The method was based on the conception that incremental relief of in-situ stress generated incrementaldisplacement on the cutting face. A release force was employed to realize the idea.
为表述复合土钉支护增量应力释放引起增量位移的变形原理，文中引入了一种释放力。
2
Sequential images of the deformation field under a model footing were digitally recorded. The DPDM technique was used to achieve the incrementaldisplacement field and the slip failure surface.
According to the law of mass conservation the incremental mass density can be inferred from the divergency of the scalar unperturbed mass density and the vectorial displacement field.