Study on slope failure evolution under surcharge loading and toe cutting with BOTDA technology

In recent years, the construction of urban highway through slope excavation becomes more and more widespread. However, the surcharge loading induced by dense buildings is often neglected. For a better understanding of the deformation characteristics and associated failure mechanism of such slopes, a series of model tests have been carried out using distributed strain sensing (DSS) technology. The coupling between DSS cables and surrounding soil is the most critical factor affecting the validity of slope deformation measurements. Therefore, a cable pull-out test is conducted to investigate the coupling effect. It is founded that 200 KPa is the critical confining pressure (CP). Once the CP exceeds this value, the synchronous deformation of DSS cable and soil can be guaranteed, which can be regarded as criterion to guide laboratory test and in-situ monitoring. After the deformation compatibility is ensured, a surcharge loading model test is designed and DSS cables are horizontally and vertically installed. The strain variation exhibited on the DSS cables reveal that the crest and toe areas of the slope show a thrust load-induced and retrogressive failure patterns respectively. It indicates that a shadow sliding surface can occur during slope excavation, which is rarely witnessed in previous studies. The safety factor can be calculated by the slice method. It is founded that the horizontal maximum strain can reflect the stability of the model slope and an exponential function has been established. The results are likely to provide a good indication of the stability of such slopes.