Terrafirma Mining case study: Stoke-on-Trent, UK 7/Bateson_Stoke-o… · Stoke-on-Trent ground motionsTrent ground motions ... • millimetres to as much as 2m of motion ... • Dereliction

Terrafirma Mining case study:Stoke-on-Trent, UK

Luke Bateson

© NERC All rights reserved

Stoke-on-Trent

• Stoke-on-Trent and the nearby townsStoke on Trent and the nearby towns make up a large industrial conurbation known as ‘The Potteries’

• Main industries were based around the local geology and have included mining (coal, clay and ironstone), iron foundries brick and tile making and the pottery industryfoundries, brick and tile making and the pottery industry.

• Halite (salt) is still extracted in the Cheshire salt fields to the north west of the conurbation.north west of the conurbation.

• Coal mining finished in the 1990’s

• Population >250 000Population >250 000.

• Area approximately 72 km2 (15 by 4.8 km).


Resources of the Stoke area• Rich in mineral resources, principally,

coal, ironstone and clays for brick and tile manufacture.

• The Sherwood Sandstone is an important• The Sherwood Sandstone is an important aquifer adjacent to the urban area.

• 6 - 7 million tons of coal extracted a year yin the first 70 years of the 20th century.

• Coal mining:• ‘footrail mines’ – pillars of coal for support• deep mines - total extraction accessed by vertical

h ftshafts. • opencast sites.

• Clay extracted from opencast sites


• Clay extracted from opencast sites

Geology of the Stoke areaStratigraphy Lithology

Quaternary - Holocene Artificial deposits Hardcore, bricks and tiles, colliery waste, foundry slag ceramic rejects domestic andfoundry slag, ceramic rejects, domestic and industrial waste

Quaternary - Holocene Alluvium Clay, silt, sand, gravel

Quaternary – Pleistocene/Holocene River Terrace and Alluvial Fan Deposits Sand, gravel

Quaternary - Pleistocene Glacial Till; Glacial Sand and Gravel Clay, silt, sand, gravel, cobbles, boulders; sand, gravel

Permo-Triassic Mercia Mudstone Group Lower Mudstone Division Mudstones and siltstones

Denstone Formation Mudstones, siltstones, sandstones

Permo-Triassic Sherwood Sandstone Group Helsby Sandstone Formation Sandstones with occasional conglomerates

Hawksworth Formation

Carboniferous Barren Measures Keele Formation Mudstones and siltstones with occasional sandstones

Newcastle FormationNewcastle Formation

Etruria Formation

Carboniferous Coal Measures Upper Coal Measures Mudstones and siltstones with coal seams and occasional sandstones

Middle Coal Measures

Lower Coal Measures


Lower Coal Measures

Stoke on Trent ground motionsStoke-on-Trent ground motions

• I d t i l h it d h f t t i t i• Industrial heritage and phases of tectonic stressing and de-stressing led to ground motions

• millimetres to as much as 2m of motion

• These movements were mostly associated withThese movements were mostly associated with mineral extraction• resulted in damage to property. • likely that poor foundation design and

construction contributed.

• Since the decrease in coal mining activities, and ultimately, its cessation, ground movements have


continued

Stoke on Trent ground motionsStoke-on-Trent ground motions

• Coal mining subsidence

• Minewater rise

• Fault reactivation

• Salt extraction subsidence

• Dereliction and artificial groundg

• Infilled quarries/waste disposal sites

• Landslides and steep slopes

• Compressible valley alluvium


y

Terrafirma Processing of Stoke-on-Terrafirma Processing of Stoke onTrent

• Stoke-on-Trent was processed as part of the first stage of Terrafirma

• Processing and interpretation carried out in 2003-2004

• Site selected due to coal mining history and opencast workings – the UK’s largest halite field is to the north

• Stoke was to be a H2 product• Geological Interpretation of H1

• PSI processing (H1 production) by TRE

• Value adding carried out by BGS


Value adding carried out by BGS

Location of Processed AreaLocation of Processed Area

• An area of 1111km2 was processedp

• 178 109 PS points with an average velocityaverage velocity

• 68 509 (38.5%) of these have a full historyhave a full history

• PSI processing date range = 1992 2001= 1992 - 2001


Average VelocityAverage Velocity

A l it /Average velocity mm/yr

Subsidence


Uplift

PS point Density (all points)PS point Density (all points)

Reference Point


PS Point density (with full time series)PS Point density (with full time series)


Interpolation of PS data (using inverted linear distance)distance)

Interpolated Points Legend

Subsidence

Uplift


Relationships bet een PSIRelationships between PSI data and Geological Datadata and Geological Data


• No relationship found between PSI ground motions and:

• Geological units• Slope steepness• Areas prone to shrink-swell• Running sand• Slope instabilityp y


Active Coal Mining and subsidence

• As underground mining has ceased, subsidence has reduced in recent years. H t th th d d i i till• However, to the south underground mining was still active for much of the period for which PSInSAR data was available. da a as a a ab e


Active Coal Mining and subsidence

• Subsidence caused by the collapse of mine workings and reactivation of faultsreactivation of faults

Blue polygons are areas of mine workings


Blue polygons are areas of mine workings

Areas of Minewater rise and Uplift• During mining groundwater levels are lowered to

below seam levels by pumpingbelow seam levels by pumping. • Once a mine is closed, pumping usually ceases and

groundwater returns towards its historical level g• As water levels rise the level of the ground surface

may also rise. • In the northern part of the coalfield mining ceased

many decades ago and water levels have risen considerably from their lowest levelsconsiderably from their lowest levels.


Areas of Minewater rise and Uplift


Fault Reactivation

• Associated with active mining and with the post-mining period as the ground stabilises and minewater levels recover.

• Seismic activity (1 – 2 on the Richter scale) observed, this correlates well with the area of uplift


correlates well with the area of uplift

Fault ReactivationDonnelly (1994) and Donnelly and Rees (2001) have studied fault reactivation in the Potteries andhave studied fault reactivation in the Potteries and have recorded substantial ground movements of many tens of centimetresmany tens of centimetres.

I t f


Images courtesy ofLaurance Donnellyand John Rees

Fault Reactivation


Fault Reactivationau t eact at o


Fault Reactivation and re-d ldevelopment

Black rectangles indicate houses that were d li h ddemolished but some have been rebuilt!been rebuilt!


Fault ReactivationFault Reactivation

• Levelling – Subsidence f 13 b tof 13cm between may

‘92 and June ‘93.• PSI – subsidence ofPSI subsidence of

0.25cm between May ‘92 and June ‘93


Salt DissolutionSalt Dissolution

• Salt is extracted by controlled pumping in the Cheshire Basinpumping in the Cheshire Basin to the north west of the Potteries.

• Subsidence associated with natural salt dissolution processes is continuingprocesses is continuing.


Differential Motion of a Landfill Site

• Infilled quarries/waste disposal sites are subject to ground movements • Waste materials settle - subsidence• Waste material decays – subsidence • Waste material decays - uplift through methane

production


Differential Motion of a Landfill Site• North Crackley - former open cast coal mine, now a restored waste site.

• It was variably backfilled at two different times• SW Filled first – now stable• NW filled second -uplift


HOUSING ESTATE, NORTH CRACKLEY, BUILT OVER FORMER OPENCAST PIT & RESTORED WASTE SITE.

WALKING & DRIVING AROUND ESTATE SHOWED NO DAMAGE TO PROPERTIES


ConclusionsConclusions• PSI results for Stoke-on-Trent havePSI results for Stoke on Trent have

• added to our understanding of the ground motions that we knew were occurring

• indicated motions that we did not appreciate

• Motions appears to be related to:• Active mining

I ti i i d i t b d• Inactive mining and minewater rebound• Mining induced fault re-activation• Salt dissolution• Salt dissolution• Settlement of made ground


Documents

Terrafirma Mining case study: Stoke-on-Trent, UK 7/Bateson_Stoke-o… · Stoke-on-Trent ground motionsTrent ground motions ... • millimetres to as much as 2m of motion ... • Dereliction