Near field wave transformation in clay and peat

in Fifth international conference on recent advances in geotechnical earthquake and soil dynamics, San Diego (2010, May)

A series of simple impact tests is performed, both on clay and on peat, in order to compare the current wave theory with the obtained data. The waves at the surface are measured with three 3D geophones ... [more ▼]

A series of simple impact tests is performed, both on clay and on peat, in order to compare the current wave theory with the obtained data. The waves at the surface are measured with three 3D geophones. With this the wave propagation and the energy dissipation in three directions has been studied both for clay and peat. Since the impact produces a group of waves, only the first arrival time can easily be detected. By transferring the wave information into a 3D energy flow, also the average arrival time and the end-of-wave arrival time can be determined. The results of all tests are very similar, the short wave group splits up in three phases: the first phase consists of compression waves, in the second phase the Rayleigh waves dominate and in the last phase, remarkably, a kind of diagonal Love waves dominate. The second phase starts with a sudden flip of the particle motion due to the arrival of the second wave. In clay 78% of the energy is found in the second phase, while in peat 72% of the energy is found in the third phase. [less ▲]

Trillingen tijdens het boren van de Hubertustunnel

in Geotechniek (2009)

Tijdens het boren van de Hubertustunnel in Den Haag zijn geen schadelijke trillingen opgetreden, maar wel onverwachte hinderlijke trillingen. Bij het boorproces in bijvoorbeeld rotsformaties zijn ... [more ▼]

Tijdens het boren van de Hubertustunnel in Den Haag zijn geen schadelijke trillingen opgetreden, maar wel onverwachte hinderlijke trillingen. Bij het boorproces in bijvoorbeeld rotsformaties zijn dergelijke trillingen bekend, maar men had dit niet verwacht in het hier aanwezige strandzand. Uit analyse van de gemeten trillingen blijkt dat de trillingen voornamelijk zijn ontstaan door de stroeve voortgang van de TBM in het zand ten gevolge van het stick-slip effect. Het vooruit schokken van de TBM veroorzaakt hoofdzakelijk trillingen in boorrichting: schuifgolven langs de wand en drukgolven aan het boorfront. [less ▲]

Dutch peat dyke failure during the dry summer of 2003

in Proc. International symposium Drougt and Construction SEC 2008 (2008, September)

ABSTRACT - In August 2003, after a once in a twenty years dry summer, one of the dykes along a canal in The Netherlands failed at night. Because of this dyke breach, the water in the canal started to run ... [more ▼]

ABSTRACT - In August 2003, after a once in a twenty years dry summer, one of the dykes along a canal in The Netherlands failed at night. Because of this dyke breach, the water in the canal started to run into a housing quarter of the village Wilnis, which is about 30 km Southeast of Amsterdam. Like many other small dykes in The Netherlands, the complete dyke in Wilnis consists of peat. Since peat has a relatively low unit weight, a peat dyke has a higher risk of being pushed aside by water pressure than sand or clay dykes. Peat also has a much higher water content than clay and sand, which makes it more vulnerable to drought. When the stability of this dyke is checked, it becomes clear that failure of the dyke was a realistic threat. The dyke was far too light and the drought reduced this weight even a little bit more, which caused the failure. RÉSUMÉ – En août 2003, après une période de sècheresse bidécennale, une des digues le long d’un canal aux Pays-Bas a rompu durant une nuit. A cause de la rupture de cette digue, un quartier du village de Wilnis situé á 30 km au sud-est d’Amsterdam a été inondé. Comme beaucoup des petites digues aux Pays-Bas, cette digue est entièrement constituée de tourbe. Puisque la tourbe est très légère, une digue constituée de ce matériau a un risque plus important de glisser par rapport á une digue en sable ou en argile. De plus, la teneur en eau de la tourbe est beaucoup plus grande que pour un sable ou une argile ce qui la rend plus vulnérable au séchage. Si la stabilité de cette digue est contrôlée, il est clair que le risque de rupture de cette digue était très sérieux. Elle était beaucoup trop légère et la sècheresse a diminué un peu plus le poids ce qui a causé la rupture. [less ▲]

Adaptation of Finite Element Models for Probabilistic Design

in 11th Baltic Sea Geotechnical Conference on Geotechnics in Maritime Engineering (2008, September)

Both a circular slip surface stability calculation (Bishop or Fellenius) and a Finite Element Method calculation (c-phi reduction) produce a safety factor but not a probability of failure or reliability ... [more ▼]

Both a circular slip surface stability calculation (Bishop or Fellenius) and a Finite Element Method calculation (c-phi reduction) produce a safety factor but not a probability of failure or reliability index. A Monte-Carlo method leads, because of the many slip surface calculations, to the most accurate calculation of the probability of safety, but this method is far too time consuming for daily FEM calculations. The idea is therefore to replace the Monte-Carlo approach by a First Order Reliability Method (FORM), based on a limited number of FEM calculations. A possible problem with this FORM is, that variable soil parameters create a correlated and therefore variable failure mechanism. However, FORM gives an indication of this non-linear behaviour and in most cases an accurate probability of failure of the structure can be calculated. This article gives a complete example of the calculation of the probability of failure of a dyke ring along a river, based on a limited number of Phi-C reduction calculations with Plaxis. The input data for this calculation is based on a limited number of given soil test data. [less ▲]

A probabilistic tool for geotechnical assessment of jack-up penetration

in Proceedings of the 6th International conference on offshore site investigation and geotechnics (2007, September)

Prediction of jack-up leg penetration requires assesment of uncertainties in calculation models and their input parameter values, including quality and extent of site investigation information. Commonly ... [more ▼]

Prediction of jack-up leg penetration requires assesment of uncertainties in calculation models and their input parameter values, including quality and extent of site investigation information. Commonly, uncertainy assesment is achieved by sensitivity analysis. This paper presents a probabilistic approach for a more accurate prediction of jack-up leg penetration behaviour, as an add-on for conventional Society of Naval Architects and Marine Engineers (SNAME) calculation models.... [less ▲]

Problemen waterkeringen New Orleans tijdens Katrina

in Land+Water (2007)

In de zomer van 2005 werd New Orleans zwaar getroffen door orkaan Katrina. Dat het waterkeringsysteem heeft gefaald is iedereen bekend, maar wat daar de redenen voor waren is veel minder bekend. De ... [more ▼]

In de zomer van 2005 werd New Orleans zwaar getroffen door orkaan Katrina. Dat het waterkeringsysteem heeft gefaald is iedereen bekend, maar wat daar de redenen voor waren is veel minder bekend. De opgetreden waterstanden hadden immers volgens Nederlandse maatstaven gekeerd moeten kunnen worden. Nu blijkt echter dat er een groot aantal problemen waren met het waterkeringsysteem. De belangrijkste worden in dit artikel beschreven. [less ▲]

Viscous Soft-Soil Modelling

in Proc. GeoDenver conference 2007 (2007, February)

Viscosity is in fact a relaxation of the shear stresses over time, which results for constant stress states in a corresponding elastic strain relaxation. In other words, viscosity is a sort of slow ... [more ▼]

Viscosity is in fact a relaxation of the shear stresses over time, which results for constant stress states in a corresponding elastic strain relaxation. In other words, viscosity is a sort of slow plasticity before the Coulomb criterion is reached. Creep settlement can be regarded as one of the viscous soil phenomena, but also the slow movement (a few mm or cm every year) of many natural slopes in mountainous area’s. Therefore a viscous constitutive model is derived from the standard principles that the reduction rate of the relative shear stress (the viscosity) is a function of this relative shear stress and that the reduction rate approaches zero while the stress-state approaches the K0-state. As an example a User-Defined (Soft) Soil Model is developed in order to model the continuous moving slopes. Although the model works fine for viscous behavior and creep problems, it seems as if the slope movements do not depend on viscosity but on dilatancy. [less ▲]

Implementation and validation of a simple probabilistic tool for finite element codes

in Numerical Methods in Geotechnical Engineering: Sixth European Conference on Numerical Methods in Geotechnical Engineering (Graz, Austria, 6-8 September 2006) (2006, August)

Both a circular slip surface stability calculation (Bishop or Fellenius) and a FEM calculation (c-phi reduction) produce a safety factor but not a probability of failure or reliability index. The mayor ... [more ▼]

Both a circular slip surface stability calculation (Bishop or Fellenius) and a FEM calculation (c-phi reduction) produce a safety factor but not a probability of failure or reliability index. The mayor problem with the probabilistical calculations is that variable soil parameters create a correlated and therefore also variable failure mechanism. The question is how much the value of the calculated probability of failure is influenced by this correlation. The Monte-Carlo method leads, because of the many slip surface calculations, to the most accurate calculation of the probability of safety. The disadvantage of this method is that it is far too time consuming for daily FEM calculations. The idea is therefore to replace the Monte-Carlo approach by another approach with only a limited amount of calculations. In this paper several methods are discussed and validated. An indication is given about the error, the number of necessary stability calculations and the optimal estimation points for an additional stability calculation. In this way a minimum number of FEM calculations is needed to obtain a certain desired accuracy. [less ▲]

Geotechnical applications and conditions of the observational method

in Heron (2005), 50(3),

Information observed during construction can be used to optimise the remaining parts of the construction or structure. In this article general conditions are indicated for the implementation of the ... [more ▼]

Information observed during construction can be used to optimise the remaining parts of the construction or structure. In this article general conditions are indicated for the implementation of the Observational Method in geotechnical engineering. The most important condition is that the uncertain field condition (the observational data) must be clear to measure. For example in case of a brittle soil behaviour, there is no clear indicator to show that the load is approaching the maximum resistance. If a project fulfils all general conditions, a financial risk analysis is necessary to find out whether the Observational Method is profitable. The success of implementation varies strongly per geotechnical discipline. In this article a simplified approach for a risk analysis is given and a number of geotechnical cases are discussed for which the Observational Method can lead to a financial profit. Most of these cases are already informally implemented in daily practice. [less ▲]

Soft Soil Creep Modelling of large settlements

in 2nd International Conference on Advances in Soft Soil Engineering and Technology (2003)

The most commonly used model in The Netherlands to predict settlements is the Koppejan Model. This model gives reasonable predictions, but sometimes there are large discrepancies with reality. This is ... [more ▼]

The most commonly used model in The Netherlands to predict settlements is the Koppejan Model. This model gives reasonable predictions, but sometimes there are large discrepancies with reality. This is caused (among others) by: 1) The inaccurate calculation of the degree of consolidation, 2) The omission of the consolidation process for creep, which causes superposition errors for (temporarily) surcharge calculations, and 3) The omission of the waterpressures caused by creep. The problems disappear when the settlement process is solved with an incremental calculation. The results of the incremental calculations are compared with several 1-D compression tests and show good results. The Incremental Koppejan Model can easily be implemented in finite element models. In this paper also an example for a 3-D Elasto-Plastic Soft-Soil-Creep Model is presented. [less ▲]