Liquefaction Screening Criteria for Earth Dam

Author(s): Dr. Ravikant Mittal and Gaurav Tyagi
Paper category: Proceeding
Book title: International Conference on Advances in Civil Engineering and Sustainable Construction
Editor(s): T.Ch. Madhavi, G. Prabhakar, Santhosh Ram, and P.M. Rameshwaran
Print-ISBN: None
e-ISBN: 978-2-35158-161-2
Publisher: RILEM Publications SARL
Publication year: 2016
Pages: 237-241
Total Pages : 5
Language : English

Abstract: Liquefaction of saturated foundation soil has often been one of the causes of earthquake damage to embankment dams. During Bhuj earthquake of 26 January 2001, a large number of dams failed. These dams were constructed to fulfil the irrigation and drinking water demand of the area. Main cause of damage was liquefaction of saturated foundation soil. Fortunately, at the time of earthquake most of dams were dry otherwise damage could be much more wide spread and severe. It is, therefore, necessary that possibility of liquefaction is examined beforehand and necessary remedial measures are adopted against damages due to liquefaction of foundation soil. Here an attempt is made to examine such provisions in the Indian seismic code IS 1893 which states that in soil deposits consisting of submerged loose sands and soils falling under classification SP with Standard Penetration N-values less than 15 in seismic zones III, IV, V and less than 10 in seismic zone II, the vibration caused by earthquake may cause liquefaction or excessive total and differential settlements. Such sites should preferably be avoided while locating new settlements or important projects. Otherwise, this aspect of the problem needs to be investigated and appropriate methods of compaction or stabilization adopted to achieve suitable N-values. Detailed liquefaction analysis is carried out which reveals factor of safety against liquefaction to be lower than 1, for cases where no liquefaction is reported by IS 1893-PART1. These criteria were found to be non-conservative in several cases. Several cases of dam failures due to liquefaction were reported during Bhuj earthquake of 2001 where SPT N values was more than 20, which suggest that these provisions need to be re-evaluated and should be made consistent as per international code of practices. Further comparison is made with various international codes of practices in which suggested SPT N value is greater than 30 for no liquefaction for clean sand. Existing guidelines are not addressing liquefaction criterion for silt, silty sand, silty clay. Critical assessments of these criterions were made and guidelines were proposed for Indian Code of practices. There is an urgent need to modify Indian code provisions related to liquefaction failure of dams.

Online publication: 2017
Publication type: full_text
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