The contribution of soil properties and implementation processes to microstructure and mechanical behaviour of earthen construction

Earthen construction is an interesting outlet for the re-use of excavated soils whiles meeting the challenges of circular economy. However, the lack of standardized criteria for soil classification remains a challenge because the specific contributions of soil properties and implementation parameters to the Unconfined Compressive Strength (UCS) and Accessible Specific Surface Area (SSA) of soils are not yet fully understood. This study aims to identify the specific contribution of soil properties and implementation parameters on the strength and microstructure of soils used in earth construction. Four soils sampled from different earth heritage sites from four regions in France were used to produce straw-fibred and non-fibred cylindrical specimens using cob and adobe techniques. The prepared specimens were dried at 40 °C and conditioned in a climatic chamber at 20 °C and 50 % relative humidity. Physical and mechanical tests (UCS, dry density, suction) as well as microstructure tests (pore volume and accessible specific surface area) were conducted on the specimens. The data from the tests were used in a Principal Component Analysis (PCA) to identify the main parameters causing variations in UCS and SSA. These parameters (water content, calcite, dolomite content, dry density, and suction) were then used in Multiple Linear Regression (MLR) models with p values at significant levels of 5 %, to quantify their respective contributions to the UCS and SSA. Based on the results from the statistical analysis, new explanatory models for UCS and SSA were developed from soil properties and implementation process parameters. These models are dependable to explain the strength and microstructural evolution of soils used in earthen construction.