Lessons from daily practice
Maurice Bottiau, Franki Geotechnics, Belgium
In the course of our daily activities, we are regularly confronted with the same small (or not so small) problems that we thought had long since been solved. Problems that , with a smooth execution, should no longer occur : insufficient ground investigation, non-existent relationship between different gauges of the same project, absurd regulations of specifications, unclear reporting.
In this article, we propose to screen the life of a project with all the lessons that we should have learned but are apparently regularly forgotten anyway. We illustrate this with some real-life examples.
Risk of slope instability due to flattening of a sandy loam layer under the influence of pile driving
Luc Maertens, Besix, Engineering Department
William van Impe, Ghent University, Laboratory for Soil Mechanics
During the execution of a quay wall in Dunkirk (France) in the vicinity of a seaward embankment, there were fears that a general sliding could occur because of a 'fluidised' sand-laden loam layer. The cause for this fear was the experience of 3 major shear events in the area, which had been attributed to this phenomenon. The necessary theoretical approaches were made to demonstrate this, and measurements were taken during the execution of the works to back them up.
Application of dynamic thrust compaction and resonant vibration compaction within a factory building under construction - a geotechnical challenge
Flor De Cock, Geo.be - Geotechnical Expert Office
J.Moens, Ingenieurs- en Expertisebureau Jopro
Only at a late stage in the erection of an extensive factory building was it established that the soil conditions locally deviated significantly from the design parameters. The presence of loose packed sand layers up to 4-5 m depth thus required ultimate soil improvement, both under existing foundation soils and at the site of the factory floor yet to be constructed. The choice was made for an unobvious application of dynamic thrust compaction and resonant vibratory compaction, combined with a preliminary PU injection under the foundation pads. Design and execution of the compaction were almost continuously supervised and adjusted via vibration measurements, settlement measurements on the existing columns and settlement measurements of the site.
Modelling of a phased embankment
François Mathijssen, Hydronamic bv, Royal Boskalis Westminster nv
An undrained analysis is normative for the stability of a phased embankment. The undrained shear strength can be determined from effective and undrained strength parameters. These methods are known as effective stress analysis and undrained stress analysis with strength increase. Both undrained methods, when correctly parameterised and modelling the stress path, can result in similar results.
The lessons of The Hague Tram Tunnel
A.F. van Tol, GeoDelft/TU-Delft
In the centre of The Hague, Souterrain is being realised on behalf of the Municipality of The Hague. This project involves the construction of an underground ligth-rail line with a length of 1250 m, including two stations and parking facilities. In the tunnel, two parking decks will be constructed underneath, under which the tram will travel at a depth of 11 to 12 m below street level. The width of the tunnel varies from 15 m to 25 m at the site of the stations. The walls of the construction pit are located at a very short distance, locally barely more than one metre, from the adjacent, mainly steel-founded buildings.
Lessons learned: 'Groundwater as a Sniper'
G.J.M. Janssen and A.W. Vos, Fugro Ingenieursbureau BV
Water in soil not infrequently causes surprises. At least, we are often surprised by it in practice when it might not have been necessary. A lot can go wrong with measuring, interpreting and using groundwater levels, heads and pore pressures. This is food for thought for geotechnicians and hydrologists and, last but not least, for the press. Publishing about this is often difficult, especially when the stage of bickering and legal proceedings has not yet been passed and the bottom stone is preferably buried even deeper than it is brought out.
Geotechnics on the internet
A. Verruijt (formerly TU Delft)
The use of the internet has increased greatly in recent years, even though the balloon of unlimited expectations was blown up a few years ago. This article gives an overview of its potential for disseminating geotechnical information, and especially for finding it. A number of websites important for geotechnical engineering are listed, with brief characteristics.
Ground nailing, possibilities and limitations
Jan Maertens, Jan Maertens BVBA and KU Leuven
The technique of soil nailing consists of applying reinforcement elements or nails that can absorb the tensile and/or shear stresses occurring in the ground. Thanks to the application of these reinforcements, much higher and steeper slopes can be created than is normally possible. The nails ensure that the active zone that would arise in case of shear is anchored in the passive zone behind. In this way, no sliding surface can occur and a stable whole is obtained.
Correcting settlements by undercutting
B.G.H.M. Wichman, RWS DWW
E.J. Huiden, BAM Grondtechniek
In the west of the Netherlands, large settlements often occur after road construction. In particular, differential settlements occur at the transition from earth track to structure, such as a viaduct. To reduce these problems, the technique of 'underhighering' is being developed. underpinning' is the controlled injection of lightweight suspension into the subsoil and the road body, with the aim of reducing settlement differences at ground level. The advantage of this technique is that traffic is virtually unimpeded. After curing, the suspension should have sufficient strength and be as light as possible. Underlays are being developed as part of the DWW project Stimulating Innovation in Infrastructure (Si2). It was one of the 5 promising topics that formed part of the so-called Heeren Huys Accord