Mechanical Properties of Soils Used by Mud Dauber Wasps under Varying Moisture Conditions

Abstract

A previous study showed mud dauber nests have high densities and high penetration resistance. The high density and penetration resistance of mud dauber nests were attributed to the vibratory compaction technique used by mud daubers (i.e., repetitive tapping produced by their legs and vibrating mandibles) and the well-graded grain size distributions of nest soils. However, the high density and strength of mud dauber nests are also attributed to soil drying under the atmospheric temperature and humidity level (i.e., drying-induced soil consolidation and hardening). This study investigated the mechanical properties of nest soils used by mud daubers with varying moisture conditions to assess the effect of drying on the mechanical properties of mud dauber nests. The suction stress characteristic curve (SSCC), soil water retention curve (SWRC), elastic modulus, and soil shrinkage curve (SSC) of the nest soils under drying were measured using the drying cake (DC) method. Furthermore, direct shear tests were performed under different moisture contents. The SSCCs showed the magnitude of suction stress increased with decrease of degree of saturation. Shear strengths of nest soil with 2% moisture content were significantly higher than saturated nest soil.