Abstract. The existence of debris flows not only destroys the facilities but also seriously threatens human lives, especially in scenic areas. Therefore, the classification and susceptibility analysis of debris flow are particularly important. In this paper, 21 debris flow catchments located in Huangsongyu Township, Pinggu District, Beijing, China, were investigated. Besides field investigation, a geographic information system, a global positioning system and remote-sensing technology were applied to determine the characteristics of debris flows. This article introduced a clustering validity index to determine the clustering number, and the fuzzy C-means algorithm and factor analysis method were combined to classify 21 debris flow catchments in the study area. The results were divided into four types: debris flow closely related to scale–topography–human activity, topography–human activity–matter source, scale–matter source–geology and topography–scale–matter source–human activity. Nine major factors screened from the classification result were selected for susceptibility analysis, using both the efficacy coefficient method and the combination weighting. Susceptibility results showed that the susceptibility levels of 2 debris flow catchments were high, 6 were moderate and 13 were low. The assessment results were consistent with the field investigation. Finally, a comprehensive assessment including classification and susceptibility evaluation of debris flow was obtained, which was useful for risk mitigation and land use planning in the study area and provided a reference for the research on related issues in other areas.
Based on the coupled SPH-DEM-FEM numerical method, this paper analyzes the dynamic interaction of solid debris flow particle-liquid debris flow slurry-retaining dam in order to explore the dynamic response of retaining dam under the impact of the solid-liquid two-phase debris flow and delves into the process of the debris flow impact on the dam, the impact force of debris flow, and the elastic-plastic time-history characteristics of the dam under different slopes of trapezoidal grooves. The calculation results show that the coupled SPH-DEM-FEM method can vividly simulate the impact behavior of the solid-liquid two-phase debris flow on the dam, reproduce the impact, climbing, and siltation in the process of the debris flow impact; the dynamic time-history curve of the retaining dam is consistent with the law of the literature, and the result of the debris flow impact force obtained is close to that of the empirical formula. Moreover, this paper studies the impact force distribution of the debris flow impact process. The results have a certain reference value for the study of the dynamic response of the retaining dam under the impact of the solid-liquid two-phase debris flow and the engineering design of the debris flow-retaining dam.
Soft soil improvement is an important subject in civil engineering, and searching for an effective admixture is an important research. Silica fume (SF) is a kind of recycled material, it can be used in engineering as a pozzolanic material. The main objective of this study is to assess the effectiveness of industrial waste silica fume (SF) as an admixture to improve the cement stabilized soft soil. The unconfined compressive test (UCT) and scanning electron microscopy (SEM) test of cement stabilized soil with different SF contents and different curing times have been carried out. UCT after 28 days revealed that the addition of SF can effectively increase the strength of cement stabilized soil and reduce the amount of cement, and 1.5% SF content is considered optimum, excessive SF will not further increase the strength. SF helped to accelerate the cement hydration reaction and significantly improve the early-age strength of stabilized soil even at 3 days, which can improve construction efficiency in actual projects. SEM analyses shows that the proper SF content could make the hydration product calcium silicate hydrate gel (CSH) fill the pores and increase the strength of the material, but excessive SF will increase the large pores content of the material and reduce the strength. This provided a basis for application of SF in improving soft soil.
Reasonable depth of pile embedment is one of the key factors for the success of deep foundation pit projects. This paper has taken a deep foundation pit project in a granite residual soil area in Shenzhen as an example and used physical model tests to study the deformation law of the piles and the surrounding soil during the excavation of the deep foundation pit, revealing the variation law of earth pressure in time and space in the pit and then verified it by numerical simulation. The influence of the embedded depth of the pile on the deformation and earth pressure of the deep foundation pit is then explicitly discussed. The study shows that the embedded depth has a significant effect on the deformation and earth pressure distribution of the foundation pit. The earth pressure in front of the pile tends to approach the passive earth pressure as the embedment depth decreases, while the earth pressure behind the pile is in between the Rankine active earth pressure and the static soil pressure; the settlement value and settlement range of the surrounding soil are doubled. The pile displacement increases as the maximum displacement point rises. The maximum displacement of the pile body was used as the basis for determining the instability of the foundation pit. The optimum embedded depth is obtained when the depth of embedment of the pile is 0.22 H (H is the excavation depth of the foundation pit).
The existence of debris flows not only destroys the facilities, but also seriously threatens 9 human lives, especially in scenic areas. Therefore, the classification and susceptibility analysis of 10 debris flow are particularly important. In this paper, 21 debris flow catchments located in Huangsongyu 11 town ship, Pinggu District of Beijing, China were investigated. Besides field investigation, geographic 12 information system, global positioning system and remote sensing technology were applied to 13 determine the characteristics of debris flows. This article introduced clustering validity index to 14 determine the clustering number, and the fuzzy C-means algorithm and factor analysis method were 15 combined to classify 21 debris flow catchments in the study area. The results were divided into four 16 types: scale-topography-human activity closely related, topography-human activity-matter source 17 closely related, scale-matter source-geology closely related and topography-scale-matter source-human 18 activity closely related debris flow. And 9 major factors screened from the classification result were 19 selected for susceptibility analysis, using both the efficacy coefficient method and the combination 20 weighting. Susceptibility results showed that the susceptibility of 2 debris flows catchments were high, 216 were moderate, and 13 were low. The assessment results were consistent with the field investigation. 22Finally, a comprehensive assessment including classification and susceptibility evaluation of debris 23 flow was obtained, which was useful for risk mitigation and land use planning in the study area, and 24 provided reference for the research on related issues in other areas. 26Efficacy coefficient method 28 hundreds of people lose their lives, resulting in irreparable losses (Kang et al., 2004). 36Debris flow susceptibility analysis (DFS), which expresses the likelihood of a debris flow 37 occurring in an area with respect to its geomorphologic characteristics (Blais et al., 2016), is very 38 important to mitigate, evaluate and control debris flow disasters (Chiou et al., 2015). Physical, 39 empirical, and statistical approaches are used to analyze debris flow, which expresses the presumption 40 of a debris flow occurring in an area with respect to its geomorphologic characteristics (Blais et al., 41 2016). Physical-based approaches (Carrara et al., 2008; Burton and Bathurst, 1998) are more applicable 42to analyze physical and mechanical factors in independent catchments. Empirical model belongs to 43 qualitative evaluation and is too subjective to be convinced. Statistical analyses which are usually 44 applied in the research of regional debris flow, belongs to quantitative evaluation and depends on the 45 completeness and accuracy of data. For a study area with a limited number of debris flows, a 46 semi-quantitative evaluation method is more appropriate. This analysis includes the extraction of 47Proterozoic sedimentary strata and Quaternary sediments. The main lithology of the Archean age ...
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