Consolidation parameters in silts from varied rate CPTU tests

<abstract> <p>The interpretation of dissipation tests from cone penetration tests (CPTU) in silt is often considered challenging due to the occurrence of an unknown degree of partial consolidation during penetration which may influence the results significantly. The main objective of the present study is to investigate the influence of penetration rate and hence partial consolidation in silt deposits on the interpretation of consolidation parameters. Rate dependency studies have been carried out so as to give recommendations on how to establish design consolidation parameters in silts and consider the effect of partial consolidation on the development of design parameters. A comprehensive field and laboratory research program has been conducted on a silt deposit in Halsen-Stj?rdal, Norway. Alongside performing various rate penetration CPTU tests with rates varying between 0.5 mm/s and 200 mm/s, dissipation tests were executed to analyze the consolidation behaviour of the soil deposit. Furthermore, a series of soil samples have been taken at the site to carry out high quality laboratory tests. Correction methods developed for non-standard dissipation tests could be successfully applied to the silt deposit indicating partial consolidation. The results revealed an underestimation of the coefficient of consolidation if partial consolidation is neglected in the analysis, emphasizing the importance of considering the drainage conditions at a silt site thoroughly. To study the drainage conditions of a soil deposit a recently proposed approach has been applied introducing a normalized penetration rate to differentiate between drained and undrained behaviour during penetration. It is suggested that a normalized penetration rate of less than 0.1–0.2 indicate drained behaviour while a normalized penetration rate above 40–50 indicate undrained behaviour. Finally, available dissipation test data from a Norwegian Geo-Test Site (NGTS) in Halden, Norway have been used to successfully verify the recommendations made for silts.</p> </abstract>

Energy Dissipation Characteristics and Parameter Identification of Symmetrically Coated Damping Structure of Pipelines under Different Temperature Environment

In this paper, a symmetrically coated damping structure for entangled metallic wire materials (EMWM) of pipelines was designed to reduce the vibration of high temperature (300 °C) pipeline. A series of energy dissipation tests were carried out on the symmetrically coated damping structure at 20–300 °C. Based on the energy dissipation test results, the hysteresis loop was drawn. The effects of temperature, vibration amplitude, frequency, and density of EMWM on the energy dissipation characteristics of coated damping structures were investigated. A nonlinear energy dissipation model of the symmetrically coated damping structure with temperature parameters was established through the accurate decomposition of the hysteresis loop. The parameters of the nonlinear model were identified by the least square method. The energy dissipation test results show that the symmetrically coated damping structure for EMWM of pipelines had excellent and stable damping properties, and the established model could well describe the changing law of the restoring force and displacement of the symmetrically coated damping structure with amplitude, frequency, density, and ambient temperature. It is possible to reduce the vibration of pipelines in a wider temperature range by replacing different metal wires.

Research on Horizontal Coefficient of Consolidation of Vietnam’s Soft Soil

The horizontal coefficient of consolidation is the most important parameter for designing the improvement of soil soft by prefabricated vertical drains (PVDs) combined with surcharge and vacuum preloading. This paper presents the experimental study on the horizontal coefficient of consolidation (ch) of some soft soils distributed in Vietnam. The ch value was determined by the laboratory test and CPTu dissipation test. The laboratory tests included the Rowe consolidation cell test and constant rate of strain consolidation with radial drainage test. Two types of consolidation laboratory tests were performed. The experimental results indicated that the ch value is always larger than the vertical coefficient of consolidation of soil (cv). The ratio of ch/cv depends on the consolidated pressure, type of soil, and the anisotropy of soil. The ratio of ch/cv is different in different types of soft soil in Vietnam. In the normally consolidated state, the ch/cv ratio ranges from 1.35 to 10.59. It was necessary to choose the ch value at the consolidated stress level for calculating the PVD spacing.

Characterization of soil permeability in the former Lake Texcoco, Mexico

The geotechnical subsoil conditions of the former Lake Texcoco represent a complex sequence of highly compressible lacustrine clays interbedded with layers and seams of harder and more permeable materials. Although the mechanical properties of these deposits have been extensively studied in the past, the information about their hydraulic properties is scarce. Currently, a comprehensive characterization of the hydraulic conductivity of this site has become necessary because of the construction of the New Mexico International Airport (NAIM). The present study describes a systematic evaluation of the hydraulic conductivity in the former Lake Texcoco through three different in-situ methods (well permeameter, LEFRANC and piezocone dissipation test). The measurements, taken from 155 locations, show a high spatial variability, with ranges spanning more than two orders of magnitude. The results also reveal that the estimated permeabilities vary significantly among methods. These discrepancies reflect the scale dependency of the hydraulic conductivity in the area caused by soil heterogeneities. A comparison of the presented results with previous studies demonstrates that piezocone tests provide representative results for the clayey formations, while LEFRANC tests better estimate the hydraulic conductivity of the permeable strata. Besides, CPTu tests yield more consistent values of hydraulic conductivity, with smaller dispersion than well permeameter and LEFRANC tests.