The quantity of energy dissipated in a unit volume of soil during cyclic loading can be used as a measure of the soil’s ability to withstand liquefaction. This energy is referred to as the normalized dissipated energy per unit volume (NDEPUV). The greater the NDEPUV required to induce liquefaction, the more seismic energy must be input into the soil during an earthquake for liquefaction to occur. The NDEPUV for a soil subjected to a seismic event or a laboratory test can be calculated from the stress-strain behavior of the soil.

In this study, the effect of specimen size on NDEPUV was examined using stress-controlled cyclic triaxial tests performed on specimens of uniform sand prepared to a relative density of 40%. Four specimens were tested at each of four volumes and the NDEPUV required to induce liquefaction was determined. The specimen volumes ranged from 87 to 1647 cubic centimeters.

It was found that the total amount of dissipated energy required to initiate liquefaction increased linearly with specimen volume, while the NDEPUV was found to be independent of the specimen volume. The fact that the NDEPUV is independent of specimen size means that no adjustments need be made to the laboratory testing results when using them to predict liquefaction in the field.

Continuous flight auger (CFA) pile is a cast in-situ concrete pile constructed by using a fully flighted hollow stem auger. CFA piles were introduced in the UK in 1960s as a solution to the construction difficulties associated with conventional piling techniques especially the need for temporary casings or slurry. Over the years, CFAs has spread across the world making its way into many construction markets, including Canada.

A CFA pile is installed in one continuous operation consisting of advancing a continuous flight auger of pile design diameter to the target depth. As the auger is advanced, its flights are filled with soils which provides lateral support to the drilled hole. Concrete is placed by pumping through the hollow centre of the auger to its tip during auger retrieval which also support the surrounding soils by positive concrete pressure. Reinforcement is installed into the pile shaft filled with fluid concrete immediately after auger withdrawal.

Initially, CFA piles were limited in diameter and depth and were used to carry light to moderate loads as a structural support element and were constructed in soft to medium soils. Technological development has expanded its use and constructability enormously. Today, it is very common to install CFA piles of diameters ranging from 300mm to 1200mm and as deep as 50m or more as well as in a variety of subsurface conditions. Technological development has led to numerous enhancements in CFA rig instrumentation with Data Acquisition (DAQ) which provides key quality control parameters on a real-time basis related to geotechnical and structural aspects of the pile.

Continuous flight auger piles have been successfully introduced in the Prairies over 15 years and installed on numerous sites as technically viable and cost-effective deep foundations system. This paper presents an overview of CFA pile background, technical considerations and case histories.

Helical piles have been extensively used in the civil engineering practice in North America in the past decades. However, the inter-helix-spacing-based failure mechanisms (FM) of these piles, currently recognized by engineers, are still obscure to engineers, as suggested by field load tests in the past decades. In addition, an affordable alternative to expensive field tests of piles is needed for soil-pile interaction investigation. Centrifuge modeling technique provides an effective approach for research in helical piles. Although centrifuge modeling has been well known, there is a lack of research of helical piles in clays on centrifuge. This research is intended to evaluate the influence of inter-helix spacing on the FM in stiff clay using the centrifuge at the University of Alberta. A single-helix and three double-helix model piles with the inter-helix spacing varying from 1.5 to 3.5 times of helix diameter were tested. The target undrained shear strength of soil was about 120 kPa. Helical piles were installed in-flight. The installation torques and axial load distributions were measured by multiple strain gauges installed along the pile shafts. These strain gauge readings provide solid evidence that supports the determination of the FM’s during axial loading. Based on the test results, three FM’s were confirmed for the three double-helix piles: two conventional FM’s, i.e., “individual plate bearing” and “cylindrical shear”, and one “transitional shear”. The end bearing factors were calculated based on the load – displacement curves. Results of the present study confirmed that geotechnical centrifuge modeling is an effective research tool that can simulate the installation and loading procedures for helical piles.

Twelve percent of Canadian landforms are covered with Muskeg. Muskeg is the landform that represents the organic terrain. Organic soils are distinguished by their high initial water content. The other two main properties of organic soils are organic content and fiber content. These three significant parameters are affecting the index and compressibility properties of organic soils. The effect of water content on the index and the compressibility properties of organic soils has been studied by many authors. However, the influence of organic content on these properties was not well examined. In this study, the effects of both the organic and water contents on different index properties (void ratio, bulk density, specific gravity, and liquid limit) and the compression index have been studied based on many data points gathered from literature for different organic soils studied in various countries. Fiber content, texture, and origin are affecting the properties of organic soils as well, but the available data for these features are not enough to be used in this study. The new relations that correlate the different index and compressibility properties with the water and organic contents are presented in this study. The results revealed that void ratio, liquid limit, and compression index are better estimated based on the water content, whereas, the unit weight and the specific gravity showed a better correlation with the organic content.

Abstract: Salt accumulation in the surface of soil mass and the structural damage during freeze-thaw cycling is a key parameter that contributes to the collapse of loess slopes in northwestern China. A simple method that is referred to as the leaching method in the literature is used for preparing intact specimens containing soluble salt for determining the shear strength. This method facilitates in uniform distribution of sodium sulfate by infiltration technique with limited disturbance to the soil structure. Triaxial shear test results on salt infiltrated test specimens show that the cohesion of specimens decreases typically after one or two freeze-thaw cycles. Specimens with more water or sodium sulfate exhibit lower values of cohesion. The cohesion-based damage coefficients are calculated based on a specific damage path considering both freeze-thaw cycles and salt erosion. The damage coefficient of freeze-thaw decreases at higher salt contents while salt erosion accounts for a major part to the total damage at salt contents that is higher than 1.0%. The ratio of freeze-thaw damage coefficient to that by salt erosion decays especially in the initial five freeze-thaw cycles, beyond which it stabilizes, similar to the attenuation of cohesion.