Translating from Kangaroo Rat Burrows to Geotechnical Engineering by Uncovering Fundamental Processes

This award supports research to understand the role of kangaroo rats' microbiome in constructing resilient structures in extreme desert environments and how this knowledge can be scaled up to human geotechnical structures in extreme environments. Kangaroo rats construct elaborate burrows over multiple years and occupy them for extended periods of time. The burrows remain open and stable in desert sand and survive the harsh desert conditions, with extreme daily and yearly relative humidity and temperature fluctuations and flash-flood events. This research tests the hypothesis that the burrow microbiome is determined by the microbial community in cheek pouches or feet of kangaroo rats and that biofilms formed in this microbiome (i.e., burrow biofilms) are crucial to burrow stability in stochastic, fluctuating desert environments. The fundamental understanding gained from this project could translate to the design of sustainable ground improvement techniques to be used in geotechnical engineering practice, particularly in locations prone to landslides and substrate collapse. The research will establish direct collaborations among researchers, graduate students, and undergraduate students in geotechnical and geoenvironmental engineering, bioengineering, and biology. The research will specifically test the hypotheses that (i) the suction stress characteristic curve of burrow-biofilm-enhanced desert soil is a non-monotonic function of saturation, due to water retention by both the soil and the biofilm, and contributes to effective stress regardless of the extreme fluctuations in humidity, saturation, and temperature, to maintain the stability of the burrows and (ii) biofilms reduce the hydraulic conductivity of burrow ceilings, and therefore prevent flooding of the burrows during storms. The experimental program will include growing the burrow biofilms in the laboratory and determining the strength of burrow-biofilm-enhanced soil over the entire range of saturation and after multiple wet/dry and heat/cool cycles. The research will also investigate how water retention by the cementing agent (i.e., burrow biofilm) contributes to suction stress to maintain burrow stability under extreme fluctuations in environmental conditions. This is important for establishing the mechanistic basis for stability in sandy soils in arid environments. In addition, the research will study how the hydraulic conductivity of desert sand changes with the addition of burrow biofilm. Results from this research will reveal how one of the most prolific ecosystem engineers digs complex, stable, and sustainable underground environments in desert sand and how an individual’s phenotype extends from their microbiome, to burrow site selection, and more broadly to landscape biogeomorphology. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.