required to meet the performance criteria of the 2014 Seismic Guidelines. 3. GEOTECHNICAL INVESTIGATION

3.1 Program of work

The field investigation was carried out from February 27 to March 1, 2018 and comprised a combination of auger drilling and CPT profiling. Ten CPTs were completed, including three seismic CPTs (i.e. SCPTs), which are CPTs with the addition of shear wave velocity profiling. The CPT profiles, test hole logs and a test hole location plans (Drawings 21847-1 to 21847-4) are attached in Appendix B. The CPTs were advanced to depths of 30 m. SCPTs 18-03, 18-06 and 18-10 included shear wave velocity measurements. The CPT provides a continuous trace of cone tip resistance, sleeve friction and pore pressure. This data was used to interpret the soil stratigraphy and estimate soil properties (e.g. strength and density). The shear wave velocity measurements were used to estimate the small-strain shear modulus of the soil, which has been used in the SSRAs and numerical deformation analyses. The CPTs were drilled out to depths of nominally 7.5 m with a solid-stem auger to confirm the soil profile and collect disturbed samples. The soil and groundwater conditions in the test holes were logged in the field by an experienced geotechnical engineer and representative disturbed samples were collected for routine moisture content testing and visual classification in our laboratory. Fines content analyses (% passing 75 µm sieve) and Atterberg limit testing were carried out on select representative samples. All test holes were located on dikes or within the dike right-of-way and were grouted in general accordance with B.C. groundwater protection regulations and MFLNRO requirements.


3.2 Results of the Investigation

The results of the investigation and laboratory testing are summarized on the attached test hole and CPT logs. The logs provide a complete, detailed description of the conditions encountered and should be used in preference to the generalized descriptions given below. The soil descriptions provided on the CPT logs are Gregg Drilling and Testing Canada’s interpretations of the CPT data using generally accepted correlations and should be considered approximate. CPT/THs 18-01 to 18-06 were carried out on the Matsqui Dike between Sumas Mountain and the tip of the Matsqui Prairie. The soil profile encountered in CPT/THs 18-01 to 18-05 generally comprised dike fill overlying silt that varied from sandy to clayey silt and extended to depths of about 6 m to 8 m. Below the silt, uniform sand was encountered to the maximum depth investigated. CPT/TH 18-06 was closest to Sumas Mountain. At this location the soil profile generally comprised dike fill overlaying clayey silt extending to a depth of about 14 m. Below the clayey silt, uniform sand was encountered to the maximum depth investigated. CPT/THs 18-07 and 18-08 were carried out on the Vedder Dike. CPT/TH 18-07 was located on the Vedder Canal and CPT/TH 18-08 was near the Barrowtown Pump Station. The soil profile encountered at these test holes generally comprised dike fill overlying and silt extending to a depth of about 3 m. Below the silt there was sand with some silt layers. The amount of silt layers increased with depth, and the sand eventually transitioned to silt at a depth of about 15 to 20 m. The silt has some sand layers, becoming siltier with depth. In CPT/TH 18-08 sand was encountered at a depth of about 26 m and extended to the maximum depth investigated. CPT/TH 18-09 was completed on the Sumas Dike on the Sumas River beside Sumas Mountain. The soil profile generally comprised dike fill overlying sandy to clayey silt to the maximum depth investigated. Sand layers were encountered in this silt deposit from depths of about 6 m to 8 m and 11 m to 13 m. CPT/TH 18-10 was carried out on the Sumas Dike on Saar Creek in Sumas Prairie. The soil profile encountered at this location comprised dike fill underlain by silt extending to a depth of about 4 m. Below the silt, interlayered sand and silty sand, becoming siltier with depth, was encountered to the maximum depth investigated. There were some silt layers in the interlayered sand and silty sand deposit. These subsurface conditions encountered during the investigation are consistent with the conditions described in the following documents:

Golder Associates’ December 13, 2007 report “Completion Report for Matsqui and Vedder Dike Upgrades – Abbottsford, B.C.”

Crippen Engineering Ltd.’s 1977 report “Subsurface Investigation – Dikes” for the west side of the Vedder Canal.

Thurber Engineering Ltd.’s September 11, 2015 report “Vedder Canal West Dike (Right Bank) Upgrades – Preliminary Design”

B.C. Surficial Geology Map 1485A


Our assessment of the seismic performance included a liquefaction assessment and numerical deformation analyses of the existing dikes and dikes with ground improvement.

4.1 Liquefaction Assessment

Liquefaction assessments using empirical methods were carried out to assess the degree of liquefaction under each of the seismic hazard return periods for each earthquake scenario type and to provide estimates of reconsolidation settlement. These liquefaction assessments were also used to compare the liquefaction predicted using empirical methods against the liquefaction predicted from the 1D numerical models. Liquefaction assessments were carried out for flat-ground (i.e. 1D) conditions for each of the three design earthquake levels using the software program CLiq published by Geologismiki. These assessments followed the methods described by Idriss and Boulanger (2008 and 2014) to evaluate the resistance to liquefaction (i.e. the cyclic resistance ratio (CRR)). The shear stress triggering liquefaction (i.e. the cyclic stress ratio (CSR)) was calculated by averaging the maximum stress ratio profiles for each scenario earthquake (e.g. the CSR for the 1 in 100-year crustal earthquake was calculated using the average of the maximum stress ratio profiles from the three crustal time-histories). The results of the liquefaction triggering analyses are presented on the plots generated by CLiq in Appendix C. These plots show layers where liquefaction is anticipated (i.e. where the CSR is greater than the CRR, or the factor of safety is less than one against liquefaction) and also provide estimates of post-liquefaction reconsolidation settlement. The liquefaction triggering assessment shows that liquefaction is anticipated to be insignificant under all of the scenario earthquakes for the 1 in 100-year return period seismic hazard for each dike section analysed. This corresponds to “No liquefaction (L0)” per the 2014 Seismic Guidelines. Under the 1 in 475 and 2475-year return period seismic hazards, the greatest amount of liquefaction was caused by the inslab scenario earthquake. The extent of liquefaction under the 1 in 475-year return period seismic hazard is interpreted to be “No Liquefaction” to “Mild Liquefaction” (L1) at the Vedder and Sumas dike sections and at the three dike sections furthest downstream on the Matsqui dike (Sections 1, 2 and 3). The extent of liquefaction under the 1 in 475-return period seismic hazard on the upstream Matsqui dike sections (Sections 4, 5 and 6) is interpreted to be “No Liquefaction”. The extent of liquefaction under the 1 in 2475-year return period seismic hazard is interpreted to be “Moderate Liquefaction” (L2) to “High Liquefaction” (L3) at the Vedder and Sumas dike sections and Sections 1, 2 and 3 on the Matsqui dike. The extent of liquefaction for the upstream Matsqui dike sections (Sections 4, 5 and 6) is interpreted to be “Moderate Liquefaction”. The table below includes descriptions of the extent of liquefaction and corresponding Liquefaction Indices and shear strengths per the 2014 Seismic Guidelines.


Extent of Liquefaction Liquefaction Index Shear Strength

No liquefaction Insignificant (L0) N/A Complete liquefaction not expected Mild (L1) 80% of drained Liquefaction occurs in zones of limited thickness Moderate (L2) Residual Complete liquefaction High (L3) Residual

The post-liquefaction reconsolidation settlement estimates under the 1 in 475 and 2475-year return period seismic hazards calculated by Cliq are presented in the table below. For the 1 in 100-year return period seismic hazard, reconsolidation settlements are anticipated to be negligible. The reconsolidation settlements are all less than the vertical deformation limits of the 2014 Seismic Guidelines. These reconsolidation settlements are based on flat ground conditions and are in addition to the vertical component of the deformations estimated from the numerical deformation analyses.

Settlement (mm)

Dike Dike section 475-year hazard 2475-year hazard

CPT/TH return period return period

Matsqui

1 12 120 2 35 200 3 30 150 4 7 80 5 5 70 6 10 80

Vedder 7 44 130 8 22 170

Sumas 9 48 130 10 46 160

4.2 Seismic Performance of the Existing Dikes

We carried out numerical seismic deformation analyses of the existing dikes using the software program Plaxis 2D. Plaxis 2D is an advanced finite element modelling program that allows for complex modelling of cyclic soil behaviour, similar to the software program FLAC, but with a user-friendly interface that allows for more rapid model construction and has a faster computation routine. The deformation analyses incorporated complex cyclic soil behaviour using the UBCSand soil model, which is the same model used in FLAC for comparable numerical deformation analysis. The numerical deformation analysis used the site-specific earthquake acceleration time-histories output from the SSRAs. The numerical deformation analyses were carried out for the 1 in 100, 475 and 2475-year return period seismic hazards for each of the earthquake scenario types.


One time-history was run for each of the scenario earthquakes for each return period seismic hazard. The time-histories were selected by taking the scenario earthquake time-histories that had the median CSR for each scenario earthquake type. In keeping with the intent of the concept that the dikes must perform under a uniform hazard framework consistent with the NRC’s probabilistic seismic hazard assessment, we have taken the performance under each earthquake return period as the largest displacements of the scenario earthquakes. The largest displacements for all of the sections analysed was the inslab scenario earthquake for the 1 in 100-year return period seismic hazards. For the 1 in 475 and 2475-year return period seismic hazards, the subduction scenario earthquake resulted in the largest displacements for all of the dike sections. The output from the Plaxis analyses provided in Appendix D presents the results from the earthquake scenario type that had the largest seismic displacements. The output includes plots of vertical and horizontal displacements for comparison with the performance requirements of the 2014 Seismic Guidelines. We have also included plots showing total displacement as this provides a clearer interpretation of the pattern of displacements. The output showing the excess pore pressure ratios can be used to interpret the extent of liquefaction predicted in the Plaxis models. Complete liquefaction (i.e. zero effective stress) occurs when the excess pore pressure ratio equals one. The table below summarizes the seismic performance of the dikes (i.e. deformation limits) in terms of which was the minimum earthquake hazard met. Dike Sections 4 and 10 met performance requirements of the 2014 Seismic Guidelines for all of the earthquake return period hazards. This is in part due to the large dike setback (~270 m) at Section 4 and the low dike and shallow channel depth of Saar Creek at Section 10. Sections 2 and 9 have no setback and failed to meet the performance criteria for any of the earthquake return period hazards. The other dike sections generally met the seismic design criteria for the 1 in 475 year and lower return periods.

Dike Dike section Dike guideline

CPT/TH minimum criteria met

Matsqui

1 475

2 none

3 475

4 2475

5 475

6 100

Vedder 7 475

8 475

Sumas 9 none

10 2475


4.3 Seismic Mitigation Measures

Seismic mitigation measures could include controlling seismic deformations using ground improvement or relocating the dikes to provide setback dikes without the need for ground improvement. The extent of ground improvement and required dike setback to meet the performance criteria of the 2014 Seismic Guidelines were assessed using the numerical models developed for the analyses of the existing dikes. Class C (±25 to 40 percent) cost estimates were developed for each of the seismic mitigation options needed to meet the performance criteria of the 1 in 475-year and 1 in 2475-year return period seismic hazards. For each dike and dike upgrade option, we have assumed that the seismic mitigation would include upgrading the dikes to the current flood construction level. We estimated the dike volumes assuming that the dikes would comprise the MFLNRO’s standard dike section with 3H:1V landside and 2H:1V waterside slopes and a 4 m wide crest. The dike volumes were estimated based on the existing dike crest elevations and required dike raisings as described in the City’s Drainage Master Plan, which was prepared by Kerr Wood Leidal in 2018. The average existing and upgraded dike crest elevations based on the Drainage Master Plan are shown in the table below. These required raisings for the upgrades are included in our cost estimates.

Dike Average Dike Crest Elevations (m)

Existing Upgraded

Matsqui 9.7 10.8

Vedder 10.8 12.3

Sumas 7.0 7.7 Our Class C cost estimates include engineering and a contingency. The cost estimates include ground improvement, dike reconstruction where there is ground improvement, dike relocation for the setback dikes, incorporating a toe filter in the upgraded dikes and upgrading the dikes to the dike crest elevations in the table above. Our estimates do not include land acquisition, appurtenant structures such as pump stations and flood boxes, erosion protection or any other items. Cost estimates for these other items can be found in the City’s Drainage Master Plan. , 4.3.1 Ground Improvement

The numerical deformation analyses were based on the 1 in 2475-year return period subduction scenario earthquake. This scenario earthquake was selected because it resulted in the largest seismic deformations for each of the dike sections, and, as discussed above, large deformations tend to initiate at a threshold level earthquake. Accordingly, if the ground-improved dikes meet he performance criteria for the 1 in 2475-year return period seismic hazard, we would also expect them to meet the performance criteria for the 1 in 100 and 1 in 475-year return period seismic hazards.


Based on the geotechnical conditions that were generally encountered in the investigation it is our opinion that ground improvement using stone columns is probably the most suitable ground improvement method for these dikes. Stone columns typically cost about $12 to $15/m3 on a treated volume basis. Compaction piles, soil mixing and jet grouting are other alternatives to increase the strength of the sand to mitigate liquefaction. These alternatives typically cost more and could be more difficult to adapt to changing or unexpected subsurface conditions than stone columns. Compaction piles would also probably need to be straight (i.e. without taper) displacement piles. Although timber piles are commonly used as compaction piles, because they are tapered they may not be able to densify the soil at depth. Compaction piles comprising precast concrete or steel pipe piles are expected to cost about 20 times stone columns on a volume basis. Soil mixing methods include deep soil mixing (DSM) and cutter soil mixing (CSM). These methods are typically about five times the cost of stone columns per treated soil volume. Jet grouting also costs more, at about seven times the cost of stone columns. Ground improvement using stone columns is typically issued for tender as a performance specification. Accordingly, the configuration of the stone columns and the effort used to install them are determined by the ground improvement contractor. Typically, area replacement ratios of about 10% to 20% are used to sufficiently densify liquefiable soil with 0.9 to 1.0 m diameter stone columns. For stone columns in a triangular layout, area replacement ratios of 10% and 20% correspond to centre-to-centre spacings equal to about 4.25 and 3 column diameters, respectively. Stone columns contractors include Hayward Baker and Menard. The following links provide a description of stone column installation by Hayward Baker and a video of stone column installation by Menard.

https://www.haywardbaker.com/solutions/techniques/vibro-replacement https://www.youtube.com/watch?v=WT3RD_MiVyw

The numerical deformation analysis indicates that ground improvement or other remedial measures will be required to meet the performance requirements of the 2014 Seismic Guidelines for dikes near riverbanks. The critical location for ground improvement is usually under the waterside toes/slopes of the dikes, where the static shear stress bias is the highest. In some situations, such as where the dikes are high, ground improvement may also be required under the landside toes/slopes of the dikes. We sized the zone of ground improvement by extending it to the bottom of the deepest liquefiable layer and then incrementally increasing its width until the dike deformations met the required performance criteria. The results of the numerical deformation analyses showing the extent of ground improvement required to meet the performance criteria of the 2014 Seismic Guidelines are provided in Appendix E. We estimated the amount of ground improvement required for each dike by identifying dike segments with similar setbacks and geometries and then selecting which of the ten dike sections analysed was most representative of each segment. Ground improvement will likely require reconstructing the dike. We foresee that the construction sequence to complete ground


improvement would include removing the existing dike, installation of stone columns and then reconstruction the dike. The dike would likely have to be removed before stone column installation to facilitate stone column installation and because the installation procedure would damage the integrity of the existing dike. The cost removal and reconstruction of the dike is uncertain as it would depend on the contractor’s procedure and logistics. The table below shows the estimated Class C (±25 to 40 percent) cost for ground improvement and reconstructing the dike needed to meet the performance criteria of the 1 in 475-year and 1 in 2475-year return period seismic hazards. This estimate used a cost of $12 per m3 on a treated volume basis for stone columns. Our estimate for removing and reconstructing the dike is based on a cost $20 per m3, which assumes reuse of the existing dike fill. We have assumed that new dike fill for raising the dike will cost $60 per m3. The calculation of the cost estimate for this option is provided in Tables 1 and 2 of Appendix G.

Dike Design Return Period Hazard 2475-Year 475-Year

Matsqui $128M $66M Vedder $137M $26M Sumas $68M $68M

Total $333M $160M 4.3.2 Setback Matsqui Dike

As a potential alternative to ground improvement, the Matsqui Dike could be set back from the river bank. Based on the results of the Plaxis deformation analyses, the required distance could be in the order of 250 m and 80 m to meet the performance criteria for the 1 in 2475-year and 475-year return period seismic hazards, respectively. Setback dikes could either require flat slopes or some ground improvement to mitigate seismic deformations (i.e. lateral spreading of the dike embankment). Drawing 21847-6 (included in Appendix E) shows these setbacks. Our Class C cost estimate for the setback dike option excludes real estate costs. The calculations for the cost estimates for this option are provided in Table 3 of Appendix G.

Seismic hazard return period (year)

Setback (m) Length of dike

requiring relocation (km)

% Relocated Cost of

relocation

1 in 475 80 6.5 55 $57M 1 in 2475 250 10.4 90 $69M

4.4 UBCSand - PM4Sand Comparison

We carried out supplemental numerical deformation analyses to assess the performance of the dikes predicted using the PM4Sand constitutive model for liquefiable sand. The purpose of this was to compare the difference in the deformations predicted using PM4Sand and UBCSand. PM4Sand and is a newer soil model that incorporates recent advances in the understanding of


the behavior of liquefiable soils. It is foreseeable that this soil model could replace the UBCSand soil model as the standard of practice in seismic numerical deformation analyses. UBCSand was developed in the 1990s by Micheal Beaty and Peter Byrne at the University of BC as a constitutive model to describe the behavior of liquefiable soil. It was released commercially for the finite difference program FLAC in 2001 and was last updated in 2011 with the release of Version 904aR. We understand that this is the final development of the model and that there will be no further support of it. The development of PM4Sand was led by Ross Boulanger and Katerina Ziotopoulou at UC Davis. Version 3.1 of the model was released in 2017, which was implemented in Plaxis 2D in 2018. As a part of this implementation, Plaxis and Delft University of Technology completed a validation of the model and concluded that it is a promising model that is being used increasingly. In particular, PM4Sand’s advantages include:

Very accurate simulation of pore pressure generation; Accurate simulation of shear strain accumulation and strength degradation; Accounts for the effects of initial static shear stresses well; Good agreement with empirical correlations and observations; Straightforward model calibration.

To be consistent with the UBCSand numerical modelling, the PM4Sand numerical deformation analyses used the same models, with the only change being using PM4Sand instead of UBCSand for liquefiable soil. The PM4Sand numerical modelling used the same earthquake acceleration time-histories that were used in the UBCSand modelling of the existing dikes. We have taken the performance under each earthquake return period as the largest displacements of the scenario earthquakes. The largest displacements for all of the sections analysed was the crustal scenario earthquake for the 1 in 100-year return period seismic hazards. For the 1 in 475 and 2475-year return period seismic hazards, the subduction scenario earthquake resulted in the largest displacements for all of the dike sections, which was the same outcome as the models that used UBCSand. The analyses using PM4Sand were carried out on Sections 2 and 5 on the Matsqui Dike and Section 7 on the Vedder Dike. Section 2 was chosen as it is predicted to have the worst seismic performance of any of the dike sections (it failed to meet the 2014 Seismic Guidelines for all the earthquake return periods). Sections 5 and 7 we selected because they had seismic performance that was typical for the dike section analysed (they met the performance criteria up to the 1 in 475-year return period seismic hazard). The results of the numerical deformation analysis using PM4Sand are provided in Appendix F. We note that for these three sections, the results from the PM4Sand analysis are significantly different than the UBCSand analysis. The PM4Sand models exhibited better seismic performance than the UBCSand models. The performance level of Section 2 increased from failing to meet all of the performance criteria to meeting the performance criteria up to and including the 1 in 475-


year return period seismic hazard. The performance of Sections 5 and 7 increased from meeting the performance criteria for the 1 in 475-year to the 2475-year return period seismic hazard, The significant difference between the results of the UBCSand and PM4Sand numerical modelling is due to the difference in the extent of liquefaction. As shown on the PM4Sand output for excess pore pressure ratios, the extent of liquefaction typically occurred in layers extending horizontally. The UBCSand excess pore pressure ratios were similar to the PM4Sand away from the riverbank slope; however, UBCSand predicts much more liquefaction at the slope. This liquefaction at the slope results in much larger predictions of seismic displacements. The difference could be due to the models’ ability to include the effects of the initial static shear stresses. The initial static shear stresses are highest where there is a stress bias at the riverbank slope. As noted above, PM4Sand can accurately include the effect of initial static shear stresses and could possibly provides a better prediction of displacement and liquefaction than UBCSand in these areas. 5. COMMENT ON THE 2014 SEISMIC GUIDELINES

We understand that the intent of the 2014 Seismic Guidelines is for construction of conventional dikes using alignments or reasonable design features to meet the required seismic performance criteria. However, extensive ground improvement is not necessarily required if the seismic performance criteria are not met. The 2014 Seismic Guidelines acknowledge that ground improvement methods are “costly and may only be practical for short sections or at appurtenant structures”, such as pump stations or flood gates. Accordingly, if cost-prohibitive ground improvement is the only way to conform to the guidelines, alternatives should be considered. The 2014 Seismic Guidelines suggest alternatives such as: 1) realigning dikes to less seismically vulnerable areas (i.e. setback dikes), 2) overbuilding dikes to accommodate seismic displacements, 3) building very wide “superdikes”, and 4) developing comprehensive flood risk and flood protection strategies, including post-earthquake dike repair plans. Selection of the acceptable level of seismic vulnerability is a policy decision that is the responsibility of the MFLNRORD. It is our opinion that selection of the acceptable seismic hazard should consider the increase in probability of flooding caused by loss of dike performance in the event of an earthquake. This would have to consider the anticipated seismic deformations of the dike, the return period of flooding anticipated under a seismically damaged dike and timeframe to repair seismic damage. The 2014 Seismic Guidelines consider the seismic performance of dikes on an acceptable deformation basis and not of the increased flooding hazard that could be caused by seismically caused dike displacements. This approach can lead to too much emphasis being placed on providing seismically resistant dikes that do very little to reduce the flood hazard. Alternative approaches could include:

Selection of an acceptable flood hazard and then identifying the contributions of all factors to that hazard.

Selecting an acceptable hazard level for each factor contributing to the flood hazard.


year return period seismic hazard. The performance of Sections 5 and 7 increased from meeting the performance criteria for the 1 in 475-year to the 2475-year return period seismic hazard, The significant difference between the results of the UBCSand and PM4Sand numerical modelling is due to the difference in the extent of liquefaction. As shown on the PM4Sand output for excess pore pressure ratios, the extent of liquefaction typically occurred in layers extending horizontally. The UBCSand excess pore pressure ratios were similar to the PM4Sand away from the riverbank slope; however, UBCSand predicts much more liquefaction at the slope. This liquefaction at the slope results in much larger predictions of seismic displacements. The difference could be due to the models’ ability to include the effects of the initial static shear stresses. The initial static shear stresses are highest where there is a stress bias at the riverbank slope. As noted above, PM4Sand can accurately include the effect of initial static shear stresses and could possibly provides a better prediction of displacement and liquefaction than UBCSand in these areas. 5. COMMENT ON THE 2014 SEISMIC GUIDELINES

We understand that the intent of the 2014 Seismic Guidelines is for construction of conventional dikes using alignments or reasonable design features to meet the required seismic performance criteria. However, extensive ground improvement is not necessarily required if the seismic performance criteria are not met. The 2014 Seismic Guidelines acknowledge that ground improvement methods are “costly and may only be practical for short sections or at appurtenant structures”, such as pump stations or flood gates. Accordingly, if cost-prohibitive ground improvement is the only way to conform to the guidelines, alternatives should be considered. The 2014 Seismic Guidelines suggest alternatives such as: 1) realigning dikes to less seismically vulnerable areas (i.e. setback dikes), 2) overbuilding dikes to accommodate seismic displacements, 3) building very wide “superdikes”, and 4) developing comprehensive flood risk and flood protection strategies, including post-earthquake dike repair plans. Selection of the acceptable level of seismic vulnerability is a policy decision that is the responsibility of the MFLNRORD. It is our opinion that selection of the acceptable seismic hazard should consider the increase in probability of flooding caused by loss of dike performance in the event of an earthquake. This would have to consider the anticipated seismic deformations of the dike, the return period of flooding anticipated under a seismically damaged dike and timeframe to repair seismic damage. The 2014 Seismic Guidelines consider the seismic performance of dikes on an acceptable deformation basis and not of the increased flooding hazard that could be caused by seismically caused dike displacements. This approach can lead to too much emphasis being placed on providing seismically resistant dikes that do very little to reduce the flood hazard. Alternative approaches could include:

Selection of an acceptable flood hazard and then identifying the contributions of all factors to that hazard.

Selecting an acceptable hazard level for each factor contributing to the flood hazard.

STATEMENT OF LIMITATIONS AND CONDITIONS

1. STANDARD OF CARE

This Report has been prepared in accordance with generally accepted engineering or environmental consulting practices in the applicable jurisdiction. No other warranty, expressed or implied, is intended or made.

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IN ORDER TO PROPERLY UNDERSTAND THE SUGGESTIONS, RECOMMENDATIONS AND OPINIONS EXPRESSED HEREIN, REFERENCE MUST BE MADE TO THE WHOLE OF THE REPORT. THURBER IS NOT RESPONSIBLE FOR USE BY ANY PARTY OF PORTIONS OF THE REPORT WITHOUT REFERENCE TO THE WHOLE REPORT.

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The Report has been prepared for the specific site, development, design objectives and purposes that were described to Thurber by the Client. The applicability and reliability of any of the findings, recommendations, suggestions, or opinions expressed in the Report, subject to the limitations provided herein, are only valid to the extent that the Report expressly addresses proposed development, design objectives and purposes, and then only to the extent that there has been no material alteration to or variation from any of the said descriptions provided to Thurber, unless Thurber is specifically requested by the Client to review and revise the Report in light of such alteration or variation.

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The information and opinions expressed in the Report, or any document forming part of the Report, are for the sole benefit of the Client. NO OTHER PARTY MAY USE OR RELY UPON THE REPORT OR ANY PORTION THEREOF WITHOUT THURBER’S WRITTEN CONSENT AND SUCH USE SHALL BE ON SUCH TERMS AND CONDITIONS AS THURBER MAY EXPRESSLY APPROVE. Ownership in and copyright for the contents of the Report belong to Thurber. Any use which a third party makes of the Report, is the sole responsibility of such third party. Thurber accepts no responsibility whatsoever for damages suffered by any third party resulting from use of the Report without Thurber’s express written permission.

5. INTERPRETATION OF THE REPORT

a) Nature and Exactness of Soil and Contaminant Description: Classification and identification of soils, rocks, geological units, contaminant materials and quantities have been based on investigations performed in accordance with the standards set out in Paragraph 1. Classification and identification of these factors are judgmental in nature. Comprehensive sampling and testing programs implemented with the appropriate equipment by experienced personnel may fail to locate some conditions. All investigations utilizing the standards of Paragraph 1 will involve an inherent risk that some conditions will not be detected and all documents or records summarizing such investigations will be based on assumptions of what exists between the actual points sampled. Actual conditions may vary significantly between the points investigated and the Client and all other persons making use of such documents or records with our express written consent should be aware of this risk and the Report is delivered subject to the express condition that such risk is accepted by the Client and such other persons. Some conditions are subject to change over time and those making use of the Report should be aware of this possibility and understand that the Report only presents the conditions at the sampled points at the time of sampling. If special concerns exist, or the Client has special considerations or requirements, the Client should disclose them so that additional or special investigations may be undertaken which would not otherwise be within the scope of investigations made for the purposes of the Report.

b) Reliance on Provided Information: The evaluation and conclusions contained in the Report have been prepared on the basis of conditions in evidence at the time of site inspections and on the basis of information provided to Thurber. Thurber has relied in good faith upon representations, information and instructions provided by the Client and others concerning the site. Accordingly, Thurber does not accept responsibility for any deficiency, misstatement or inaccuracy contained in the Report as a result of misstatements, omissions, misrepresentations, or fraudulent acts of the Client or other persons providing information relied on by Thurber. Thurber is entitled to rely on such representations, information and instructions and is not required to carry out investigations to determine the truth or accuracy of such representations, information and instructions.

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Geotechnical engineering and environmental consulting projects often have the potential to encounter pollutants or hazardous substances and the potential to cause the escape, release or dispersal of those substances. Thurber shall have no liability to the Client under any circumstances, for the escape, release or dispersal of pollutants or hazardous substances, unless such pollutants or hazardous substances have been specifically and accurately identified to Thurber by the Client prior to the commencement of Thurber’s professional services.

7. INDEPENDENT JUDGEMENTS OF CLIENT

The information, interpretations and conclusions in the Report are based on Thurber’s interpretation of conditions revealed through limited investigation conducted within a defined scope of services. Thurber does not accept responsibility for independent conclusions, interpretations, interpolations and/or decisions of the Client, or others who may come into possession of the Report, or any part thereof, which may be based on information contained in the Report. This restriction of liability includes but is not limited to decisions made to develop, purchase or sell land.

HKH/LG_Dec 2014

Documents

Attachment C - Thurber Report