Notice: This page was translated automatically. If anything seems unclear, please refer to the German version.

Comments on the information sheet on the use of geosynthetics in earthworks for road construction (M Geok E)

Introduction

In addition to the recommendations for the design and calculation of earth structures reinforced with geosynthetics – EBGEO of the German Society for Geotechnical Engineering (DGGT) (DGGT), the information sheet on the use of geosynthetics in earthworks for road construction (M Geok E), which has been developed since 1995 under the leadership of the Research Association for Road Engineering and Transport, is the compendium of knowledge for the practical use of geosynthetics in road construction, with a significant influence on many other areas of application with a geotechnical background. Over the years, there have been many meetings and site visits by the committee members. Throughout this time, the knowledge of

experts with their different perspectives, new developments in the industry and, above all, practical experience from application has been incorporated into the information sheet. Since each revision required the many discussions and proposed solutions to be reduced to a short, concise and understandable text for the information sheet, many ideas and considerations were lost. Against this background, the idea arose to take up the further content from the discussions during the meetings on the information sheet and during the breaks and make it available to users of geosynthetics.

System

In the FGSV's system of technical publications, the information sheet is a document that has been assigned to category 2 of the regulations. The FGSV therefore recommends that the information contained therein be taken into account as the state of the art for the planning and implementation of structures. The regulations have been agreed within the FGSV. The information sheet therefore forms the technical basis for the Technical Delivery Conditions for Geosynthetics in Earthworks for Road Construction or the sections of the Additional Technical Contract Conditions for Earthworks for Road Construction (ZTV E-StB), which regulate the use of geosynthetics. However, references to the information sheet can also be found in the regulations of the German Railway and the Federal Waterways Engineering and Research Institute. In addition, the information sheet is also discussed and, in some cases, adopted abroad. These wide-ranging fields of application, even beyond earthworks in road construction, ensure a continuous gain in knowledge and a continuous updating of the information sheet.

Contents

General

The content of the information sheet covers a very wide range of functions and applications of geosynthetics. It is written for the practical application of geosynthetics and primarily contains practical information that does not go into every last detail of mathematical proofs, but should be used to accompany the planning and implementation of measures involving geosynthetics.

Geotextile robustness classes

In addition to the filter criteria and weather resistance, dimensioning under site-specific conditions is limited to the classification of geosynthetics. For this purpose, the information sheet specifies geotextile robustness classes that take into account the mechanical stresses caused by the fill material, the installation process and construction operations. The geotextile robustness classes are derived from a matrix of application and stress cases. They must be determined individually for each construction site.

A distinction is made between 5 application cases (AS), which are defined according to Table 1 based on the fill material.

Table 1: Definition of application cases (AC)

When covering geosynthetics used as separating elements with a frost protection or gravel and crushed stone base course made of qualified material, it should be noted that the 0/56 and 0/63 sieve line ranges already allow a maximum grain size > 63 mm, i.e. stones. The stress on the geosynthetic material due to installation, compaction and construction traffic increases approximately exponentially with grain size.

The information sheet also distinguishes between round-grained and sharp-edged bulk material. Sharp-edged material can always be assumed to be present if the mineral mixture contains broken particles. Based on the classification in Table 1, this results in the applications for the grain size distributions of round-grained and sharp-edged bulk materials.

The distinction between stress cases (AB) in Table 2 takes into account the installation technology of geosynthetics, the compaction of the overlying fill layer and construction traffic on the fill layer above the geosynthetic in determining the geotextile robustness class.

Table 2: Definition of stress cases (AB)

The geotextile robustness classes for round-grained (Table 3) and sharp-edged (Table 4) bulk material can be determined from the application and stress cases using the following tables.

Table 3: Definition of geotextile robustness classes (round-grained fill material)

Table 4: Definition of geotextile robustness classes (sharp-edged bulk material)

Filter rules

Simplified application rules without mathematical verification are used for the dimensioning and selection of separation layers made of geosynthetics. These are, on the one hand, the simplified filter criteria in Table 5, which specify the opening width O₉₀ for nonwovens and woven fabrics.

Table 5: Filter criteria for separation elements

For the application of geotextile filters in accordance with the information sheet, a distinction is made between hydraulic safety cases I and II (Table 6). While generally applicable opening widths for nonwovens and woven fabrics are specified in the information sheet for hydraulic safety case I, the characteristic opening width for hydraulic safety case II depends on the soil to be drained (Table 7). Only nonwoven fabrics should be used here.

Table 6: Criteria for hydraulic safety cases

Table 7: Requirements for hydraulic safety cases for O ₉₀

Environmental safety

The environment is a valuable asset that must be protected. This information sheet is currently the only document in Germany that explicitly refers to the impact of geosynthetics on the environment and outlines a method for assessing environmental safety. In order to remain consistent with geotechnical terminology and to obtain results comparable to those obtained from soil assessments, the environmental safety of geosynthetics is assessed in accordance with the Federal Soil Protection Ordinance. By converting the mass per unit volume of geosynthetics to a cubic metre of soil, the flotation ratio of water to soil was modified to reflect the unfavourable use of geosynthetics in earthworks for road construction, thus enabling an assessment to be made on the basis of the limit values for the soil-water pathway specified in the Federal Soil Protection Ordinance. This approach has now also become established in railway transport infrastructure construction and hydraulic engineering and can be found in the relevant regulations and recommendations of the responsible federal authorities and institutions.

The environmental safety of geosynthetics must be verified by the manufacturer or supplier through appropriate tests.

A geosynthetic is considered environmentally safe if the constituents of the eluates produced in accordance with the information sheet comply with the test values for assessing the soil-groundwater pathway specified in the Federal Soil Protection Ordinance.

Quality control

The IVG certificate is awarded at the end of the voluntary quality control certification process, which goes beyond the pure requirements of CE marking and involves approved monitoring bodies. It is awarded by the Industrial Association for Geosynthetics. This includes external monitoring with regular sampling and testing in accredited laboratories on the basis of the parameters specified in the information sheet for the respective functions of geosynthetics. This combination of initial inspection and ongoing monitoring, generally at six-monthly or annual intervals, is recognised as equivalent to the building material entry test specified in ZTV E-StB.

With the IVG certificate, the manufacturer or the party placing a product on the market has the opportunity to label its

products with the IVG quality seal. The regulations for the granting of the IVG certificate cover all applications specified in the product standards for geotextiles and geotextile-related products as well as geosynthetic sealing membranes. This means that the advantages of this extended quality monitoring can be utilised in all relevant areas of application for geosynthetics, in particular those described in the information sheet, and result in immediate time and cost savings on the construction site.

Summary

Since 1994, the information sheet has been a pioneer in the use of geosynthetics in earthworks for road construction. The revisions in 2005 and 2016 took into account the continuously evolving state of knowledge. The particularly noteworthy regulations on geotextile robustness classes, the filter rules for separation and filter elements, and the environmental safety of geosynthetics are not only applied in road construction and not only in Germany. In addition, the information sheet on the use of geosynthetics in road construction forms the basis for the product quality and control requirements set out in the IVG certificate.

As there have been many discussions between the experts involved in the leaflet over the years, which are not reflected in the text of the leaflet, we have summarised these in a commentary handbook on the leaflet, which will soon be available from NAUE GmbH & Co. KG.