00 CALGARY, Alberta T2H OSS >< c Phone (403) 253-921 7 z Fax - - PDF document

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THURBER ENGINEERING LTD.

#190. 550-71 Avenue S.E. CALGARY, Alberta T2H OSS Phone (403) 253-921 7 Fax (403) 252-8159

June 25, 1998 Stewart Weir & Co. Ltd. 11405 - 163rd Street Edmonton, Alberta T5M 3Y3 Attention: Reg R. Kotch Manager, Highway Engineering

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THURBER

File: 19-273-36 SECONDARY HIGHWAY 726:02 AT EUREKA RIVER CROSSING INCLINOMETER READINGS -SITES 1 AND 2 Dear Mr. Kotch: This letter summarizes the results of the latest inclinometer readings at these two si'"- - taken on May 5, 1998. Potential slope stability issues are also outlined. For proper interpretation, this letter should be read in conjunction with the following documents:

• Thurber's report to the M.D. of Clear Hills dated December 17, 1997 (our

file 14-13-0);

• Stewart Weir's letter to Mr. Ron Wolsey of AT&U dated January 30, 1998

(your file 12.7.7789);

• Stewart Weir's letter to Mrs. Faye Kary of the M.D. of Clear Hills dated

February 6, 1998 (your file 12.7.24975);

• Thurber's letters to Stewart Weir dated February 19, 1998 and June 22,

1998 (our file 19-273-36).

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A general location plan is shown on Figure 1. Slope indicator data for Sites 1 and 2 are summarized in Appendices A and B respectively. This letter report is subject to the attached Statement of General Conditions

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THURBER ENGINEERINS

Stewart Weir 2 June 25, 1998 SITE 1 Background Repairs were carried out at this location in late February/early March, 1998, under the supervision of Mr. Harold Miskey of Stewart Weir. The repairs followed the guidelines set out in our letter of February 19, 1998 and included installation of five counterfort drains, a gravel buttress near the highway and a temporary curb and culvert on the east shoulder of the highway.

• Dr. Heinrich Heinz, P.Eng. of Thurber was present on-site on February 26 and 27,

1998 and observed the installation of the first counterfort drain. It was noted that the excavation of this drain intercepted a discontinuous water bearing gravel layer approximately 30 em thick, believed to be the remnants of the blanket drain installed by AT&U in 1987. This observation supports our previous assessment, made in our report to the M.D. of Clear Hills in December, 1997, that the original blanket drain became disturbed due to slide activity, contributing to the reactivation

• f the slide in 1997.

Slope Indicator Readings Readings were taken on March 8, 1998 and May 5, 1998 in the two inclinometers installed at Site 1 in November, 1997. Depth-displacement plots for these instruments are included in Appendix B. The following observations are applicable: Inclinometer 97-2 (west side of highway): Readings in this instrument taken on March 8 and May 5, 1998 showed no movements (Figure A 1, Appendix A). The apparent displacement in the 8 direction (parallel to the highway) is due to an error associated with accelerometer rotation and does not reflect actual movements. Inclinometer 97-3 (east side of highway): . ' This instrument had shown movements in the: order of 1 0 mm over a 1 0 day period

in November, 1997, at approximately 4.5 m below surface (see· our report of December, 1 997). The instrument was damaged during construction of the gravel buttress and could not be repaired on March 8, 1998, due to frozen ground

• conditions. The instrument was repaired on May 5, 1998, at vvhich time it was

found that the casing was blocked at a point approximately 4.3 m below surface. This blockage is likely associated with excessive deformation of the inclinometer

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THURBER ENGINEERING

Stewart Weir 3 June 25, 1998 casing, caused by slope movements believed to have occurred prior to execution

• f the repair works.

Assessment and Recommendations Based on our recent observations, it is apparent that the measures installed last February have provided some reduction in the piezometric levels within the slope, but have not been sufficient to provide long term stabilization of this slope. Additional drainage measures and deep stabilization will be required, as discussed in our letter dated June 22, 1998. SITE 2 Background This site is at the approximate location of a major slide which occurred in 1988 and was apparently repaired using stone columns, light weight fill and a shear key. A schematic sketch obtained from the AT&U Bridge File is shown on Figure 81, Appendix B. The possible shear surface associated with the 1988 slide is also noted on this figure, as well as layers of organic soil up to about 0.9 m thick. A significant depression of the highway pavement was noted at this location in November, 1997. As landslide activity is evident at the river bank, near the toe of the slope (see Photos 3 and 4), two inclinometers were installed on March 8, 1998, to evaluate the risk that the highway depression might be related to landslide activity (see test hole logs - Figures 82 and 83, Appendix B). Slope Indicator Readings Readings taken on May 5, 1998 indicate that no significant movements are taking place within the depths investigated (see Figures 84 and 85, Appendix 8). It is noted that the soils drilled during installation of the inclinometers showed evidence of previous landsliding throughout the depths investigated, in the form of slickenslides (see test hole logs in Appendix B). As well, active river erosion and landsliding is taking place near the toe of this slope (see Figures 86, and 87, Appendix 8). Assessment and Recommendations The information collected suggests that the deformation which has been observed

• n the highway pavement is related to settlement of the underlying strata (e.g.,

layers of peat and sawdust light-weight fill, which is known to undergo aerobic deterioration if placed above the water table). It should be noted, however, that the

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THURBER ENGINEERING

Stewart Weir

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June 25, 1998 investigation undertaken at Site 2 to date is very limited and further test holes, with installation of piezometers, would be required to establish the exact nature of these deformations. It is expected that river erosion will continue and will likely cause further landsliding that could affect the highway. It is therefore possible that a major landslide could still develop at this location. It is recommended that visual inspections and slope indicator readings be performed at least twice a year, to monitor the progress of the landslide. It is also recommended that some form of bank protection (e.g., rip-rap or gabion mats) be designed and constructed at the toe of the slope, to protect the river bank and reduce the rate of landslide progression. Closure Both sites remain a concern with respect to slope stability. Survey hubs should be installed along the highway shoulder at both sites, for monitoring of horizontal and vertical movements over the summer of 1998. The need for additional stabilization measures should be evaluated after review of this survey, in the fall of 1998. Please call if there are any questions. Yours truly, THURBER ENGINEERING L TO. Nick Hernadi, P.Eng. Review Engineer Heinrich K. Heinz, Ph.D., P.Eng. Senior Geotechnical Engineer

Attachments: Appendix A - Summary of Site 1 Data Appendix 8 - Summary of Site 2 Data .

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• Approx. Scale (m)

STEWA.RT WEIR- S.H. NO. 726 - EUREKA RIVER CROSSING

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Site Plan showing Location of Inclinometers FIGURE 1

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T h u r b e r Consultants Ltd. -

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19-273-36, Inclinometer 97-2

Stewart Weir

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