Herman Peiffer

Unsaturated permeability and retention curve determination from in-flight weight measurements in a bench-scale centrifuge

Centrifuges have been used in many ways to determine permeabilities, as they can significantly shorten testing times in low-permeable soils. Typically equilibrium profiles are used, or inflow-outflow measurements, or direct measurements from inside the sample, like from tensiometers or radioactive decay. Recently weight measurements of the sample outside the centrifuge were used effectively in an adapted setup. We present the results of the possibilities offered by doing transient weight measurements of a soil-sample during rotation in the centrifuge. We present the set-up of such an experiment and how the unsaturated permeability and water retention curve can be recovered from it. This eliminates the overhead of doing measurements inside the sample.

3D printing of an instrumented DMT: design, development and initial testing

This paper describes the design, fabrication and initial testing of an instrumented Flat Dilatometer Test (iDMT) device. Compared to the DMT test involving pressure readings at two-fixed displacements, this device is designed to have a direct displacement-measuring system and a larger-displacement range to evaluate the continuous pressure-displacement relation of a soil, which may afford an opportunity to improve the interpretation to take non-linear soil behaviors into account rather than using linear elasticity in the DMT analysis. However, technical constraints are encountered in the iDMT blade machining using traditional technologies, alternatively, a 3D printing technology is successfully applied to fabricate the iDMT blade. Then, the calibrations of the iDMT device are performed, followed by an iDMT test in conjunction with a DMT test in a calibration chamber, demonstrating that the new iDMT device can be used to investigate non-linear soil behaviors, and the 3D printing technology is proved not only to be an expedient solution but also to be used as a routine tool in improving geotechnical testing apparatus.

Inverse determination of saturated and relative permeability with a bench-scale centrifuge

It is well established that the centrifuge can be an important tool to determine permeabilities of porous materials. Nevertheless, up to this date, for geotechnical applications, they are not used outside research laboratories. We attribute this to the cost of a centrifuge, the apparent requirement of measurements in the sample and the more complicated handling of samples for use in the centrifuge. As a first step towards an affordable centrifuge, we present an adaptation to a common bench-scale centrifuge, which allows to obtain measurements in a fraction of the time needed by standard infiltration methods, especially for clayey soils. The permeabilities are determined by measuring global transient data only: water level in an inflow or outflow chamber and gravitational centre of the sample or the rotational momentum of the sample. These are all measured outside of the centrifuge in a start-stop regime. A method of lines approach to solve the Richards’ equation is used, combined with interface tracking, which was previously shown to be an accurate method. Permeabilities are assumed to behave according to the van Genuchten–Mualem formula. We present the experimental set-up, accuracy of the measurements and the numerical solution method. For saturated flow, we compare with standard tests, while for unsaturated flow we compare with a pressure plate result (ASTM D2325). The results indicate the strengths and limitations of this approach, but overall we can conclude that measuring the global characteristics during rotation should provide accurate permeabilities.

Geotechnical Analysis of the Stability and the Seepage for an Artificial Energy Atoll Close to the Belgian Coast

The subject of this work is to analyze the behavior and stability of the dams of an energy atoll. A study of the site conditions of the Northsea was done in order to get a general layout of the problem. The study focuses on the achievement of a reduction of the seepage and the impermeability of the dams. Step by step, an optimal concept of the dam is obtained by investigating different solutions for different problems such as seepage, slope stability, bearing capacity and feasibility. The different failure mechanisms are analyzed based on a parametric analysis and using a numerical model. Different concept proposals are proposed and evaluated.

Evaluating the Effect of Fines on Hydraulic Properties of Rammed Earth Using a Bench Scale Centrifuge

Unstabilized Rammed Earth (RE) has been historically used to form earth walls or blocks. Recently RE has resurfaced as a sustainable building material with little attention given to it in building codes and manuals. The percentage of the fine-grained fraction in RE is one of the most important factors affecting its behavior. Such percentage has been selected in practice based on experience and rules of thumb, not on a scientific rationale. This research examines the influence of the amount and type of fine particles on the hydraulic conductivity and water retention characteristics of compacted soils using a bench scale centrifuge. A Durner curve (1994) was applied to describe the water retention curve as it allows portraying a bimodal pore structure. In an attempt to understand the basis on which fines contribute to the strength of RE, two different types of fine grained soils were used in the mixtures, plastic fines (PF) and non-plastic fines (NPF). Each type was divided further into different mixtures, each with different percentages of fines. The influence of the fines’ percentage was tested using different methods and by using saturated and unsaturated samples of the soil mixtures. Larger suction developed in samples with PF in comparison to those with NPF. Suction increased as the percentage of fines in the mixture increased. Such effect is more pronounced in samples with PF.

One-dimensional model for large-strain consolidation in a bench-scale centrifuge

We present a mathematical model for large-strain consolidation in a bench-scale centrifuge, which is not based on scaling laws. The model allows for different boundary condition setups at the base of the sample: free outflow, imposed head or containment. Constitutive relationships for effective stress and permeability both in terms of void ratio are required inputs. A numerical algorithm is proposed to solve the constructed mathematical model based on the method of lines. Example numerical problems are discussed, and solution strategies are proposed to deal with anomalies in the numerical solution. A limited experimental test was performed to test the feasibility of the approach. The outcome of the test was positive for preconsolidated grounds. For a slurry, vibration effects appear to be present in the used centrifuge, which are not included in the model.