Basalt fiber-reinforced polymer (BFRP) anchors are increasingly utilized in geotechnical anchoring engineering; however, there remains significant potential for studying the erosion characteristics of the BFRP anchor-slope system under rainfall conditions. This paper investigated the hydrological and spatial–temporal characteristics of three-level bridge foundation slope (TLBFS) reinforced by BFRP anchors through laboratory rainfall experiments. An index (rill density \(\beta\) ) was defined to quantify the degree of slope erosion. The experimental setup included a flume measuring 2 m in length, 1.2 m in width, and 1.5 m in height, a uniform rainfall intensity of 20.0 mm/h, and four sensors used for monitoring moisture content V, earth pressure E, anchor dynamometer T, and strain gauge S. The results indicated that the rill densities of third-level and first-level slopes after soil saturation were 2.37% and 0.98%, respectively. However, relying solely on the rill density index may lead to an overestimation of slope stability. Conversely, the high moisture content (25.72%) of the first-level slope correlated with its deformation and failure. It is proposed that the moisture content index can serve as a reliable indicator for evaluating slope stability. A strong correlation existed between moisture content \(\omega\) and erosion amount \(\delta\) , which suggested that real-time monitoring of slope erosion can be conducted using the moisture content index. The damage to TLBFS resulted from the coupling of the internal and external factors, and the specific failure mode was identified as shallow slip. While the flexible reinforcement capabilities of BFRP anchors effectively mitigated slope deformation, but additional engineering measures need to be added to TLBFS. These findings provide valuable insights for soil and water conservation and disaster prevention in multi-level slopes.
