Internal erosion of gravelly mudstone due to drying/wetting and hydraulic pressure cycles in oedometer test.

When disintegrated mudstone due to the slaking, subjected to hydraulic pressure, could lead to internal erosion. To examine the combined effects of slaking and internal erosion of gravelly mudstone in 1D deformation under a constant vertical load, a series of modified oedometer tests and laboratory penetration tests were conducted with drying/wetting and hydraulic pressure cycles. Some loading conditions showed the sever erosion in progressing of the cycle, susceptibility of the internal erosion was evaluated in terms of non-filter and fitter factors coefficient Keywords: Vertical strain, Slaking, Internal-erosion, Particle-breakage.

Laboratory Evaluation of Mechanical Properties of Draupne Shale Relevant for CO2 Seal Integrity

The mechanical integrity of caprocks overlying injection formations is one of the key factors for safe storage of carbon dioxide in geological formations. Undrained effects caused by CO2 injection on strength and elastic parameters should be properly considered in the operational design to avoid fracture creation, fault reactivation and unwanted surface uplift. This study presents results from eleven undrained triaxial compression tests and one oedometer test on the Draupne shale, which is the main caprock of the Smeaheia site in the North Sea, to extract parameters relevant for seal integrity. Tests have been performed on samples oriented perpendicular to and parallel with the horizontal layering of the rock to study the effects of sample orientation relative to the loading direction. Results from undrained triaxial tests showed only minor effects of sample orientation on friction and cohesion. However, when loading during undrained shearing was parallel with layering (horizontal samples), measured Young’s modulus was roughly 1.4 times higher than for the vertical samples. Undrained shearing of vertical samples generated 30–50% more excess pore pressure than for horizontal samples with similar consolidation stress owing to more volume compaction of vertical samples. With apparent pre-consolidation stress determined from a high-stress oedometer test, the normalized undrained shear strength was found to correlate well with the overconsolidation ratio following the SHANSEP (Stress History and Normalized Soil Engineering Properties) procedure.

Method to Determine the Constitutive Permeability Parameters of Non-Linear Consolidation Models by Means of the Oedometer Test

This paper presents an easy-to-apply methodology that allows obtaining the permeability index and the initial hydraulic conductivity of clayey soils, basic constitutive parameters in non-linear models of consolidation, based on the laboratory oedometer test. For this, the data of the void ratio, compressibility index and characteristic consolidation time are taken from the test and, as an inverse problem, the constitutive permeability parameters sought are determined by applying the universal solutions of the characteristic time for a general non-linear consolidation model with constitutive relations void ratio-effective soil stress and hydraulic conductivity-void ratio of logarithmic type. The application protocol of the inverse problem is described in detail and illustrated by a series of applications carried out on real laboratory data belonging to two different soils. The influence that errors in laboratory parameter measurements can have on the final values of the permeability index and initial hydraulic conductivity is studied, showing the maximum deviations that may appear and, by last, the precision of the results obtained.

Determination of Creep Properties of Clays from VRS Oedometer Tests

The determination of creep properties still relies almost entirely on the incrementally loaded oedometer test introduced about 100 years ago. Although the simplicity of the test assures a robust evaluation of soil parameters, it also introduces some shortcomings like discontinuity of the evaluated parameters and the long duration of the test. In this study, the performance of the variable rate of strain (VRS) oedometer test for determination of creep properties of a sensitive soft clay is studied. The results from a comprehensive test series of VRS oedometer tests on a soft sensitive clay is presented. Three different setups for the strain rate variation were used, and each test was repeated thrice. The tests showed good consistency and yielded equal creep parameters compared to values from traditional incrementally loaded (IL) oedometer tests. The tests further verified that it is possible to describe the complex stress dependency of creep parameters with just one additional parameter to the primary deformation parameters. Compared to the IL tests, the VRS tests offers a faster determination and continuous creep properties for a wide range of stress.

COMPRESSIBLITY OF PEAT SOIL IMPROVED WITH POLYURETHANE

This research investigated the compressibility of natural peat soil and peat soil improved with polyurethane foam. High natural moisture content, high compressibility, low bearing capacity and medium to low permeability is a problem and characteristic of a peat soil. This problem can be solved by reducing the compressibility of the peat soil. The objective of this study is mainly to prove whether the presence of polyurethane foam as a lightweight material on peat soil can reduce the compressibility of peat soil or otherwise. Fifteen samples of peat soil taken from Johan Setia, Klang were tested using Oedometer test with load is doubled at each increment until it reaches the maximum required load which is 10kPa, 20kPa, 40kPa, 80kPa, 160kPa, 320kPa and 640kPa. Polyurethane foam is a lightweight material, therefore reduces the overburden pressure to the underlying soil, hence future settlement can be minimized to a tolerable settlement value. Based on the data obtained from analysis of Oedometer test, the compressibility parameters including void ratio, compression index and swelling index of the peat soil alone are very high which denoted extremely poor condition of the peat soil. The compressibility parameters improved significantly with the PU foam stabilization as PU act as a void filler for peat soil. A slight increase in the compressibility parameters are recorded with higher ratio of isocyanate. However, the maximum pre-consolidation pressure recorded was with PU ratio of 1:1. Therefore, the optimum ratio for PU peat stabilization is in the ratio of 1:1.

Genuine and false pre-consolidation and yield pressures

“It remains a mystery why the international profession still uses the awkward e-log p plots, and the incomplete and useless coefficient Cc which is not even determined from the measured data, but from a constructed line outside the measurements”. These are the words of Nilmar Janbu (1998). This paper does not solve the mystery; what it does is highlight the issue behind the mystery in the hope that the profession will face up to the defects of the log scale. An examination is made of oedometer test results when plotted to both scales. Examples are given for sedimentary and residual clays, and sands. It is shown that the e-logp plot routinely produces graphs from which pre-consolidation pressures or yield pressures can be determined. However, when plotted using an arithmetic (linear) scale, this apparent pre-consolidation or yield pressure is found, in most cases, to disappear. It is a false value created by the way the data are plotted. The paper does not deny that pre-consolidation or yield pressures exist in many soils; it gives examples for each of the soil types listed above. It is recommended that the term “yield pressure” be used in preference to “pre-consolidation pressure”, and that only the use of a linear scale will reveal whether such a pressure exists.