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The laboratory evidence of phase transformation from landslide to debris flow
Ogbonnaya Igwe,Fawu Wang,Kyoji Sassa,Hiroshi Fukuoka 한국지질과학협의회 2014 Geosciences Journal Vol.18 No.1
The dominant factors initiating the transformation of landslides into catastrophic debris flow are examined. The research found that a threshold pore pressure determined from theoretical and experimental analysis was enough to initiate liquefaction type of failure in sandy materials. Loading tests to failure on source-area sandy soils from a catastrophic landslide location show that under definite conditions of loading, a threshold state, characterized by the equality and constancy of pore pressure and shear resistance develops in the sands at a threshold density. Sands at this density clearly define the boundary between contractive and dilative specimens under same effective normal stress. Confirmatory experiments were then conducted using silica sand. Analyses showed that samples in which the threshold pore pressure was exceeded readily liquefied while those in which the pore pressure was below the limit dilated. The concept of threshold pore pressure fills the gap created by classical theories of soils liquefaction that have identified densities at which phase transformation and steady state lines can be defined. The new concept shows there is a density at which both lines merge and it is proposed that sands transiting from dense to loose and vice versa will first pass through the threshold state. While the stability of a slope founded on sandy soils may be breached when the pore pressure exceeds a certain limit, it is possible to make estimates of the limit. Where such estimates are accompanied with adequate field measurements, the effectiveness of landslide prevention projects may be enhanced.
AutoML을 이용한 산사태 예측 및 변수 중요도 산정
남경훈 ( Kounghoon Nam ),김만일 ( Man-il Kim ),권오일 ( Oil Kwon ),왕파우 ( Fawu Wang ),정교철 ( Gyo-cheol Jeong ) 대한지질공학회 2020 지질공학 Vol.30 No.3
이 연구는 도로 비탈면에서 발생하는 산사태의 확률론적 예측에 기반된 산사태 발생에 영향을 미치는 인자의 중요도 산정 및 예측 모델을 개발하는 것이다. 산사태 예측 모델을 개발하기 위해 한반도 전 지역을 대상으로 2007년부터 2020년까지 조사된 30,615사면의 현장조사 자료를 활용하였다. 전체 131개의 변수 인자 중 지형인자 17개, 지질인자 114개(기반암 89개를 포함), 도로와의 이격거리를 사용하였다. 산사태 발생에 영향을 미치는 인자를 자동화된 머신러닝인 AutoML을 실시하여 예측 성능이 뛰어난 XRT(extremely randomized trees)를 선정하였다. 변수 중요도 분석결과 지형적 요인 10개, 지질인자 9개, 사회적 영향성인 도로와의 이격 거리와 관련된 항목순으로 급경사지 불안정에 가장 많은 영향을 주는 것으로 분석되었다. 개발된 모델의 신뢰성 검증을 수행한 결과 AUC 83.977%의 예측율을 확보한 것으로 나타났다. 이 모델은 산사태 이력을 기반으로 한 현장조사 자료만을 이용하여 변수 중요도의 순위를 도출함으로써 그에 따른 산사태 발생 가능성을 확률적 및 정량적으로 평가하였다. 향후 의사 결정자들에게 현장조사를 통한 사면진단 안전평가 시 신뢰성 있는 근거를 제공하리라 판단된다. This study was performed to develop a model to predict landslides and determine the variable importance of landslides susceptibility factors based on the probabilistic prediction of landslides occurring on slopes along the road. Field survey data of 30,615 slopes from 2007 to 2020 in Korea were analyzed to develop a landslide prediction model. Of the total 131 variable factors, 17 topographic factors and 114 geological factors (including 89 bedrocks) were used to predict landslides. Automated machine learning (AutoML) was used to classify landslides and non-landslides. The verification results revealed that the best model, an extremely randomized tree (XRT) with excellent predictive performance, yielded 83.977% of prediction rates on test data. As a result of the analysis to determine the variable importance of the landslide susceptibility factors, it was composed of 10 topographic factors and 9 geological factors, which was presented as a percentage for each factor. This model was evaluated probabilistically and quantitatively for the likelihood of landslide occurrence by deriving the ranking of variable importance using only on-site survey data. It is considered that this model can provide a reliable basis for slope safety assessment through field surveys to decision-makers in the future.