Background

The adverse effects of climate warming on the built environment in (sub)arctic regions are unprecedented and accelerating. According to Canada’s Changing Climate Report (2019), in the Arctic regions, temperatures have been warming at approximately twice the rate of the rest of the world. This drastic trend in climate warming will no doubt affect permafrost temperatures and conditions, continued rise in greenhouse gas emissions, and further adding to the high cost of development in northern regions. Planning and design of climate-resilient northern infrastructure as well as predicting deterioration of permafrost from climate model simulations require characterizing permafrost sites accurately and efficiently.

Design and construction of structures on permafrost normally follow one of two broad principles which are based on whether the frozen foundation soil in ice-rich permafrost is thaw-stable or thaw-unstable. This distinction is determined by the amount of ice content within the permafrost. Ice-rich permafrost contains ice in excess of its water content at saturation. The construction on thaw-unstable permafrost is challenging and requires remedial measures since upon thawing, permafrost will experience significant thaw-settlement and suffer loss of strength to values significantly lower than that for similar material in an unfrozen state. Consequently, remedial measures for excessive soil settlements or design of new infrastructure in permafrost zones affected by climate warming would require a reasonable estimation of the ice content within the permafrost (frozen soil). The rate of settlement relies on the mechanical properties of the foundation permafrost at the construction site. Furthermore, a warming climate can accelerate the microbial breakdown of organic carbon stored in permafrost and can increase the release of greenhouse gas emissions, which in return would accelerate climate change.

The characterization of permafrost or frozen soil includes the measurement of both physical properties (e.g., unfrozen water, ice, and porosity) and mechanical properties (e.g., bulk modulus and shear modulus, or compression and shear wave velocity). Current techniques are insufficient for efficient characterization of permafrost samples. In remote areas, the development of portable, time-efficient and cost-effective techniques for the characterization of permafrost (frozen) soils can play an important role in the preliminary geotechnical investigation. In geotechnical practice, the physical and mechanical properties are obtained through field and laboratory geotechnical testings. The conventional field methods require heavy equipment that may not be accessed in remote areas. For the laboratory tests, soil samples from projects in remote areas are required to be transported to a geotechnical laboratory for various tests, which can cause the disturbance of soil samples and potentially lead to erroneous conclusions. Currently, the ability to quantitatively and non-invasively characterize permafrost (frozen) soils in remote areas is still a major challenge to the engineering and construction.

Technology Overview

The technology proposes innovative ultrasonic-based systems and physics-based signal interpretation methods for instant in-situ and laboratory characterization of permafrost and frozen soils. The technology quantifies the physical and mechanical properties of the foundation soils such as ice content and unfrozen water content and their spatial distribution within the samples. This information will be essential for design, construction, rehabilitation programs, as well as decision making.

This technology employs an integrated poromechanical and machine learning-based optimization model to characterize soil samples using ultrasonic techniques. In this proposed method, a unique approach has been employed to interpret the ultrasonic signal recorded by a set of receivers positioned around the sample regardless of the type of wave. The proposed signal interpretation method in this invention is physics-based unlike the existing subjective empirical signal interpretation methods. Quantitative Ultrasound (QUS) sensing system developed in this invention can be used as a portable and instant characterization tool for frozen or permafrost soil samples. With a simple portable setup, the physical and mechanical properties are measured using only a single ultrasonic test.

Benefits

The invention will enable new tools for use in geotechnical investigations for construction site assessment and rehabilitation programs. This setup will be portable and cost-effective in comparison to traditional in-situ and lab testing equipment, which makes it ideal for site investigation, especially in remote areas. The invention is also critical for the early detection and warning systems to monitor infrastructure impacted by permafrost-related geohazards, and to detect the presence of layers vulnerable to permafrost carbon feedback and emission of greenhouse gases into the atmosphere.

Applications

The invention can be applied by municipal governments and stakeholders in zones experiencing intermittent or uniform permafrost, especially in remote areas where access to conventional site investigation tools or equipped geotechnical laboratories is limited and cost prohibitive.

Opportunity

The technology is ready for prototype demonstration in a simulated environment.