Economic Sampling and Extraction of Undisturbed, High Quality Samples in Normally Consolidated Lacustrine Clays Using a Large Diameter Tube

Abstract

This paper describes the development, design and use of a large diameter sampling tube. High quality test specimens are essential for the investigation of mechanical properties of a soil for high risk projects and when complex and expensive testing methods are to be used. Block sampling is recommended to give the highest sample quality for clayey soils, however, extracting blocks of normally consolidated lacustrine silty clay without excessive disturbance was challenging due to the inherent structure of the soft varved silty clay and difficulty in maintaining K o conditions, as well as no vertical strain, in the sample. A new sample tube, with an inner diameter of 196 mm, an area ratio of 4% and an outer cutting-edge angle of 11°was designed to offer a larger cross sectional area than conventional thin walled sampling tubes, to provide the necessary side support and to prevent water ingress at the sides of the sample. The length-diameter aspect ratio was 1.275 to optimise the amount of clay sampled for subsequent testing and in an attempt to minimize the pressure in front of the tube. Samples were taken in initially newly excavated trenches at a depth of c. 1 m with this new sampler and with conventionally sampled soil specimens, prior to the main testing programme with samples from 6 m depth. A comparative study was then performed including preliminary unconsolidated unconfined compression tests followed by anisotropically consolidated undrained triaxial compression tests. It was important to establish whether this approach had led to an improvement in sample quality prior to embarking on an extensive triaxial stress path testing programme on this varved soil (Messerklinger, Non-linearity and small strain behaviour in lacustrine clay, 2006; Messerklinger and Springman, Geotech Test J 30(6), 2007; Messerklinger and Springman, Geotech Geol J, 2008). The results showed that the undrained shear strength of the specimens from the new sampler was consistently around 20% higher than that of specimens extruded from conventional thin walled tube samplers. This confirmed that samples with a significantly higher quality could be extracted from normally consolidated, fine grained, varved lacustrine deposits with this large diameter 'block' sampling tube.

Non-Linear Elasto-Plastic Behaviour of Lacustrine Clay

“…Block sampling techniques were developed in order to minimize disturbance. Samples were extracted as described in Messerklinger (2006) and Messerklinger and Springman (2009). This Kloten clay is classified as low plastic Clay, CL, after USCS (Table 1).…”

Measuring strength and consolidation properties in lacustrine clay using piezocone and self-boring pressuremeter tests

“…Detailed information about the extremely soft lacustrine clay conditions is best attained from a combination of laboratory and field experiments. Site investigation tools like the piezocone (CPTu) or self-boring pressuremeter (SBPM) allow for rapid and reliable geotechnical characterisation in the field, hence circumventing concerns associated with sampling-induced disturbances (Messerklinger and Springman 2009;Clayton et al 1998;Hover et al 2013) and the oftentimes costly transportation of soil samples from the site to a testing facility.…”

Compressibility of Undisturbed Silt Loam Soil—Measurements and Simulations

“…We conducted confined uniaxial compression tests on 79 undisturbed soil specimens at five different initial suctions. Specimens of relatively large volume (1000 cm 3 ) were used to capture features of secondary structure (aggregates, cracks, and biopores at the millimeter to centimeter scale) and to limit the influence of sampling artifacts (for details on undisturbed sampling, see Baligh et al, 1987; Clayton and Siddique, 1999; McIntyre, 1974; Messerklinger and Springman, 2009). The specimens were collected from the same field site that had been studied by Berli et al (2003, 2004) for traffic experiments with heavy construction machinery.…”