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Cone penetration testing in the clay tills of Skåne - An investigation of the cone factor

Lindström, Johan LU (2017) In TVGT-5000 VGTM01 20171
Geotechnical Engineering
Department of Construction Sciences
Abstract
The undrained shear strength is a key parameter in the design process of
geotechnical structures. One of the most frequently used methods to investigate this parameter is the cone penetration test (CPT). The CPT does not measure the undrained shear strength directly, but instead the resistance that a conic probe encounters as it is pushed into the ground. A calibration factor, the cone factor (Nkt), relating the two quantities is, therefore, needed. The Swedish Geotechnical Institute suggests to use a cone factor of 11 when using CPT in the clay tills of Skane. However, in Denmark, a value of 10 is recommended for similar soils. The magnitude of the calibration factor is critical when determining the undrained shear strength and,... (More)
The undrained shear strength is a key parameter in the design process of
geotechnical structures. One of the most frequently used methods to investigate this parameter is the cone penetration test (CPT). The CPT does not measure the undrained shear strength directly, but instead the resistance that a conic probe encounters as it is pushed into the ground. A calibration factor, the cone factor (Nkt), relating the two quantities is, therefore, needed. The Swedish Geotechnical Institute suggests to use a cone factor of 11 when using CPT in the clay tills of Skane. However, in Denmark, a value of 10 is recommended for similar soils. The magnitude of the calibration factor is critical when determining the undrained shear strength and, consequently, for further design.

To investigate the cone factor, measurements of the undrained shear strength and the net cone resistance were compared for five types of clay till found in Skane at a total of three different sites. Depending on availability, other soil parameters were considered in the analysis in order to explain variations of the calibration factor Nkt.

The comparison between the undrained shear strength measurements, from
field vane tests, and the net cone resistance gave a mean value of Nkt in the range of 9.3 to 10.2. However, a significant standard deviation, ranging from 0.7 to 1.7, is connected to the evaluated cone factors.

Due to the significant degree of scatter in the data, partially caused by the inhomogeneous nature of the soil and partially influenced by primarily using field vane tests to evaluate the undrained shear strength, it is hard to draw exhaustive conclusions. However, for the different soils studied in this project, it seems reasonable to use a cone factor lower than 11. It also appears that the cone factor is closely linked to the overconsolidation ratio, though more tests at various locations are needed to verify this hypothesis. (Less)
Popular Abstract (Swedish)
Vid marktekniska undersökningar i finkorniga jordar är det av stor vikt att
korrekt kunna bestämma den odränerade skjuvhållfastheten. Detta görs idag
vanligtvis ute i fält med en uppsjö av sonderingsmetoder som ger olika mått
på hur fast jorden är. För homogena leror och sand finns det en stadig empirisk grund för hur dessa sonderingsparametrar räknas om till odränerad
skjuvhållfasthet, men hur ser det ut for lermoran? Tillgodoräknas verkligen
materialet sin fulla potential?
Please use this url to cite or link to this publication:
author
Lindström, Johan LU
supervisor
organization
course
VGTM01 20171
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
Geotechnical engineering, Cone Penetration Testing, CPT, Clay Till, Skåne, Undrained shear strength
publication/series
TVGT-5000
report number
TVGT-5061
ISSN
0349-4977
language
English
id
8923263
alternative location
http://www.geoteknik.lth.se/english/publications/masters-dissertations/
date added to LUP
2017-08-23 12:12:21
date last changed
2017-08-23 12:12:21
@misc{8923263,
  abstract     = {The undrained shear strength is a key parameter in the design process of
geotechnical structures. One of the most frequently used methods to investigate this parameter is the cone penetration test (CPT). The CPT does not measure the undrained shear strength directly, but instead the resistance that a conic probe encounters as it is pushed into the ground. A calibration factor, the cone factor (Nkt), relating the two quantities is, therefore, needed. The Swedish Geotechnical Institute suggests to use a cone factor of 11 when using CPT in the clay tills of Skane. However, in Denmark, a value of 10 is recommended for similar soils. The magnitude of the calibration factor is critical when determining the undrained shear strength and, consequently, for further design.

To investigate the cone factor, measurements of the undrained shear strength and the net cone resistance were compared for five types of clay till found in Skane at a total of three different sites. Depending on availability, other soil parameters were considered in the analysis in order to explain variations of the calibration factor Nkt.

The comparison between the undrained shear strength measurements, from
field vane tests, and the net cone resistance gave a mean value of Nkt in the range of 9.3 to 10.2. However, a significant standard deviation, ranging from 0.7 to 1.7, is connected to the evaluated cone factors.

Due to the significant degree of scatter in the data, partially caused by the inhomogeneous nature of the soil and partially influenced by primarily using field vane tests to evaluate the undrained shear strength, it is hard to draw exhaustive conclusions. However, for the different soils studied in this project, it seems reasonable to use a cone factor lower than 11. It also appears that the cone factor is closely linked to the overconsolidation ratio, though more tests at various locations are needed to verify this hypothesis.},
  author       = {Lindström, Johan},
  issn         = {0349-4977},
  keyword      = {Geotechnical engineering,Cone Penetration Testing,CPT,Clay Till,Skåne,Undrained shear strength},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVGT-5000},
  title        = {Cone penetration testing in the clay tills of Skåne - An investigation of the cone factor},
  year         = {2017},
}