Jaargang 26, 2022 - nummer 2

Dit artikel beschrijft de opzet van de elfde Stress Wave Conferentie die van 19 tot en met 22 september 2022 in Rotterdam zal plaatsvinden. Het gaat in op de wetenschappelijke ontwikkelingen rondom. De conferentie belichten de ontwikkeling voor statische en dynamische testmethoden op diepe funderingen on- en offshore, paal belastingproeven, trillingsanalyse en monitoring van palen en damwanden en de ontwikkeling van ontwerp- en test richtlijnen voor deep funderingen, inclusief case studies. Afgesloten wordt met een test- en demonstratiedag.

Meer informatie op www.sw2022.org.

Piled embankments are an interesting solution for soft soil environments, where the construction of conventional embankments is often associated with stability problems and/or excessive settlements. Instead of loading surficial soft soil, the embankment weight is carried by piles and founded on deeper seated, more competent soil layers. To improve the load transfer from the embankment to the piles, usually pile caps are used.

In de zomer van 2020 is er grote schade ontstaan aan een woonhuis in Rekken. Deze zomer was de derde opeenvolgende droge en warme zomer. Als gevolg hiervan is de kleiondergrond waarop het huis staat (erg) uitgedroogd. Metingen laten zien dat het volume van deze klei sterk afhangt van het watergehalte. Dit zwel- maar vooral krimpgedrag is waarschijnlijk de oorzaak van de ontstane schade. Op verschillende plaatsen rond het huis zijn peilbuizen geplaatst waarmee het waterniveau als functie van de tijd is gemeten. Met gegevens uit de literatuur is een mogelijke oplossing van het probleem geformuleerd. Door in het voorjaar van 2021 plaatsen van horizontale en verticale vochtbarrières rond het huis zou schade in de toekomst voorkomen kunnen worden. Met verschillende sensoren wordt het effect hiervan gemonitord.

De verbreding van de snelweg A9 is complex door de uitdagende bodemopbouw van deze locatie. Om de geo-risico’s te verkleinen is door Fugro aan FFC Construcción voorgesteld om een nauwkeurig 3D ondergrondmodel te maken. Met de lokale geologische kennis van ervaren geotechnische adviseurs, ondersteund door uitgebreid grond- en laboratoriumonderzoek, zijn grote hoeveelheden Geo-data verwerkt, geanalyseerd en inzichtelijk gemaakt voor alle betrokken partijen ten behoeve van het ontwerp van de snelwegverbreding.

Voor het bepalen van samendrukkingsparameters worden internationaal proeven uitgevoerd. De uitvoering van de proef is in diverse normen en richtlijnen vastgelegd. Onderscheid wordt gemaakt in meertraps samendrukkingsproeven (Engels: Incremental Loading Test of Oedometer Test) en CRS-proef (Engels: Constant Rate of Strain Test). De interpretatie van de proef, ofwel het afleiden van samendrukkingsparameters is meestal niet vastgelegd, mede omdat de interpretatie afhankelijk is van het toe te passen zettingsmodel. Om parameters voor een zettingsmodel af te leiden uit samendrukkingsproeven en CRS-proeven is een simulatie van deze proeven een uitstekend instrument. Alleen op deze wijze kan aangetoond worden hoe parameters dienen te worden bepaald uit proeven. In dit artikel wordt de simulatie van een CRS-proef afgeleid en de karakteristieken van het resultaat onderzocht. In een eerder verschenen artikel is de simulatie van een samendrukkingsproef behandeld. De simulatie van een CRS-proef toont aan dat de gebruikelijke afleiding van parameters niet geheel correct is en dat aanscherping van de interpretatie noodzakelijk is.

As 15 cm² cone penetrometers are pushed by Ø 3.6 cm rods, a transition from the wider penetrometer to the smaller pushing rods is needed. It has been noticed in practice that CPT sounding companies prefer and use configurations in which the transition is in between 5 to 7 times the cone diameter, D, above the cone shoulder. However, according to NEN-EN-ISO 22476, the transition should be positioned at least 11.2D above the cone shoulder. In order to fuel discussion, a first step was made by performing two series of 9 CPTs with different penetrometer configurations. The results have been analysed and no systematic differences between the different penetrometers are found. Better understanding and validation is needed, but if all results point in the same directions, the standards can be updated.

Insitu Geotech Services Pty Ltd (IGS) is an Australian in situ testing and sampling company that provides services to construction, infrastructure and mining. It is the largest company that specialises in this field in Australia, but still numbers only about 30-40 personnel. See www.insitu.com.au.

IGS has built its business around providing high quality test data to their clients and is thus very much results-focused; if something seems to be lacking or warrants improvement then they will focus on solving that issue or improving on it. The small company has driven several innovations, in particular in the past in regard to better quality sampling of soft soils.

The most recent innovation driven by IGS has been the conception/development of a CPT cone capable of detecting and measuring extremely low sleeve friction (f_s) values.

This cone was conceived and developed in conjunction with IGS’s CPT equipment supplier-partner Geomil Equipment B.V. of The Netherlands (Geomil), and it involved shifting a design paradigm.

The concept, design, paradigm shift etc, and the successful outcome, are described in a paper to be published as part of the proceedings of the Conference CPT’22, to be held in June 2022 in Bologna Italy.

The 2022 conference paper closes with the following: “So far the new CPT, calibrated and managed as described ………, is meeting or exceeding the authors’ expectations”.

Nigeria is one of the most populated countries in Africa. With approximately 200 million inhabitants in a country three times the size of Germany and a massive growth rate, there is a large demand for infrastructure. This is also the case in Onitsha, a town in the centre of Nigeria. The city is located next to the river Niger. There is only one single two-lane bridge to cross the river. The bridge was constructed in 1964 and part of the Pan-African highway system. It provides the access to the massive city of Lagos, with over 15 million inhabitants in the south-western part of the country.

At the time of construction of the bridge, Onitsha had only 130.000 inhabitants. Currently the city has over 1.500.000 people. This enormous growth has resulted in increased traffic intensity, massive congestions, and an overuse of the not well-maintained bridge. A decade after the construction of the bridge it was already concluded that the capacity was insufficient, but it took over 40 years to start the actual construction of a new 1,590 m long second Niger bridge and corresponding infrastructure of 10 km length. In 2018 the locally well-known contractor Julius Berger Nigeria acquired the key project as a design and construct contract.

In the area of Lubmin on the Baltic Sea, the existing coastline with sand dunes has been severely impacted by multiple storm surges. A solution is being implemented with an underground protection structure using Geotextile Sand Containers (GSC). To reinforce approximately 2 km of coastline, a total of 34,000 elements are being installed of approximately 1.4 tonnes each.

Geotextile Sand Containers (GSC) are soft and flexible construction elements which can adapt very well to the surrounding coastal conditions and can provide effective erosion control. Geotextile Sand Containers are a worldwide used construction method for anti-scouring for example around bridge foundations, offshore wind parks or beach protection. They can be applied in sand dune beach protection systems, like the project in Lubmin. In Nigeria at the Second Niger Bridge project, Geotextile Sand Containers were used in a different application, being a scour protection system around the bridge foundations in the middle of the river.

Normal sand subsoils can be quite vulnerable to erosion, when subjected to large hydraulic forces from wave attacks, flows and currents. By putting sand into high performance nonwoven elements (containers), stable confinements can be realized as a durable and permanent solution. In order to be able to guarantee the durability of the structures, comprehensive knowledge of the design, dimensioning and the project boundary conditions is required.

While the official reason for this special issue of Geotechniek is the CPT’22 conference, another equally good reason for this issue could have been that Cone Penetration Testing turns 90 this year. Over the years this soil investigation technique, which started out as a simple solid mechanical cone that was pushed by hand into the soil, has developed into a sophisticated testing method, where a digital instrument with multiple sensors is pushed down using a hydraulic pusher. But as pointed out in this article, the developments continue and that is why CPT is an old and proven soil investigation method with a bright and exciting future.

Examenvraag CGF1 – juni 2021

The Cone Penetration Test (CPT) cabin as working environment, built on trucks, crawlers or Track-Trucks®, will more and more develop from a workshop into an office. Before, operators were mainly dealing with manual operations to keep the production going. Nowadays and in the future, it can be increasingly expected that time "on board" will be spend on design or other office-related work next to performing CPTs. By integrating the patented SingleTwist™ technology in a CPT cabin with the COSON continuous pushing system, A.P. van den Berg has developed an automatic and hands-free CPT machine.