Are you prepared?

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 geo-engineering 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 geo-engineering 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.

IntroductionLet’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 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.

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.

As you leaf through this booklet, you will see pages with tick boxes.

These pages list project factors that may affect subsurface 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.

Guide for the reader

Contents

1 INTRODUCTION

3 FOCUS POINTS

3 Local conditions

5 Challenging structures

7 Time and space constraints

9 Water defences

11 Groundwater

13 Subsurface composition

15 Unexpected obstacles

17 PAST SUCCESSES

18 Conservatorium Hotel

20 Villapark Eikelenburgh

22 University Medical Center Groningen

24 Boxtel-Oost overflow replacement

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>>>>

Local conditionsThis focus point refers to the immediate physical locality of your construction project: the rule of thumb is an area of at least twenty-five metres around the site. It can extend to more than two hundred metres when drainage work and vibrations are involved.

Have you ticked one or more boxes, or do you have any doubts about an answer?

Read the information overleaf!

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.

Is there a railway nearby?

Are there any vulnerable cables or lines in the subsurface, such as high-pressure gas pipes, sewers or high-voltage cables?

Are there access routes that are crucial for the surrounding area?

If you haven’t ticked any boxes and you

are sure about the answers, then you can

go straight to the next focus area.

>>>>

PossibilitiesYou can obtain information

about the locality from,

for example, the Land

Registry or municipal

authority. Many municipal

authorities keep records

about building foundations.

The Netherlands’ Cadastre,

Land Registry and

Mapping Agency (Kadaster)

offers information about

subsurface cables and

pipes. A geo-engineering

consultant specialising in

excavation pits and risk

management for the local

area can provide you with

detailed advice.

Construction work, and particularly

subsurface construction, can easily

cause soil deformation or vibrations

in the vicinity. Sheet piles, for

example, are vibro-driven or pile-

driven: these vibrations can cause

permanent deformation in the

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 vibration-

free techniques (such as pressing-in

sheet piles or casting piles on-site).

Local conditions

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Of course, every structure needs to be robust but there are times when new foundations need extra attention. This focus point addresses these situations.

Challenging structures

>>>>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?

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.

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?






PossibilitiesIn the Netherlands

the DINOloket (www.

dinoloket.nl) is a free on-

line database containing

subsurface data. Geological

Surveys in other countries

offer comparable services.

You can call in a geo-

engineering 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.

Challenging structures

>>>>The foundations hold up the

structure and they are a major

factor in safeguarding stability.

So if requirements relating to

deformations and vibrations

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.

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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?

Are there major time pressures affecting your project?

Is access to your project difficult?

>>>>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.






Time and space constraints

Time and space constraints

PossibilitiesIt 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. Try 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.>>>>When a project has to be completed

quickly, sound soil surveys are often

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 equipment or modular

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.

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Is there a water defence structure within a distance of about twenty-five metres from the construction site?

Water defencesFor 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.

>>>>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.

Water defences

PossibilitiesThe 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 between

your consultant and the water

management authority.

>>>>

Construction can have a

negative impact on water

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 in the water

defences, or avoid working

close to the defences.

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Will you be building below the water table, for example to construct a cellar or tunnel?

GroundwaterThe 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.

Do you need a dry construction pit?

>>>>Have you ticked one or more boxes, or do you have any doubts about an answer?





Groundwater

PossibilitiesYou 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.>>>>

If you want to work in a dry

construction pit below the water

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.

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>>>>Are you planning to build in or on soft soils such as

peat, soft clay or loosely-packed sand?

Subsurface compositionDigging 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.

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?






Subsurface composition

PossibilitiesFor your project, it can

make sense to commission

additional geo-engineering

soil and laboratory 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 forward. You

may also wish to consider

agencies and experts from

Belgium and Germany who

have, for example, more

experience with limestone.

>>>>

A soft soil settles relatively quickly as

a result of subsurface construction or

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.

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>>>>Have any archaeological remains been

excavated in this locality?

Unexpected obstacles

Is there a meaningful probability of soil contamination?

Is it likely that unexploded ordnance will be located below the surface?

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.

Has there been subsurface building activity before in this location? Could there be any

old grout anchors, for instance?






Unexpected obstacles

PossibilitiesStudying 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.

>>>>

Unexpected obstacles can

easily cause delays. Work

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 founda-

tions to the right depth, with

the effect that different

engineering solutions are

required. Thorough explora-

tory studies, both in archives

and in the field, can prevent

many delays and unexpected

costs.

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.

Past successes

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 3Challenging structures, page 5 Time and space constraints, page 7Groundwater, page 11

PAST SU

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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.

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.


Groundwater, page 11 Subsurface composition, page 13

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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 new information and adapted residual settlement

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.

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.


Groundwater, page 11 Subsurface composition, page 13

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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 pre-

loaded 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.

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.


Local conditions, page 3 Subsurface composition, page 13

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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 geo-

engineering 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.

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 geo-

engineering risks better. This booklet therefore helps projects to be geØké, in other words to keep geo-

engineering risks well under control.

Working groupAnnemarij 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

PrintFirst edition: December 2013

Second, improved edition: June 2014

TextMembers of the working group, see above

TranslationPete Thomas Vertalingen/Translations

Editing and layoutMarije Nieuwenhuizen

Digital versionThis publication is available free

of charge in digital form from www.geoimpuls.org

Cover photoVincent 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

CopyrightThe 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).

ARE YOU PREPARED? How principals can avoid

subsurface surprises

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Are you prepared?