Roskoden, Robert

INTERCOAST Profile

Current: Project Pore Pressure


At MARUM a new small calibration chamber, called MARUM calibration chamber (MARCC) has been developed which can simulate BC1 to BC5 boundary conditions with an overburden stress up to 5 MPa and a maximum penetration rate of 2 m/s . The features of the MARCC are its small sample volume (54.5 cm height, 30 cm diameter) which makes it especially efficient in its usage. The lateral stress is applied via water pressure while the vertical stress is induced via a water filled latex cushion. The samples are confined by individually designable latex membrane. A geotextile on the water cushion serves aa a connector to the pore water pressure. Three-litre high pressure syringe pumps control the boundary conditions and the pore pressure. The current mini-cone is pushed via a hydraulic cylinder into the sample (Fleischer et al., 2015). Further description of the MARCC may be read in Fleischer et al. (2015).

Motivation

In my master thesis I investigated the soil classification via dynamic penetrometer tests. Here, I demonstrated that pore pressure measurements can -so far- not be used for dynamic soil classifications. This is given due to the fact that the acceleration and deceleration of the dynamic
penetration velocity affects the pore water measurements during the penetration. Therefore, the pore water pressure needs to be corrected in order to be of greater use for the data analysist. In respect to the results of my master thesis, the striven goal in this project shall be to design a
penetration rate experiment which will investigate the behaviour of the piezometer of the CPT device for unconventional penetration rates and to develop a correction method if necessary.

Hence, an experiment will be designed following the outlines of Kim et al. (2010) and Chung et al. (2006). The CPT program after Kim et al. (2010) shows the application of a minicone with an area of 1 cm², a diameter of 11.3 mm and apex angle of 60°. The minicone was rented from Fugro Engineers B.V., Netherlands and could also be rented for this project.

The objective of Kim et al. (2010) was to investigate the penetration rate effects on the drainage conditions for clayey sediments. Two properties are described which might affect the drainage conditions:

1. Drainage effect
2. Loading rate effect

The latter describes the consolidation of a clayey soil around the advancing cone penetrometer during a sufficiently low penetration rate. The smaller the penetration rate, the higher the cone resistance. The drainage effects describe basically the opposite effect. Here, the rate of loading will affect the shear strength of the clayey sediment due to the viscosity of the clay. Therefore, the lower the penetration rate the smaller the undrained shear strength (Kim et al. 2010).

Kim et al. (2010) characterized 3 different stages in the behaviour of the cone resistance.

1. The undrained penetration phase for normalized velocities higher than 1.
2. The partially drained penetration phase for normalized velocities from 1 to 0.05.
3. The drained penetration phase for normalized velocities lower than 0.05.


Application and Outlook

For the project at hand the object will be to use a similar experimental setting as Kim et al. (2010) but with different specimens and penetration rate configuration

The experiment shall have at least three stages in which the pore water pressure behaviour from the piezometer in the CPT is investigated.

1. Stage: The MARCC is filled with water and the probe is moved with different penetration rates and modifications (static and dynamic).
2. Stage: The specimen shall be fluid mud and the probe is moved with different penetration rates and modifications (static and dynamic).
3. Stage: The specimen shall be clayey silt, and depending on the setup time the probe is moved with three to five different dynamic velocities is the specimens.
4. Additionally, if time and other requirements allow it, a more natural case, with a hard sand layer imbedded in the silt layer, shall also be investigated with two different velocities.

The acquired knowledge might be used to correct former studies (as my own master thesis) to see its applicability.

Literature


Chung, S. F., Randolph, M. F., Schneider, J. A., Effect of penetration rate on penetrometer resistance in clay, 2006, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 132, Issue 9, Pg. 1188-1196

Fleischer, M., Kreiter, S., Mörz, T., Huhndorf, M., 2015, A small volume calibration chamber for cone penetration testing (CPT) on submarine soils. Submarine Mass Movements and their Consequences, Volume 41 of the series Advances in Natural and Technological Hazards Research pp 181-189

Kim, K., Prezzi, M., Salgado, R., Lee, W., 2010, Penetration rate effects on cone resistance measured in a calibration chamber, 2nd International Symposiumon Cone Penetration Testing