A design procedure was developed for a relatively unknown slope stabilization technique consisting of a series of parallel sheet piles installed parallel to the direction of slope movement. This technique was introduced in Alberta by R.M. Hardy in the 1970s and is locally referred to as “Hardy Ribs.” A case study is discussed where Canadian National (CN) Rail installed Hardy Ribs to stabilize a landslide affecting its rail line in western Manitoba. A proposed design procedure is discussed that consists of a de-coupled approach with a separate limit equilibrium slope stability analysis and laterally loaded pile analysis using p–y curves, where p is the soil reaction per unit length and y is the lateral deflection of the pile, to model the soil–pile interaction. Example calculations are provided for the proposed design procedure for the CN case study site to illustrate its use and to estimate the stabilizing effect from the Hardy Ribs at this site.

Vibrating wire strain gauges are often the preferred technology for measuring strain in driven piles. However, measuring the residual strain after pile driving is challenging to accomplish using vibrating wire gauges. The driving process can cause a shift in the no-load reading from a relaxation of locked-in manufacturing strains in the pile or relaxation of the gauge wire tension. Also, there are temperature effects from installing piles below ground. A test pile program was developed using driven steel H-piles instrumented with vibrating wire strain gauges. The piles were subjected to dynamic forces by striking against a steel plate in attempt to relax the locked-in manufacturing strain prior to installation. The strain gauges and thermistors were connected to a data logger during pile driving to record strain and temperature changes following installation. It was observed that applying a dynamic impact to the piles prior to installation resulted in a shift of 0 to 5 microstrain. Temperature effects from installing the piles in cooler ground resulted in a shifts of strain in excess of 60 microstrain in some strain gauges. It is concluded that temperature induced shifts to strain must be measured following pile driving to interpret residual stresses.

Evaluation of pile capacity using dynamic testing and CAse Pile Wave Analysis Program (CAPWAP) analysis has been shown to provide reasonable measurements of capacity and separates the shaft and tip resistance. It is a common method for verifying pile capacities, however consideration of setup and presence of residual loads at the time of testing are necessary for interpreting the resistance distribution. A test pile program was conducted that included dynamic testing of piles at end of initial driving and early restrikes to measure the rate of setup. The piles were instrumented to measure residual stresses. The shaft resistance and tip stiffness were interpreted from analyzing multiple blows and corrected for residual stresses. The results from CAPWAP were compared to measurements from static load tests. It was found that correcting CAPWAP results for residual loads resulted in better interpretation of the rate of setup and resistance distribution. Analyzing successive blows with CAPWAP provided an improved estimate of the tip load-movement curve by extrapolating the increase in tip capacity with penetration. The results demonstrate the importance of correcting CAPWAP results for residual stresses to gain a better understanding of the pile capacity, resistance distribution, and tip stiffness for design purposes.

Negative skin friction caused by ground settlement is an important consideration for deep foundations in limit states design. However, there are inconsistencies in the methodology whereby negative skin friction and associated drag force are considered in assessing the geotechnical capacity or geotechnical ultimate limit state (ULS) in various design codes. This includes two current North American bridge design codes, the Canadian Highway Bridge Design Code and AASHTO LRFD Bridge Design Specifications. A test pile program was developed to observe effects of ground settlement on pile settlement, capacity, and drag force. Two instrumented steel H-piles were driven through a compressible clay layer to a hard end-bearing stratum, subjected to ground settlement by constructing a 1.5 m high embankment, followed by static load testing. A load-transfer model was calibrated from the test pile program observations. Test results and the calibrated model were used to compare geotechnical ULS requirements of the two bridge design codes. It is demonstrated that drag force did not detrimentally impact pile capacity. The results showed that for conditions of the test pile program, assessing the geotechnical ULS can be more conservative when adhering to the current AASHTO LRFD Bridge Design Specifications than the Canadian Highway Bridge Design Code.

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