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Are you prepared? How principals can avoid subsurface surprises

Studies have shown that a substantial proportion of failure costs in the construction industry are linked to the subsurface:

“The knowledge platform SBR has calculated that geoengineering failure costs account for 25% of all construction costs. The Dutch Association for Foundation Contractors (NVAF) found that failure costs make up 20% of the turnover of pile driving contractors. TNO Building and Construction Research has said that efficiency shortfalls in the construction process associated with geo-engineering failures cost more than nine million euros.” Source (in Dutch): ‘Breng geo-risico’s zo vroeg mogelijk in beeld’, Fugro Info, July 2013

For these reasons, the Geo-Impuls programme was launched in 2009 to develop tools that will help to prevent geoengineering failure. This booklet is one of those tools. On www.geoimpuls.org (in Dutch) you can find more products that can help you to manage subsurface risks.

Introduction Let’s say you’re about to go on holiday. A week on a tropical island. It doesn’t matter how simple your plans are – lounging around on the beach, an occasional bite to eat – you mustn’t forget the essentials. You check your passport, you decide what to pack. Obviously. Construction projects are no different. Nobody just issues instructions for a design or for construction without taking pause for thought, to take a good look at the project and the locality. And you check for potential risks. That is where this booklet comes in. This booklet primarily targets principals of construction projects, project developers, contractors and architects.

However detailed our surveys and investigations, we cannot map out every cubic centimetre below a construction site. So there are always subsurface risks, often related to geo-engineering (which can be roughly summed up as ‘subsurface technologies’), such as the construction of foundations, site preparation works, or digging a construction pit.

This publication tells you about the possible subsurface risks that may affect your construction project. This isn’t your field? No worries: what matters is to get thinking about the subsurface early and throughout the process (during the planning phase as well). That can produce major benefits. Even though each project is unique, there are still some subsurface risks that recur regularly. Keeping an eye on them can prevent delays, cost overruns and damage to your reputation. There will also be openings for smart solutions that will give your project added value. Of course, this booklet won’t eliminate subsurface risks or identify every conceivable risk, but it will give you a clearer picture. It could be the key to success for your construction project.






Local conditions


Conservatorium Hotel


Challenging structures

20 Villapark Eikelenburgh


Time and space constraints

22 University Medical Center Groningen


Water defences


Boxtel-Oost overflow replacement

11 Groundwater 13

Subsurface composition


Unexpected obstacles

Guide for the reader As you leaf through this booklet, you will see pages with tick boxes. These pages list project factors that may affect subsur face risks. Does one of these factors apply to your project, or are you are unsure? Then turn the page to find information that will help you take the right decisions about your project. If none of the factors apply, you can move on to the next focus point. Is everything important? As you are reading, you may get the impression that all focus points are relevant to your project. That may be right, because this booklet addresses issues that crop up frequently. In reality, there are many more focus points to consider. This booklet shows the most important themes for an initial assessment.

Local conditions This focus point refers to the immediate physical locality of your construction project: the rule of thumb is an area of at least twentyfive metres around the site. It can extend to more than two hundred metres when drainage work and vibrations are involved. Are there any buildings that are particularly vulnerable to vibrations or settlement? These may be old or brick-walled buildings, buildings with shallow foundations or premises where people work with sensitive electronic equipment. Are there any vulnerable cables or lines in the subsurface, such as high-pressure gas pipes, sewers or high-voltage cables? Is there a railway nearby? Are there access routes that are crucial for the surrounding area?

Have you ticked one or more boxes, or do you have any doubts about an answer? Read the information overleaf! If you haven’t ticked any boxes and you are sure about the answers, then you can go straight to the next focus area.


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Local conditions Construction work, and particularly


subsurface construction, can easily

You can obtain information about the locality from, for example, the Land Registr y or municipal authority. Many municipal authorities keep records about building foundations. The Netherlands’ Cadastre, Land Registr y and Mapping Agency (Kadaster) offers information about subsur face cables and pipes. A geo-engineering consultant specialising in excavation pits and risk management for the local area can provide you with detailed advice.

cause soil deformation or vibrations in the vicinity. Sheet piles, for example, are vibro-driven or piledriven: these vibrations can cause permanent




subsurface or have a direct impact on nearby cables, pipes or buildings through the foundations. Digging a construction pit can also cause soil deformation. For all these reasons, the success of your project depends upon a close inspection beforehand of all the local structures. That way you will for instance know in good time whether extra support is needed for the sheet piling or whether you should use vibrationfree techniques (such as pressing-in sheet piles or casting piles on-site).

Challenging structures Of course, every structure needs to be robust but there are times when new foundations need extra attention. This focus point addresses these situations. Are there special requirements relating to the deformation (bending, settlement, etc.) of the structure? This is often the case when an extension is added to an existing building, for example. Is the structure or the activity in a building particularly vulnerable to vibrations? Will the building be used to house, for instance, sensitive electronic equipment? Will the load on the subsurface be distributed unevenly? Is one side of the building higher than the other? Is it a complex structure such as an extremely high building or a structure that is built completely or partially underground?

Have you ticked one or more boxes, or do you have any doubts about an answer? Read the information overleaf! If you haven’t ticked any boxes and you are sure about the answers, then you can go straight to the next focus area.


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Challenging structures The foundations hold up the


structure and they are a major

In the Netherlands the DINOloket (w w w. dinoloket.nl) is a free online database containing subsur face data. Geological Surveys in other countries offer comparable services. You can call in a geoengineering consultancy for a soil survey. Specialist foundation consultancies can also provide you with specific information and/or detailed recommendations about the right foundations for your project.

factor in safeguarding stability. So if requirements relating to deformations



in the structure are strict, it certainly makes sense to make the foundations stronger. This in turn requires a clear picture of what is below the ground since the effectiveness of foundations greatly depends on the particular subsurface. For example, if a number of foundation piles don’t reach the right layer, your building may tilt or crack. You certainly don’t want that to happen.

Time and space constraints Time and space are really two separate themes but they amount to the same thing in terms of subsurface risks: the project conditions complicate the work. Is there a lack of space to work in, for example because the construction takes place in a city centre, in an existing building or below a bridge? Is access to your project difficult? Are there major time pressures affecting your project?

Have you ticked one or more boxes, or do you have any doubts about an answer? Read the information overleaf! If you haven’t ticked any boxes and you are sure about the answers, then you can go straight to the next focus area.


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Time and space constraints When a project has to be completed


quickly, sound soil surveys are often

It helps if you don’t let yourself be rushed during the preparation stages: if something goes wrong during the operational stage, any time you gained will be lost again (many times over), your reputation could be at risk and cost overruns may occur. Tr y and find out exactly where the time pressures come from, and talk to the responsible party. You could also look for a contractor who specialises in working in unusual conditions.

neglected, even though there are actually more risks in busy locations. Special techniques, such as pile driving below an existing structure, can prevent problems in good time. Special measures and alternative methods – such as more manpower, lighter




construction systems – are often needed to complete the project when the schedule is tight or space is at a premium. In general, this will mean more costs, additional preparations and extra supervision, all things that you need to take into account.

Water defences For many people, ‘water defences’ mean dikes and dunes. But not all water defences are so easily recognisable. Many towns and villages have water defences that no one notices because they comprise a road or the ground supporting a row of houses. Is there a water defence structure within a distance of about twenty-five metres from the construction site?

Have you ticked the box, or do you have any doubts about the answer? Read the information overleaf! If you haven’t ticked the box and you are sure about the answer, then you can go straight to the next focus area.


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Water defences Construction negative



have on




The local water management authority will have maps showing all water defences, and areas where you are not allowed to build or dig. For information about the specific risks on your project, you are best advised to get in touch with a hydraulic engineering consultant or a geo-engineering consultant specialising in hydraulic engineering. It is also useful to arrange for a meeting bet ween your consultant and the water management authority.

defences. For example, if soil settles when a construction pit is excavated, the resulting deformation can stop a dike working effectively. The same applies to the installation of foundation elements or using heavy cranes. Rules and permits relating to water defences are strict, and the procedures often take a long time. So you should engage at an early stage in discussions about permits for (temporary) adjustments




defences, or avoid working close to the defences.

Groundwater The groundwater level is a major factor in each construction project. In the Netherlands, levels vary from less than a metre to some tens of metres below ground level. Will you be building below the water table, for example to construct a cellar or tunnel? Do you need a dry construction pit?

Have you ticked one or more boxes, or do you have any doubts about an answer? Read the information overleaf! If you haven’t ticked any boxes and you are sure about the answers, then you can go straight to the next focus area.


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Groundwater If you want to work in a dry


construction pit below the water

You can obtain information about groundwater levels from the local water management authority and/or make a rough estimate on the basis of the water levels in open water. Be aware though that groundwater levels can be a lot higher or lower in surrounding waters. A drainage specialist with a geo-engineering or geohydrological background can provide you with specific information and/or detailed advice. You should also arrange for a discussion with the licensing authority’s geohydrologist.

table, there are – broadly speaking – two options: drainage (lowering the groundwater level) or excavating in a pit with water retaining walls. The first option is subject to strict regulations and requires a permit because drainage affects the water regime throughout a wide area. Lowering the water table can result in land subsidence, the diffusion of soil pollution and, if drainage continues over a period of months, in the rotting of the foundation piles. Groundwater can also be a significant factor when watertight walls are used. The bottom of the construction pit may, for example, burst open as a result of the pressure of the water. So you should not underestimate the impact of groundwater on your project.

Subsurface composition Digging in soft soil is of course easier than in hard soil. But building in or on soft soil is a different story. The structure and composition of the subsurface are factors that play a crucial role in your construction project. Are you planning to build in or on soft soils such as peat, soft clay or loosely-packed sand? Could there be gravel layers in the subsurface? Are you planning to build on an extremely hard subsurface? Is the subsurface composition extremely varied; could it change drastically over very short distances?

Have you ticked one or more boxes, or do you have any doubts about an answer? Read the information overleaf! If you haven’t ticked any boxes and you are sure about the answers, then you can go straight to the next focus area.


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Subsurface composition A soft soil settles relatively quickly as


a result of subsurface construction or

For your project, it can make sense to commission additional geo-engineering soil and laborator y testing. You should ask a range of agencies for quotations for risk-based soil surveys and base your appraisal of their proposals primarily on the arguments put for ward. You may also wish to consider agencies and experts from Belgium and Germany who have, for example, more experience with limestone.

surface loads. This can result in local damage or render the new structure unstable. On the other hand, hard, stony ground is not ideal either: gravel, for example, represents an obstacle to pile driving and the installation of sheet piling. Furthermore, a varied soil profile can make for unwelcome surprises. To select and apply the right techniques it is therefore important to establish a clear picture of the local subsurface structure. A wide margin of uncertainty about the subsurface means that there will also be considerable uncertainty about the robustness and feasibility of the project as designed.

Unexpected obstacles There are few locations in the Netherlands where the subsurface is entirely undisturbed. So you should already be thinking about the obstacles that you could encounter. Have any archaeological remains been excavated in this locality? Is it likely that unexploded ordnance will be located below the surface? Is there a meaningful probability of soil contamination? Has there been subsurface building activity before in this location? Could there be any old grout anchors, for instance?

Have you ticked one or more boxes, or do you have any doubts about an answer? Read the information overleaf! If you haven’t ticked any boxes and you are sure about the answers, then you can go straight to the next focus area.


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Unexpected obstacles Unexpected obstacles can


easily cause delays. Work

Studying records and local enquiries about how the site has been used earlier make it possible to assess the risk of unexpected obstacles. An agency specialising in archaeology or environmental science, for instance, can supply you with more detailed information or specific advice about your project.

may have to be suspended to look at archaeological finds and action is often required when soil pollution is discovered. Not only this, obstacles can also make it impossible to dig foundations to the right depth, with the







required. Thorough exploratory studies, both in archives and in the field, can prevent many delays and unexpected costs.

Past successes To show you how checking subsurface risks can produce genuine benefits, we have collected a number of stories about real-life situations. These demonstrate how an early and ongoing focus on the subsurface contributes to project successes. The stories also show that it is not difficult to take subsurface risks into account and that doing so is a logical part of any project preparations.

Conservatorium Hotel A strong emphasis on geo-engineering was one of the success factors in the renovation of the Conservatorium Hotel in Amsterdam. Between 2008 and 2011, the listed building dating back to 1897 was transformed into a luxury property. The busy location, with tourist attractions and other historical buildings, in combination with the client’s stringent standards, resulted in a complex geo-engineering challenge.

This project covered the following areas: Local conditions, page 3 Challenging structures, page 5 Time and space constraints, page 7 Groundwater, page 11

One requirement was a cellar with a pool in the courtyard of the building. Space was very much at a premium: the walls of the construction pit were less than one and a half metres from the outer wall. Extensive soil surveys and a range of design calculations were used to obtain a detailed picture of how the excavation of the construction pit could affect the existing building. A monitoring plan was then established with limits and alarm levels, and there were extensive discussions with all stakeholders about the measures that would be triggered by exceedances of the limit values. The thorough preparations proved their worth on several occasions during the construction phase: as a construction pit was being pumped dry, it was noted that a section of the second strut frame had subsided. The supervisor was able to intervene quickly, and work out and implement measures immediately using the monitoring data available. The strut frame was repaired within two weeks and the construction pit was completed without any significant delay. Other incidents were managed without any meaningful additional costs or delays as well. The resulting savings more than compensated for any of the investments made in advance.


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Villapark Eikelenburgh On Friday, 9 November 2012, the first pile for Villapark Eikelenburgh was driven in Rijswijk. Approximately three hundred homes will be built during the construction phases for this new residential area. Site preparation work began in 2012. The costs were reduced considerably by taking the local subsurface structure into account.

This project covered the following areas: Groundwater, page 11 Subsurface composition, page 13

The site preparation work for Villapark Eikelenburgh used the conventional method of pre-loading with sand and soil to prevent subsidence in the subsurface in the future. This process can be accelerated using vertical drains that remove the groundwater. The residual settlement requirement (to what extent will the subsurface still settle after the construction phase?) determines whether drainage is required, the depth of the drains and how thick the sand and soil layer needs to be. Usually, the same residual settlement requirement is used for the entire area under development but the contractor here split up the area into four sections, tailoring the requirements in line with future use. He also decided to conduct additional soil surveys. It emerged that the local subsurface was less susceptible to settlement than expected: the subsurface consisted of small layers of clay and sand, a composition that could not have been identified earlier when the geo-engineering advisory report was drafted. The







requirements resulted in a number of changes to the pre-loading plan. Drainage was installed in only half of the area and, in the other half, the drains were installed at a depth of six, rather than eighteen, metres. In addition, it emerged that the pre-loading material did not have to be two metres high everywhere: fifty centimetres was adequate in one third of the area. Given the size of the area under development as a whole, these changes represented considerable cost savings.


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UMC Groningen In 2001, a new facilities building was built at the University Medical Center Groningen (UMCG). A three-storey parking lot and a new logistical transfer facility were built below this building. A smart approach was adopted to benfit from the local subsurface conditions.

This project covered the following areas: Groundwater, page 11 Subsurface composition, page 13

The UMCG is located on the edge of what was a glacier during the ice age and so the subsurface contains very dense clay. This glacial clay is ‘overconsolidated’: the pressure of the glacier caused the soil to be preloaded and very compact. This can represent a major geo-engineering challenge. It may, for example, often be difficult to insert foundation piles to the required depth. Glacial clay is also so strong that, when it swells (after the removal of the top load), it can push up structural elements in unexpected ways. However, the client was able to use the difficult conditions to everybody’s advantage. A detailed survey looking at the subsurface structure was conducted with a geo-engineering consultant in the early stages so that the conditions could be taken into account during the design of the car park. As a result, the water-tight layer of glacial clay has now been used as the floor of the car park, cutting costs considerably. The size and shape of the car park were also adapted specially on the basis of the soil survey to make optimal use of the natural conditions.


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Boxtel-Oost overflow replacement To prevent flooding and other problems with excess water, the Boxtel municipal authority replaced four overflow facilities in 2012. That involved digging down to a depth of about three metres close to housing that was known to be highly vulnerable to construction activity. As a result, the municipality was particularly critical during the preparatory stages and in the selection of a contractor.

This project covered the following areas: Local conditions, page 3 Subsurface composition, page 13

The authority commissioned an extensive soil survey and the local subsurface proved to be extremely unpredictable, so it was difficult to say what the impact on the locality would be. The geo-engineering consultant was asked to draft a proposal for the work that took the vulnerable surroundings into account. The proposal included a recommendation not to use steel sheet piles because of the risk of vibration damage but to conduct excavations using trench shoring. It also noted that compensatory measures could be required locally to prevent damage. The consultant’s suggestions were included as an information document with the specifications. The municipality, the specifications writer and the geoengineering consultant then made a joint assessment of the tenders on the basis of completeness and quality. The contractor who was selected followed the proposed approach in most respects. A compensatory measure that was adopted involved installing a return drainage system between the excavated area and the houses. This measure, the thorough preparations and the meticulous approach to execution meant that the work was completed without any noteworthy problems.


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ARE YOU PREPARED? How principals can avoid subsurface surprises This booklet was published by the working group Subsurface to the forefront, as part of Geo-Impuls. The national Geo-Impuls programme brings together more than thirty organisations from the civil and hydraulic engineering sector with the aim of reducing geo-engineering failures. For more information, see www.geoimpuls.org (in Dutch). By focusing on subsurface risks in good time and continuously, it will be possible to manage geoengineering risks better. This booklet therefore helps projects to be geØké, in other words to keep geoengineering risks well under control. Working group Annemarij Kooistra (chair), IBA - Auke Balder, CRUX Engineering - Jurjen van Deen, Deltares - Jan Pieter Eelants, CROW - Jan Jaap Heerema, Rijkswaterstaat - Mario Niese, Royal HaskoningDHV - Bart van Paassen, BAM Infraconsult - Maarten Profittlich, Fugro - Stijn Schoen, Royal HaskoningDHV - Gerhard Wibbens, BAM Infraconsult Print First edition: December 2013 Second, improved edition: June 2014 Text Members of the working group, see above Translation Pete Thomas Vertalingen/Translations Editing and layout Marije Nieuwenhuizen Digital version This publication is available free of charge in digital form from www.geoimpuls.org

Cover photo Vincent Basler Images accompanying projects • Pages 18/19, all images: CRUX Engineering • Pages 20/21, all images: AM • Pages 22/23, from top to bottom: UMCG/KuiperCompagnons, KuiperCompagnons, KuiperCompagnons, Fugro/Ingenieursbureau Wassenaar, KuiperCompagnons • Pages 24/25, all images: Fugro Copyright The text in this booklet may be quoted freely on condition that the source is clearly stated. To use imagery, you should contact the relevant source (see above).

Profile for Geo- Impuls

Are you prepared?  

Starting a construction project and want to reduce the risks? Check this booklet to see what subsurface risks may affect your project. No wo...

Are you prepared?  

Starting a construction project and want to reduce the risks? Check this booklet to see what subsurface risks may affect your project. No wo...

Profile for geoimpuls