The influence of the shaft friction and pile shape on the pile tip bearing capacity

in The 17th Nordic Geotechnical Meeting Reykjavik Iceland 25th - 28th of May 2016 (2016, May)

In 1920 Prandtl published an analytical solution for the bearing capacity of a maximum strip load on a weightless infinite half-space, based on a sliding soil part, with three sliding zones, which is ... [more ▼]

In 1920 Prandtl published an analytical solution for the bearing capacity of a maximum strip load on a weightless infinite half-space, based on a sliding soil part, with three sliding zones, which is nowadays called the Prandtl wedge. This solution was extended by Reissner in 1924 with a surrounding surcharge. Keverling Buisman (1940) , and many researchers after him, extended the Prandtl-Reissner formula for the soil weight, but this part can be neglected for the deep pile foundations. It was Terzaghi (1943) who wrote the formula with bearing capacity factors and Meyerhof (1953) who started to write this formula with both inclination factors and shape factors. Because of the this development for shallow foundations , many researchers thought that failure of a pile tip in a deep sand layer will also show a Prandtl-wedge type of failure and that the stresses on the pile tip are constant and depend only on the shape factor, the friction angle of the soil and the vertical effective stress near the pile tip ( ), so not on the shape and size of the pile tip. This means that a Cone Penetration Test gives the average stress of a real pile and can in principle be used without a reduction for calculating the bearing capacity of a pile, just as Boonstra (1940) showed with his field test and just as the method of Van Mierlo & Koppejan (1952) assume and also many more recent predicting models do. The problem is that many researchers (Jardine et al, 2005, Lehane et al, 2005, Clausen et al, 2005) and recent field tests show that bearing capacity design based on unreduced Cone Penetration Test data are more than 30% too high (Van Tol et al. , 1994, 2010, 2012). Therefore all this has been modelled and studied, as far as possible, with Finite Element Modelling (Plaxis 2D axial-symmetric) . Many remarkable results were found. The shape and size of the pile tip did not matter indeed. But the currently used surcharge shape factor is incorrect. There is also no Prandtl-wedge type of failure at the pile tip, but a zone of plasticity, but still the surcharge bearing capacity factor of Reissner is correct. Also the stresses below the pile tip are not constant, but higher near the centre of the pile. Additional calculations show that the pile shaft friction does not influence the stresses at the pile tip, but the normal stresses of the pile tip do influence the shear stresses along the shaft. [less ▲]

Laboratory tests on Dutch limestone (Mergel)

in Schubert, W.; Kluckner, A. (Eds.) Future Development of Rock Mechanics - Proceedings of the ISRM Regional Symposium EUROCK 2015 & 64th Geomechanics Colloquium (2015, October 09)

In this note, results of triaxial laboratory tests on very weak sedimentary limestone from the construction of the “Geusselt A2” tunnel in Maastricht in the Netherlands are presented. The main purpose of ... [more ▼]

In this note, results of triaxial laboratory tests on very weak sedimentary limestone from the construction of the “Geusselt A2” tunnel in Maastricht in the Netherlands are presented. The main purpose of the triaxial tests was to evaluate the strength of this rock. Particularly interesting was that the strength parameters obtained in the laboratory, were much lower than what was expected after preliminary visual inspections. The two most popular models in soil and rock mechanics, the Mohr-Coulomb and Hoek-Brown failure criteria, were used to estimate the strength parameters and both did not give satisfying results. Still the Mohr-Coulomb model is the best model to use. [less ▲]

PROPAGATION OF HARMONICAL VIBRATIONS IN PEAT

in International Journal of GEOMATE (2014), 7(2), 1101-1106

In order to check the reliability of man-made vibration prediction methods, vibration tests were performed on one of polders in the North-West of the Netherlands. The polder was chosen because it has a ... [more ▼]

In order to check the reliability of man-made vibration prediction methods, vibration tests were performed on one of polders in the North-West of the Netherlands. The polder was chosen because it has a rather homogenous, thick and soft peat top layer. Here sufficient harmonical vibrations could be generated by a rather small shaker. The shaker was designed and manufactured in order to produce harmonical vibrations at the soil surface. It consists of two counter rotating electric vibrators (with rotating eccentric masses) in order to produce a vertically oscillating force. For the recordings of the vibrations, six 2D or 3D geophones were placed on the soil surface and one 2D geophone was placed on top of the shaker. The measured vibration amplitudes of the vertically oscillating shaker were compared with 1. Two different analytical methods used for the design of vibrating machine foundations, 2. The Confined Elasticity approach and 3. The Finite Element Method, for which Plaxis 2D software was used. Also the measured vibration amplitudes at the soil surface were compared with Barkan-Bornitz’s solution and Finite Element Modeling. [less ▲]

Fatigue of geomaterials

in Oka, Fusao; Murakami, Akira; Uzuoka, Ryosuke (Eds.) et al Computer Methods and Recent Advances in Geomechanics (2014, September 23)

Vibrations due to hydroshield tunnelling

in Proceedings of the 9th International Conference on Structural Dynamics, EURODYN 2014 (2014, June)

The Hubertus tunnel in Den Hague, the Netherlands, is a 1.5 km long bored tunnel, mostly below groundwater level, constructed with a hydro-shield Tunnel Boring Machine in 2006 and 2007. The vibrations due ... [more ▼]

The Hubertus tunnel in Den Hague, the Netherlands, is a 1.5 km long bored tunnel, mostly below groundwater level, constructed with a hydro-shield Tunnel Boring Machine in 2006 and 2007. The vibrations due to the tunnelling have been recorded both inside the tunnel and at ground surface. No harmful vibrations were observed while the Hubertus tunnel was being bored, although unexpected vibration nuisance did occur. This is an effect that is widely known when tunnelling in rock, but was not expected when tunnelling in beach sand. Analyses of the recorded vibrations showed that the vibrations were mainly caused by the trembling motion of the TBM in the sand as a result of the stick-slip effect. This creates shear waves along the TBM shaft and pressure waves at the bore front. Both waves travel in an axial direction. [less ▲]

The soil of Luxembourg and the weak Rhaetian clay

in Cahier Scientifique - Revue Technique Luxembourgeoise (2014), 2013(2), 34-37

Luxembourg is geologically divided into two parts: Oesling in the North and Gutland in the Middle and South. Oesling is part of the Ardennes plateau. Gutland was formed in the Triassic and Jurassic ages ... [more ▼]

Luxembourg is geologically divided into two parts: Oesling in the North and Gutland in the Middle and South. Oesling is part of the Ardennes plateau. Gutland was formed in the Triassic and Jurassic ages and is much younger than Oesling. It consists mainly of sedimentary rocks. Luxembourg has a variety of interesting, weak or problematic soils, such as the swelling gypsum layers, the layered schists of Wiltz and especially the weak Keuper-Rhaetian-clay. The Rhaetian clay layer is mostly rather thin and is found at a relatively constant altitude and the band where it comes to the surface is identified by the varying erosion erratically found throughout Gutland. Approximately two third of all landslides are found along this line. Hence it was decided to investigate the Rhaetian clay in the geotechnical laboratory of the University of Luxembourg. Samples were taken from a pit at Rue de Mühlenbach on the north side of the city of Luxembourg and from a sliding slope of a building pit in Schutrange. The friction angle was found to be phi = 8° at Mühlenbach and phi = 13° at Schuttrange, which are both record low friction angles, which explains the high number of landslides in Luxembourg. [less ▲]

Decomposition of measured ground vibrations into basic soil waves

in Pietruszczak, Stan; Pande, Gyan (Eds.) Proceedings of the 3rd International Symposium on Computational Geomechanics (ComGeo III), Krakow, Poland, 21-23 August, 2013 (2013, August 21)

Man-made vibrations from different types of sources are usually measured on the surface of the ground or building. The measured signal is always the superposition of all travelling basic waves. For a ... [more ▼]

Man-made vibrations from different types of sources are usually measured on the surface of the ground or building. The measured signal is always the superposition of all travelling basic waves. For a homogeneous half space there are three basic waves – the Compressional (P-wave), Shear (S-wave) and Rayleigh wave (R-wave). Depending on the measuring equipment, only the accelerations or velocities in time of the superposed wave can be measured, but not the distribution of the individual basic waves. Additional problems are that each of the basic waves has its own velocity, besides the body and surface waves have different attenuation laws. By using the rules of superposition of harmonic waves and also the propagation laws of the P-, S- and R-waves, it should be theoretically possible to split the measured superposed signal into the basic waves, because mathematically a system of equations can be assembled which describes the displacements at multiple measuring points in time. In this paper this problem has been solved for a homogenous, elastic and isotropic soil, which is disturbed by a harmonically oscillating disc on the surface. A numerical simulation was performed using a finite element method. The displacements in time were recorded in 10 points on the surface and a system of superposed equations was assembled and solved. The findings prove that each of the three basic waves has its own phase shift with the source, something which was not known before. [less ▲]

Seismic techniques for surveying the underground of shallow foundations

in Conference Testing and Design Methods for Deep Foundations 2012 kanazawa (2012, September)

For civil structures founded on shallow foundations, the ground underneath the foundation often holds the greatest risks of the total structure. In this paper the surveying of the subsurface below shallow ... [more ▼]

For civil structures founded on shallow foundations, the ground underneath the foundation often holds the greatest risks of the total structure. In this paper the surveying of the subsurface below shallow foundations has been studied for three mayor risks; the risk of soft soils, the risk of an inhomogeneous subsurface and the risk of dangerous hidden objects. The research question here is whether a kind of seismic technique can be used to detect those risks. As an example one could look at non-seismic wave detection techniques. There are “only-listen” detection techniques like passive sonar, infrared camera detection, and multi-microphone noise localization, but these have not been used as an example for seismic techniques in this paper. And there are “tap-and-listen” detection techniques, like active sonar, radar, echoscopy and the deep geophysical surveying techniques of the oil and gas exploration. This last technique is of course already a seismic technique in which the applied pulse or blast creates a combination of compression, shear and surface waves. These waves have all different wave velocities and will return at different time intervals. For a shallow subsurface technique though, all these waves will overlap unfortunately. Even for a single wave technique this problem is difficult to avoid, so it is best to create a very short and single pulse. For the creation of the wave both the shortness and the singleness is very difficult. Instead of a single pulse, also single-frequency, multiple waves (constant vibration) can be used as intentional wave initiation. Then there will be even more an overlap of waves, but maybe the effects of interference and resonance can lead to positive results in the detection. For the quantification of the risk of (dangerous) hidden objects, it can be concluded from Finite Element Calculations that the recording of the hidden objects by the “tap-and-listen” technique will very likely not work for smaller objects in an inhomogeneous subsurface. Also when we try to preserve the reflected energy as much as possible by tapping and listening at the same position on the ground surface right above the (hidden) object, it does not work. Even if we assume no frictional or viscous energy dissipation in the calculation, the relative amount of reflected energy is simply too low in comparison to the energy of the still present original wave. This means that it will be difficult or even impossible to design good seismic techniques for surveying the underground of shallow foundations for hidden shallow objects like water pipelines, undetonated bombs, dead bodies, coffins, potholes, etc. [less ▲]

Causes of major geotechnical disasters

in 3rd International Symposium on Geotechnical Safety and Risk, München, (2011, June)

Many disasters are related to geotechnical failure. Both for risk management and for future research it is important to know what new knowledge is needed to prevent these disasters. Therefore elev-en ... [more ▼]

Many disasters are related to geotechnical failure. Both for risk management and for future research it is important to know what new knowledge is needed to prevent these disasters. Therefore elev-en geotechnical disasters or failing projects of the last ten years in modern countries are studied and com-pared in this paper. All examples show that the disasters or failing projects had nothing to do with a large spread of the strength or load in a foreseen failing mechanism. There was also not an unknown failure mechanism or a lack of existing scientifical knowledge. All cases show a lack of available knowledge (or incompetence) of the designing part of the construction management. The mistakes which were made were often of a level not higher than a BSc or MSc teaching level. In none of these cases these mistakes were tackled by an internal project auditing and in none of these cases these mistakes were tackled by an exter-nal project design control, for example for a building permit. The biggest risk parameter in geotechnical design is therefore not the spread of load or strength parame-ters, but by far the existence and quality of the internal project auditing and the external project design control. [less ▲]

Keynote Lecture: Dike failures; Risks, Causes and Costs

Presentation (2010, June 01)