The document describes a 3D laser scan inspection of historic Bath Stone mine workings in the UK prior to a proposed residential development. The laser scan provided a highly accurate 3D model of the workings, revealing greater detail and extent than prior abandonment plans. Discrepancies were found between the laser scan and 1950s plans. A visual inspection confirmed the workings and pillars were stable with no signs of failure. The laser scan will help accurately assess the impact of the workings on the proposed development.

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Proceedings of the XVI ECSMGE
Geotechnical Engineering for Infrastructure and Development
ISBN 978-0-7277-6067-8
© The authors and ICE Publishing: All rights reserved, 2015
doi:10.1680/ecsmge.60678
Inspection of historic Bath Stone (Jurassic) workings
using 3D laser scanning prior to proposed surface
redevelopment.
Inspection d’une site d’exploitation minière historique de “Bath Stone” (Jurassic)
abandonée a l’aide d’un scanneur laser 3D avant le projet de réaménagement.
P.Taylor*1
, N. Romaniw2
and K.H. Nicholls3
1
Opus International Consultants, Doncaster,UK
2
Tower Surveys Ltd, Nottingham,UK
3
Opus International Consultants, Nottingham,UK
*
Corresponding Author
ABSTRACT Due to the age, scale and detail of many mine abandonment plans their accuracy can often be of
concern particularly when development is proposed above or close to the historic workings. This can often re-
sult in both expensive and time consuming investigations to prove the accuracy or not of these plans. During
recent investigation works for a proposed residential development above an area of historic Bath Stone work-
ings the opportunity to access a section of historic workings arose. This allowed both a visual inspection of the
workings, as well as the opportunity to undertake a detailed 3Dimensional laser scan which could be transposed
onto both current and proposed surface features. The output of the laser scan showed the workings in greater
clarity and accuracy than that afforded by the traditional visual inspection, and allowed an assessment of the
impact of the workings on the proposed development to be made. This paper describes the work undertaken on
site in detail, and presents the detailed survey imagery.
RESUME En raison de l’âge, l’échelle et le niveau manquant de detail de nombreux plans d’abandon de mine,
leur exactitude peut souvent être une source d’inqiètude, particulièrement quant un nouveau développement est
proposé au-dessus ou près d’une mine abandonnée. Cela peut souvent entrainer des enquêtes coûteuses et chro-
nophages pour prouver l’exactitude ou non de ces plans. Au cours de récentes enquêtes pour un project de dé-
veloppement residential au-dessus d’une zone d’exploitation minière historique de “Bath Stone” (roche calcaire
du region de Bath en Angleterre), la possibilité d’accéder a une section de mine abandonée s’est posée. Cela a
permis a l’inspection visuelle, ainsi que la possibilité de scruter l`intérieur avec un scanneur au laser et produire
un modèle 3D qui pourrait être transposé sur les traits caracteristiques de surface actuelles et proposées. Le
modèle produit par le scanneur laser a montré les rouages intérieures avec plus de clarité et de précision que
celle offerte par l’inspection visuelle traditionelle, et a permis une évaluation de l’impact des travaux minières
historiques sur le projet de développement proposé. Cet article décrit le travail réalisé sur le site en détail et pré-
sente les images de levé détaillé.

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3614
1 INTRODUCTION
In the UK, shallow mine workings (those present at
depths of less than 30m) are predominantly associat-
ed with historic coal and ironstone workings, most of
which date back several centuries, and are often
poorly or unrecorded and have long since become in-
accessible. It was therefore of considerable interest
when we were asked to look at a potential residential
development site situated to the north of Corsham in
Wiltshire which was underlain by shallow accessible
Bath Stone workings. The workings are concentrated
in the Bath Oolite Member,a sub-unit of the Chalfield
Oolite Formation (Fig 1) which varies in thickness
from 3 to 9m.
Figure 1. Geological Section Simplified from BGS
The site in question is ear marked for development
for low rise residential properties with associated in-
frastructure and therefore our first concern was to de-
termine the exact depth to the working, the height of
the workings, their full extent, and the current condi-
tion.
A review of the available abandonment plans
showed that the quarry beneath the site was named
the Traveller’s Rest and was first quarried in 1810
and abandoned in 1958. It should be noted that the
Bath Stone workings in this area are generally re-
ferred to as quarries, although they are in fact shal-
low underground workings. The Traveller’s’ Rest
Quarry is part of the larger Hartham Park Quarry
which encompasses a number of smaller quarries in
the area.
The abandonment plans were slightly ambiguous
as several headings were shown to be truncated with
dashed lines possibly indicating that the headings ex-
tended beyond the area mapped. In addition no levels
were provided indicating the depth of any of the
workings. This made it imperative that the workings
were fully and accurately mapped.
2 3D LASER SCANNING
Given that the workings were accessible via a drift
into the adjacent active workings in the Hartham
Park Quarry, it was concluded that the most accurate
cost effective and efficient way of mapping the aban-
doned workings would be by 3D laser scanning.
Firstly, control from an existing topographical survey
of the site to be developed, was transferred under-
ground using a Trimble S6 total station. This provid-
ed a baseline relative to the surface from which to
commence survey works of the quarry. A 3D laser
scan was undertaken using a Leica P20 laser scanner,
which can map to an accuracy of 6mm at a range of
100m. Due to the nature of the site, line of sight was
around 50m, reducing the accuracy to 3mm at this
range. A total of 27 scan locations were used to cap-
ture the data across the mine workings. This allowed
for maximum coverage of the site to eliminate any
‘blindspots’ or ‘shadowing’, (areas not visible to the
scanner), within the dataset. The scans were regis-
tered onto the same co-ordinate system using Leica
Cyclone point cloud processing software. Once all
the scans were aligned onto the same grid, the point
cloud was reduced down to a point spacing of 4mm.
Figures 2 and 3 show actual data from the survey
and show an in-situ crane, and typical pillar and stall
workings.
On completion of the laser survey a visual inspec-
tion was undertaken by two geotechnical engineers to
confirm the accuracy of the survey and to observe the
stability of the workings.

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Figure 2. Screen shot from Leica TruView web enabled point
cloud viewer showing historic crane in-situ, with the yellow trian-
gles showing adjacent scan world locations.
Figure 3. Screen shot from Leica TruView web enabled point
cloud viewer showing Pillar and Stall Workings.
2.1.1 Results of Survey and Inspection
The laser scanner surveyed the workings at such a
high resolution that graffiti left by the miners was
clearly visible. The visual inspection confirmed Pillar
condition throughout the Hartham Park workings was
good, with little to no signs of spalling, stress fractur-
ing or significant weathering, with the exception of a
significant joint within the roof area of the main ac-
cess drift. This was noted as being along the line of
the prominent joint set in the rock mass. The mas-
sive, competent bedding units which comprise the
Bath Stone were clear to see and where areas of frac-
turing had occurred steel reinforcement had been
placed as a precaution. The steel work was noted as
being in good condition with no visible indications of
stress apparent.
The laser survey showed that the top of the work-
ings were shown to sit at depths ranging between
11.15m and 14.12m below existing ground level,
with the height of the workings shown to range in
height between 3.55m and 3.98m. Figures 4 and 5
below show screenshots of the full laser survey.
Figure 4. Ariel view of the laser survey data.
Figure 5. Birds eye view of the laser survey data.
When reviewed against the original 1950’s aban-
donment plan (as shown in figure 6), it can be seen
that there are several discrepancies between the two
surveys. The laser survey shows that the workings
are more extensive than those shown on the aban-
donment plans.
The discrepancies are shown in blue on figure 6
and these include a missing connecting tunnel be-
tween the Traveller’s Rest Mine and the connection
to Pickwick Quarry as well as truncated extensions to
various areas of the mine.
Taylor, Romaniw and Nicholls

4. Geotechnical Engineering for Infrastructure and Development
3616
Figure 6. Extract from 1950’s abandonment plan, supplied by the
BGS showing a number of areas of workings missing compared to
the laser survey.
2.1.2 Roof Collapse
The underground stability survey did not encounter
any evidence of vertical or lateral displacement along
roof rock discontinuities or indications of significant
bedding de-lamination. The use of more substantial
structural support (Steel supports, RSJ type cross
beams and brick columns), was notably concentrated
in areas where the spacing of roof fracturing was
closest and where the general fracture density was
greatest. These supports did not appear to have suf-
fered any stresses related to bed de-lamination or
roof rock displacement.
2.1.3 Pillar failure
The condition of the Hartham Park Quarry workings
beneath the site was seen to be very good with no ev-
idence to suggest that pillar failure is occurring, or is
likely to occur at any time in the near future. The
Bath Stone is massively bedded (up to 2 m thick)
with near horizontal bedding surfaces. Literature
sources (Hansons, 2014) indicate that the Uniaxial
Compressive Strength of the Bath Stone is relatively
high, in the region of 20.0 MN/m2 to 29.3MN/m2.
Given the current extent of the mine workings be-
neath the site it is believed that over-stressing the ex-
isting pillar layout is unlikely. No evidence of pillar
stress or failure was noted during the site inspection.
It is therefore considered that pillar failure (by crush-
ing), is not considered a viable mode of failure for
the historical Hartham Park Quarry workings, the
risk of pillar failure is therefore, considered to be
negligible.
2.1.4 Void Propagation
The risk of a roof collapse propagating to ground sur-
face in this geological setting is considered to be very
low. Bulking factors for limestone are reported to be
in the region of 1.6, with this in mind it is considered
that any form of roof collapse within the overlying
Forest Marble Formation would rapidly fill the work-
ings and choke the roof void well before significant
upward void migration was possible. The extent and
height of the loosely placed waste rock stowed within
the Hartham Park workings by Hanson, further re-
duces the potential for void propagation brought
about by any future roof collapse in these areas.
2.1.5 Survey Data
A current restriction on the use of the 3D laser scan-
ning technique is the size of the data set. Whilst this
is not necessarily an issue for organisations who re-
quire the use of this data internally, significant issues
can occur when the data needs to be shared between
numerous different organisations. The raw data from
the initial survey was approximately 40 Gigabytes
which following processing was reduced to 4 Giga-
bytes. Therefore some consideration needs to be giv-
en to how this information is handled and stored as it
cannot be quickly transferred via email.
3 CONCLUSION
Using traditional techniques, such as rotary boreholes
it would not have been possible to investigate the
workings in sufficient detail to allow us to determine
with confidence the condition and precise extent of
the workings, particularly given the discrepancies
identified between the abandonment plan and the la-
ser survey. Without the laser survey it is likely that
we would as a precautionary measure have specified
some kind of remedial measures the costs of which
would have far outweighed the cost of the survey. As
it stands the survey has allowed us to determine that
no remedial measures are currently required for the
existing workings as this clearly shows that the work-
ings are in good condition with no evidence of spall-
ing or roof collapse. In addition, we now have a base

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data set which can be utilized should further long
term monitoring be required in the future.
ACKNOWLEDGEMENT
We would like to thank Gladman Developments for
allowing us present the acquired data. Thanks are al-
so due to Wesley Fallon of Opus Dayton Knight for
translation of the title and abstract.
REFERENCES
Hawkins, D. 2011. Subterranean Britain Bath Stone Quarries Fol-
ly Books, India.
Hanson Bath and Portland Stone - Hartham Park Bath ground
stone Technical Guidance Note
http://www.heidelbergcement.com/NR/rdonlyres/5A07D7A9-63F7-4CD9-
A904-7B5F1892B605/0/PDFHarthamParkbathbuildingstone.pdf Last ac-
cessed 15.09.14
Taylor, Romaniw and Nicholls