0104-00-22537.002 - 14 - September 2001 Aug2001 slide tour report.doc Slide Name: (GP 6a) Hwy 40:36 Sheep Creek - Railway Track - Backslope Inspection Date: June 12, 2001 Inspection By: Alberta Transportation Staff (see attached list of attendees) EBA Staff (Karl Li and Tony Ruban) 1.0 BACKGROUND Refer to EBA 2000 Report for site conditions and details of risk assessment. Instrumentation was not installed at this site. This site is located approximately 1.2 km south of Sheep Creek. 2.0 OBSERVATIONS • The slide has deteriorated from a planar slide of 0.5 to 1 m depth (1999 to 2000) to a shallow semi-circular slide with the deepest zone of movement estimated at an approximate 3 m depth. The deterioration was due to erosion resulting from the past 2 years of runoff infiltration and groundwater seepage. This area is designated the centre slide . • Two more shallow slippage slides developed on the north and south sides (approximately 40 to 70 m distance) of the centre slide. The newly developed slides developed during the past year and were not noted in the 2000 inspection. These new slides are designated the north slide and south slide . • The backslope of this major cut was constructed with intermediate benches and swales along the benches. The swales are lined with tarpaulin woven geotextile to function as a liner. However, deterioration of this liner was observed. Breaches in the swales and seepage flow from several swales was noted to cause rilling erosion down the slope. • Seepage flow of groundwater exiting from this cut slope was observed. • As described in the previous report, the above slope distress and deterioration of previously installed surface/subsurface drain system (original construction in mid 1980's) is more apparent during this 2001 slope inspection. The subsurface drainage system includes "french drains, finger drains, sheet drain system" comprising granular material encapsulated and/or underlain with non-woven geotextile. • Due to deterioration of the planar slide (centre slide) to a deeper depth, it was recognized that: • The use of bioengineering cannot be fully effective for such slide depth (3 m) movement. • For effective remediation should rebuild slope with granular material with a toe bench and perforated pipe system to be carried out at toe of slope. Clean out of the slide material will be required. • The backslope cut is significant (approximately 2H:1V slope at 40 to 50 m height at maximum) with intermediate benches. • Any disturbance of the existing drainage system by equipment may cause further damage and deterioration to the existing slope. • The feasibility of rebuilding of slope from the toe area was discussed with the
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0104-00-22537.002 - 14 - September 2001
Aug2001 slide tour report.doc
Slide Name: (GP 6a) Hwy 40:36 Sheep Creek - Railway Track - BackslopeInspection Date: June 12, 2001Inspection By: Alberta Transportation Staff (see attached list of attendees)
EBA Staff (Karl Li and Tony Ruban)
1.0 BACKGROUNDRefer to EBA 2000 Report for site conditions and details of risk assessment.Instrumentation was not installed at this site. This site is located approximately 1.2 kmsouth of Sheep Creek.
2.0 OBSERVATIONS• The slide has deteriorated from a planar slide of 0.5 to 1 m depth (1999 to 2000) to
a shallow semi-circular slide with the deepest zone of movement estimated at anapproximate 3 m depth. The deterioration was due to erosion resulting from thepast 2 years of runoff infiltration and groundwater seepage. This area is designatedthe centre slide .
• Two more shallow slippage slides developed on the north and south sides(approximately 40 to 70 m distance) of the centre slide. The newly developedslides developed during the past year and were not noted in the 2000 inspection.These new slides are designated the north slide and south slide .
• The backslope of this major cut was constructed with intermediate benches andswales along the benches. The swales are lined with tarpaulin woven geotextile tofunction as a liner. However, deterioration of this liner was observed. Breaches inthe swales and seepage flow from several swales was noted to cause rilling erosiondown the slope.
• Seepage flow of groundwater exiting from this cut slope was observed.• As described in the previous report, the above slope distress and deterioration of
previously installed surface/subsurface drain system (original construction in mid1980's) is more apparent during this 2001 slope inspection. The subsurfacedrainage system includes "french drains, finger drains, sheet drain system"comprising granular material encapsulated and/or underlain with non-wovengeotextile.
• Due to deterioration of the planar slide (centre slide) to a deeper depth, it wasrecognized that:• The use of bioengineering cannot be fully effective for such slide depth (3 m)
movement.• For effective remediation should rebuild slope with granular material with a toe
bench and perforated pipe system to be carried out at toe of slope. Clean out ofthe slide material will be required.
• The backslope cut is significant (approximately 2H:1V slope at 40 to 50 mheight at maximum) with intermediate benches.
• Any disturbance of the existing drainage system by equipment may causefurther damage and deterioration to the existing slope.
• The feasibility of rebuilding of slope from the toe area was discussed with the
0104-00-22537.002 - 15 - September 2001
Aug2001 slide tour report.doc
local maintenance contractor to be feasible. This will limit the pragmaticremediation to the toe area and will not cause disturbance to the upper portionsof the slope.
• It was recognized that:• A survey of the slope should be carried out for the lower slope to delineate the
distress area. This should include the north, centre and south slides as well asthe rills down the lst bench. The survey will provide mapping of the distressarea and allow the design of remediation and construction management.
• Bioengineering designs may be viable along the rills down the slope and otherselective shallow slippage areas.
• Design remediation with granular material, finger drains, and toe berms will bethe main remedial strategy for the north, centre and south slides.
• It was recognized that:• Deterioration of the existing excavation backslope and shallow sliding
movement along the general area in the vicinity is starting to happen. Regularmaintenance clean out of ditches is required in the event of debris flow intoditches.
3.0 RISK ASSESSMENTPF (5) * CF (4) = 20Risk rating has not changed from that assessed in January 2001 Inspection Report.Any current additional comments are provided in the 2001 Spring InstrumentationMonitoring Report.
Note:This Risk Assessment rating is based on scheme proposed by AT in 2000.
Probability Factor (PF):Consequence Factor (CF):
1 to 20 scale1 to 20 scale
4.0 ACTIONS• It is recommended to undertake a review regarding the urgency to design remedial
works for this backslope as the area is showing signs of deterioration. For thisbackslope, it is believed that a combination of selective drainage reconstruction(finger drains) together with granular berm construction along the lower bench isfeasible.
• As discussed in earlier reports, the stability of this steep backslope (with the presentstate of deterioration of previous shallow drainage installation) can be improved,however, remediation will be very difficult and labor intensive. Remediation of theupper portion of this vast backslope is not considered practical because of lowconsequence of shallow failures and high costs in repairs. Repair efforts should beconcentrated at the lower portion of the slope close to highway level.
• It is reminded that the present semi-circular slide was the result of site deteriorationfrom a shallow planar slide (0.5 to 1 m thick) over a duration of 2 years. It is
0104-00-22537.002 - 16 - September 2001
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advised that the above course of actions be delayed no further and undertaken priorto further deterioration of the site and retrogression of the instability further uphill.
22537d34a.cdr
October, 20010104-00-22537.002Site GP6a, GP6b - Slides SouthofSheepCreek
Highway 40:38
Figure 11993 Aerial Photograph
N
Hwy 40:36 (GP 6a)Sheep Creek - Railway Track - Backslope
Issues:• Backslope shallow (to medium) depth failure• Deterioration from shallow depth to deeper
failure• Deterioration of existing drainage (perforated
pipe system)• Deterioration of adjacent slopes
Hwy 40:36 (GP 6a)Sheep Creek - Railway Track - Backslope
Solution: design to be submittedCosts
•Granular berming and reconstructionof slope
•30,000 •5,000 +15,000
Construction Engineering Design Project Mgmt
Totals: 30,000 20,000
GP 6a (Sheet 1 of 5)Hwy 40:36
Sheep Creek Backslope
0104-00-22537.002 June, 2001Regional Geotechnical Assignment
Grande Prairie Area
GP 6a (Sheet 2 of 5)Hwy 40:36
Sheep Creek Backslope
0104-00-22537.002 June, 2001Regional Geotechnical Assignment
Grande Prairie Area
GP 6a (Sheet 3 of 5)Hwy 40:36
Sheep Creek Backslope
0104-00-22537.002 June, 2001Regional Geotechnical Assignment
Grande Prairie Area
GP 6a (Sheet 4 of 5)Hwy 40:36
Sheep Creek Backslope
0104-00-22537.002 June, 2001Regional Geotechnical Assignment
Grande Prairie Area
GP 6a (Sheet 5 of 5)Hwy 40:36
Sheep Creek Backslope
0104-00-22537.002 June, 2001Regional Geotechnical Assignment
Grande Prairie Area
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