BegrensSkade/REMEDY Risk Reduction of Groundwork Damage

Deliverable 4.1

Vibration induced damage due to construction work – State of the Art Report

Work Package 4 – Vibrations due to construction activities

Deliverable Work Package Leader: Karin Norén-Cosgriff Revision: 0 NGI

08 / 2019

Note about contributors

Lead partner responsible for NGI the deliverable: Deliverable prepared by: NGI

Other contributors: Multiconsult, National Public Authority

Project information

Project period: 1. September 2017 – 21. August 2022 Web-site: www.ngi.no/nor/Prosjekter/BegrensSkade-II-REMEDY-Risk- Reduction-of-Groundwork-Damage Project partners: Norwegian Geotechnical Institute, (p.nr. 20170774) Sintef Norwegian University of Science and Technology Norconsult Geovita Multiconsult Rambøll Hallingdal bergboring Entreprenørservice Keller Kynningsrud Jetgrunn Skanska Veidekke Finans Norge Huth & Wien Engineering National Public Road Authority (Statens Vegvesen) National Railroad Authority (Bane NOR)

Risk Reduction of Groundwork Damage

Acknowledgements Research Funding organizations

Risk Reduction of Groundwork Damage Deliverable no.: D4.1 Date: 2019-08-29 Rev.no.: 0

Summary

Construction activities such as blasting, piling, compaction, excavation, and construction traffic can produce vibrations of sufficient strength to cause damage to neighbouring buildings and structures. Guideline limit values for construction vibrations are set in Norwegian Standards. However, building damages assumed to originate from vibrations are seldom observed. This may indicate that today's limit values are unnecessarily strict. A lot of research on how much vibration buildings can actually tolerate without damage were performed between the 50's - 70's, especially in and North America. The limit values used in many countries today are based on these comprehensive studies. This State-of-the-Art report summarizes the current knowledges about damages caused by vibration from construction work, and current rules and regulations in different countries. The report also gives an overview of an instrumented blast study which was performed in Norway in November 2018. The results of this study, which have been analyzed within the Remedy project, indicate that the Norwegian limit values for blast induced building vibration inherit a large safety margin for buildings founded on rock.

Vibration may also be a trigger for in vibration sensitive ground. The Norwegian Standard gives guideline limit values for vibrations from blasting triggering landslides. However, there is a concern that other sources such as vibro-compaction, having a lot of repetitive cycles, may induce large enough loads to cause strains that could soften and weaken the enough to trigger a slope failure. This State-of-the-Art report summarizes the current knowledges about construction vibration as a trigger for landslides and gives recommendations about mitigation measures near slopes with vibration sensitive materials. It also briefly describes a numerical tool to evaluate the effect of vibratory compaction on slope stability, which has been developed within the Remedy project.

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Contents

1 Introduction 6 1.1 Background 6 1.2 Contents 6 2 Rules and regulations 7 2.1 Norwegian regulations and standards 7 2.2 Overview of regulations and standards in other countries 9 3 Effect of vibration from construction activities on buildings and other structures 15 3.1 Damage mechanisms 15 3.2 Cracking and critical strain for building components. 18 3.3 Classification of damages 19 3.4 Earlier studies in other countries 19 3.5 Blast study performed in Norway 2018 24 4 Triggering of landslides in vibration sensitive ground 28 4.1 Case histories vibration induced landslides 28 4.2 Effect of vibration on triggering landslides 32 4.3 Mitigation measures near slopes with vibration sensitive materials 35 5 References 39

Review and reference page

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1 Introduction 1.1 Background Construction activities such as blasting, piling, compaction, excavation, and construction traffic can produce vibrations of sufficient strength to cause damage to neighbouring buildings and structures. Vibration may also be a trigger for landslides in vibration sensitive ground. Limit values for vibration from construction work are given in Norwegian Standards NS 8141:2001 (blasting) [2], NS 8141-2 (construction work other than blasting) [4], and NS 8141-3 (triggering of landslides) [5]. However, building damages assumed to originate from vibrations are seldom observed. This may indicate that today limit values are unnecessarily strict. The determination of true limit values is very important since strict limit values effects the efficiency of the blasting process and may delay the progress and increase the costs.

Vibration may also be a trigger for landslides in vibration sensitive ground. NS 8141-3 gives guideline limit values for vibrations from blasting triggering landslides. However, there is a concern that other sources such as vibro-compaction, having a lot of repetitive cycles, may induce large enough loads to cause strains that could soften and weaken the soil enough to trigger a slope failure.

1.2 Contents This State-of-the-Art report summarizes the current knowledges about damages caused by vibration from construction work, and current rules and regulations in different countries. Chapter 3 describes effect of vibration from construction activities on buildings and other structures. Chapter 4 describes effect of vibration from construction activities on triggering landslides. This part of the report focuses on vibration from blasting, vibro-compaction and sheet piling, and is based on earlier work performed in the NIFS program [26].

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2 Rules and regulations

This chapter summarizes the requirements regarding vibration from construction work in current Norwegian regulations and standards, and gives an overview of similar regulations in other countries.

2.1 Norwegian regulations and standards Requirements on effect of construction activities with respect to surrounding areas is given in the Norwegian regulations by "Grannelova", (Lov om rettshøve mellom grannar, LOV-1961-06-16-15), [1].

Lov om rettshøve mellom granner (Grannelova) - Aktsomhetsplikt §2 ”Ingen må ha, gjera eller setja i verk noko som urimeleg eller uturvande er til skade eller ulempe på granneeigedom. Inn under ulempe går òg at noko må reknast for farleg.”

§5 ”Ingen må setja i verk graving, bygging, sprenging eller liknande, utan å syta for turvande føregjerder mot utrasing, siging, risting, steinsprut, lufttrykk og anna slikt på granneeigedom. ”

Paragraph §2 states that no one may execute work, which can cause harm or inconvenience to neighbouring property. Hazardous acts are considered an inconvenience.

Paragraph §5 states that no one may start excavation, construction, blasting or other activities, without executing mitigating measures for stability, vibration, flyrock, air blast or other consequences for neighboring property.

2.1.1 Norwegian standards Guideline limit values for vibration from construction activities are given in the Norwegian Standard series NS 8141.

NS 8141 was first issued in 1993, and revised in 2001. NS 8141:2001, [2], covers measurement of vibration and calculation of guideline limit values in order to avoid damage on constructions. The scope of the Standard is limited to ground work, such as blasting, piling, sheet piling, compaction, excavation and construction traffic. The guideline limit values in NS 8141:2001 are intended to prevent damage, and are values that buildings are supposed to withstand through repeated exposures. They contain a good safety margin up against values where one can expect that damages will occur, and should therefore not be considered as damage limits.

The vibration measure used in NS 8141:2001 is peak particle velocity (PPV) measured in vertical direction on the building without any frequency weighting. The

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calculated guideline limit values in NS 8141:2001 depends on the ground condition, building category, type of foundation, building material, distance from building and type of vibration source. Table 1 presents typical range of guideline limit values calculated from NS 8141:2001, covering different ground conditions, building types, building materials and distances.

Table 1. Typical range of blast vibration guidance values for buildings, as prescribed by the NS8141:2001

Case Ground condition Building type Building material Foundation Distance Guidance value no [m] [mm/s]

A Soft Particularly senitive Brittle tiled stove Column 20m 2.6 B Clay Ordinary residential Masonry Plate 20m 9.8 C Shale Ordinary residential Masonry On rock 20m 50.0 D Hard glacial till Ordinary residential Wooden Plate 20m 26.4 E Hard glacial till Ordinary residential Wooden Plate 150m 18.0 F and Industrial and office Reinforced concrete piles 20m 19.8 G Hard rock Heavy structure Reinforced concrete On rock 10m 142.8

Table 1 indicate that guideline limit values from NS 8141:2001 may vary from a highly strict value of about 3 mm/s for a vibration-sensitive and brittle building on soft soil, to about 140 mm/s for a sturdy massive reinforced concrete structure, like e.g. a quay with foundation on hard rock. In total, the tables and equations defined in NS 8141:2001 have the flexibility to prescribe a maximum span in guidance values from about 1 mm/s to about 140 mm/s.

Vibrations at low frequencies are expected to be more damaging to structures than vibrations at higher frequencies. In NS 8141:2001 effect of the vibration frequency is indirectly taken into account by the fact that the limit value depends on the distance, ground conditions and foundation method, in addition to the properties of the structure. This is based on the assumption that long distance and soft ground conditions cause vibrations with lower frequencies than short distance and foundation on stiff soil or rock. However, the ground conditions and foundation method are often unknown, and the calculation of limit values according to NS 8141:2001 therefore contains a high degree of uncertainty. It is also a common claim that vibration limit values for buildings on soft ground conditions, calculated according to NS 8141:2001, are far too strict, which leads to over conservative blasting and high costs.

In order to remedy the situation, a revision of the standard was carried out in the years 2012-2014. In the revised standard, peak value of frequency-weighted vibration velocity was introduced as vibration measure. This measure takes the frequency of the vibrations directly into account by placing more emphasis on vibrations at low frequencies and less emphasis on vibrations at higher frequencies. By using this frequency-weighted vibration measure, the limit value in the revised standard depends only on the vibration source and properties of the building structure, i.e. type of construction, building material and building condition.

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In the 2012-2014 revision, NS 8141 was divided into three parts:

- NS 8141-1, [3], covering effect of vibration from blasting on constructions including and rock caverns, - NS 8141-2, [4], covering effect of construction activities other than blasting on constructions, - NS 8141-3, [5], covering effect of vibration from blasting on triggering in .

However, it turned out that the frequency weighting in some cases resulted in the limit value according to the new standard being exceeded, while the same vibrations measured and evaluated according to NS 8141:2001 were below the limit value. This applied primarily to blasting in short distance from nearby buildings founded on rock. After massive complaints from the industry, it was decided to withdraw NS 8141-1 in 2016. Pending a new revised Part 1, NS8141: 2001 is again made applicable. NS 8141 Part 2 and Part 3 are still valid

Nevertheless, the problem with the unknown factors in the calculation of the limit value is still present and need to be solved. At the same time, building damages thought to originate from vibrations are seldom observed, and it is therefore suspected that the current limit values in some cases may be unnecessarily strict, especially for buildings on soft soil. This highlights the fact that there is little knowledge about how much vibration buildings can actually tolerate without damage, and about what role the frequency of the vibration plays. The purpose of the activities performed within Remedy is to fill in this knowledge gap, in order to have a revised standard with limit values that can be determined easily and with low uncertainty, and which are not stricter than what can be justified on the basis of the risk of building damage.

2.2 Overview of regulations and standards in other countries 2.2.1 Sweden The of Sweden and Norway is much the same, with large areas of exposed hard rock. Rock blasting is therefore an essential part of most construction projects in both countries. Comparing the Swedish standards is therefore of particular relevance in this project.

At present valid standard on vibration from blasting in Sweden is SS 4604866:2011, [7]. The Swedish standard uses peak particle velocity (PPV), measured in vertical direction on the building foundation as the metric for assessing compliance with guidance values of the standard. The guidance values aim at minimizing the risk of damage on nearby buildings and structures. Sweden emphasize that the values in the standard are really guidance values and not legal limit values.

The calculated guidance values in SS 4604866:2011 depend on the ground condition, building category, building material, distance from building and type of blasting activity.

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No frequency weighting is to be applied to the measured signals. Table 2 presents typical range of guidance values calculated from SS 4604866:2011, covering different ground conditions, building types, building materials and distances.

Table 2. Typical range of blast vibration guidance values for buildings, as prescribed by the Swedish national standard SS 4604866:2011

Case Ground condition Building type Building material Distance Blast activity Guidance value no [m] [mm/s] A Soft clay Particularly senitive Brittle tiled stove 20m Temporary 7.7 B Soft clay Ordinary residential Masonry 20m Temporary 16 C Hard glacial till Ordinary residential Masonry 20m Temporary 28 D Hard rock Ordinary residential Wooden 20m Temporary 61 E Hard rock Ordinary residential Wooden 150m Temporary 26 F Hard glacial till Industrial and office Reinforced concrete 20m Temporary 40 G Hard rock Heavy structure Reinforced concrete 10m Temporary 140

For all cases covered in Table 2 the blasting activity is temporary, like e.g. excavation for a construction site. For a permanent blasting activity, like a mine or a stone , the guidance values may be reduced by 25%.

Table 2 indicate that guidance values from SS 4604866:2011 may vary from a value of about 8 mm/s for a vibration-sensitive and brittle building on soft soil, to about 140 mm/s for a sturdy massive reinforced concrete structure. This can be compared to the guideline limit values according to NS 8141:2001 which for the same conditions are 3 mm/s and 140 mm/s respectively. In total, the tables and equations defined in the Swedish standard have the flexibility to prescribe a maximum span in guidance values from about 3 mm/s to about 190 mm/s.

In addition to SS 4604866:2011, which deals with blast induced building vibration, there also is a Swedish standard on air blast effect on buildings: SS 025210:1996, [8]. The basic content of this standard is the specified guidance value to be 500 Pa reflection pressure against the closest wall of neighbouring buildings facing the blast.

2.2.2 Great Britain The BS 7385 series of standards covers evaluation and measurement for vibration in buildings. Part 1 Guide for measurement of vibrations and evaluation of their effects on buildings was replaced by the international standard ISO 4866:2010, [9] in 2010. ISO 4866 establishes principles for carrying out vibration measurement with regard to evaluating vibration effects on structures, and classifies different building types according to their resistance to vibration. Guide values for building damage caused by vibration are given in BS 7385-2 [10], which is currently under review. The maximum of the measured PPV on the base of the building in three orthogonal components are used for the assessment. The risk of vibration damage are evaluated taking into account the magnitude, frequency and duration of the vibration with consideration of the type of building which is exposed. No frequency weighting is to be applied to the measured vibration, but a frequency based vibration criterion is given. Hence, the frequency content of the vibration also need to be determined. The criterion is judged to give a

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minimal risk of vibration induced damage. Limit values for transient vibration, e.g. from blasts, above which cosmetic damages could occur are shown in Figure 1. Below 4 Hz a maximum displacement of 0.6 mm is recommended as limit value. This corresponds to a limit value of 4 mm/s at 1 Hz and 15 mm/s at 4 Hz respectively. The limit value applies for unreinforced or light framed structures, residential or light commercial buildings. For reinforced or framed structures, industrial and heavy commercial buildings the limit value is 50 mm/s above 4 Hz.

Figure 1. Frequency dependent guide values for cosmetic damage for transient vibrations. Maximum peak vibration, measured at the base of the building

2.2.3 Germany The present valid standard in Germany on ground transmitted vibration and effect on structures, is DIN 4150-3:2016-12, [11]. The standard treats short-term and long-term vibration separately. In the context of construction activity, short-term vibration typically cover blasting / blast excavation, while long-term typically covers vibro- compaction, vibro-driving of foundation plies and sheet-piles etc. The standard states that no damage due to vibration, which adversely will affect the serviceability of a structure, will occur if the guideline values of the standard are complied with.

The evaluation of the structure are based on horizontal vibration measured in its topmost floor of the building. The largest PPV among those measured in two orthogonal horizontal directions is to be rated against the guideline values of the standard. These guideline values are the same for all frequencies, i.e. they are frequency independent. The standard considers these measured values to provide the maximum horizontal response of the structure to the excitation at its foundation. Table 3 lists the guideline values.

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Table 3. Guideline vibration values for maximum horizontal short-term vibration at the topmost floor of a building Guideline value Max PPV (mm/s) Line Type of structure Short time Long time vibrations vibrations Buildings used for commercial purposes, 1 industrial buildings, and buildings of 40 10 similar design Residential buildings and buildings of 2 15 5 similar design and / or occupancy Structures that because of their particular sensitivity to vibration, cannot be 3 8 2,5 classified under lines 1 and 2 and are of great intrinsic value (e.g. listed buildings)

For long-term vibration, the standard also specifies guideline values for vertical peak vibration of floors. For long-term vibration, the guideline value is PPV 10 mm/s vertical on floors. The standard also presents an alternative, more involved approach to evaluate dynamic stress in floor slabs, due to long-term vibration excitation.

As an alternative to evaluate the effect of short term vibration, measurements can be taken at the building foundation instead of at the topmost floor. At foundation, measurements must be taken in three orthogonal directions – two horizontal and one vertical. Largest PPV among the three is to be evaluated against the guideline values of the standard. For foundation vibration, the guideline values depend on the frequency of the vibration, Figure 2. The standard assumes these frequency curves describes the dynamic amplification of vibration from foundation to horizontal vibration in the buildings topmost floor.

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Figure 2. Frequency dependent guideline values for maximum PPV, measured on the foundation of a building

The standard points out the challenge of estimating a representative frequency to be applied in evaluation using Figure 2. To bypass entirely the problem of estimating a representative frequency for foundation vibration, the German standard introduces an alternative approach, where the vibration time records are filtered through a transfer function, depending on the type of structure as defined in lines 1, 2 or 3 in Table 3. These transfer functions actually approximate the inverse of the frequency dependent guideline curves in Figure 2. Thus this filtering results in a frequency weighted vibration velocity record.

The DIN-standard also specifies guideline values for linings of underground cavities and for vibration acting on buried pipelines.

2.2.4 USA The only federal regulation, which controls blasting effects in the USA is the one issued by the Office of Surface Mining (OSM), which have jurisdiction over surface coalmines in the . The regulations are found in the U.S. Code of Federal Regulations (CFR) 30 §715.19, §816.67 and §817.67. The regulation allow coalmine operators a choice among three options:

The first option is that the operator elects to conform to PPV limits, without the need to record vibration frequency. These limit values are valid for any frequency in the range of relevance. Limit values (converted to metric units) are shown in Table 4, column 3. The second option is that the operator elects to design blast according to Scaled Range

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(S.R.), depending on the same tree distance ranges. Scaled Range is here defined as a square root scaling, i.e. S.D. = range / sqrt(charge per delay). Table 4, column 4 specifies the limits of minimum S.R. The second does not require any measurement of the actual vibrations; it must therefore compensate for a large uncertainty, and will therefore in reality result in far lower limit values than the first method.

Table 4. Peak vibration limits and limits of minimum S.R. according to U.S. OSM for surface coalmine blasts Range no Range [m] PPV limit (mm/s) Limit minimum S.D. (m/√kg) 1 0 - 91 31.8 22.6 2 92 - 1524 25.4 25.9 3 Beyond 1524 19.1 29.4

The third method requires monitoring of both PPV and frequency. The method allows the vibration limit value to increase with increasing frequency. Figure 3a, reproduces the limit values of the third method in graphical form. Figure 3b shows the somewhat stricter vibration limit values established by U.S. Bureau of Mines, which are often allied in the USA, even though not a federal regulation.

a b Figure 3 Vibration PPV limits a) according to U.S. OSM regulations for surface coalmines. b) according to U.S. Bureau of Mines

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3 Effect of vibration from construction activities on buildings and other structures 3.1 Damage mechanisms The energy released when a charge detonates largely performs useful work by breaking and moving rock. However, part of the energy produces wave movements in the surrounding ground. A blast initiates different types of ground waves which propagates with different speed, relatively fast compression waves, shear waves with about half the speed of the compression waves (unless in saturated lose ), and surface (mainly Rayleigh-type) waves with slightly slower speed than the shear waves. Rayleigh waves appear only down to a depth corresponding to about one wavelength, and decays therefore slower than the other two wave types. Hence, Rayleigh waves dominates already at relatively short distances from the source. Figure 4 shows an illustration of the different type of vibration waves propagating from a source on the surface and how they attenuate with distance from the source.

Figure 4. Wave propagation in a homogenous elastic half space, from [12]

Many studies have shown that the particle velocity (PPV) is the most relevant parameter in assessing blasting vibrations effect on structures, but also that the propagation speed in ground plays a role since the starting point for the assessment of damage risks is the shear and bending that building element are exposed to, [13], [14], [15], and [16].

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The solution of the wave equation can be written as:

= ( ) Equation 1

𝑣𝑣0 where:𝑦𝑦 𝐷𝐷 𝑠𝑠𝑠𝑠𝑠𝑠 𝜔𝜔𝜔𝜔 − 𝑘𝑘𝑘𝑘 y is the vertical particle motion, Dv0 is the amplitude of the vertical particle motion, k is the wave number = = 2𝜋𝜋 2𝜋𝜋𝜋𝜋 Figure 5 illustrates the reaction𝑘𝑘 of 𝜆𝜆a building𝑐𝑐 exposed to a propagating wave.

Vertical displacement

DV

DH x c - propagation speed of wave in action

Figure 5. Building exposed to propagating wave

The shear strain in the building can then be calculated as:

= = ( ) 𝑑𝑑𝑑𝑑 𝑥𝑥𝑥𝑥 𝑑𝑑𝑑𝑑 𝑉𝑉0 The𝛾𝛾 maximum− 𝑘𝑘shear𝐷𝐷 𝑐𝑐𝑐𝑐 strain𝑐𝑐 𝜔𝜔𝜔𝜔 is−: 𝑘𝑘𝑘𝑘

, = = = 𝑉𝑉0 𝑉𝑉0 2𝜋𝜋𝜋𝜋𝐷𝐷 𝑉𝑉 𝑥𝑥𝑥𝑥 𝑚𝑚𝑚𝑚𝑚𝑚 0𝑉𝑉 𝑐𝑐 𝑐𝑐 Where𝛾𝛾 𝑘𝑘𝐷𝐷 Vv0 is the amplitude of the vertical particle velocity, c is the propagation speed of the wave.

The shear strain imposes a tensile strain at 45 ° angle to the shear strain:

1 , = , = 2 2𝑉𝑉0 𝑉𝑉 𝜀𝜀𝑥𝑥𝑥𝑥 𝑚𝑚𝑚𝑚𝑚𝑚 𝛾𝛾𝑥𝑥𝑥𝑥 𝑚𝑚𝑚𝑚𝑚𝑚 𝑐𝑐

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Since surface waves have the lowest propagation velocity and the highest amplitude, they will cause the highest shear strain and hence expose buildings to the greatest stresses. Rayleigh like surface waves will also involve a horizontal motion DH. Depending on the ground conditions DH0 and DV0 are about the same. Leading to a total strain of:

, = Equation 2 𝑉𝑉0 𝑉𝑉 𝑥𝑥 𝑚𝑚𝑚𝑚𝑚𝑚 𝑐𝑐 Equation𝜀𝜀 2 takes into account tension and shearing of the building as the wave front passes. However, for low propagation speeds also bending of the building when the vibrations wave passes can be a possible damage mechanism. This is because for waves with low propagation speed the extension of a vibration wave can be in the same range as the length of a building causing the building to bend as the wave passes. This damage mechanism will not be as pronounced for waves with higher propagation speed, since waves with wave lengths similar to the length of the building then will have considerably higher frequency and attenuate much faster with distance.

Figure 6 shows the bending of a building exposed to a vibration wave.

δx

εH ∆ x H

R

γx

ε εx x

∆x Figure 6. Bending of a building exposed to vibration wave.

The radius of curvature for the vibration wave can be determined as:

3� = 𝑑𝑑𝑑𝑑 2 2 Equation 3 �1+ �𝑑𝑑𝑑𝑑� � 𝑑𝑑2𝑦𝑦 𝑅𝑅 �𝑑𝑑𝑥𝑥2�

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The maximum strain in the building is found where the radius of curvature has its minimum. Entering Equation 1 into Equation 3 gives the minimum radius of curvature:

= = = Equation 4 (2 ) 1 𝜆𝜆 𝑐𝑐𝑐𝑐 2 2 𝑅𝑅𝑚𝑚𝑚𝑚𝑚𝑚 𝐷𝐷𝑣𝑣0𝑘𝑘 𝐷𝐷𝑣𝑣0 2𝜋𝜋 𝑉𝑉𝑣𝑣02𝜋𝜋 The maximum strain from bending in a building with a height H can then be estimated from Equation 2 and Equation 4:

, , = = = , Equation 5 𝑣𝑣0 𝐻𝐻 𝑉𝑉 2𝜋𝜋𝜋𝜋 4𝜋𝜋𝜋𝜋 𝑥𝑥 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑚𝑚𝑚𝑚𝑚𝑚 𝑅𝑅 𝑐𝑐𝑐𝑐 𝑥𝑥𝑥𝑥 𝑚𝑚𝑚𝑚𝑚𝑚 𝜆𝜆 Anoth𝜀𝜀 er possible damage mechanism𝜀𝜀 is the amplification of the vibration velocity because of building resonances. Building resonances occur in the whole frequency range, but the first modes are the most important since they have largest amplitude and causes highest strains. They are usually found in the frequency range from about 4 Hz to 15 Hz, [9]. Attenuation factors in buildings were investigated in [17] and [18]. In [17] typical values of 1.5 for the structure as a whole, and 4 for mid-walls at their respective resonance frequency were reported. Above 40 Hz the amplification factor was below 1 for all frame residential structures. In [18] maximum amplification factors between 2.6 and 5.2 were reported for normal structures in the frequency range between 2.5 and 24 Hz. In addition to amplification, different building parts may vibrate out of phase, or move relative to each other, leading to clacking, see below.

3.2 Cracking and critical strain for building components. Cracking occurs naturally over time in all buildings. Building materials expand and converge in connection with changes in the material's moisture content, temperature and creep and in some cases pre-stressing forces and settlements. If this movement is prevented or if two different materials with different movements are joined, stresses that can lead to cracking occur [19]. According to [19] moisture and temperature movements in walls of concrete and light concrete are so large compared to the critical strain, that it is very difficult to avoid the natural formation of cracks. According to [20] strain caused by moisture and temperature movements are large compared to strain caused by vibration. Vibrations usually do not produce strains that are above the critical strain of building materials. However, vibration induced cracking may occur when the vibration induced strain combined with the pre-existing strain exceeds the critical strain of the material.

Tests on masonry and concrete were reported in [17]. The tests showed that poured concrete walls are much stronger than block walls and require high levels of strain to induce cracking, i.e. typically about 300 μstrain. Block walls on the other hand do not act as monolithic bodies, but strain concentrates at the joints leading to about 10 times higher strain levels across the joints compared to adjacent blocks. In [17] typical failure strains of the mortar joints were reported to be about the same as for concrete, i.e. 300 μstrain, while the block wall typically failed when the surface strain on the blocks were

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around 30 μstrain. According to [19] the critical strain for most stone materials is about 100-200 μstrain, while it is much lower for the joints. However, it is not clear if this conclusion takes into consideration that the joints may be exposed to higher strain levels than the stones if the building is exposed to a uniform shear deformation.

According to [10] the wall and ceiling material are often the most vibration sensitive parts of the building. In [17] results from several studies on strength of building materials were compiled. Old plaster and lath wall were shown to have lower critical strain than more modern gypsum wallboards with paper backing. Results from strength tests showed large variances, with typical values for tensile failure strain of gypsum wallboard of about 1,000 μstrain. Assuming a stress concentration of 10 above doorways and windows, this corresponds to a uniform shear deformation that gives 100 μstrain.

3.3 Classification of damages Damages are often classified into the following categories, [9]: • Cosmetic. The formation of hairline cracks on drywall surfaces or the growth of existing cracks in plaster or drywall surfaces; in addition, the formation of hairline cracks in mortar joints of brick/concrete block construction. • Minor. The formation of large cracks or loosening and falling of plaster or drywall surfaces, or cracks through bricks/concrete blocks. • Major. The damage to structural elements of the structure, cracks in support columns, loosening of joints, splaying of masonry cracks, etc.

3.4 Earlier studies in other countries 3.4.1 Swedish studies Already in 1956 the Swedish Nitroglyserin Aktiebolaget – Gyttorp issued a report about damaging effect of ground vibration during blasting, [21]. It was based on experience gained in Sweden and abroad up till that time. As the most important advice, the report states that peak particle velocity (PPV) in mm/s is the vibration metric that best relates to observed damage to buildings. It also presents a table of vibration limit values and the expected corresponding degree of damage. Common to the houses in these first surveys was that they were all founded on rock and that they were in good condition.

In [13] results from [21] were used as a basis for a characterization of risk for building damage for different soil conditions, Figure 7. However, no information was given about measurements supporting the vibration values for softer soil conditions in Figure 7. It seems likely that these values have been calculated by using the velocity values for hard rock as a basis and reduce the PPV for softer soils to keep the maximum strain calculated from Equation 2 constant. Today's Swedish guidance values in the Swedish standard are based on the values for "No noticeable cracks" in Figure 7.

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Figure 7. Damage risk in relation to vibration velocity from, [21].

Further measurements and studies were carried out in Sweden in the 70's and 80's. In [22] a large number of studies on ground vibrations and how they affect and possibly damage buildings are compiled. 91 buildings exposed to blasting vibrations between a few to over 100 mm/s were investigated. The investigations showed a probability for cosmetic damages of approximately 40% at a peak value of 50 mm/s, but a likelihood of only 3-4 % for larger damages. The investigation, however, was based on the difference between pre- and post-event inspection of properties. It is therefore likely that some of the reported damages could be conditions that were present before the blasts, but not discovered during the pre-examination. Further the investigation showed that the greatest number of damages occur inside the buildings, in wall-covering materials inside the premises and not in the façades.

In [23] a full scale test of building damages caused by vibration from blasting are described. A detached house made of light concrete was used as a study object. The house was founded on good rock without any observed weaknesses. The facade material was plaster and bricks. Since the house was planned to be demolished, no consideration needed to be taken, and the house could be exposed to vibration velocities far above the recommended limit value of PPV = 35 mm/s. Vibration velocity and frequency were measured from 45 blasting rounds with distances from about 100 m to just a few meters from the house. Since the level of vibration was not evenly distributed from low to high values, an exact determination of the level at which the house was damaged could not be made. However, the damages that were seen occurred at very high values, PPV ≥ 300 mm/s, and the results showed that the critical vibration level in respect of damages was higher than PPV = 90-110 mm/s. From the large number of blast rounds with low vibration values, PPV ≤ 30 mm/s, which did not cause any damages, the conclusion was drawn that when vibrations are below the damage level the risk of damage due to fatigue is insignificant.

Also [24] describes a full scale test of building damages caused by vibration from blasting. The study object was a 1 floor detached house with two parts, both founded 1 2

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on rock. The pressure wave velocity in ground was determined to 6500 m/s indicating hard rock quality. The house had basement walls and floors in casted concrete, while the walls above ground were made of light concrete with a brick cladding. Samples of both the casted and light concrete were tested in laboratory after the study. The casted concrete was found to hold normal quality, while the light concrete had slightly lower quality than expected. The house was planned to be demolished, and hence no considerations about vibration limits needed to be taken. Under normal circumstanced the vibration limit for the house would have been PPV = 70 mm/s. PPV and frequency were measured from 8 blasting rounds, all in quite short distances from the house (horizontal distance 1-45 m). Vibration velocities up to PPV = 1000 mm/s were registered during the study. The measurements showed no damages below PPV = 110 mm/s and no major damages occurred until PPV = 185 mm/s. The test building was a complicated construction with several clearly weak parts, and it was observed that the damages occurred almost exclusively in these parties.

3.4.2 North American studies In 1958 a Canadian study was performed of six buildings subjected to progressively closer blasting until damages occurred, [15]. The buildings, which were old but in good conditions, were either founded on a soft sand-clay, or on well-consolidated glacial till. The study showed that damage was not likely to occur before the PPV was over 4 inch/s. Based on that a safe vibration limit of 2 inch/s was recommended.

In [14] and [16] results from [21], [15] and other previous studies conducted by the United State Bureau of Mines were compiled, and a safe vibration limit of 2 inch/s was recommended, Figure 8.

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Figure 8. Damage risk in relation to vibration velocity from, [21].

Between 1976 – 1979 the Bureau of Mine conducted a series of field studies of ground vibration and air blast damages, [17]. A total of 76 houses, were monitored during 219 production blasts, largely performed in large surface coal mines. Threshold damages were reported down to vibration velocities of 0.7 inch/s, and minor damages from 6-10 inch/s. All reported threshold damages were superficial cracking of the same type as caused by natural settlement, drying of building materials and variation in weather conditions. These results were compiled with results from earlier studies and an updated figure of damage risk in relation to PPV was presented, see Figure 9. In the frequency range below 40 Hz, the recommended safe vibration limit was reduced to 0.75 inch/s for modern homes with drywall interiors, and to 0.5 inch/s for older homes with interior walls with plaster on wood laths. An ultimate maximum displacement of 0.030 inch was also recommended, which would come into effect only for the very low frequencies below 4 Hz. This led to the proposed safe level of blasting vibration curve as shown in Figure 3b.

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Figure 9. Damage risk in relation to vibration velocity from, [17].

3.4.3 Indian study In [18] a comprehensive study of building damages caused by mining blasting is presented. A mud house, a brick-mud-cement plaster house and a two storey reinforced concrete and cement mortar structure (RCC) were constructed at two test sites close to opencast mines. The test buildings were monitored both near the foundation and at and at different locations in the structures. Distance between the test structures and the blasting were between 10 m to 1800 m starting with the largest distances and working gradually closer. The range of recorded PPV was from 0.3 mm/s to > 250 mm/s. The range of dominant frequency was from 2-40 Hz. Cosmetic cracks in the brick-mud- cement house were detected at a PPVs about 50 mm/s. The RCC structure experienced cosmetic cracks at PPV levels of about 70 mm/s measured at the first floor. Minor damage in brick-mud-cement house occurred at PPVs of about 80–90 mm/s, while the RCC structure experienced minor damage at PPVs of about 100 mm/s measured at the first floor. The brick-mud-cement house experienced major damage at PPVs of about 100–110 mm/s, while major damage was observed in the RCC structure at PPVs of about 120 mm/s.

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3.5 Blast study performed in Norway 2018 In November 2018 blast test were performed in a rock quarry in Våler municipality in Hedemark, Norway. The tests were conducted in cooperation with the upper secondary school, Solør VGS, avd Våler. The school personnel and students performed the drilling and blastings, while the measurements were carried out by NGI and Multiconsult. The results from the test have been analysed within Remedy. The tests are described briefly below. A more detailed description is given in [25].

3.5.1 Description of the tests

Two small (5 x 2 x 2.4 meter) buildings were erected on leveled and compacted layer of gravel over rock. One building had 200 mm thick concrete walls without reinforcement. The other building was constructed of Leca blocks (lightweight ) with plastered surface. The buildings had door and window openings. At the top of the buildings, joists were laid and filled with crushed rock to simulate the mass and ground pressure from a typical detached house on top of a basement. Figure 10 shows the test buildings and the test area.

a b Figure 10. a) Test area (left) and test buildings (right). The casted concrete building is under construction. b) Leca building with plaster on outside

Vibration velocity and dynamic strain were measured on both buildings, Figure 11. In addition, vertical vibration on ground and air blast pressure were measured.

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Z X Y a b Figure 11. Instrumentation of test buildings. The blast is to the right of the buildings. Dashed line illustrates sensor on backside of buildings a) Position of geophones. b) Position of strain gauges. The blasting area is to the right of the figures

Five blasts rounds were fired. The blasts were designed to give equal dynamic loading on each of the two test structures, as well as increased vibration strength, starting at a low value for the longest distance and increasing progressively as the blasts came closer to the test structures. Figure 12 and Table 5 show the blast setup.

Table 5. Description of blasts Blast round Min dist (m) No holes Total Max Leca Concrete charge (kg) charge/ delay (kg) 1 28.9 30 46 222 8.4 2 26.5 23.5 2 6.5 3.5 3 17.5 18.5 53 404 14 4 12.3 13.2 24 287 16.4 5 7.4 7.2 20 266 34.2

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Test buildings N

5 2 4

3

1

Figure 12. Localisation of the blast rounds.

The buildings were visually inspected between each blast round to detect and document any damage. In addition, the results from the strain measurements were reviewed correspondingly to detect any cracks not visible to the naked eye.

3.5.2 Results Table 6 shows measured maximum PPV, frequency, peak air blast pressure and peak strain.

Table 6. Maximum measured peak air blast, PPV, frequency and strain. Blast Air blast PPV (mm/s) Freq 1) (Hz) Strain (µstrain) round pressure (Pa) Leca Concrete Leca Concrete Ground Leca Concrete 1 234 32 22 80 86 100 75 17 2 42 30 50 46 65 72 15 3 339 89 53 52 51 26 159 24 4 425 133 101 22 47 41 334 40 5 750 >260 >260 733 > 1748

1) Frequency in vertical direction, determined around maximum peak value by the measurement system 2) see Figure 11a for coordinate system

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The measured vibration and strain values were consistently higher in the Leca building than in the concrete building. The last and closest blast round was however an exception producing vibration values outside the measurement range of the recording system on both buildings, and very high strains on the concrete building. No visible damage was however found on any of the buildings during the inspections after each blast round. Nevertheless, the closest blast produced a small crack above the door on the concrete building, which was not visible to the naked eye, but could be detected by a measured residual strain of 500 µstrain over 110 mm long sensor, corresponding to a 0.05 mm wide crack.

The guideline limit value for both buildings calculated according to today's Norwegian standard NS8141:2001 are 50 mm/s. The last three blast rounds produced vibration values above the calculated guideline limit values on both buildings. The last two blast rounds also showed strain measurements above the critical strain levels discussed in section 3.2. This may indicate that these newly erected and rather stiff constructions tolerate higher strain levels than what has been found to produce cracking in other studies. Cured, but still young and flexible concrete and mortar, may get more brittle during further curing. In addition drying makes permanent tension stresses develop over time. Nevertheless, the results of the test indicate that today's limit values inherit a large safety margin for buildings on rock as long as focus is on damages to outer walls, which this study was designed to investigate.

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4 Triggering of landslides in vibration sensitive ground

Norway have large areas covered with marine sediments now above sea level due to land heave after the last ice age. Due to fresh water leaching out the salt particles in between the clay and particle, many areas have loose soils (i.e. high ) with large . Such soils are known to be sensitive, i.e. they lose almost all of their strength after failure. The cause of landslides in sensitive clays and loose soil deposits is usually associated with natural factors (e.g., erosion and precipitation), human activities e.g., placing of fill, excavation, or a combination of both. In addition to this, vibrations and loads from , blasting, piling and other construction activities are known to have triggered landslides in sensitive clays and loose soils.

Earthquake induced landslides are very common and a lot of the knowledge related to vibration behaviour of soils have been developed to deal with the seismic stability of natural and engineered slopes. The information compiled in this report is to some extent based on literature dealing with seismic slopes stability. However, since quick clay slides are common in Norway information pertinent to vibration susceptibility of slopes with quick clay is also given.

In 2015, a report (in Norwegian) was issued dealing with construction vibrations, and possible impact on the stability of slopes with vibration sensitive materials, [26]. The work in the present SOA-report builds on parts of the 2015 report and extends it. Further, in 2014, NGI was engaged through the NIFS organisation (Natural Hazard, Infrastructure, Flooding and Landsliding) in the investigation of the technical cause for the landslide at Nord-Statland on 29 January 2014, [27]. The landslide led to a that caused great material damage. The conclusion of the investigation was that the landslide with high probability was triggered in the area where construction activity was taking place, and the vibro-compaction of fill masses may have had significant impact on the local stability. On the basis of this work, it became clear that there was a need to look further at how vibrations from construction work can disturb the soil and trigger slides in slopes.

In [28] the Nord-Statland case is described in more detail and a numerical tool is applied to evaluate the effect of vibro-compaction on the slope stability. Below are some examples of landslides where blasting, and vibro compaction is contributing factor to the triggering. Mitigation measures related to vibro compaction and sheet pile installation near shore line slopes are listed in section 4.3.

4.1 Case histories vibration induced landslides Release of landslides in sensitive clays and other deposits with vibration sensitive material, such as loose sand and silt, is usually associated with natural factors (e.g., erosion and precipitation), human activities (e.g., filling, ), or a combination of both. In addition to this, vibrations and loads from earthquakes, blasting, vibro- compaction, piling and construction traffic are known to have triggered landslides in

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sensitive clays and other soils with brittle properties. The chapter gives a brief overview of historical slides in clay, silt and sand where vibrations have been a contributing factor.

4.1.1 Slide where blasting has been a triggering factor There seems to be a common opinion in the geotechnical environment, especially in Norway, that vibrations from blasting do not have a high probability of triggering landslides in sensitive clays. However, as presented in Table 7, several historical landslides in sensitive clays in , Norway and Sweden may be related to rock blasting activity. It is emphasized that blasting itself is often not the only cause of a landslide. The literature review shows that landslides are usually triggered by a combination of destabilizing conditions such as low stability before blasting, unfavourable groundwater conditions (heavy precipitation or snow melting, artesian pressure), erosion, filling, etc.

As presented in Table 7, there have recently been several incidents where vibrations from construction activities may have contributed to triggering. There has therefore been a lot of focus on vibrations and landslides in quick clays in recent years. In 2014, the Norwegian standard NS 8141-3 [5] was issued, which sets a limit value for vibrations from blasting to avoid triggering of landslides, based on a study in [29]. The limit value in NS 8141-3 is a frequency weighted PPV of 45 mm/s, which corresponds to an unweighted PPV of 25 mm/s measured in or on top of the quick clay. The limit value in the standard is set to ensure that vibrations from rock blasting do not trigger slides in quick clay, where conditions are such that an initial failure of clay material may develop into a landslide. There is a good safety margin in the limit value.

It is an ongoing discussion around the limit value and whether it is too strict, [30]. Further study of the measured blast vibrations and slope conditions may allow us to understand better how vibrations have affected the slope stability, and if it is possible to increase the limit value.

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Table 7. Landslides possibly triggered by blasting or where blasting was recorded before landslides. References are given in [26] Location Country Date Volume PPV (mm/s) Time range (x 106 m3) Lade, Norway 04.25.1990 6 >20-25 3h21 Trondheim Finneidfjord Norway ??.01.1978 0.2 ? ? Finneidfjord Norway 06.20.1996 1 > 9.25 2-3 t Finneidfjord Norway 03.11.2006 0.2 ? ? Kattmarka Norway 03.13.2009 0.4 5.2 30 s Sandnessjøen Norway 01.06.1967 0.3-1 ? Shortly after blasting Toulnustouc Canada 23.05.1962 ? ? Shortly after River, blasting La Romaine, Canada 08.01.2009 ~0.5 300 ? Quebec Uddevalla Sweden 05.06.1973 ? ? ? Lödöse Sweden 2011 ? 30 < 24 t Fröland Sweden 1973 ? ? 30-60 s

4.1.2 Slides where construction activities other than blasting may have been a contributing factor Except for blasting, other construction activities which can induce vibrations large enough to trigger landslides are e.g vibro-compaction, and vibro-driving of sheet piles. Conventional hammer driving of piles is known to have caused landslides, but it is mainly thought to be due the static loads impose by the soil mass displacement. These types of effects are studied in a separate Remedy subproject.

Vibrations from vibro-compaction cause cyclical stresses and strains, which can lead to pore pressure build-up, cyclical degradation and failure of vibration sensitive soils. Too high water content in the ground can also create difficulties for the compaction work. If cyclic stresses from the compaction reach down to a fine-grained saturated soil, the pore pressure may increase in the material and thus reduce the strength, [26].

Table 8 give a brief list of landslides possibly triggered vibratory compaction or induced vibrations, which are described further below.

Table 8. Landslides possibly triggered vibratory compaction or induced vibrations. Location Country Date Reference Trestycke vatten, South of Uddevalla Sweden 1990 [31] Åsele Sweden 1983 [32] Lake Ackerman, Michigan USA 1987 [33] Nord-Statland Norway 2014 [27][26][34][35]

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The investigation committee of the landslide of 29 January 2014 at the Nord-Statland in the Namdalseid municipality concluded the landslide was likely triggered by the construction activity, and that the impact of the compaction work with a vibratory roller may have been significant for the local stability, [27]. The vibratory roller used at Statland, was a Volvo SD115 D6 with vibration frequencies in the range of 23-33 Hz, and a maximum dynamic load of 258 kN [36][37]. Vibration analysis showed that the soil down to a depth of some 5 m may have been weakened due to the compaction work. The landslide occurred about an hour to an hour and half after compaction work was finished for the day. Based on these conditions, the simplified calculations in [27] showed that the cyclic shear stresses, due to underlying ground geometry and resonance, likely exceeded the cyclic strength of the soil materials in the shore area at Statland.

In Sweden, vibratory roller compaction caused a slope failure of a filling along the road RV 351 in Åsele on October 4, 1983, [32]. The landslide was triggered by a 3.3-ton tractor pulled roller doing repairs to the road fill, Figure 13. The road was partly submerged and consisted of mass surplus from surrounding masses.

Figure 13. Overview of slide area at Åsele, 1983 (after [32]).

On July 24, 1987, a landslide was triggered in a road closure along Lake Ackerman on Highway 94 in Michigan, USA [33]. The landslide was triggered by six 22-ton (196- kN) trucks that generated seismic vibrations for a seismic reflection study. The road filling was a hydraulic filling consisting of loose and fine - medium sand. Studies by Hryciw et al. [33] indicate the vibrations from the seismic sources generated shear strains up to 0.055% and a shear stress ratio (τ / σ'v) estimated at 0.12. Each car at 2 meter intervals produced at least 25 load cycles above γ = 0.01% every 15 seconds. Results from stability evaluation show that the residual of the loose sand was on the order of 8-12 kPa.

A vibratory roller is also believed to have caused a landslide into a lake in Sweden in 1990. The following description is based on [31]. Some 80 km north of , south of Uddevalla, a slide occurred in connection with the construction of a berm designed to provide additional stability to an embankment for the E6 highway. The highway embankment was 1 year old when a layer of for vegetation was being

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placed with bulldozers and compacted by heavy vibratory roller. The embankment did not fail since it was founded on rock fill down to a competent base. However, a slide occurred towards the end of the placement of top soil. All the way from the highway embankment toe to the lake shore, the slope of the original ground surface was uniform and remarkably small (≈ 1°), which indicates the cause of the slide was related to the ongoing construction work and not due to inherent instability. The roughly 5 m high supporting berm had been constructed already in the fall of 1989 but was completed about a year later by adding a layer of topsoil for vegetation. The heavy berm had thus remained stable for more than a year, and during this period the underlying soil had been subject to drainage and consolidation. It seems, therefore, very unlikely that the slide was initiated solely by the weight of the thin layer of humus-rich topsoil, constituting only some 5 % of the total weight of fill that had already been placed more than a year before. Hence, the impact of the heavy vibratory roller on the is assumed to have been the triggering agent in the slide initiation process.

4.2 Effect of vibration on triggering landslides 4.2.1 Vibro compaction Ground vibrations from vibratory rollers transmits large loads to the soil which can cause build-up of pore pressure and reduce soil strength in vibration susceptible soils such as loose silt and sand, and sensitive clays. This should be considered when carrying out construction work near slopes with such soils. The strength reduction is dependent on soil state, load amplitude and number of cycles.

Vibratory roller compaction is performed by passing over the same area up to 8 times [6], which means that a soil element is exposed to a large number of vibration cycles. The number of load cycles a soil element is subjected to depends on the speed of the roller, the vibration frequency and the depth. Vibratory rollers typically have vibration frequencies between 20-40 Hz. Both the load amplitude and vibration frequency varies with the type of soil and the thickness of the compacted layer. The operating speed is usually between 0.5 m/s (2 km/h) to 1.5 m/s (6 km/h). In [27] it was estimated that soil the elements were subjected to several hundreds of load cycles. A shallow soil element is in general subjected to larger amplitudes than a deeper soil element. Even though a deeper soil element is subjected to smaller vibration amplitude it is influenced by the vibratory equipment over a wider area.

To estimate the effect of compaction induced vibrations on a slope with vibration sensitive material, one can use empirical equations, e.g. [38], to estimate vibration amplitudes. However, such equations give vibration amplitude on the ground surface, while the slope failure is likely to be induced at some depth beneath the vibratory equipment. To evaluate the potential effect of vibro-compaction on the slope stability a numerical tool has been developed further and applied in the Remedy project to analyse the Nord-Statland landslide, see further description in [28].

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An important aspect of predicting vibrations induced by construction activities is to account for the load dependent behaviour of the soil materials. Therefore, a nonlinear soil model has been used to capture the reduction of stiffness and increase in damping with increasing strain in the soil. The tool used in Remedy is promising in that results compare well with field experiments of vibratory compaction and pile experiments. The numerical tool has been used to analyse the effect of vibrations from compaction on the stability of the slope in connection with the Statland landslide described in section 4.1.2. The analysis supports the earlier findings in [27], that vibratory compaction can likely have caused an initial failure in the upper part of the slope, which then may have induced a wider large-scale failure of the slope. The effect of the vibrations from the vibratory roller in the analysed case reached to a depth of 4 m beneath and 13 m in front of the roller. An earlier study [39] suggested and influence zone of about 5 m thick by 15 m wide. Thus it seem pertinent to be very careful when performing vibratory compaction within some 15 m of the shore line.

4.2.2 Vibration from vibratory installation of sheet piles We have not been able to find examples in the literature about slope failures or landslides caused by sheet pile installation. However, vibratory sheet pile installation do induce large vibrations that cause settlements in sand, and can cause damage to buildings close to the installation locations (see e.g. [40], [41], [37]). This indicates that vibratory sheet pile installation can cause failure in vibration sensitive soils. Therefore, one should plan carefully for installation of sheet piles in the vicinity of slopes with vibration sensitive materials as shown in Figure 14.

Vibration sensor?

Soil profile with vibration sensitive soils

Boulder

Rock

Critical sliding surface

Figure 14. Vibratory sheet pile installation next to slope with vibration sensitive material. When the sheet pile hit strong materials like moraine or a boulder, vibrations in the soil can be become large. Driving-stop criteria can help avoiding large vibrations.

When the sheet pile is driven through quick clay material very little driving force is necessary to install the pile and thus induced vibrations are not very large. The fact that quick clay loses its strength also means it cannot transfer stresses and vibrations in to the surrounding soil. On the other hand, when the sheet pile hits strong materials such as moraine or a boulder outside or beneath the quick clay, the induced vibrations in the

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soil can become large, which could increase the loads on the slope. Hitting harder materials can cause damage to the toe of the sheet piles and also bend the bottom part of the sheet pile. With bent sheet piles a sheet pile wall may not fulfil its intended function, e.g. reducing leakage of water into the construction site. Research is going on to detect when the sheet pile is hitting hard material, and to develop criteria to stop the driving [42]. Such driving-stop criteria will also be useful to prevent excessively large vibrations when installing sheet piles near slopes with vibration sensitive materials.

There are several numerical and empirical methods to predict vibrations from pile driving and vibratory sheet pile installation, e.g. [40],[41],[43],[44],[45]. Each tool has its advantages and limitations. Most of the tools are not available for free use and ease of use is not known. The tool used in Remedy is available for use by anyone, however it requires currently a license for the finite element software Comsol Multiphysics. The approach taken in the tool can easily be implemented in any open source software which can perform frequency domain dynamic analysis.

The numerical tool used in Remedy to analyse vibro-compaction has also been applied to a case of vibratory installation of sheet piles, to improve our understanding of how sheet piles transfer vibrations to the surrounding soil ([40],[43]). Figure 15 shows a comparison between when only the toe, or only the shaft of the sheet pile, or both are transferring vibrations to the soil. The analysis with only the toe transferring the vibrations turned out to give the better fit with measured vibrations during field experiment. This indicates that the soil near to the shaft is very much remoulded and do not transfer so much of the vibrations. Hence, the shaft is likely of less importance than previously understood. The current version of the tool allows for studying many different important aspects of the modelling, such real 3D geometry of the sheet pile and soil and account for soil non-linearity. However, further development to refine the model may allow for event better prediction of sheet pile installation induced vibration.

Figure 15. Comparison of vibrations induced by sheet pile driving, a) both toe and shaft transfer vibrations into soil , b) only toe is transferring vibrations , and c) only shaft is transferring vibrations.

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4.3 Mitigation measures near slopes with vibration sensitive materials The mitigation measures near slopes with vibration sensitive materials can be divided into site investigation and design evaluations performed by geotechnical expertise and operative mitigation measures.

4.3.1 Procedure for evaluating slope stability accounting for compaction vibrations A three step procedure for dealing with potentially vibration susceptible slope is presented below. A flow chart for the procedure is given in [26]. The first step is to evaluate the geology and if the soil type is vibration susceptible. The second step is to perform a slope stability evaluation accounting for effect of construction vibrations. If the stability do not fulfil the requirements, the third step is to suggest remedial measures such as vibration measurements and/or increasing the stability before construction work starts.

4.3.1.1 Evaluation of soil type and vibration susceptibility Step 1: Evaluate the geology and soil types. Perform a detailed geological and geotechnical investigation to evaluate if the slope consists of vibration susceptible soil types.

Step 1a: Determine the type of geological deposit at the site and nearby areas. Information in [26] can be used to determine probability for vibration induced strength degradation based on and geological maps. Also determine if the area is within or near an existing landslide hazard zone.

Step: 1b. Determine if the soils are vibration susceptible. Different figures for evaluating vibration susceptibility of clayey and sandy soils are compiled in [26] based on a literature review. Also evaluate it the soil deposit is layered. Layered soil deposits are more vibration susceptible and are often found in fjord and fluvial deposits, near shore areas and deltas.

If the site under consideration is close to hazard zone or if the soil is considered vibration susceptible based on evaluation in step 1 above, a pseudo static stability analysis is recommended as described below.

4.3.1.2 Slope Stability evaluation and monitoring If the slope contains vibration susceptible soil types a to account for the effect of construction vibration are recommended. The method suggested here is based on the use of two-dimensional limit equilibrium analysis considering effect of vibrations from compaction equipment on the local slope stability. In Norway there exist also a concept of area-stability, in which the possible retrogression has to be accounted for in the slope stability evaluation, which is not described here. Point 1-7 below are

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under the assumption that the static slope stability do not fulfil the requirement by the design standards. If the static slope contains vibration susceptible material but static stability fulfils the requirements in the design standard, it is recommended for documentation purposes to follow up with monitoring of slope displacements before, during and after the construction activities.

1. Identify critical profiles, based on terrain and rock geometry, and distance to vibration source etc. 2. Define a zone to be subjected to strength degradation due to vibration, as shown in Figure 16 The size of the zone is dependent on properties of the soil and the vibratory equipment. In the analysis performed for the Statland landslide, the zone reaches down to 5 m depth and 15 m width. 3. Determine residual strength for the zone subjected to strength degradation with help of figures and equations compiled in the NVE report [26]. The strength will depend on material type and number of vibration/loading cycles. The number of cycles is on the order of 100 to 1000, and depends on the size of the equipment and number of roller passes. There is a figure in [26] for correcting strengths for number of cycles. If unknown use 1000 cycles for determining a correction factor. It is also recommended to compare the selected residual strength with empirical equations from the literature [46]. 4. Selected drained and undrained strengths not subjected to strength degradation according to geotechnical practice. 5. Stability during and before construction activities should be compared to understand the effect of vibratory compaction on slope stability. 6. Compare results with requirement in design standard for failure mechanisms and consequence classes. 7. If stability requirements are not fulfilled more detailed analysis or remedial measures are necessary to increase the stability.

4.3.1.3 Vibration measurement and other monitoring It is possible to measure vibration near a vibratory roller. However, the vibration reduces quickly with distance and it may be difficult to estimate properly the vibration beneath the drum especially since the roller is moving around during the compaction. Therefor it is also difficult to estimate how large strains are induced in the soil. Figure 16 shows possible situations during compaction near shore. Further work would be necessary to establish a vibration limit and vibration measurement procedure to be used during compaction near vibration sensitive slopes.

Monitoring slope displacement, and maybe also pore pressures, at some critical locations before, during, and after the construction work, is recommended for documentation of the impact of compaction on the slope stability.

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Vibration sensor? Situation B W W D D Situation A Soil profile with vibration sensitive soils

Rock

Critical sliding surface

Figure 16. Zone subjected to strength degradation due to vibratory compaction. Vibration sensor location is tentative and has to be adopted to the specific project. The idea is to measure vibrations as close as possible to vibratory equipment and the potential sliding surface.

4.3.2 Operative counter measures for vibro-compaction If vibro-compaction is going to be performed near a slope with vibration sensitive soil the following points can be considered. This is especially important within 10-15 m from the shore line. • Have a good understanding of the geological and geotechnical conditions, such as static slope stability, existence of layers with artesian pressures in the slope etc. This means involving geotechnical specialist before performing the work. • Use lighter compaction equipment, higher loading frequencies, smaller loads (low excentric moment), or perform compaction without vibration. • Avoid excessive jumping of the vibratory roller drum. • Apply thinner layers and more time between compaction passes. Allow for more time between placing of layers to reduce the number of load cycle sensed by the soil and allow for drainage of potential built up pore pressures. • Monitor slope horizontal and vertical displacements at some critical points. • Monitor pore pressures at critical points if possible.

4.3.3 Operative counter measures for sheet-pile installation While there are no known cases of slope failures or landslides induced by vibratory sheet pile installation, it is important to plan carefully for installation of sheet piles in the vicinity of slopes with vibration sensitive materials. The following counter measures should be considered.

• Have a good understanding of the geological and geotechnical conditions, such as static slope stability, existence of layers with artesian pressures in the slope etc. This means involving geotechnical specialist before performing the work.

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• The operator should be careful when driving, especially if it is suspected that the sheet pile can be hitting boulders or entering into stronger materials such as moraine. • Use smaller sheet piles, lighter vibration equipment, higher loading frequencies and smaller loads • Perform installation without vibration, i.e. with so called "silent piler" which pushed the sheet piles into the ground. • Allow for more time between installing sheet piles to reduce the number of load cycle sensed by the soil and allow for drainage of potential built up pore pressures. • Monitor slope horizontal and vertical displacements at some critical points. • Monitor pore pressures at critical points if possible. • Start using driving-stop criteria for sheet piles when they have been developed

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5 References

[1] Grannelova (Lov om rettshøve mellom grannar, LOV-1961-06-16-15) [2] NS8141:2001 Vibration and shock. Measurement of vibration velocity and calculation of guideline limit values in order to avoid damage on constructions. (In Norwegian) [3] NS8141-1:2013 Vibration and shock. Guideline limit values for construction work, open-pit and pit mining and traffic. Part 1: Effects of vibration and air blast from blasting on construction works, including tunnels and caverns. (In Norwegian) [4] NS8141-2:2013 Vibration and shock. Guideline limit values for construction work, open-pit and pit mining and traffic. Part 2: Effects of vibration on construction works from construction activities other than blasting, and from traffic. (In Norwegian) [5] NS8141-3:2013 Vibration and shock. Guideline limit values for construction work, open-pit and pit mining and traffic. Part 2: Effects of vibration on triggering on landslide in quick clay. (In Norwegian) [6] NS 3458:2004, Compaction - Requirements and execution. (In Norwegian) [7] SS 4604866:2011 - Vibration och stöt – Riktvärden för sprängningsinducerade vibrationer i bygnader ("Vibration and shock – Guidance levels for blasting- induced vibration in buildings") [8] SS 025210:1996 - Vibration och stöt – Sprängningsindicerade luftstötvågor – Riktvärden för bygnader ("Vibration and shock – Blast induced airborne shock waves – Guidance levels for buildings") [9] ISO 4866:2010. Mechanical vibration and shock — Vibration of fixed structures - Guidelines for the measurement of vibrations and evaluation of their effects on structures. [10] BS 7385-2:1993 Evaluation and measurement for vibration in buildings – Part 2: Guide to damage levels from groundborne vibration [11] DIN 4150-3:2016-12 - Erschütterungen im Bauwesen – Teil 3: Einwirkungen auf bauliche Anlagen ("Vibrations in buildings – Part 3: Effects on structures"). [12] F.E. Richart, J.R. Hall, R.D. Woods. Vibration of soils and foundations. Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1970 [13] Langefors, U. and Kihlström, B. The modern technique of rock blasting (3rd ed). Wiley, New York, 1978. [14] Nicholls, H.R., Johnson, C.F., Duvall W.I. Blasting vibrations and their effects on structures. Bulletin 656, US Department of Interior, Office of surface mining Reclamation and Enforcement, 1970. [15] Edwards, A. T., and Northwood, T. D. Experimental Studies of the Effects of Blasting on Structures. The Engineer, v. 210, Sept. 30. 1960, pp. 538-546.

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[16] Duvall, W.I., Fogelson, D.E. Review of criteria for estimating damage to residences from blasting vibrations. Report of investigations 5968, US Department of the Interior, Office of surface mining Reclamation and Enforcement, 1962. [17] Siskind, D.E., Stagg, M.S., Kopp J.W., and Dowding C.H. Structure response and damage produced by ground vibration from surface mine blasting. Report of investigations 8507, US Department of Interior, Office of surface mining Reclamation and Enforcement, 1983. [18] Singh, P.K., Roy, M.P. Damage to surface structures due to blast vibration. International Journal of Rock Mechanics & Mining Sciences 47 (2010) 949-961. [19] Rundqvist G. Naturlig sprickbildning I nya småhus – Hjälpmedel för besiktning efter sprängning. SBUF Projekt nr 2139. 1994 (In Swedish) [20] Dowding, C. H. and Aimone-Martin, C. T. Micro-meter Crack Response to Rock Blast Vibrations, Wind Gusts & Weather Effects. Proceedings Geo-Denver 2007 February 18-21, 2007 Denver, , United States [21] U. Langefors, H. Westerberg and B. Kilström. Tekniska Meddelanden Nr. 5 "Skadeverkan av Markskakningar vid Sprängning", 1956 the Swedish Nitroglyserin Aktiebolaget – Gyttorp. (In Swedish) [22] Holmberg, R., Lundborg, N., Rundqvist, G. Soil Vibrations and Damage Criteria https://doi.org/10.4224/20358507 [23] Byggforskningen Rapport R42:1975 Lättbetonghus utsatt för vibrationer från sprängning. (In Swedish) [24] Byggforskningen Rapport R32:1977 Betong – lättbetonghus utsatt för vibrationer från sprängning. (In Swedish) [25] Remedy deliverable 4.2 Vibration induced damage due to construction work – Blasting tests. Rev 0, 08/2019 [26] NVE, NIFS – N-6.3 Dynamiske påkjenninger og skredfare, State-of-the-art rapport og anbefalinger http://publikasjoner.nve.no/rapport/2016/rapport2016_16.pdf [27] NVE (2014) Skredet ved Nord – Statland. Utredning av teknisk årsakssammenheng. Rapport nr. 93-2014. ISBN-nr. 978-82-410-1042-2. [28] Remedy deliverable 4.3 Vibration induced damage due to construction work – Effect of vibrations on slope stability. Rev 0, 08/2019 [29] NGI report 20120700-01-R. Virkning av sprengning på sensitive løsmasser. (In Norwegian) [30] Rikke Bryntesen and Samson Degago, SVV, Experiences from vibration measurements due to blasting activities near quick clay areas, Presentation at at the forth Nordic Ground Vibration Day, Trondheim 18th of October 2018, http://folk.ntnu.no/gudmundr/NGV2018/Presentations%20NGV%202018.htm

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[31] Bernander, Stig, Progressive landslides in long natural slopes: Formation, potential extension and configuration of finished slides in strain-softening soils. 2011. 240 p. Doctoral thesis, Luleå University of Technology. [32] Ekström, A., & Olofsson, T. (1985). Water and frost-stability risks for embankments of fine-grained soils. In From Proceedings of the Symposium on Failures in , organized by the Institution of Civil Engineers, held in London, March 6-7, 1985 [33] Hryciw, R., Vitton, S., and Thomann, T. (1990). ”Liquefaction and Flow Failure During Seismic Exploration.” J. Geotech. Engrg., 116(12), 1881–1899. [34] Glimsdal, S., et al. The 29th January 2014 submarine landslide at Statland, Norway—landslide dynamics, tsunami generation, and run-up. Landslides , 13 (6), 1435–1444. https://doi.org/10.1007/s10346-016-0758-7, 2016 [35] Johansson, J. and L’Heureux , J.-S.,Influence of vibratory compaction on slope stability – an ongoing research topic in Norway, Anniversary Symposium – 40 Years of Roller Integrated Continuous Compaction Control (CCC), D. Adam & S. Larsson (eds.), November 29th, 2018, Vienna, Austria [36] Volvo Construction Equipment. Personal communication through e-mail. 2019. [37] Volvo Construction Equipment. Specifications for SD 115 vibrocompactor. [38] Caltrans, Transportation and Construction Vibration Guidance Manual, Department of Transportation, Division of Environmental Analysis Environmental Engineering, Hazardous Waste, Air, Noise, Paleontology Office, September 2013. [39] Johansson J., Bouchard S., L’Heureux JS. (2017) Vibratory Roller Influence Zone Near Slopes with Vibration Susceptible Soils. In: Thakur V., L'Heureux JS., Locat A. (eds) Landslides in Sensitive Clays. Advances in Natural and Technological Hazards Research, vol 46. Springer, Cham. [40] Deckner, F. (2017). Vibration transfer process during vibratory sheet pile driving : from source to soil (PhD dissertation). Stockholm. Retrieved from http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-203946 [41] Piet Meijers, Settlement during vibratory sheet piling, Ph.D. thesis, ISBN 978- 90-9022570-8 [42] K. Viking; O. Båtelsson, R. Lund Tebäck, T. Forsberg, and P. Björgúlfsson, Difficulties of vibrodriving in till -causing costintensive measures. ECSMGE 2019 Reykjavik, proceedings of the XVII ECSMGE-2019, foundation of the future, ISBN 978-0-7277-6067-8. [43] Deckner, F., Johansson, J., Viking, K., Hintze, S., Major vibration source during vibratory sheet pile driving – shaft versus toe, ECSMGE 2019, Reykjavik, proceedings of the XVII ECSMGE-2019, Geotechnical Engineering foundation of the future, ISBN 978-0-7277-6067-8.

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[44] Holeyman, A. , Bengt Broms lecture at the forth Nordic Ground Vibration Day, Trondheim 18th of October 2018, http://folk.ntnu.no/gudmundr/NGV2018/Presentations%20NGV%202018.htm [45] Whenham, V. 2011. Power transfer and vibrator-pile-soil interactions within the framework of vibratory pile driving, Ph.D. thesis, University of Louvain, Belgium. [46] Olson, S. M., & Stark, T. D. (2002). Liquefied strength ratio from liquefaction flow failure case histories. Canadian Geotechnical Journal, 39(3), 629-647.

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Review and reference page Document information Deliverable title Deliverable No. Vibration induced damage due to construction work – State of the Art Report D4.1

Work package No. Distribution Date 4 Open 2019-08-29

Rev. No and date 0 Client The Research Council of Norway

Keywords Vibration, damage, blast, ground work, landslide

Document control

Quality assurance according to NS-EN ISO9001 Inter- Colleague Self review Independent disciplinary Rev. Reason for revision review by: review by: review by: by: 29/8- 29/8- 0 Original document KNC CM 19 19

Risk Reduction of Groundwork Damage