ABSTRACT
An investigation was performed to characterize the nature of conditioned clay soil through a successfully excavated zone of high clogging potential earth pressure balance TBM tunneling. An examination of belt conveyor samples revealed three clear constituents, including unaltered clay clods (indistinguishable from native clay), clod coating and paste. The paste is very loosely bound to the clod coating. The clod coating has been altered by conditioning but is still bound to the clods. Testing of the three constituents revealed no change in clod moisture content, significant increase in paste moisture content (from the GDR reference state) and mild changes in clod coating moisture content. The liquid limit of the paste was determined to have been decreased, while the plastic limit remained the same. The resulting paste consistency index https://www.w3.org/1998/Math/MathML" display="inline"> I c https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003559047/7d063ab1-def6-400a-82c8-63fc91eea9c2/content/inline-math394_1.tif"/> decreased significantly to below zero, conveying the significant https://www.w3.org/1998/Math/MathML" display="inline"> I c https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003559047/7d063ab1-def6-400a-82c8-63fc91eea9c2/content/inline-math394_2.tif"/> influence that polymer addition has beyond just the liquid-based modification of https://www.w3.org/1998/Math/MathML" display="inline"> I c https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003559047/7d063ab1-def6-400a-82c8-63fc91eea9c2/content/inline-math394_3.tif"/> . Stickiness testing of the paste samples revealed insignificant clogging potential, as would be expected from such low https://www.w3.org/1998/Math/MathML" display="inline"> I c https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003559047/7d063ab1-def6-400a-82c8-63fc91eea9c2/content/inline-math394_4.tif"/> material. The gross https://www.w3.org/1998/Math/MathML" display="inline"> I c https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003559047/7d063ab1-def6-400a-82c8-63fc91eea9c2/content/inline-math394_5.tif"/> of the conditioned muck ranged from 0.4–0.8, including well within the range where high clogging potential is predicted. Clearly though, the gross https://www.w3.org/1998/Math/MathML" display="inline"> I c https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003559047/7d063ab1-def6-400a-82c8-63fc91eea9c2/content/inline-math394_6.tif"/> , while a straightforward parameter used to estimate clogging risk, is not the governing https://www.w3.org/1998/Math/MathML" display="inline"> I c https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003559047/7d063ab1-def6-400a-82c8-63fc91eea9c2/content/inline-math394_7.tif"/> . Here, the paste is serving as the driving mechanism for material flow through the cutterhead.
