ground penetrating radar (gpr) · baldonnel airmotive concrete slab testing ground penetrating...

Baldonnel Airmotive

Concrete Slab Testing

Ground Penetrating Radar (GPR)

Report Status: Final

MGX Project Number: 5804

MGX File Ref: 5804d-005.doc

19th

May 2014

Confidential Report To: TMS Environmental Ltd. 53 Broomhill Drive Tallaght Dublin 24

Report submitted by : Issued by: Minerex Geophysics Limited

Unit F4, Maynooth Business Park Maynooth, Co. Kildare

Ireland Tel.: 01-6510030 Hartmut Krahn (Senior Geophysicist) Fax.: 01-6510033 Email: [email protected]

Subsurface Geophysical Investigations

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Baldonnel Airmotive Concrete Slab Testing

Ground Penetrating Radar (GPR) Survey

Minerex Geophysics Limited Report Reference: 5804d-005.doc

CONTENTS

1. INTRODUCTION ...................................................................................................................... 1

1.1 Background ..................................................................................................................................... 1

1.2 Objectives ........................................................................................................................................ 1

1.3 Report ............................................................................................................................................... 1

2. GEOPHYSICAL SURVEY ...................................................................................................... 2

2.1 Methodology ................................................................................................................................... 2

3. RESULTS AND INTERPRETATION ..................................................................................... 3

4. REFERENCES .......................................................................................................................... 4

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Minerex Geophysics Limited Report Reference: 5804d-005.doc

List of Maps and Figures:

Title Pages Document Reference

Map 1: GPR Survey Location Map Area A - C 1 x A3 5804d_MapsFigs.dwg

Map 2: GPR Survey Location Map Area AB 1 x A3 5804d_MapsFigs.dwg

Map 3: GPR Survey Location Map Area C 1 x A3 5804d_MapsFigs.dwg

Map 4: GPR Survey Location Map Area D 1 x A3 5804d_MapsFigs.dwg

Map 5: GPR Survey Location Map Area E 1 x A3 5804d_MapsFigs.dwg

Map 6: GPR Survey Location Map Area F 1 x A3 5804d_MapsFigs.dwg

Map 7: GPR Survey Location Map Area G 1 x A3 5804d_MapsFigs.dwg

Figure 1: GPR Sections for Area A 1 x A3 5804d_MapsFigs.dwg

Figure 2: GPR Sections for Area B 1 x A3 5804d_MapsFigs.dwg

Figure 3: GPR Sections for Area AB and C 1 x A3 5804d_MapsFigs.dwg

Figure 4: GPR Sections for Area D 1 x A3 5804d_MapsFigs.dwg

Figure 5: GPR Sections for Area E 1 x A3 5804d_MapsFigs.dwg

Figure 6: GPR Sections for Area F 1 x A3 5804d_MapsFigs.dwg

Figure 7: GPR Sections for Area G 1 x A3 5804d_MapsFigs.dwg

Figure 8: GPR Sections for Area H 1 x A3 5804d_MapsFigs.dwg

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Minerex Geophysics Limited Report Reference: 5804d-005.doc Page 1 of 4

1. INTRODUCTION

1.1 Background

Minerex Geophysics Ltd. (MGX) carried out a Ground Penetrating Radar (GPR) Survey within the Baldonnel

Airmotive facility. The survey was carried out at certain areas where chemicals have been stored or placed

and where potentially spillage may have happened. The purpose of the survey was to structurally assess the

concrete slabs and to test their integrity. A structurally intact concrete floor slab would have acted as a barrier

for potential leachate of liquid material into the subsurface. The survey was commissioned by TMS

Environmental Ltd.

1.2 Objectives

The main objectives of the survey were

• To test the concrete floor slabs

• To establish the presence of rebar

• To estimate the concrete slab thickness

1.3 Report

This report includes the results and interpretation of the geophysical survey. Maps and figures are included to

illustrate the survey and the results. More detailed descriptions of geophysical and utility surveying methods

and measurements can be found in GSEG (2002), Milsom (1989), Radiodetection (1986) and Reynolds

(1997).

The interpretative nature and the non-intrusive survey methods must be taken into account when considering

the results of this survey and Minerex Geophysics Limited, while using appropriate practice to execute,

interpret and present the data give no guarantees in relation to the existing subsurface.

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2. GEOPHYSICAL SURVEY

2.1 Methodology

The GPR measurements were taken using the GSSI SIR-3000 system and a 900 MHz antenna. Some

other antennas were also tested but the 900 MHz showed the best results. The scan spacing was 0.02 m.

The depth range was tested on the site and the depth of penetration is between 0.5 and 1.0m b.g.l. The

horizontal distance was measured using the odometer of the survey system. Notes were taken about the

location of the walls and other items.

An orthogonal grid of GPR profiles was recorded and 0.5 m grid spacing was maintained over the survey

areas that were unobstructed.

The survey was carried out on the 14th and 15

th of April 2014.

A survey profiles are indicated on Maps 1 – 7.

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3. RESULTS AND INTERPRETATION

The interpretation of geophysical data was carried out utilising the known response of geophysical

measurements, typical physical parameters for subsurface features that may underlay the site and the

experience of the authors.

All factual data for the GPR is shown on the figures 1 – 8. The GPR sections have been plotted as grey-scale

cross-sections of distance (in meters) along the horizontal axis versus depth on the vertical axis. The GPR

file names are given. A velocity of 0.1 (Areas A, B, C, D, E) or 0.09 m/ns (Areas AB, F, G, H) was used to

convert the GPR sections to depth after testing various velocities by matching hyperbolas. This depth

conversion will give an approximate depth for underground objects within the detection range of the GPR.

Surface features visible on the ground have been marked in blue colour on the figures in order to avoid

confusing them with possible underground objects or defects.

After eliminating surface items no defects in the floor slab could be found. The concrete slabs are in good

order and have a good integrity.

Area AB in a profile inside a drain and there is no rebar present in the drain. The concrete appears thick and

continous and without failures in this drain.

Area C is partially raised and the rebar is less continous but the concrete appears in good condition.

All other areas show a dense pattern of rebar with a mesh size of around 0.15m. The rebar is typically 0.15m

deep. The floor slab underside cannot generally be seen through the rebar but is at least 0.2m thick and

continous. All floors are in good condition and continous and there are no faults visible in the GPR data.

The good condition of the floor slabs with almost continous rebar and a thickness of at least 0.2m would have

create a good barrier against possible spillages in the past.

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4. REFERENCES

1. GSEG 2002. Geophysics in Engineering Investigations. Geological Society Engineering Geology Special

Publication 19, London, 2002.

2. Milsom, 1989. Field Geophysics. John Wiley and Sons.

3. Reynolds, 1997. An Introduction to Applied and Environmental Geophysics. John Wiley and Son.

4. GSSI, 2004. TerraSIRch SIR system-3000 User’s Manual. Geophysical Survey Systems Inc.

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