Proposal of Strength Estimation Formula of Wall Clays Using Multiple Regression Analysis

Mud walls, which have been used since ancient times in Japanese timber structures, have the advantages of being harmless to the human body and having a low environmental impact. However, as the quality of the materials is not uniform, it is difficult to clarify the mechanical properties without conducting the strength test. Therefore, in this study, compression and shear tests were performed on the wall clay. Furthermore, authors performed multiple regression analysis to derive the estimation formulas for the wall clay strength using the material properties, e.g., mixing ratio, particle size distribution, and wall clay density. As a result, the soil source, maturity period, and sand volume in the second coating soil affect the wall clay strength. The strength ratios of compression and shear of the wall clay were divided between 57% and 64% of the passing mass percentage of grain size 0.075 mm. The estimation formulas for the compression and shear strengths of the wall clay agreed with the measured values when the soil test data, water content, and density of the wall soil during construction and after drying were combined. Furthermore, shear strength could be estimated using the passing mass percentage of grain size 0.075 mm and average compressive strength.