Numerical analysis of piled embankments on soft soils

The construction of embankments on soft soils is a common problem. Soft soil cannot sustain external loads without having large deformations. Piled embankments system provides a possible solution for the construction of roads and railways over soft soils. Until now, the system behaviour could only be described by analytical models such as those included in British or German codes. This paper describes research undertaken to investigate the effects of pile embankment construction in soft soils. Experimental results are used to help investigate arching effect developed due to differential settlement between pile and surrounding soft soil. A numerical parametric study was carried out to examine the impact of various soil parameters on the pile-embankment system behaviour. The outcome of the parametric study implemented using numerical analysis has been investigated and discussed throughout this paper. Based on the numerical analysis carried out in this research, it was found that the earth pressure coefficient normalized by the passive earth pressure Kp plotted on a vertical profile at the midpoint between piles can give a good illustration of arching behaviour. The findings presented in this paper can be considered as guides for numerical analysis and design criteria of soil arching for embankments constructed over piles

Numerical investigation of geogrid back-anchored sheet pile walls

peer reviewedIn the last decades, geosynthetic reinforcement has been widely used in geotech-nical applications. Recently, geogrid has also been used to back-anchor sheet pile walls. However, this system has not received sufficient attention neither in research nor in construction. Due to the complex interactions between soil, geogrid and sheet pile wall, the applicability of common design guidelines for conventionally back-anchored walls to this particular system has to be proven. To develop a fundamental understanding about the influence of various components of the system on its behaviour, numerical investigations have been conducted within this study. In this paper the influence of geogrid inclination, design of geogrid-sheet pile connection including prestressing and geogrid position on the earth pressure distribution and wall deformation is discussed. The numerical results revealed that the position of geogrid and design of geogrid-sheet pile connection significantly affect the earth pressure distribution. The wall deformations are mainly influenced by the geogrid position

Ontwerp pilot Kyotoweg bij Giessenburg: Baggerspeciematras op houten palen

GeoDelft bedacht een milieuvriendelijk wegbouwconcept: de Kyotoweg. De ‘Kyotoweg’ is een milieuvriendelijke weg die bestaat uit gemodificeerd baggerslib op houten palen. Deze weg heeft tal van milieuvoordelen boven traditionele wegen op zand. GeoDelft werkt samen met onder andere Van Biezen (Willem van Delft), Kantakun (Arnout Beeker) en HUESKER Synthetic GmbHaan de ontwikkeling van dit concept. Om te demonstreren hoe een Kyotoweg wordt ontworpen en gebouwd, wordt op het opslagterrein van gebroeders de Kreij, Parallelweg Schelluinen, Giessenburg een pilot-Kyotoweg gebouwd. Dit rapport doet verslag van de ontwerpberekeningen en de plannen voor monitoring van spanningen en vervormingen tijdens en na de aanleg en belasten. Dit onderzoek is een deel van een groter Delft Cluster onderzoek, ‘innovatieve wegconstructies’, nummer CT 02.10.03, en wat weer een onderdeel is van het Delft Clusterproject ‘Blijvend Vlakke wegen’ (CT 02.10)

Uitvoering pilot Kyotoweg - werkplan

In Schelluinen zal een pilot worden aangelegd van de Kyotoweg. Deze weg bestaat uit een matras op houten palen. De matras wordt gebouwd van Hegemann materiaal, dat is een baggerspecieproduct. De matras wordt gewapend met een geotextiel. De pilot zal van 18 t/m 23 november 2005 worden aangelegd in Schelluinen. Dit rapport geeft in hoofdstuk 2 een beschrijving van het precieze ontwerp van de pilot. Bij de pilot zal een uitgebreid monitoringsplan worden uitgevoerd, waarbij horizontale en verticale vervormingen, de krachtswerking op de palen, waterspanningen, rekken in geotextielen en meer wordt gemeten. Hoofdstuk 3 van dit rapport geeft een beschrijving van het monitoringsplan. Hoofdstuk 4 geeft stap voor stap aan hoe de pilot en de meetinstrumenten moeten worden aangelegd. Tenslotte gaat hoofdstuk 5 in op het meetplan zoals dat tijdens en na de aanleg van de pilot wordt uitgevoerd

Basal Reinforced Piled Embankments

A basal reinforced piled embankment consists of a reinforced embankment on a pile foundation. The reinforcement consists of one or more horizontal layers of geosynthetic reinforcement (GR) installed at the base of the embankment. The design of the GR is the subject of this thesis. A basal reinforced piled embankment can be used for the construction of a road or a railway when a traditional construction method would require too much construction time, affect vulnerable objects nearby or give too much residual settlement, making frequent maintenance necessary. The GR strain needs to be calculated to design the GR. Multiplying this GR strain by the GR stiffness gives the tensile force, which needs to be smaller than the long-term GR tensile strength. The GR strain is calculated in two steps. Calculation step 1 divides the load – the weight of the embankment fill, road construction and traffic load – into two load parts. One part (load part A) is transferred to the piles directly. This part is relatively large because a load tends to be transferred to the stiffer parts of a construction. This mechanism is known as ‘arching’. The second, residual load part (B+C) rests on the GR (B) and the underlying subsoil (C). Calculation step 2 determines the GR strain on the basis of the result of step 1. Only the GR strips between each pair of adjacent piles are considered: they are loaded by B+C and may or may not be supported by the subsoil. The GR strain can be calculated if the distribution of load part B+C on the GR strip, the amount of subsoil support and the GR stiffness are known. An implicit result of this calculation step is the further division of load part B+C into parts B and C. Several methods for the GR design are available, all with their own models for calculation steps 1 and 2. The methods give results that differ immensely. The Dutch CUR226 (2010) and the German EBGEO (2010) adopted Zaeske’s method (2001). However, measurements that were published later (Van Duijnen et al., 2010; Van Eekelen et al., 2015a) showed that this method could be calculating much higher GR strains than those measured in practice, leading to heavier and more expensive designs than necessary. The objective of the present study was to establish a clearer picture of load distribution in a basal reinforced piled embankment and, on that basis, to develop and validate an analytical design model for the geosynthetic reinforcement in a piled embankment. The results were described in five papers published in the international scientific journal ‘Geotextiles and Geomembranes’. Those journal papers can be found in Chapters 2, 3, 4, 5 and Appendix A of this thesis (Van Eekelen et al., 2012a, 2012b, 2013, 2015a and 2011 respectively). Chapter 2 presents a series of twelve 3D experiments that were carried out at the Deltares laboratory. The scaled model tests were carried out under high surcharge loads to achieve stress situations comparable with those in practice. A unique feature of these tests was that load parts A, B and C could be measured separately, making it possible to compare the measurements with calculation steps 1 and 2 separately. In these tests (static load, laboratory scale), smooth relationships were obtained between the net load on the fill (surcharge load minus subsoil support) and several measured parameters such as load distribution and deformation. Consolidation of the subsoil resulted in an increase in arching (more A) and more tensile force in the GR (more B and more GR strain). The measured response to consolidation depends on the fill’s friction angle. A higher friction angle results in more arching during consolidation. One of the major conclusions based on the test series was that the load on a GR strip is approximately distributed as an inverse triangle, with the lowest pressure in the centre and higher pressure close to the piles. This conclusion was the basis for the remainder of this doctorate study and the development of the new calculation model. Chapter 3 considers calculation step 2. This chapter starts by comparing the measurements in the experiments with the calculation results of step 2 of the Zaeske (2001) model, which uses a triangular load distribution on the GR strip and considers the support of the subsoil underneath the GR strip only. It was found that Zaeske’s model calculates GR strains that are larger than the measured GR strains (approximately a factor of two for GR strains larger than 1%). Chapter 3 continues with the suggestion of two modifications to Zaeske’s step 2. Firstly, the load distribution is changed from a triangular to an inverse triangular load distribution. Secondly, the subsoil support is extended from the support by the subsoil underneath the GR strip to the subsoil underneath the entire GR between the piles. The new step 2 model with these modifications produces a much better fit with field measurements than Zaeske’s model. Chapter 4 considers calculation step 1, the arching. Additional tests were conducted for this purpose, varying factors such as the fill height. This chapter gives an overview of the existing arching models and introduces a new model. This Concentric Arches model (CA model) is an adaptation and extension of the models of Hewlett and Randolph (1988), and Zaeske (2001), which have been adopted in several European design guidelines. Some countries use piled embankments without GR. Introducing GR changes the load distribution considerably. A major part of the load is then exerted on the piles and the residual load is mainly exerted on the GR strips between the piles, with the load being distributed approximately as an inverse triangle. Chapter 4 explains the development of the load distribution as a result of continuing GR deflection; new small arches grow within the older larger ones. Smaller arches exert less load on their subsurface. This idea is related to the concentric arches of the new model, which gives an almost perfect description of the observed load distribution in the limit state situation. Furthermore, the new model describes the influence of the fill strength and embankment height correctly. Chapter 5 compares the existing, and the newly introduced, design models with measurements from seven full-scale projects and four series of scaled model experiments. Two of these seven field projects were conducted in the Netherlands and they were carried out in part for this doctorate research. One of the four experimental series – the one presented in Chapters 2 and 4 – was conducted specifically for the present research. The other measurements were reported earlier in the literature. The calculations were carried out using mean, best-guess values for the material properties. The calculation results from the CA model match the measurements much better than the results of the arching models of Hewlett and Randolph (1988), and of Zaeske (2001). The results of the CA model are also the closest match with the results of the 3D numerical calculations, as described in Van der Peet and Van Eekelen (2014). These authors also show that the new CA model responds better to changes in the fill friction angle than any of the other models considered. When there is no subsoil support, or almost no subsoil support, the inverse triangular load distribution on the GR strips between adjacent piles gives the best match with the measurements. When there is significant subsoil support, the load distribution is approximately uniform. This difference between the situation with or without subsoil support is understandable when one considers that most load is attracted to the construction parts that move least. In the cases with limited subsoil support, the load distribution that gives the minimum GR strain should be used to find the best match with the measurements. The GR strain calculated with Zaeske’s model is on average 2.46 times the measured GR strain. The GR strain calculated with the new model is on average 1.06 times the measured GR strain. The calculated GR strain is therefore almost a perfect match with the measured GR strain. The new Dutch CUR226 (2015) has therefore adopted the model proposed in this thesis.Geoscience & EngineeringCivil Engineering and Geoscience

Ontwerp paalmatrassystemen: Literatuurstudie en interviews

De maatschappij stelt nieuwe eisen aan wegenbouw. De verkeersdoorstroming moet maximaal en de verkeershinder moet minimaal zijn. De aanleg moet dus sneller en er moet minder onderhoud nodig zijn. Bovendien wordt met nieuwe contractvormen de verantwoordelijkheid hiervoor bij de aannnemer gelegd. Hiermee worden innovatieve wegconstructie-methoden interessanter. Eén van die snelle en onderhoudsarme technieken is een weg op een aardebaan op palen (paalmatrassystemen). In Nederland zijn al een aantal van deze wegen aangelegd, maar in sommige andere landen gebeurt dit al veel vaker. Eén van de redenen hiervoor is dat er in Nederland nog geen richtlijnen zijn voor het ontwerp van paalmatrassystemen. Dit maakt het lastig om bij een tender, waarbij meestal beschikbare tijd kort is, mee te doen met een paalmatrassysteem. Er is immers geen tijd beschikbaar voor discussie over het ontwerpen. Enkele CUR werkgroepen, die in 2005 en 2006 zijn gestart, houden zich bezig met consensusvorming voor het ontwerp van paalmatrassystemen. Parallel hieraan ontwikkelt Delft Cluster een softwaretool waarmee paalmatrassystemen op analytische wijze snel kunnen worden ontworpen. Het is de bedoeling om met de inhoud van deze softwaretool aan te sluiten op de wensen van de gebruikers van de Mserie, en op de bevindingen van de CUR commissies die zich bezig houden met paalmatrassystemen. De softwaretool zal in ieder geval de mogelijkheid bieden om te rekenen met de meest gangbare internationale normen: de britse en de duitse normen. Dit rapport geeft de resultaten van een studie naar de gangbare ontwerpmodellen. Mede op basis van dit rapport worden de keuzes gemaakt voor de ontwerpmodellen waar MPiro mee zal gaan rekenen

Workshop Dutch Chapter of IGS: Geosynthetics in levee improvement - "An innovation is only an innovation when applied successfully!"

Geoscience & EngineeringCivil Engineering and Geoscience

Validation of analytical models for the design of basal reinforced piled embankments

AbstractVan Eekelen et al. (2012a,b, 2013) have introduced an analytical model for the design of the geosynthetic reinforcement (GR) in a piled embankment. This paper further validates this model with measurements from seven full-scale tests and four series of scaled model experiments. Most of these measurements have been reported earlier in the literature.The new model describes arching with the “Concentric Arching model” (CA model). This model is an extension of the single arch model of Hewlett and Randolph (1988) and the multi-scale model of Zaeske (2001), which is also described in Kempfert et al. (2004). For load-deflection behaviour, Van Eekelen et al. (2012a,b, 2013) proposed the use of a net load distribution that is inverse triangular instead of uniform or triangular. These authors also proposed the inclusion of all the subsoil support beneath the GR in the calculations.On the basis of comparisons between the measurements and calculations, it is concluded that the CA model matches the measurements better than the models of Zaeske or Hewlett and Randolph.Where there is no subsoil support, or almost no subsoil support, the inverse triangular load distribution on the GR strips between adjacent piles gives the best match with the measurements. Cases with subsoil support generally lead to less GR strain. In the cases with significant subsoil support, the load distribution is approximately uniform. In the cases with limited subsoil support, it should be determined which load distribution gives the minimum GR strain to find the best match with the measurements

Model experiments on geosynthetic reinforced piled embankments, 3D test series

Geoscience & EngineeringCivil Engineering and Geoscience