Study on damage constitutive relationship of mudstone affected by dynamic pile driving

The mudstone around the pile is damaged during pile driving, altering the mechanical properties of the mudstone. This study conducts standard penetration, uniaxial compression, and triaxial shear tests before and after pile driving. It develops a constitutive damage model of mudstone affected by pile driving based on the statistical damage theory and triaxial test data. The findings in this study show that: (1) The standard penetration number (N) of the clay around the pile remains unchanged after driving because of the thixotropic recovery effect. However, the N of mudstone surrounding the pile decreases by 35.1% on average, (2) The average uni-axial compressive strength is 1.56 MPa before pile driving and 1.12 MPa after pile driving, which decreases by 28.2%. After pile driving, c (cohesion) = 217.2 kPa, phi (internal frictional angle) = 21.6 degrees, (3) The calculated value agrees well with the measured one, verifying the rationality of the model, and (4) The mechanical properties of mudstone change considerably after pile driving, and it is unrealistic to use the mechanical parameters of un-disturbed mudstone to design the pile. This research provides theoretical support and parameter preparation for calculating pile driven mudstone foundations.