Monitoring Dutch government centre renovation with tenth-of-a-millimetre accuracy

It is one of the most appealing and prestigious renovation projects in Europe: that of the government centre of the Netherlands, the ‘Binnenhof’, in The Hague. Fides Expertise is responsible for monitoring the impact of the demolition, construction and renovation work, and is measuring noise, vibrations, deformations and groundwater levels using traditional surveying technology, including total stations. Fred Pannekoek, director of Fides Expertise, took GIM International on a crawl-through, sneak-through tour of this immense project.

The Binnenhof in The Hague is a monumental building complex that has its origins in the Middle Ages, and has been expanded over the centuries. Meanwhile, the Senate and House of Representatives, Council of State and the Ministry of General Affairs reside in the complex, which totals some 4,000 rooms, spaces, chambers, halls, corridors, attics and cellars. The total floor area is almost 90,000m². Renovation of the complex was necessary to ensure healthy and safe workplaces for everyone who works there, but also to make the building – as the heart of Dutch democracy – more accessible to citizens. The renovation is mainly about necessary repairs of defects in fire safety, wood rot, leaking roofs, technical installations and security. There are also a number of functional improvements. With a new public entrance, the Lower House will soon be ready for a flow of 500,000 visitors a year.

The renovation is a major operation carried out by consortia of well-known contracting companies in the Netherlands, supplemented by smaller specialist construction and demolition companies. The Rijksvastgoedbedrijf (State Property Agency or ‘RVB’) is responsible for the renovation and hired Fides Expertise to take care of continuously monitoring the impact of all the demolition, construction and renovation work. Fides Expertise has been active in all three sub-complexes at the Binnenhof (the Senate, the House of Representatives and General Affairs) since 2021 – at first only with foundation inspections, monitoring wells, measuring bolts and prisms to register displacements, then gradually this grew into an advanced and complex monitoring system.

Founded in 2009 by director Fred Pannekoek together with Iris Remmé and Daniel Sijtsma, Fides Expertise is a structural damage expertise and consultancy firm. Currently with 16 employees and owning a total of 17 total stations, the firm has years of experience in risk inspection, monitoring and reporting. For instance, the roof construction of the plenary hall of the Dutch Senate had been monitored periodically by Fides Expertise for years, when the State Property Agency knocked on the door in 2018 asking if the firm would also do foundation inspections for the benefit of the renovation of the Binnenhof.

Everything started with a preliminary report in 2019. This was based on a comprehensive survey of the foundations of the old complex in the city centre of The Hague. Additionally, interviews were conducted with stakeholders to know what measurements needed to be made: what did people want to monitor, what factors were important? The outcome of the interviews, merged with Fides’ expertise, resulted in a complex-transcending basic monitoring plan.

Monitoring plan

The basic monitoring plan has been developed across complexes and is comprehensible to all parties involved in the renovation. From the chosen set-up, the risk of damage to the monumental buildings due to miscommunication, for example, can be reduced to zero. From a joint plan supported by the four design teams (structural engineers ABT, Arcadis and Arup, in combination with the monitoring party Fides Expertise), the objective of preventing damage will have a greater chance of success. For each section of the complex, the monitoring requirements for all subprojects are worked out in detail. Limit values are set in consultation with the structural engineers, and the high-quality measuring equipment to be deployed (as an extension to the Trimble T4D monitoring software including advanced analysis and alarm capabilities) and measurement frequency with which the monitoring will be carried out are specified.

Supplemented by a clear decision protocol, immediate action will be taken in the event of signals and/or intervention values being reached. The measured values are compared with the alarm and limit values set out in the monitoring plan before and during implementation. If signalling and/or intervention values are approached during implementation, technical consultation will follow. After analysing the measurements, it will be decided whether additional measures may be needed in the implementation to minimize the potentially harmful impact of changes such as different groundwater flow (modes), vibrations or deformations.

Consequence of exceeding

The effect of exceeding the intervention value has two categories. Category 1 includes exceedances that cause damage (groundwater level, settlements x,y,z, vibrations SBR-A and SRB-C) and Category 2 includes exceedances that only cause nuisance (noise and SBR-B vibrations). If Category 1 is exceeded, the work is stopped immediately. In case of Category 2 violations, Fides Expertise first contacts the project supervisor to determine whether the work must be stopped immediately or whether the work can be continued, possibly with the implementation of restrictive measures. In case of relevant overruns, the first contact is contacted. If they cannot be reached, the responsibility regarding the consultation and resulting decisions is immediately and without loss of time transferred to the second contact. These back-up contacts are also all defined per discipline.

Separately from the short line of communication between the project supervisor, the contact person at Fides Expertise, the structural engineer and the contact person at the contractor, the project supervisor also informs the building control surveyor of the Municipality of The Hague. The management manager of the complex section in question organizes an expert meeting between the structural engineers, Fides Expertise, the building control surveyor and other relevant parties as soon as possible to determine the next steps. Naturally, the competent authority has its own and independent role in this.

Exceeding the set limit values has only happened once so far, says Pannekoek: “When the concrete pedestal of the fountain at the Binnenhof had to be removed, a mechanical vibrating drill was used. When we received a report that several measurements had a value outside the permitted values, the work was stopped immediately. Later, the work was resumed with other equipment that caused less vibration. The communication lines and warning system worked perfectly. It was a good test.”

Measuring set-up

The monitoring of the renovation of the Binnenhof, aimed at keeping an eye on vibrations, noise, deformations and groundwater levels, is done by an ingenious system of total stations and prisms, crack meters, measuring bolts, noise, vibration and moisture meters, and groundwater-level meters. It is mainly the set-up of total stations in combination with prisms that meticulously monitors the big picture to check for subsidence or shifts. Eight total stations have been set up: six at the Binnenhof, one in the plenary hall of the Senate and one on the Mauritstoren tower to link outdoor reference points in the software to all measurements at the Binnenhof.

The total stations measure a total of 327 prisms affixed throughout the Binnenhof complex (and some in the Senate Chamber and outside on buildings at the Buitenhof). Needless to say, the prisms have been fitted so that they do not leave marks when they are removed. At each measurement point, at least two prisms have been attached pointing in different directions. This is so that they can be approached by two total stations, and any blockages do not create a gap in the 24/7 measurement series. The S9 Trimble total stations are deliberately complemented with Trimble prisms. Pannekoek believes this benefits the measurement results, which are all extremely precise: “We leave nothing to chance. We measure changes down to tenths of a millimetre.”

A total station forms the link to the outside, with a number of checkpoints on buildings on the Buitenhof bringing all measurements inside, into a coordinate system. All the data comes together in Trimble’s T4D software. The men from Fides Expertise set up the T4D software so that all measurements are merged into one coordinate system, with the individual total stations monitoring each other. The Trimble dealer Geometius and a specialist from Trimble helped with some fine-tuning and further optimizations. The monitoring platform in which the measurement results of the groundwater level monitoring, crack meters, tilt meters and the Weather Station are presented, can be accessed with one login and all can be compared in the system. “It’s a special achievement to set up and use this software in this way. We are very happy with the help of Geometius and the contacts they have, which enabled a specialist to come over from Germany to help set everything up properly. It was a laborious job for him too, but it worked out,” comments Pannekoek.

Incidentally, the measurements from the moisture, vibration and noise meters come in other software. These measurements are local in nature, measuring one component at one point: moisture, vibration, noise or groundwater level. Pannekoek points out that this is the first time that things like vibrations and changes in a span of the plenary hall of the Senate, for instance, are being tracked: “A building is always moving, and now that we are tracking it so accurately, we record everything. That includes changes due to wind, weather, seasonality and associated dryness or humidity. You have to know how to separate that kind of ‘natural’ change from changes resulting from the interventions now being done in the complex.”

From outside to inside and vice versa

In the vicinity of the Binnenhof building complex, there are other monumental buildings, local residents and invaluable masterpieces. In fact, paintings by Dutch masters from the 17^th century, including Johannes Vermeer’s Girl with a Pearl Earring, hang in the Mauritshuis, less than a hundred metres as the crow flies from some of the hard demolition, construction and renovation work. Monitoring by Fides also keeps track of any nuisance and damage to the surrounding area. For this purpose, noise and vibration meters have been installed on and in nearby buildings, for use as baseline reference points to control the points collected inside the Binnenhof. The connection between outside and inside is thus constantly monitored. The RVB is in constant consultation, not only with local residents but also with the Mauritshuis management, including to pick up any complaints and try to remedy them. Very little noise from machinery can be heard on the construction site, as electrical equipment is used. Even Pannekoek himself continues to be amazed by the fact that the construction site is so quiet.

Maintenance

On a project this prestigious, performance and quality are crucial. Therefore, to avoid the risk of technical issues, the total stations are returned to Geometius every three to five months, depending on the operating circumstances. “Some equipment stands measuring 24 hours a day in all weather conditions. Due to the wind, sand and dust particles get into the axles, making the total stations run less smoothly and increasing the likelihood of wear and tear,” explains the director of Fides Expertise.

Continuation

The Binnenhof renovation project will take several more years and it is possible that unexpected issues may crop up during the project. In any case, it means that the Binnenhof will remain the workplace of Fred Pannekoek and his crew for the time being. They are not always on site, by the way; much of the data can be read remotely. But in case of changes in the set-up of the equipment or developments in demolition or construction, there are definitely a few Fides employees in The Hague. The Fides employees – who are not geodesists and surveyors, but monitoring experts – are proud of their work. Pannekoek: “I have zero knowledge of land surveying, but the deployment of total stations traditionally used for that profession is a golden opportunity that is working out very well, partly due to the cooperation with Geometius and Trimble. That we get to do this is great. Because let’s face it, it’s a once-in-a-lifetime experience.”