Rheological Parameters and Numerical Analysis of Cohesive Soils for the Maokong Landslide

• Main Authors: Felly Patricia Hendriks, 舒芳莉
• Other Authors: Hsien-heng Lee
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/27033308834294696606

碩士 === 國立臺灣科技大學 === 營建工程系 === 97 === On September 29th 2008, a landslide happened in Maokong area around pile T16 of Gondola, Taipei. The landslide looks like mudflow on the bottom of the slope. To confirm the landslide type, it is needed a study in rheology, for mud is a viscous liquid that flow under its own mass by gravity force. The soil starts to behave like a fluid when the water content of the soil passes over liquid limit state. To conduct the liquid limit state there are two classic ways of tests, Atterberg limit test and fall cone test. In this research there is another way to get liquid limit besides the classic tests, by observing shear strength of the soil in the solid phase and in liquid phase. To observe the solid phase of the soil, direct shear test is a way to test the soil at low water content. To define the shear strength of the soil in liquid phase it is needed to conduct a study in rheology in a form of a test called moving ball test. The rheological parameters of the soil will be the best way to get the shear strength at very high water content. The liquid limit values that resulted from Atterberg limit tests, fall cone test and direct shear and moving ball test are close. The similarity of liquid limit values leads to the similarity of soil classifications. The Atterberg limit and fall cone test point ML or OL, CL-M, CL as the soil types of on the slope, and moving ball test and direct shear test as well conclude that the soil type should be ML or OL and CL-ML. Analyzing the shear strength of those tests above, Atterberg limit test can not provide any information, while fall cone give a certain value of 1.6 kPa for all cohesive soil types, and moving ball test with direct shear test gives various values of shear strength of the soil. These values are 0.5 to 0.99 kPa at range 25 to 33% of liquid limit. These values are agreeable with Karlsson’s (1977) range of 0.5 – 4.0 kPa for all cohesive soils. Confirming the factor of safety along the slope by numerical analysis, it is revealed that along the slope of Maokong after 24 hours rain only several places are unsecure. After 48 hours and 72 hours of rain, all places along the slope have factor of safety less than 1. In general meaning, after the rain the landslide that occurs is truly mudflow.