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20 June 2017

GEOTECHNICAL DESIGN REPORT

T'Seax 80 Bridge (#6444) Replacement, Near Terrace, BC

REPO

RT

Report Number: 1771779-004-R-Rev0

Distribution: 2 Copies - BC Ministry of Transportation and Infrastructure 2 Copies - Golder Associates Ltd. (Terrace/Vancouver)

Submitted to: Ministry of Transportation and Infrastructure Northern Region 4825 Keith Avenue Terrace, BC V8G 1K7

T'SEAX 80 BRIDGE (#6444) REPLACEMENT, TERRACE, BC

20 June 2017 Report No. 1771779-004-R-Rev0 i

Table of Contents

1.0 INTRODUCTION .................................................................................................................................................... 1

2.0 PROPOSED BRIDGE UPGRADING ..................................................................................................................... 1

3.0 GEOTECHNICAL INVESTIGATION ...................................................................................................................... 2

3.1 Previous Drilling Investigation ................................................................................................................... 2

3.2 Site Reconnaissance ................................................................................................................................ 3

4.0 SUBSURFACE CONDITIONS ............................................................................................................................... 3

5.0 SEISMIC DESIGN CONSIDERATIONS ................................................................................................................ 4

5.1 Seismic Design Parameters...................................................................................................................... 4

6.0 GEOTECHNICAL DESIGN RECOMMENDATIONS.............................................................................................. 5

6.1 Subgrade Preparation ............................................................................................................................... 5

6.2 Permanent Embankment Fill Construction ............................................................................................... 6

6.3 Stability Analyses ...................................................................................................................................... 7

6.4 Settlement Analyses ................................................................................................................................. 9

6.5 Permanent Cut Slope Development ......................................................................................................... 9

6.6 Material Re-Use ........................................................................................................................................ 9

6.7 Bulking Factors ......................................................................................................................................... 9

6.8 Geotextile Separators ............................................................................................................................. 10

6.9 Bridge Foundations ................................................................................................................................. 10

6.10 Pavement Requirements ........................................................................................................................ 11

7.0 CLOSURE ............................................................................................................................................................ 12

8.0 REFERENCES ..................................................................................................................................................... 13

TABLES Table 1: 2%/50 years (0.000404 per annum) Probability ................................................................................................ 4

Table 2: 5%/50 years (0.001 per annum) Probability ...................................................................................................... 4

Table 3: 10%/50 years (0.0021 per annum) Probability .................................................................................................. 4

Table 4: Slope Analysis Material Properties - Embankment Fill Slopes .......................................................................... 7

Table 5: Minimum Geotextile Specifications .................................................................................................................. 10

Table 6: Inventory of 2003 Geotechnical Investigation Test Holes ................................................................................ 14


20 June 2017 Report No. 1771779-004-R-Rev0 ii

FIGURES Drawing 6444-21 – Foundation Investigation

Drawing 6444-22 – Summary Logs

APPENDICES APPENDIX A April 2004 Geotechnical Report

APPENDIX B 2015 NBCC Seismic Hazard Calculation


20 June 2017 Report No. 1771779-004-R-Rev0 1

1.0 INTRODUCTION Golder Associates Ltd. (Golder) was retained by the BC Ministry of Transportation and Infrastructure (MoTI) to provide geotechnical engineering design recommendations for the proposed replacement of the T’seax 80 Bridge (#6444) near Terrace, BC (see Location Map on Drawing 6444-21). This final design report documents our geotechnical input to the 90% design submission for the project as prepared by WSP Canada Inc. (WSP) and MoTIs structural group.

Golder previously carried out a geotechnical investigation at the existing bridge crossing on September 24/25, 2003 with the factual results of the investigation provided in a report entitled, “Geotechnical Investigation, T’seax #80 Bridge Crossing, Nisga’a Highway, Nass River Valley, BC”, dated 1 April 2004. A copy of this previous geotechnical report is included in Appendix A.

This report includes factual results of the detailed subsurface geotechnical investigation carried out at the site by Golder in September 2003, together with our interpretation of the investigation results, and our comments and recommendations regarding the geotechnical aspects of the highway and bridge design. We have provided ongoing geotechnical input to the design team, as documented in email transmittals and meeting minutes, and this input is summarized in this geotechnical design report.

The scope of this report is limited to the provision of geotechnical engineering services only and does not include any provision for archaeological, bio-environmental, or hydrotechnical services for the project which are being provided by others. In addition, this report does not include any review or assessment of the potential for soil and/or groundwater contamination at the site.

This report should be read in conjunction with the “Important Information and Limitations of this Report” which is included following the text of this report. The reader’s attention is specifically drawn to this information, as it is essential that it is followed for the proper use and interpretation of this report.

2.0 PROPOSED BRIDGE UPGRADING The existing T’seax Bridge crosses the Nisga’a Highway (Highway 113) at the T’seax River some 80 km north of Terrace, roughly 15 km south of New Aiyansh, BC. At this location, the highway and bridge are aligned roughly north-south with the river running approximately east-west under the bridge and flowing to the east. The site is in the Nass River Valley, within the Lava Bed Park boundaries and within the Nisga’a Lisims treaty lands.

We understand that the existing bridge structure is a single lane 21 m single span bridge with steel I-beams and a timber deck with concrete roadside barriers fanning out from all four corners of the bridge. The deck elevation of the existing bridge is at about 183.0 m (Geodetic datum). It is also understood that the abutments for the existing bridge structure are supported on spread footings founded on bedrock.

Based on the 90% design submission, dated May 2017, and site surveys completed on June 18, 2016 and November 2016 by WSP, the existing bridge will be replaced by a 33 m long, two lane single span steel girder structure with a concrete deck and abutments. We also understand that site grades will increase by about 1.3 to 1.8 m respectively at the centreline of the south and north abutments, with a centreline deck elevation of 184.4 m at the south abutment and 184.7 m at the north abutment. The site grades are expected to be increased up to about 1.3 and 3.4 m respectively at the centreline of the south and north approaches, and the approach



embankment footprints will be widened by up to about 15 m to accommodate the two lane bridge. Based on the project stationing (L100 along the centreline of the proposed Nisga’a Highway 113 roadway alignment), the bridge will be between Stations 104+74.5 and 105+06.5 and the roadway upgrades (i.e., limits of construction) will extend from Station 102+08.0 to 106+15.5 (i.e., total length of 407.5 m). The limits of construction are at about 179.5 m elevation at the north limit and about 183.0 m on the south limit.

A BC Hydro Right of Way (RoW) crosses the existing highway in the south end of the project limits with an existing Hydro tower situated at about Station 106+05 and offset about 15 m east of the centreline of the highway. In addition, an elevated pond exists between Stations 105+20 and 105+40 and offset about 20 m east of the centreline of the highway with an invert elevation of about 179 m. We understand that the pond drains to the north to northeast and enters the main river channel at the Hydro RoW.

We understand that the 200 year design flood elevation is about 181 m beneath the bridge, as estimated by Northwest Hydraulic Consultants (NHC), and the invert of the river channel beneath the bridge is about 178 m elevation. We also understand that the typical water level beneath the bridge is between about 179 and 180 m, however, during portions of some years no water is present beneath the bridge (e.g. 18 October 2016).

During construction a temporary detour roadway and single lane 36 m long bridge crossing will be constructed downstream and to the east of the existing and proposed roadway. The proposed detour alignment will tie into the existing roadway and will have a total length of about 280 m. The centreline site grades will increase by up to 1.5 m along the detour alignment and the centreline bridge deck elevation will be about 182.5 m at the north abutment and about 183.0 m at the south abutment. We understand that the temporary crossing and detours during construction will be the responsibility of the contractor, and geotechnical input from Golder will not be required for these.

The proposed design has been carried out in accordance with the Canadian Highway Bridge Design Code S6-14 (CAN/CSA S6-14). The bridge classification is “Other” and will be required to meet the Life Safety design criteria under seismic loading. The bridge foundations will consist of spread footings founded on bedrock.

3.0 GEOTECHNICAL INVESTIGATION 3.1 Previous Drilling Investigation As detailed in our April 1, 2004 geotechnical report (Appendix A), MoTI carried out a drilling program at the existing bridge on 24 and 25 September 2003, during which two testholes, TH03-01 and TH03-02, were drilled. TH03-01 was drilled about 6.1 m north of the northeast corner of the existing bridge deck and TH03-02 was drilled about 5.2 m south of the southwest corner of the existing bridge deck. Both testholes were drilled in the gravel shoulder of the existing highway. The testholes were measured in the field and were not surveyed following the investigation. The drilled depth of TH03-01 and TH03-02 were about 16.0 and 12.9 m, respectively, below the existing ground surface. Based on the locations of the testholes and the available topographic information, we estimate that the top of TH03-01 was at about 182.5 m elevation and the top of TH03-02 was at about 183.0 m elevation. The approximate locations of the testholes are shown in Figure 2 of the April 2004 report (Appendix A) and Drawing 6444-21 of the current report.



Split spoon sampling was carried out to collect soil samples for laboratory testing, along with Standard Penetration Testing (SPT) to determine the relative density of the existing soils. Continuous core samples were collected where bedrock was encountered.

We understand that there have not been any changes to the existing bridge structure and approach fills since 2003 and as such no additional intrusive geotechnical investigation was carried out and the existing 2003 geotechnical investigation data was considered to be sufficient for detailed design.

3.2 Site Reconnaissance Golder visited the project site with others from the project team to carry out visual reconnaissance of the site for the proposed bridge replacement. The site visits were completed on 9 August 2016 and 18 October 2016. The intention of the reconnaissance was to observe/record visual indications of existing slope instability, river erosion, pavement distress, as well as to verify topographic features. A detailed pavement assessment was not carried out during our site reconnaissance.

Based on observations made during our 9 August 2016 site visit, no visual signs of scour were observed or confirmed by probing at the existing north abutment, however, we could not confirm with the foundations below the water level. The south abutment was founded on stepped bedrock and no scour issues were observed at the south abutment. The elevated pond area located to the southeast of the existing bridge had about 50 mm of water and was generally covered with wood debris and moderate tree cover. The river water depth below the bridge was measured to range between about 0.5 and 1.7 m. We understand that the existing bridge abutments and footings will remain in place.

Based on observations made during our October 18, 2016 site visit, the T’seax River was generally dry with the exception of some limited areas of ponded water within the river channel.

4.0 SUBSURFACE CONDITIONS Detailed descriptions of the subsurface conditions encountered in the testholes are reported on the Summary Log sheets in Appendix I of our previous geotechnical report, prepared in conformance with the format specified by MoTI and are included in the attached Appendix A. Classification of the sub-surface soil conditions is in accordance with the MoT modified Unified Soil Classification System (USCS).

It should be noted that the site soil and rock conditions are accurate only at the testhole locations. The elevations of the testholes were not surveyed at the time of the investigation and were estimated based on current site grades. Variations in the thickness, composition, and properties of the fill, soil, and rock strata were encountered at the testholes. Similar, and possibly greater variations in the subsurface conditions may be encountered along the bridge alignment and beneath the highway.

A plan view of the area showing the proposed footprint of the existing bridge structure and roadway alignment and the approximate 2003 testhole locations are shown on the top part of Drawing 6444-21. A profile cross-section showing the approximate locations and elevations of the 2003 testholes is presented on the lower part of Drawing 6444-21. The cross-section also shows the proposed roadway centerline, as well as the ground surface profile along the existing roadway centreline.



The testholes generally consisted of inferred compact gravel with trace sand and silt at TH03-01 and inferred dense sandy gravel in TH03-02 to about 3.5 m and 2.4 m depth, respectively, below the existing ground surface.

Volcanic basalt bedrock was encountered below the granular fills. This bedrock extended to the termination of the testholes, TH03-01 and TH03-02, at about 16.0 and 12.9 m depth below the existing ground surface, respectively. Diametral Point Load Is(50) tests were carried out on one sample from near the surface of the bedrock in each of the testholes with results of 5.1 and 7.5 MPa. Point load test values can be correlated to approximate Unconfined Compressible Strength (UCS) values based on an index to strength conversion factor K. This conversion factor can be highly variable depending on the rock type, rock structure, and other factors. Based on an estimated range of K=16 to 18 for the site, the UCS equivalent results would range between about 80 and 135 kPa. Based on visual examination of the bedrock, and the UCS equivalent results, the volcanic bedrock is generally considered to be strong to very strong (i.e., UCS range of 50 to 250 MPa). The bedrock is also considered to be generally fresh (i.e., no weathering was observed).

Groundwater seepage was not confirmed within the testholes at the time of drilling. However, we expect that the natural groundwater level will be at or near the water level in the river. Perched water levels may also develop within or above any silty zones below the ground surface or above the bedrock surface during periods of sustained wet weather.

5.0 SEISMIC DESIGN CONSIDERATIONS 5.1 Seismic Design Parameters Golder obtained site-specific seismic hazard results from National Resources Canada (NRC) for the Tseax Bridge site located at 55.1136°N and 128.9770°W and have presented the results in Appendix B. In accordance with the new seismic design requirements presented in the Canadian Highway Bridge Design Code (CAN/CSA S6-14), the 2015 seismic hazard reference results (i.e., Site Class C-very dense soil and soft rock) are as follows:

Table 1: Seismic Hazard Parameters - 2%/50 years (0.000404 per annum) Probability

Sa(0.05) Sa(0.1) Sa(0.2) Sa(0.3) Sa(0.5) Sa(1.0) Sa(2.0) Sa(5.0) Sa(10.0) PGA PGV

0.074 0.112 0.138 0.138 0.133 0.111 0.079 0.030 0.011 0.068 0.186



0.045 0.068 0.087 0.094 0.095 0.083 0.060 0.022 0.008 0.045 0.137



0.031 0.046 0.061 0.068 0.071 0.064 0.046 0.017 0.006 0.032 0.103



In accordance with the CAN/CSA S6-14 the following seismic parameters apply to the T’seax Bridge site:

We understand the bridge classification is “Other” and will be required to meet the Life Safety design criteria under seismic loading.

Site Classification for seismic site response: Site Class B – Rock (Table 4.1)

Seismic Performance Category: 1 (i.e., S(0.2) <0.10 and S(1.0) <0.10)

The site coefficient factors F(T) for Site Class B can be calculated using Tables 4.2 to 4.9 in Section 4.4.3.3 and the design spectral acceleration values S(T) can be determined from Section 4.4.3.4 in CAN/CSA S6-14.

It is noted that detailed time-history ground response analysis has not been carried out for the T’seax bridge site. Given the near surface rock overlain by compact to dense granular fills at the site, the risk of liquefaction of the subsurface soils beneath the proposed foundation elements for the new bridge structure due to seismic loading is considered to be very low.

6.0 GEOTECHNICAL DESIGN RECOMMENDATIONS 6.1 Subgrade Preparation We understand that clearing and grubbing on the west side of the highway will be taken from the existing gravel shoulder to about 1 m beyond the design embankment toes. We also understand that clearing and grubbing on the east side of the highway will be taken from the existing gravel shoulder to about 3 m beyond the design permanent and detour embankment toes, with the exception of areas where space constraints exists (e.g. near hydro tower).

The existing asphalt pavement should be removed from along the entire alignment where grade increases are proposed along the alignment. Consideration may be given to milling the existing asphalt and underlying granular base course fills to provide a maximum 50 percent asphalt millings by volume (i.e., mill to at least two times the depth of the existing asphalt). This milled material could be re-used as Type D fills in the proposed embankment fills. If re-use of the asphalt millings is not proposed, the milling may be limited to the underside of the asphalt pavement and disposed of off-site.

Topsoil, organic, deleterious or loose fill materials are not considered suitable for direct subgrade support or re-use as embankment fill and should be stripped/sub-excavated from the entire footprint of the proposed fill, cut, structure foundations and pavement areas. It is recommended that stripping/sub-excavation of these materials be carried down to the underlying, undisturbed, competent mineral soil/fill deposits or to the competent volcanic bedrock surface; and this prepared subgrade should be adequately sloped/shaped to prevent ponding of surface and/or groundwater.

Since testholes were not put down along and beyond the toe of the existing embankment slopes, the stripping depths for the project have not been confirmed. For project costing purposes we suggest an average 100 mm thick stripping depth along the existing embankment slopes and between 100 and 300 mm stripping depth (average 150 mm) beyond the toe of the existing highway embankment slopes. It should be noted that the stripping



depths could locally exceed our estimates, particularly in poorly drained, low lying areas. It is recommended that a non-woven geotextile fabric (see Section 6.8 for specifications) be placed below the proposed permanent embankment fills situated beyond the existing highway embankment toes in areas where the fills are placed over bedrock with open fractures observed or where there is a concern about migration of finer particles between the fills and underlying subgrade. We recommend that Golder inspect the subgrade following stripping to confirm where the geotextile would be required. The non-woven geotextile may also be considered beneath the portions of the temporary detour alignment that extend beyond the permanent embankment toes to provide a physical barrier when the temporary fills are removed. However, if this barrier is not required for the detour, placement of the geotextile would not be necessary beneath the detour (beyond the permanent embankment toes).

6.2 Permanent Embankment Fill Construction Embankment construction will be required for the new bridge approach fills and for the detour bridge approach fills. These will generally be fills that will be placed adjacent to the existing highway fill slopes. The embankment subgrade preparation should be carried out as outlined in Section 6.1 above. The prepared subgrade should be inspected by a geotechnical engineer prior to placing highway embankment fills.

Following the subgrade preparation, the proposed highway fills may be constructed consistent with SS 201.37 of the BC MoTI 2016 Standard Specifications for Highway Construction (Standard Specifications), except where Bridge End Fill zones are required. As per the specification, the new embankment fills should be terraced in a continuous series of minimum 1.5 m wide steps into the existing highway embankments. Step heights should be no more than about 1 m high.

Permanent embankment fill slopes should be developed at 2 Horizontal to 1 Vertical (2H:1V), or flatter. Steeper slopes may be considered where a riprap facing and geogrid reinforcement is used as described below. Temporary embankment fill slopes may be developed at 1.5H:1V, or flatter (i.e., detour fill slopes). The embankment fills should be placed in maximum 200 mm lifts and compacted to at least 95 percent standard Proctor maximum dry density (SPMDD), as per ASTM D698. Bridge End Fill zones should be placed and compacted to at least 100 percent SPMDD, as per SS 202.23 of the Standard Specifications.

For the proposed pavement structure, MoTI has recommended 600 mm of 25 mm well graded base (WGB) for the combined base and sub-base fills compacted to at least 100 percent SPMDD, overlain by 100 mm asphalt placed in two lifts.

We understand that the borrow pit source for the proposed Bridge End fills and Type D borrow fill materials will likely be from the Kseadin Gravel Pit located about 20 km from the site. The Type D fills will generally be imported and unprocessed 75 mm minus pit run sand and gravel and the Bridge End fills and pavement structure base and sub-base course fills will be 25 mm WGB fills. We understand that the 25 mm WGB fills will consist of screening the 25 mm minus particles from the pit run, crushing the greater than 25 mm particle sizes down to a 25 mm minus crushed rock fill, and mixing these fills.

Consideration may be given to using the Basalt rock Type A excavation as embankment fills. However, there is expected to be limited Type A excavation for the project and it would need to meet the SS201.36 specification for rock fill embankment. There is a requirement in SS201.36 that the top 500 mm of the rock fill must be a transition between either soil embankment or pavement structure that overlies it.



6.3 Stability Analyses Golder has carried out slope stability analyses for the up to about 4.5 m high fill slopes constructed of Type D borrow fills overlain by a 600 mm thickness of 25 mm WGB fills (i.e., pavement base/sub-base). We have also carried out slope stability analyses for the up to about 4.5 m high fills slopes within 8 m of the abutment locations which will consist of Bridge End fills consisting of 25 mm WGB fills overlain by a 600 mm thickness of 25 mm WGB fills (i.e., pavement base/sub-base).

The commercially available slope stability software program Slope/W© (Version 7.20) was used to calculate the forces and moments on circular slip surfaces passing through an embankment and compare them with the available strength of the soils along potential failure (slip) surfaces. The ratio of the forces and moments resisting failure to those tending to cause failure along a slip surface within a particular soil mass is referred to as the Factor of Safety (FOS) for that slip surface. The theoretical method used to calculate the FOS for this analysis was the Spencer method, which calculates a FOS based on satisfying both force and moment equilibrium equations.

The analysis was carried out for 1.5H:1V to 2H:1V fill slope configurations based on available testhole information. The soil stratigraphy between the testhole locations is based on our interpretation of the geological conditions of the area and consequently the actual field conditions may vary from that used in our models.

The slope stability analyses assumed the material properties tabulated below:

Table 4: Slope Analysis Material Properties - Embankment Fill Slopes

Material Soil Model Friction Angle Cohesion Unit Weight

25 mm WGB Mohr-Coulomb 36o 0 21 kN/m3

Bridge End Fills (25 mm WGB) Mohr-Coulomb 36o 0 21 kN/m3

Type D Borrow Fills (75 mm minus pit run) Mohr-Coulomb 34o 0 21 kN/m3

Riprap (100 kg Class) Mohr-Coulomb 42o 0 21 kN/m3

Existing Granular Fills Mohr-Coulomb 34o 0 21 kN/m3

Basalt Bedrock N/A N/A N/A N/A

The groundwater level in our analysis was assumed to be at 180 m elevation which is generally about 0.5 m, or greater below the toe of the proposed embankments slopes. Traffic loading based on BCL-625, Class A Highway live loading as per CAN/CSA S6-14 was also considered in our analyses.

Based on the recommendations in CAN/CSA S6-14, the recommended resistance factors range between 0.6 and 0.7 for permanent slopes under static loading conditions (i.e., Factor of Safety (FOS) against slopes instability of 1.43 to 1.67, average 1.54). We consider a FOS of at least 1.45 under static loading conditions and at least 1.1 under design seismic loading conditions to be acceptable for the project. For our slope stability analyses we assumed a minimum slip surface thickness of 1 m to avoid considering shallow surficial failures.



The slope stability analysis for a 1.5H:1V fill slope configuration using the above parameters indicate a calculated static FOS against slope instability of about 1.45 for embankment slopes up to about 2.1 m high with Bridge End fills and up to about 1.8 m high with Type D fills. For the up to 4.5 m high fills slopes the FOS reduces to about 1.25 for the Bridge End fills and to about 1.20 with the Type D fills which is less than recommended by MoTI for permanent embankments slopes but is considered to be acceptable for the proposed temporary detour embankment slopes. Some erosion and sloughing of the surface of 1.5H:1V slopes is expected, in particular during and following heavy rainfall and seeding or a coco-mat type cover could be considered to prevent soil loss due to heavy rainfall. We understand that spillway rock lined drains with 10 kg Class riprap underlain by a non-woven geotextile will be installed in a few locations to discharge water off the road surface and down the embankment.

The calculated static FOS against slope instability for a 2H:1V fill slope is 1.45, or greater for the up to 4.5 m high permanent embankment slopes proposed which is considered acceptable.

The computed Factor of Safety under design seismic loading (0.5 of the site-specific 2475 year return period PGA for design, equal to 0.02) is greater than 1.1 for 1.5H:1V and 2H:1V fill slopes up to 4.5 m thickness.

It is understood that the design team would prefer to use 1.5H:1V embankment slopes within the Bridge End fills zone and transition to 2H:1V slopes beyond this. To provide a desired FOS against slopes stability of at least 1.45 under static loading conditions, the following was recommended for the 1.5H:1V to 1.75H:1V embankment slopes:

1 layer of 3.5 m long uniaxial geogrid reinforcement recommended between underside of pavement structure and top of riprap/Bridge End fills where riprap is proposed across the embankment slopes. 100 kg Class riprap recommended to be a minimum 1 m thickness where placed. Non-woven geotextile was recommend below the riprap and between top of riprap and geogrid.

3 layers of 3.5 m long geogrid recommended where 1.5H:1V to 1.65H:1V slopes are proposed without riprap to the north of the bridge. Top layer to be situated at underside of pavement structure with other two layers at 1 m spacing. The lowest layer of geogrid may require some excavation into the existing embankment slopes but if bedrock is encountered, no removal of bedrock is required (i.e., stop excavation if bedrock encountered).

2 layers of 3.5 m long geogrid recommended where 1.65H:1V to 1.75H:1V slopes proposed without riprap, and to 1 m beyond 1.75H:1V slopes to the north of the bridge. Top layer to be situated at underside of pavement structure with other layer 1 m below.

1 layer of 3.5 m long geogrid recommended on the east and west sides of the roadway south of the bridge extending from the concrete wingwall to 1 m past (south of) the 1.75H:1V slopes.

In areas where riprap spillways are proposed, the geogrid may terminate at the back of the spillways.

Uniaxial geogrid to consist of Tensar UX1400MSE (or approved alternative).



6.4 Settlement Analyses The fills required for the proposed new roadway construction will induce settlements within the fills and native soils which overlie the volcanic bedrock. Analyses were carried out to estimate the settlements due to construction of the new highway embankments. Estimates of total settlements have been based on the mineral fill thickness required to construct the embankments. There are expected to be differences in total settlement across the embankment due to variations in the fill thickness stemming from topography, as well as from differences in the underlying subsurface soil and groundwater conditions.

Granular fill (i.e., mineral fill) having a unit weight of approximately 21 kN/m3 was assumed in the analyses. Settlement estimates were based on cross sections provided on the 100% design submission prepared by WSP dated May 24, 2017 which included permanent embankments developed with 1.5H:1V to 2H:1V side slopes. Settlement estimates were calculated using one-dimensional consolidation theory with the commercially available computer settlement analysis software package Settle3D (Version 2.016) by RocScience Inc. and estimated soil parameters.

The analyses involved the placement of conventional granular embankment fills with up to 300 mm thickness of topsoil/organics stripping completed.

Based on the results of our analyses, it is estimated that the potential settlement of embankment fills will range between about 5 and 15 mm per metre of fills placed. It is estimated that the up to 4.5 m high embankment fills (up to 3.5 m thickness of additional fills) could range between approximately 25 and 50 mm of settlement. It is anticipated that the majority of settlement due to compression of the underlying subgrade soils will occur during construction of the embankment fills.

6.5 Permanent Cut Slope Development Permanent cut slopes of up to about 1 m height will be required in some ditch areas adjacent to the toe of the embankment fills. The up to 1 m high permanent soil cuts may be developed at 1.5H:1V, or flatter.

6.6 Material Re-Use The limited cut materials (Type D excavation) originating from the site are expected to be generally sand and gravel fills with trace fines. If the existing fills are considered for re-use as embankment fills they should contain less than 5 percent fines and be approved for re-use by Golder during construction. Granular fills with greater than 5 percent fines may be considered for re-use but these materials may prove difficult to transport, place and compact, particularly in wet weather conditions and if the materials are above their optimum moisture content.

6.7 Bulking Factors For the existing granular fills, which will likely form the majority of the Type D excavation material, we suggest a bulking factor of about 1.1 be assumed to determine the fill material volume after compaction compared to volume before excavation for material placed to 95 percent SPMDD (i.e., it is estimated that the compacted volume will be greater than the bank volume by about 10 per cent). A bulking factor of about 1.2 to 1.25 may be assumed to determine the loose, un-compacted, fill volume after excavation compared to the volume before excavation.



It should be noted that loss of material due to wetting, screening of large particle sizes and material handling has not been considered in the above estimates.

6.8 Geotextile Separators The recommended geotextile specifications for use as separation layers between fine grained soils/rock with openings and the proposed embankment fills, and between the proposed embankment fills and riprap layers should be non-woven and needle-punched such as Nilex 4553 (or approved equivalent). The geotextile properties should meet or exceed the following minimum average roll values:

Table 5: Minimum Geotextile Specifications Grab Tensile Strength: (ASTM D4632); 0.90 kN Grab Tensile Elongation: (ASTM D4632); 50 % CBR Puncture Strength: (ASTM D6241); 2.336 kN UV Resistance: (ASTM D4355); 70 % @ 500 hrs Trapezoidal Tear: (ASTM D4533); 0.356 kN Apparent Opening Size: (ASTM D 4751); 0.180 mm Permittivity: 1.5 sec-1 (ASTM 4491); and 1.5 sec-1 Water Flow Rate: 4480 l/min/m2 (ASTM D4491). 4482 l/min/m2

The selected geotextile should be installed in accordance with the manufacturer’s recommendations. The recommended overlap for the geotextile is dependent on the application, but it is typically 0.5 m.

6.9 Bridge Foundations We understand that the proposed bridge structure will be a single span structure supported on abutment walls, with spread footings founded on the volcanic basalt rock. Based on this, we provide the following geotechnical recommendations for foundation design consistent with the CAN/CSA S6-14 Bridge Code.

Bearing Capacity for Footings Bearing on Fresh Strong Basalt Bedrock

Ultimate Bearing Resistance – Ru: 3 MPa

Geotechnical Resistance Factor for ULS design – φgu: 0.5 (assumes Typical degree of understanding)

Serviceability Bearing Resistance – Rs: 1 MPa (limited to 10 mm of settlement)

Based on the 90% structural design drawings, the proposed north abutment is in the vicinity of TH03-01 and the south abutment is in the vicinity of TH03-02. Based on the locations of the testholes and the available topographic information, we estimate that the top of TH03-01 is at about 182.5 m elevation and the top of TH03-02 is at about 183.0 m elevation with the top of bedrock at these locations at about 178.99 m elevation at TH03-01 and about 180.56 m elevation at TH03-02. However, it should be noted that the elevations at the testhole locations were not surveyed and may vary from the estimated elevations which were based on recent survey data at the approximate testhole locations. In addition, since the depth to bedrock was only confirmed at a single location near each abutment, the actual elevation of the bedrock may vary along the footings.



Based on discussions with the project structural engineer, the underside of the north abutment footing will be 179.2 m elevation and the underside of the south abutment footing will be 179.3 m elevation on the east side, step up to 180.0 m elevation, and then step up to 180.7 m elevation on the west side. On a geotechnical basis the south abutment footing may be benched/stepped vertically or sloped at each step. We recommend that a minimum 75 mm layer of lean mix concrete be placed between the bedrock surface and the underside of the abutment footings to provide a suitably flat working floor and infill any surficial voids in the bedrock. The concrete working floor should be placed on a clean rock surface and free from any loose materials. We understand that the lean mix concrete will be the same concrete mix that is used for the concrete footings.

Based on the proposed footing elevations and assuming the bedrock elevation is generally at the elevations assumed, limited to no ripping or blasting of the bedrock surface is anticipated. However, the actual depths to bedrock and surveyed elevations will need to be confirmed at the proposed abutment locations during construction with geotechnical inspection carried out during or following initial excavation. If needed, additional geotechnical recommendations will be provided if the bedrock surface varies from what was assumed.

Prior to placement of the lean concrete working surface, some limited dewatering may be required to provide a relatively dry bedrock surface. This can likely be carried out using conventional sump and pump methods, however if the water levels are higher than the underside of the abutment footings during construction, more significant dewatering measures may be required.

We understand that the abutment wall height on the north side of the bridge is about 5.2 m and the south side of the bridge is about 4.8 m, with a wall thickness of 1.2 m. We also understand that the abutments will be connected to the superstructure with elastomeric bearings and anchor rods. As such, both top ends are very slightly restrained, but negligible. Since backfills will be placed prior to the superstructure construction lateral pressures would likely occur on the cantilever system.

Based on the estimated soil friction angle of 36 degrees in the Bridge End fill materials proposed and assuming some movement of the abutment walls would be acceptable, an active earth pressure coefficient of Ka=0.24 can be assumed. However, if un-tensioned dowels are installed between the abutment footing and bedrock to resist against sliding, we recommend a K=0.33 which is between at-rest and active conditions and assumes some small wall movements would occur during the construction of the concrete abutments.

In addition, we recommend an equivalent fluid pressure of 8z which is an average between active and at-rest conditions (i.e., 6z and 10z) if un-tensioned dowels are installed, or an equivalent fluid pressure of 6z if no dowels are proposed. We also recommend that compaction surcharge pressures be considered in the design of the foundations (12 kPa at surface reducing to 0 kPa at 2 m below the surface).

The geotechnical resistance factor for sliding (based on friction) will be 0.8. Based on an estimated coefficient of friction of 0.5 between the concrete and rock, the factored sliding resistance would be 0.4.

6.10 Pavement Requirements Pavement design for the new highway embankments are typically carried out consistent with the 1993 AASHTO Guide for Design of Pavements as well as with the current MoTI Pavement Structure Design Guidelines (Technical Circular T-01/15). However, Golder was not provided traffic loading information and did not provide geotechnical input to the pavement design for this project. The pavement design recommendations were provided by MoTI.



8.0 REFERENCES BC Ministry of Transportation and Infrastructure, 2012 Standard Specifications for Highway Construction;

11 November 2011;

Canadian Standard Association, Canadian Highway Bridge Design Code, CAN/CSA-S6-14, December, 2014;

BC Ministry of Transportation, Bridge Standards and Procedures Manual, Volume 1, Supplement to CHBDC S6-06, August 2007;

BC Ministry of Transportation, Pavement Structure Design Guidelines – Technical Circular T-01/15, 26 January 2015;

Canadian Geotechnical Society, Canadian Foundation Engineering Manual, 4th Edition, 2006;

American Society of State Highway and Transportation Officials, AASHTO Guide for Design of Pavement Structures, 1993;

American Society of State Highway and Transportation Officials, AASHTO Standard Specifications for Highway Bridges, 17th Edition, 2002;



Table 6: Inventory of 2003 Geotechnical Investigation Test Holes

Testhole

Approximate UTM Coordinates (NAD 83)

Approximate Project Grid Coordinates

Northing Easting Northing Easting Approximate Elevation Date Depth

(m)

TH03-01 61074131 5014731 1074592 5014732 182.53 24 Sep 2003 16.0

TH03-02 61074441 5014621 1074902 5014622 183.03 25 Sep 2003 12.9

Notes: 1 – Coordinates determined by Golder Associates as measured from corners of existing bridge deck 2 – Survey coordinates based on average combined scale factor 0.99957250602 with grid shift of -6000000m in N 3 – Elevations estimated by Golder Associates using recent survey data provided by WSP



IMPORTANT INFORMATION AND LIMITATIONS OF THIS REPORT Standard of Care: Golder Associates Ltd. (Golder) has prepared this report in a manner consistent with that level of care and skill ordinarily exercised by members of the engineering and science professions currently practising under similar conditions in the jurisdiction in which the services are provided, subject to the time limits and physical constraints applicable to this report. No other warranty, expressed or implied is made.

Basis and Use of the Report: This report has been prepared for the specific site, design objective, development and purpose described to Golder by the Client. The factual data, interpretations and recommendations pertain to a specific project as described in this report and are not applicable to any other project or site location. Any change of site conditions, purpose, development plans or if the project is not initiated within eighteen months of the date of the report may alter the validity of the report. Golder cannot be responsible for use of this report, or portions thereof, unless Golder is requested to review and, if necessary, revise the report.

The information, recommendations and opinions expressed in this report are for the sole benefit of the Client. No other party may use or rely on this report or any portion thereof without Golder’s express written consent. If the report was prepared to be included for a specific permit application process, then upon the reasonable request of the client, Golder may authorize in writing the use of this report by the regulatory agency as an Approved User for the specific and identified purpose of the applicable permit review process. Any other use of this report by others is prohibited and is without responsibility to Golder. The report, all plans, data, drawings and other documents as well as all electronic media prepared by Golder are considered its professional work product and shall remain the copyright property of Golder, who authorizes only the Client and Approved Users to make copies of the report, but only in such quantities as are reasonably necessary for the use of the report by those parties. The Client and Approved Users may not give, lend, sell, or otherwise make available the report or any portion thereof to any other party without the express written permission of Golder. The Client acknowledges that electronic media is susceptible to unauthorized modification, deterioration and incompatibility and therefore the Client cannot rely upon the electronic media versions of Golder’s report or other work products.

The report is of a summary nature and is not intended to stand alone without reference to the instructions given to Golder by the Client, communications between Golder and the Client, and to any other reports prepared by Golder for the Client relative to the specific site described in the report. In order to properly understand the suggestions, recommendations and opinions expressed in this report, reference must be made to the whole of the report. Golder cannot be responsible for use of portions of the report without reference to the entire report.

Unless otherwise stated, the suggestions, recommendations and opinions given in this report are intended only for the guidance of the Client in the design of the specific project. The extent and detail of investigations, including the number of test holes, necessary to determine all of the relevant conditions which may affect construction costs would normally be greater than has been carried out for design purposes. Contractors bidding on, or undertaking the work, should rely on their own investigations, as well as their own interpretations of the factual data presented in the report, as to how subsurface conditions may affect their work, including but not limited to proposed construction techniques, schedule, safety and equipment capabilities.

Soil, Rock and Groundwater Conditions: Classification and identification of soils, rocks, and geologic units have been based on commonly accepted methods employed in the practice of geotechnical engineering and related disciplines. Classification and identification of the type and condition of these materials or units involves judgment, and boundaries between different soil, rock or geologic types or units may be transitional rather than abrupt. Accordingly, Golder does not warrant or guarantee the exactness of the descriptions.



Special risks occur whenever engineering or related disciplines are applied to identify subsurface conditions and even a comprehensive investigation, sampling and testing program may fail to detect all or certain subsurface conditions. The environmental, geologic, geotechnical, geochemical and hydrogeologic conditions that Golder interprets to exist between and beyond sampling points may differ from those that actually exist. In addition to soil variability, fill of variable physical and chemical composition can be present over portions of the site or on adjacent properties. The professional services retained for this project include only the geotechnical aspects of the subsurface conditions at the site, unless otherwise specifically stated and identified in the report. The presence or implication(s) of possible surface and/or subsurface contamination resulting from previous activities or uses of the site and/or resulting from the introduction onto the site of materials from off-site sources are outside the terms of reference for this project and have not been investigated or addressed.

Soil and groundwater conditions shown in the factual data and described in the report are the observed conditions at the time of their determination or measurement. Unless otherwise noted, those conditions form the basis of the recommendations in the report. Groundwater conditions may vary between and beyond reported locations and can be affected by annual, seasonal and meteorological conditions. The condition of the soil, rock and groundwater may be significantly altered by construction activities (traffic, excavation, groundwater level lowering, pile driving, blasting, etc.) on the site or on adjacent sites. Excavation may expose the soils to changes due to wetting, drying or frost. Unless otherwise indicated the soil must be protected from these changes during construction.

Follow-Up and Construction Services: All details of the design were not known at the time of submission of Golder’s report. Golder should be retained to review the final design, project plans and documents prior to construction, to confirm that they are consistent with the intent of Golder’s report.

During construction, Golder should be retained to perform sufficient and timely observations of encountered conditions to confirm and document that the subsurface conditions do not materially differ from those interpreted conditions considered in the preparation of Golder’s report and to confirm and document that construction activities do not adversely affect the suggestions, recommendations and opinions contained in Golder’s report. Adequate field review, observation and testing during construction are necessary for Golder to be able to provide letters of assurance, in accordance with the requirements of many regulatory authorities. In cases where this recommendation is not followed, Golder’s responsibility is limited to interpreting accurately the information encountered at the borehole locations, at the time of their initial determination or measurement during the preparation of the Report.

Changed Conditions and Drainage: Where conditions encountered at the site differ significantly from those anticipated in this report, either due to natural variability of subsurface conditions or construction activities, it is a condition of this report that Golder be notified of any changes and be provided with an opportunity to review or revise the recommendations within this report. Recognition of changed soil and rock conditions requires experience and it is recommended that Golder be employed to visit the site with sufficient frequency to detect if conditions have changed significantly.

Drainage of subsurface water is commonly required either for temporary or permanent installations for the project. Improper design or construction of drainage or dewatering can have serious consequences. Golder takes no responsibility for the effects of drainage unless specifically involved in the detailed design and construction monitoring of the system.

TSEAX KM 80 BRIDGE REPLACEMENT

FOUNDATION INVESTIGATION

SKEENA HIGHWAY DISTRICT

NISGA`A HIGHWAY No. 113

6444-21

AS NOTED

SL MAY. 2017

MAY. 2017

AW MAY. 2017

1

8

2

1

8

0

182

1

8

0

1

8

2

1

7

8

1

8

0

1

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1

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0

1

8

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90% DESIGN

CANCEL PRINTS BEARING PREVIOUS LETTER

H-308k-r3(05-17)

PREPARED UNDER THE DIRECTION OF

ENGINEER OF RECORD

DATE

FILE No.PROJECT No. DRAWING No.REG.

R E V I S I O N S

DESIGNED

CHECKED

DRAWN

DATE

DATE

DATE

SCALE

SEAL

NEGATIVE No.

DateRev Description Init

Northern Region

Ministry of TransportationBRITISHCOLUMBIA & Infrastructure

DIRECTOR, ENGINEERING

AUTHORIZED BY

DATE

REGIONAL DIRECTOR, HIGHWAYS

DATE

TH03-01o/s 2.4 m

TH03-02o/s 5.7 m

EST. 182.50 m EST. 183.00 m

AutoCAD SHX Text

G702

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N.

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E.

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ELEV.

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STATIC

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G702

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501456.570

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107502.085

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182.653

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26°14'07"

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E

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N

AutoCAD SHX Text

501500

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107500

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E

AutoCAD SHX Text

N

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501400

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107500

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BRIDGE SITE

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%%uLOCATION MAP

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SCALE NTS

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THE BRIDGE SITE IS LOCATED 84km NORTH OF TERRACE ON HIGHWAY 113

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37

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ROSSWOOD

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TERRACE

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NEW AIYANSH

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KITSUMKALUM

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LAKE

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NASS

AutoCAD SHX Text

RIVER

AutoCAD SHX Text

NISGA'A HWY

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MOUNT KENNEY

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OSCAR PEAK

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CEDARVALE

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KITWANGA

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16

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16/37

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16

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113

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SKEENA

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RIVER

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SEVEN SISTERS

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MOUNTAIN

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SEVEN SISTERS

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PROVINCIAL

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PARK

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NISGA'S MEM'L LAVA BED

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PROVINCIAL PARK

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37

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1. SURVEY BY: WSP (NOV./2016)

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2. DATUM: GEODETIC

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3. BENCH MARK: No. HUB G702, ELEV. 182.653m

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%%uNOTES:

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N 107502.085, E 501456.570

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FILL MATERIAL

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%%ULEGEND:

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ROCK MATERIAL

TSEAX KM 80 BRIDGE REPLACEMENTSUMMARY LOGS

SKEENA HIGHWAY DISTRICTNISGA`A HIGHWAY No. 113

6444-22

AS NOTED

SL MAY. 2017

MAY. 2017

AW MAY. 2017

90% DESIGNCANCEL PRINTS BEARING PREVIOUS LETTER

H-3

08k-

r3(0

5-17

)

PREPARED UNDER THE DIRECTION OF

ENGINEER OF RECORD

DATE

FILE No. PROJECT No. DRAWING No.REG.

R E V I S I O N S

DESIGNED

CHECKED

DRAWN

DATE

DATE

DATE

SCALESEAL

NEGATIVE No.

DateRev Description Init

Northern Region

Ministry of TransportationBRITISHCOLUMBIA & Infrastructure

DIRECTOR, ENGINEERING

AUTHORIZED BY

DATE

REGIONAL DIRECTOR, HIGHWAYS

DATE


20 June 2017 Report No. 1771779-004-R-Rev0

APPENDIX A April 2004 Geotechnical Report


20 June 2017 Report No. 1771779-004-R-Rev0

APPENDIX B 2015 NBCC Seismic Hazard Calculation

2015 National Building Code Seismic Hazard CalculationINFORMATION: Eastern Canada English (613) 995-5548 francais (613) 995-0600 Facsimile (613) 992-8836

Western Canada English (250) 363-6500 Facsimile (250) 363-6565

Site: 55.1135 N, 128.977 W User File Reference: Tseax Bridge

Requested by: Shawn Lange, P.Eng., Golder Associates Ltd.

May 30, 2017

National Building Code ground motions: 2% probability of exceedance in 50 years (0.000404 per annum)

Sa(0.05) Sa(0.1) Sa(0.2) Sa(0.3) Sa(0.5) Sa(1.0) Sa(2.0) Sa(5.0) Sa(10.0) PGA (g) PGV (m/s)

Ground motions for other probabilities:

Probability of exceedance per annum

Probability of exceedance in 50 years

Sa(0.05)

Sa(0.1)

Sa(0.2)

Sa(0.3)

Sa(0.5)

Sa(1.0)

Sa(2.0)

Sa(5.0)

Sa(10.0)

PGA

PGV

0.010

40%

0.0021

10%

0.001

5%

0.074 0.112 0.138 0.138 0.133 0.111 0.079 0.030 0.011 0.068 0.186

0.012

0.018

0.025

0.031

0.036

0.035

0.024

0.0086

0.0034

0.013

0.047

0.031

0.046

0.061

0.068

0.071

0.064

0.046

0.017

0.0061

0.032

0.103

0.045

0.068

0.087

0.094

0.095

0.083

0.060

0.022

0.0079

0.045

0.137

Notes. Spectral (Sa(T), where T is the period in seconds) and peak ground acceleration (PGA) values aregiven in units of g (9.81 m/s2). Peak ground velocity is given in m/s. Values are for "firm ground" (NBCC2015 Site Class C, average shear wave velocity 450 m/s). NBCC2015 and CSAS6-14 values are specified inbold font. Three additional periods are provided - their use is discussed in the NBCC2015 Commentary.Only 2 significant figures are to be used. These values have been interpolated from a 10-km-spaced gridof points. Depending on the gradient of the nearby points, values at this location calculated directlyfrom the hazard program may vary. More than 95 percent of interpolated values are within 2 percentof the directly calculated values.

References

National Building Code of Canada 2015 NRCC no. 56190;Appendix C: Table C-3, Seismic Design Data for Selected Locations inCanada

User’s Guide - NBC 2015, Structural Commentaries NRCC no.xxxxxx (in preparation)Commentary J: Design for Seismic Effects

Geological Survey of Canada Open File 7893 Fifth GenerationSeismic Hazard Model for Canada: Grid values of mean hazard to beused with the 2015 National Building Code of Canada

See the websites www.EarthquakesCanada.caand www.nationalcodes.ca for more information

Aussi disponible en francais

Natural ResourcesCanada

Ressources naturellesCanada CanadaCanada

129.5˚W 129˚W 128.5˚W

55˚N

55.5˚N

0 10 20 30

km

Golder Associates Ltd. Suite 200 - 2920 Virtual Way Vancouver, BC, V5M 0C4 Canada T: +1 (604) 296 4200

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