Of late, deformation of subgrade soil has led to an increasing number of road subsidence diseases. Real-time monitoring of subgrade deformation is critical to ensure the safety of subgrade operations. In this paper, a sensor-enabled piezoelectric geoelectric cable (SPGC) with impedance strain effect and piezoelectric effect is tested. The SPGC impedance and voltage signals obtained by cyclic shear test under vertical static load and cyclic shear test under vertical cyclic load are used to evaluate the monitoring effect. The results showed that normal stress had the greatest effect on the shear strength of the soil, whereas the normal stress and horizontal shear displacement amplitude significantly influenced the strain in the soil. Varying the normal and horizontal shear frequencies had little effect on the shear strength and strain of the soil. The normalized impedance and voltage of the SPGC, respectively, decreased and increased rapidly during the initial stage of the shear cycle; these changes were relatively small during the middle and late stages of the shear cycle. The SPGC voltage waveform revealed the changes in the shear stress and vertical displacement under different normal and horizontal shear frequencies, from which the stability of the subgrade soil under the aforementioned conditions could be evaluated. The variations in the SPGC impedance and effective voltage from the cyclic shear tests under both vertical static and vertical cyclic loads remained essentially consistent with the number of cycles. However, there was a difference in that the trough of the SPGC impedance under the vertical cyclic load was larger than that under the vertical static load; likewise, the effective SPGC voltage under the cyclic load was larger than that under the static load. Through an analysis of the SPGC impedance and voltage signals in the subgrade soil, the consistency of the SPGC-normalized impedance and effective voltage with shear stress was clarified; this helped us evaluate the health of the subgrade and monitor the characteristics of the precursor signals before a slide were to occur, thereby affording us an opportunity to issue timely warnings.

The soil surrounding bucket foundations that are subjected to vertical cyclic loading would become softened but not consolidated. This would reduce the uplift resistance and even cause foundation failure. The paper firstly investigates the development, especially the dissipation of excess pore pressure and base suction (the suction between the bucket lid and soil) under vertical cyclic loading through 1 g model tests. The test results demonstrate that although base suction can bear 54 % of the uplift resistance of the bucket foundation at the beginning, the upward movement of foundation causes cracks at the soil surface, which accelerates excess pore pressure dissipation and leads to faster foundation failure. Therefore, the base suction should not be considered in the foundation design under long-term cyclic uplift loading. Then, an amended kinematic hardening model that can consider the strain softening effect of soil is employed to obtain the uplift resistance under vertical monotonic and cyclic loadings for various soil softening parameters and cyclic load level (the ratio of cyclic mean load to the monotonic ultimate uplift resistance). Through extensive fatigue analyzes with tens of thousands or even hundreds of thousands of cyclic loadings in each analysis, it is concluded that the fatigue cyclic number increases as the cyclic load level decreases or softening parameters (xi 95 and delta rem) increase. A prediction formula of fatigue curve of bucket foundation is proposed and verified to predict the fatigue cyclic number. The prediction error is within 10 %, and the formula can provide a convenient reference for the design of bucket foundation.