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Influence of strain rate in CRS tests: A laboratory study of three Swedish clays
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
2016 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Deformationshastighetens inverkan på CRS försök : en studie av tre svenska leror (Swedish)
Abstract [en]

The Constant Rate of Strain (CRS) test is currently the most widely used method for determination of consolidation parameters in Sweden. These parameters are used to calculate the probable settlements and behavior of soils. With the Swedish standard strain rate, the duration of a single the test is about 24h, but a higher strain rate would allow for more tests to be performed in the same amount of time. For all clays in Sweden, the Swedish standard for the CRS test suggests a fixed rate of strain that is independent of soil properties, while the North American standard proposes a strain rate that generates a pore pressure ratio of 3-15%. Soil properties such as water content, liquid limit, sensitivity and shear strength vary greatly between different regions of Sweden. It would be beneficial if these properties could be used to find the ideal strain rate for the CRS test. Performing the tests at a higher strain rate, and thus performing more tests within a shorter amount of time, would save both time and money. In this report, 24 CRS tests are performed on three different clays with distinctive properties. Each clay is tested with three different strain rates: the Swedish standard rate of 0.680%/h, a higher rate of 3.00%/h and a lower rate of 0.154%/h. The results are evaluated according to both standards, and are compared and analyzed to determine whether there is any indication that the strain rate can be selected based on the soil properties. The results indicate that the selection of the strain rate is dependent on the soil properties. In addition, the majority of the tests can be conducted with higher strain rates than what is required by the Swedish standard and still manage to lie within the 3-15% limit of the pore pressure ratio, which is acceptable for the North American standard. However, the preconsolidation pressure does rise with increased strain rates, which can generate problems and erroneous results when calculating the settlements. A more extensive testing program with CRS tests and full-scale field tests must be carried out before any recommendation of a higher strain rate can be made. 

Place, publisher, year, edition, pages
2016. , 67 p.
Examensarbete Jord- och bergmekanik, ISSN 1652-599X ; 16/07
Keyword [en]
Constant rate of strain, Pore pressure ratio, Strain rate, Preconsolidation pressure, Water content
National Category
Geotechnical Engineering
URN: urn:nbn:se:kth:diva-192212OAI: diva2:963064
External cooperation
Skanska Teknik Stockholm
Subject / course
Soil and Rock Mechanics
Educational program
Master of Science in Engineering - Urban Management
Available from: 2016-09-09 Created: 2016-09-07 Last updated: 2016-09-09Bibliographically approved

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