Internal Stability of a Core Material of Glacial Till
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
This report is based on four different seepage tests that have been performed on a silty, sand glacial till. The glacial till was collected from a borrow area in Västerbotten and it has been used as core material in a dam. The tests were performed with purpose to investigate the internal stability of glacial tills and the effect the amount of fines and the degree of compaction has on the phenomenon internal erosion. The results from the seepage tests were compared with two available internal erosion criteria, developed to assess if a soil is susceptible to internal erosion. The comparison was performed in order to find out it is possible to apply the methods to the studied glacial till soils.The first seepage test was conducted on a natural glacial till soil, test GR1. Then to reduce the fines content the glacial till was mixed with 40 % and 70 % by mass of gravel in aggregate sizes between 8-30 mm, test GR2 and test GR3 respectively. These three tests were compacted to a degree of compaction of 90 %. The final test was compacted to a degree of compaction of 95 %, with mixed aggregate sizes of gravel (8-30 mm) of 45 % by mass, test GR4.The seepage test of GR1 showed to be stable after a test-duration of 14 days. Test GR2 were stopped after four days, it was unstable and had eroded in a combination of suffusion and global backward erosion. Test GR3 were stopped after one day, seemingly being unstable only by suffusion. Test GR4, with a larger percentage of mixed gravel than the stable test GR2, was compacted to 95 % instead of 90 % as the other tests. It proved to be stable after being tested for 15 days.The initial grain size distribution for each sample was compared to two different methods for assessing internal stability; i) Li-Fannin with Kenney and Lau and ii) the method by Wan and Fell. Both methods showed that all tests have unstable grain size distributions except test GR1, the natural glacial till. The seepage test of GR4, with a degree of compaction of 95 %, was also stable in the seepage tests. The conclusion is that compaction affects the resistance to internal erosion, thus indirectly, in this case, also influences the internal stability of the soil. Furthermore a glacial till with more stones and less amount of fines behaves more unstable. The limit of stability seems to lye somewhere with a fines content of 16 % and some percentage higher if it is low compacted. Both the method i) by Li-Fannin with Kenney and Lau and the method ii) by Wan and Fell seem to be working for predicting instability for this type of soil. However, compaction is not considered in the methods, which means that the soil can perform stable despite a grain size distribution that is theoretically unstable.
Place, publisher, year, edition, pages
2015. , 112 p.
Teknik, Morän, inre erosion, suffusion, genomströmningsförsök, permeameter, glacial till, internal erosion, seepage tests
IdentifiersURN: urn:nbn:se:ltu:diva-46781Local ID: 46663c6b-3174-4a68-97bc-de97fde499a3OAI: oai:DiVA.org:ltu-46781DiVA: diva2:1020096
Subject / course
Student thesis, at least 30 credits
Civil Engineering, master's level
Rönnqvist, HansViklander, Peter
Validerat; 20151016 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved