Separation testing for clogging risk evaluation: influencing factors and critical analysis of the test method

Clogging is a common phenomenon in challenging ground conditions where tunnel excavation using tunnel boring machines encounters fine-grained soil that exhibits adhesive be-haviour on metal surfaces. Various laboratory tests and empirically determined methods exist to quantify the risk beforehand during the ground investigation, which aim to measure or evaluate the clogging potential of the encountered soil. The most common methods include estimating clogging risk based on the Atterberg limits, the RUB-Queens Clay Adhesion Tool (ATUR) test and its predecessors, the cone pull-out test, and the plate separation test. This paper aims to iden-tify crucial factors that influence the results of the plate separation test. First, all the procedures mentioned above for clogging risk evaluation are explained to facilitate comparison of the meth-ods. The results of 72 separation tests on reconstituted illite are then presented. We developed a factorial design for this study, varying the consistency of the clay (controlled by preloading stress), the loading or contact time, the loading stress-to-preloading stress ratio, and the separation speed. Excellent reproducibility is achieved using the described vacuum mixing of clay powder followed by consolidation. Moreover, it becomes evident that all stated test parameters signifi-cantly influence the measured separation resistance, often referred to as adhesion. The results derived from plate separation tests must be obtained under identical conditions to compare differ-ent soils. Only when the same testing procedure and sample preparation method are employed can the results be considered comparable. A longer contact time is recommended if the test method proves insightful. Separation resistance alone should not be used to assess the risk of clogging. It is crucial to include other properties such as mineralogy, plasticity, and soil permea-bility in the engineer's qualified assessment. Other, more established methods for clogging risk evaluation should be given preference.

DDC Class

624.15: Geotechnical Engineering

Funding(s)

Adhäsion zwischen ebenen Stahloberflächen und kohäsiven Böden

Lizenz

https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication version

publishedVersion

Name

Separation testing for clogging risk evaluation_ Influencing factors and critical analysis of the test method_26_10_19_17_43_12.pdf

Type

Main Article

Size

187.32 KB

Format

Adobe PDF

Options

Separation testing for clogging risk evaluation: influencing factors and critical analysis of the test method