Field research on the performance of various drainage materials in Lithuania
Abstract Field evaluation of the performance of a drainage system or of various drainage materials is a long-lasting research, very often with disappointing results. These disappointing results stem either from a too wide a spread of the field data, or one or more necessary parameters which were not measured, or an insufficient knowledge of the flow occurrence in the vicinity of the drain resulting in a wrong interpretation and evaluation of the research findings. Yet, a correct evaluation of the performance of a drainage system is of primary importance to ascertain the real value of a drainage system or to compare various drainage materials. As a result of the wide spread of field data within a measuring season, a large amount of data from several seasons is required to obtain reliable results. From discharge and total head loss measurements a second-degree polynomial results which only permits a determination of whether the design criteria are met. The similarity with Hooghoudt’s equation allows the determination of soil hydraulic conductivity and the equivalent depth of the impervious layer. With this data the drain spacing can be checked. Too wide a spacing can be the cause of malfunctioning of a drainage system, but the drainage materials can also affect its performance. To evaluate or compare drainage materials it is necessary to measure the so-called approach-flow head loss in the vicinity of the drain. The relationship between discharge and approach-flow head loss should theoretically be linear and the regression coefficient gives the approach-flow resistance. However, the relationship depends to a large extent on the approach-flow occurrence in the vicinity of the drain. For non-linear relationships, the approach-flow resistance can be estimated from the slope of the tangent line, which tends to a constant value at greater discharges for flow patterns covering the whole drain circumference. The approach-flow resistance depends on the hydraulic conductivity of the soil and does not permit a direct comparison of various drainage materials. Therefore, the approach-flow constant or the dimensionless approach-flow resistance is calculated. This parameter is related to the material itself and to the installation conditions reflected in the hydraulic conductivity of the trench backfill. Consequently the comparison of the various drainage materials includes the trench backfill. The approach-flow head loss fraction is that part of the total head loss which is dissipated by the approach-flow. The relationship between approach-flow head loss and total head loss should theoretically be and is, indeed, linear so that the slope of the regression line gives the approach-flow head loss fraction. This parameter combines the influence of drainage material and flow pattern so that real flow situations in the vicinity of the drain, which are not necessarily the same for all materials, can be compared.
Field research on the performance of a rice husk envelope in a subsurface drainage system (case study Behshahr, Iran)
This study was conducted to evaluate the performance of subsurface drainage and a rice husk envelope in Behshahr, a coastal region in the northern part of Iran. The subsurface drainage system was monitored in the rainfall seasons of 2006 and 2007 (22 November to 19 March). Various parameters such as daily groundwater table fluctuations and drain discharge rate were measured. To evaluate the drainage envelope, the gradation curve, bulk density and natural durability of rice husk and also the head loss of the groundwater table in the vicinity of the drain were measured. The large difference between the approach‐flow head and entrance‐flow head could be related to clogging of the external part of the rice husk envelope. The overall conclusion of this study was that subsurface drainage system performance was not satisfactory due to poor control of groundwater table depth, which could be related to clogging of the rice husk drain envelope. Hooghoudt's equation is not recommended to be used for evaluation of design parameters in this case. The basic uncertainty in application of a rice husk envelope was its durability, which was found to be very variable and depended on soil environmental conditions. Copyright © 2010 John Wiley & Sons, Ltd.
Concrete Pavement Preservation Guide
This document provides valuable guidance and information on the selection, design, and construction of cost-effective concrete pavement preservation treatments. It is based on a document prepared in 2008 but has been revised and expanded to include updated information to assist highway agencies in effectively managing their concrete pavement network through the application of timely and effective preservation treatments. The preservation approach typically uses low-cost, minimally invasive techniques to improve the overall condition of the pavement. In addition to several introductory chapters covering pavement preservation concepts and pavement evaluation, eight chapters on specific concrete pavement preservation treatments are included: slab stabilization, partial-depth repairs, full-depth repairs, retrofitted edge drains, load transfer restoration, diamond grinding, joint resealing, and concrete overlays. Each of these chapters discusses the purpose of each treatment, its limitations and effectiveness, material and design considerations, construction recommendations, and quality assurance/troubleshooting information. In addition, a final chapter is included on strategy selection procedures.