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Geological influence on tunnelling under the Western Front at Vimy Ridge
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Geological influence on tunneRing under the Western Front at Vimy Ridge M. S. Rosenbaum ROSENBAUM, M. S., 1989. Geological influence on tunnelling under the Western Front at Vimy Ridge. Proc. Geo/. Ass., 100(1), 135-40. Geolog~sts were appointed as .Staff Ad~isers in Army Headquarters for the first time during the FIrSt World War. Thetr expertise was particularly sought during the planning for underground warfare that developed .a!ong the Western Front of northern France and Belgium. Vimy Ridge is typical of the condItIons th~t prevailed and an account of the geol~gy there a~d its i~fluence on the underground works IS presented. Part of the workings are stIli open for inspectIon at the present day.
Department of Geology, Imperial College, Prince Consort Road, London, SW72BP
1. INTRODUCTION A recent account (Robinson, 1988) of the roles of geologists in the First World War illustrated the various ways in which geological advice was sought and applied by the military. This was in fact th.e first time that Army Headquarters employed geologists as such and their roles developed as the war progressed, commencing with the urgent need to develop groundwater supplies, particularly for ho~s~s, and progressing to predicting likely ground condItIons for trenches and mines, location of materials for battlefield repair, and assessing the likely crosscountry mobility of the newly invented tanks. Most notably these geological investigations were done by Lt. (Later to become Professor) W. B. R. King for the British, Major (also later to become Professor) Edgeworth David for the Australians, and a number of geologists (names unknow~) for th~ Germans.. A detailed account of some of thIS work, Illustrated wIth coloured maps and cross sections, was subsequently published in a special volume by the Institution of Royal Engineers (1922a).. .... Of interest to both geologIst and hlstonan alIke IS the sister volume published by the Institution (1922b). This provides a wealth of fascinating detail regarding the ground and the means of overcoming the adv~rse conditions prevailing, military as well as geologIcal. Geophysicists will be particularly fascinated by the early use of geophones which were used rather like a medical stethoscope for detecting underground vibrations, thereby gaining intelligence of enemy mining activities and impending underground attacks. 2. UNDERGROUND WORKS AT VIMY RIDGE There is still an active link between the military geologists and the defensive work on the Western Front since one of the tunnel systems, the Grange Subway, is still in existence and a detailed technical
study is currently under way by the Royal Engi~eers on behalf of the Canadian Memorial Park CommIttee. The aim is to assess the feasibility of repairing and extending the preserved parts of the system so as to make them accessible to the public as a part of the Memorial Park, which also includes the prominent twin spires of the Canadian War Memorial lying just to the east of the Calais to Paris motorway. The general location is shown on Fig. 1. The study includes a survey of the geology and tunnel stability conditions as a precursor to the design of appropriate remedial and protection works. It is hoped, if approval is given by the authorities, that the construction work will commence in 1989 and be undertaken by a Royal Engineers Squadron. The Grange Subway, located 8 km north of Arras in northern France, was an access route leading from the relatively safe rear assembly areas to the trench system at the Front. It was constructed in only four months by 172 Tunnelling Company of the Royal Engineers, commencing at the .end ~f 1916, in preparation for the assault on Vlmy RIdge by the Canadian Corps in the Spring of 1917. The Grange Subway itself was 800 m long, linking the r~ar areas where infantry reserves could be mustered In safety with the front line (Fig. 2). Fighting tunnels had also ~een constructed wh~n the British took over Vimy RIdge from the French In April, 1916. These initially led from the trench system and were a downward projection of the trenches, but later shallow inclines were constructed to counter German mining activities and then a chain of defensive listening posts were established. All of these excavations were later connected up with the subway which then together formed part of an underground complex extending for over 6 km. The arrangement of mines and tunnels excavated to form a system such as found at Vimy is shown in Fig. 2 as a general schematic diagram to illustrate the relationships between the various excavations employed.
135
136
M. S. ROSENBAUM
Fig. 1. Location map for Vimy Ridge showing principal subways. The Grange Subway is the only accessible system at present. The Canadian and German Lines are shown as they were immediately prior to the Canadian attack in the spring of 1917. Contours are at 10 m intervals.
137
TUNNEL GEOLOGY UNDER THE WESTERN FRONT
Ventilation Shaft (Downdraft ) 32m deep
_
TO NEXT MINING SYSTEM
%
NEXT MINING SYSTEM
o
r
»
z o fire irenC~::::: __ ::.:::.::,: contInUes
f:==:j:j::==::O-
TO NEXT MINING SYSTEM
TO
Ventilation Shaft (Exhaust) 30m deep
GC
LEGEND Principol trench
--
= GO
0,=.=====-50~===~~om
Tunnel Stepped inCline Gas door
EGO
Emergency gos door
GC
Gas curtoin General airflow direction
Fig. 2. General layout of military underground excavations and associated terminology employed along the Western Front, based on the system fed by the Grange Subway.
138
M. S. ROSENBAUM
FORWARD FIRE TRENCHES
71 Sleep incline down to tunnels /
for mines and listening posts
-.......... Steep incline down 10 deep ~........... defensive laterals and "''..:-.:-flghting tunnels
FORWARD DEFENCE LINE Former entrance. now blocked
..,
)-
CROSS SECTION
;:
"'"
en w
C!J
.., Z
a:
C!J
LINE OF CROSS-SECTION
x
Approximate Scale Rooms
In
Brigade Headquarters
A Signals office B C o E F
Sleeping quarters Commanders offIce Operations Room Officers Mess First Aid Post and DreSSing Station
x=gnU or 9,,/1 door (no through access)
To support trenches
Fig. 3. A sketch map of the military underground mines, excavations and principal trenches connected with the Grange Subway which are accessible as part of the Canadian Vimy Memorial Park. The map is based in part on the field survey conducted by Lt. Col. G. P. G. Robinson RE on 14 Nov, 87 and on the authors own observations. IMPORTANT NOTE: There is no access beyond the grills and grill doors marked on the site plan. The tunnels beyond are known to contain major hazards, particularly unstable rock in the tunnel roof and poisonous gases. On no account should these tunnels be entered.
TUNNEL GEOLOGY UNDER THE WESTERN FRONT
139
There were also connections, partly for ventilation and partly for access, along "laterals" (deep tunnels) to some of the eleven other similar subways along Vimy Ridge which together contributed substantially to the many tens of kilometres of excavation achieved dUring the years of attrition. Each of these subways had access from the rear areas allowing reserves to reach the front line with reasonable protection and out of sight of enemy observers. They not only provided covered approaches but also incorporated command posts, first aid dressing stations, water supply points (some with wells), electricity power stations, magazines and accommodation. Many had tramlines (often wooden so as to minimise the noise) for assisting removal of spoil and the supply of munitions, and the main subways also had light railways established within them. After the war an area of Vimy Ridge, including the Grange Subway, was donated in perpetuity by France to the Canadians as a memorial to commemorate both the Canadian contribution to the struggle on the Western Front and to the storming of Vimy Ridge which had been a major component.
beyond the fault was considered to be a major threat and an extensive system of air lines was installed within the deeper workings. Carbon monoxide was also given off in considerable quantities from mine and camouflet explosions. The release and absorption of carbon monoxide into the porous chalk and associated joints was a particularly difficult phenomenon to predict, depending greatly on the prevailing atmospheric pressure, the moisture content of the exposed chalk rock, and the degree of air circulation within the tunnel workings. In addition, the use of gas by the enemy proved to be a very dangerous problem. To the north of the Memorial Park on Hill 145, around the area known as The Pimple, the Ridge is capped with Tertiary sediments, essentially sands overlying the Louvil sediments which unconformably overly the chalk. The sands are similar in composition to the Thanet Beds of southeast England and the clays to the London Clay, although the stratigraphy is not directly comparable. The lower part of the Louvil sediments are sands similar to those of the Thanet Beds above but between them lies a continuous bed of overconsolidated clay.
3. GEOLOGY OF VlMY RIDGE
4. INFLUENCE OF GEOLOGY ON UNDERGROUND WARTIME WORKS
The Ridge is an extensive feature which stands about 60 m above the Douai Plain to the northeast. It is effectively a scarp slope developed in the upper part of the Upper Cretaceous chalk, with the more marly Middle Chalk outcropping at the foot of the slope. The ground drops away to the southwest at a much gentler angle, following the dip of the Upper Chalk. The presence of the Ridge is largely due to the major disturbance known as the Marqueffles Fault which runs in a north westerly direction. This disturbance has thrown the north eastern side down by over 100 m, partly by faulting and partly by folding. This has also brought the underlying Hercynian basement close to the surface and is responsible for the extensive coalfield centred on Lens that extends as far north as Lille and east towards Mons. The excavations for the Grange Subway lie for the most part in the Upper Chalk, the near surface zones of which are considerably weakened by periglacial frost shattering and solifluction. This chalk is similar to that outcropping in southeast England around Dover, a weak rock with numerous flint nodules mostly forming bands sub-parallel to bedding. A 1 to I! m thick mantle of loess blankets the area and this is also found up to 15 m below ground level along solution cavities within the chalk. Additional shattering of the chalk accompanies minor normal faults which are thought to be associated with the Marqueffles Fault. During the tunnelling of 1916 the presence of gas, particularly methane and carbon monoxide, passing into the workings through the fracture system from these Carboniferous rocks
During the wartime offensive mmmg, it was imperative that silence by maintained in the forward advancement of each tunnel and much effort was expended in trying to predict the position of the Louvil Clay. Tunnelling within this stratum not only proved easier due to the longer stand-up time before the need to apply support, but also benefitted from the clay acting as an effective sound baffle. Indeed, the early development of geophones already noted had arisen from the need to detect enemy excavation in order to predict the direction and depth of mining activity and to determine the likely onset of an underground attack. Uncontrollable collapse of the excavations needed to be avoided and the chalk fracture spacing was a major control in determining the detailed design of the tunnels. However, it was also important to minimise the tunnel size in order to keep spoil removal to a minimum and to achieve the greatest possible rate of advance. The predominant joint orientations are subvertical and subhorizontal (both tectonic and exhumation stress relief, the subhorizontal joints often taking advantage of clay or marl seams within the chalk). This gave rise to slabs of rock which could fall directly from the roof, thus the tunnel width was limited to 0.8 m in order to provide sufficient bridging maintained by the friction along the joint surfaces. As a matter of standard procedure, the tunnels were supported by timbers for every 1 m of advance, consisting of two pillars driven into small recesses in the wall supporting a roof beam, the whole
140
M. S. ROSENBAUM
being driven home by wooden wedges. The tunnels were 1.3 m high and so working conditions were very cramped. Most of the mine timbers were salvaged after a successful attack due to the chronic shortage of wood in the war zone. Those mine timbers which were left behind have now rotted completely but the tunnel profile has survived largely intact through the succeeding 70 years. However, the standard tunnel size was too small for the assaulting infantry to pass through rapidly so the main access subways were built to the larger profile of 1 m width and 2 m height. This has been too great for long term stability of the roof and 10 years after the War concrete beams had to be installed in order to maintain the roof against further collapse. The other major hazard in tunnelling was caused by the inflow of water. Indeed the water table rose and fell by as much as 10 m between the winter and summer months. This would be a particular problem if a sand channel or bed were intersected. The remedy was to excavate all tunnels at a slope of at least 1 in 100 and to provide sumps in side passages capable of storing excess water until it could be either pumped out or carried away. The need to maintain as dry conditions as possible underfoot need not be elaborated in view of the well known conditions of the trenches at that time! Knowledge of the underground geological structure was not altogether lacking, but much was located in university libraries or behind enemy lines. A general understanding of the regional geology could therefore be compiled but this required a considerable input
from geological advisers able to access and interpret the diverse records and maps. At the local level the geology was insufficiently well defined for practical purposes and so field mapping, particularly of new craters(!), supplemented by shallow borings was undertaken. Within the tunnels further detailed mapping and section drawing could be undertaken by the military geologist. Once the tunnelling commenced, there was an ongoing requirement to check on the excavation progress and in particular to warn of likely hazards which had not hitherto been anticipated. Limited use was made of advance boring to supplement geological measurements within the tunnels, but the presence of sedimentary sand channels within the Louvil Clay and the close proximity to the ground surface, not to mention the enemy counter-mining activities, made this a hazardous task.
5. VIMY RIDGE TODAY Anyone who would like to visit the old tunnels and defences of the Western Front at Vimy may do so by visiting the Canadian Vimy Memorial Park which is open daily from 1 April to 15 November. Guides (English and French speaking) are available to escort visitors around the 250 m of the Grange Subway which has been preserved, starting from the Information Kiosk near the car park at the southern end of the Park. A sketch map of the military excavations accessible as a part of the Memorial Park is presented in Fig. 3. However the fighting tunnels are barred to public access but may be viewed at one point in the tour.
References INSTITUTION OF ROYAL ENGINEERS. 1922a. The Work of the Royal Engineers in the European War, 1914-19: Geological Work on the Western Front. Institution of Royal Engineers, Chatham, 71pp. - - , 1922b. The Work of the Royal Engineers in the
European War, 1914-19: Military Mining. Institution of Royal Engineers, Chatham, 148pp. ROBINSON, E., 1988. Geologists at War. Geologists' Association Circular, 867,30-31.
Geological influence on tunneRing under the Western Front at Vimy Ridge M. S. Rosenbaum ROSENBAUM, M. S., 1989. Geological influence on tunnelling under the Western Front at Vimy Ridge. Proc. Geo/. Ass., 100(1), 135-40. Geolog~sts were appointed as .Staff Ad~isers in Army Headquarters for the first time during the FIrSt World War. Thetr expertise was particularly sought during the planning for underground warfare that developed .a!ong the Western Front of northern France and Belgium. Vimy Ridge is typical of the condItIons th~t prevailed and an account of the geol~gy there a~d its i~fluence on the underground works IS presented. Part of the workings are stIli open for inspectIon at the present day.
Department of Geology, Imperial College, Prince Consort Road, London, SW72BP
1. INTRODUCTION A recent account (Robinson, 1988) of the roles of geologists in the First World War illustrated the various ways in which geological advice was sought and applied by the military. This was in fact th.e first time that Army Headquarters employed geologists as such and their roles developed as the war progressed, commencing with the urgent need to develop groundwater supplies, particularly for ho~s~s, and progressing to predicting likely ground condItIons for trenches and mines, location of materials for battlefield repair, and assessing the likely crosscountry mobility of the newly invented tanks. Most notably these geological investigations were done by Lt. (Later to become Professor) W. B. R. King for the British, Major (also later to become Professor) Edgeworth David for the Australians, and a number of geologists (names unknow~) for th~ Germans.. A detailed account of some of thIS work, Illustrated wIth coloured maps and cross sections, was subsequently published in a special volume by the Institution of Royal Engineers (1922a).. .... Of interest to both geologIst and hlstonan alIke IS the sister volume published by the Institution (1922b). This provides a wealth of fascinating detail regarding the ground and the means of overcoming the adv~rse conditions prevailing, military as well as geologIcal. Geophysicists will be particularly fascinated by the early use of geophones which were used rather like a medical stethoscope for detecting underground vibrations, thereby gaining intelligence of enemy mining activities and impending underground attacks. 2. UNDERGROUND WORKS AT VIMY RIDGE There is still an active link between the military geologists and the defensive work on the Western Front since one of the tunnel systems, the Grange Subway, is still in existence and a detailed technical
study is currently under way by the Royal Engi~eers on behalf of the Canadian Memorial Park CommIttee. The aim is to assess the feasibility of repairing and extending the preserved parts of the system so as to make them accessible to the public as a part of the Memorial Park, which also includes the prominent twin spires of the Canadian War Memorial lying just to the east of the Calais to Paris motorway. The general location is shown on Fig. 1. The study includes a survey of the geology and tunnel stability conditions as a precursor to the design of appropriate remedial and protection works. It is hoped, if approval is given by the authorities, that the construction work will commence in 1989 and be undertaken by a Royal Engineers Squadron. The Grange Subway, located 8 km north of Arras in northern France, was an access route leading from the relatively safe rear assembly areas to the trench system at the Front. It was constructed in only four months by 172 Tunnelling Company of the Royal Engineers, commencing at the .end ~f 1916, in preparation for the assault on Vlmy RIdge by the Canadian Corps in the Spring of 1917. The Grange Subway itself was 800 m long, linking the r~ar areas where infantry reserves could be mustered In safety with the front line (Fig. 2). Fighting tunnels had also ~een constructed wh~n the British took over Vimy RIdge from the French In April, 1916. These initially led from the trench system and were a downward projection of the trenches, but later shallow inclines were constructed to counter German mining activities and then a chain of defensive listening posts were established. All of these excavations were later connected up with the subway which then together formed part of an underground complex extending for over 6 km. The arrangement of mines and tunnels excavated to form a system such as found at Vimy is shown in Fig. 2 as a general schematic diagram to illustrate the relationships between the various excavations employed.
135
136
M. S. ROSENBAUM
Fig. 1. Location map for Vimy Ridge showing principal subways. The Grange Subway is the only accessible system at present. The Canadian and German Lines are shown as they were immediately prior to the Canadian attack in the spring of 1917. Contours are at 10 m intervals.
137
TUNNEL GEOLOGY UNDER THE WESTERN FRONT
Ventilation Shaft (Downdraft ) 32m deep
_
TO NEXT MINING SYSTEM
%
NEXT MINING SYSTEM
o
r
»
z o fire irenC~::::: __ ::.:::.::,: contInUes
f:==:j:j::==::O-
TO NEXT MINING SYSTEM
TO
Ventilation Shaft (Exhaust) 30m deep
GC
LEGEND Principol trench
--
= GO
0,=.=====-50~===~~om
Tunnel Stepped inCline Gas door
EGO
Emergency gos door
GC
Gas curtoin General airflow direction
Fig. 2. General layout of military underground excavations and associated terminology employed along the Western Front, based on the system fed by the Grange Subway.
138
M. S. ROSENBAUM
FORWARD FIRE TRENCHES
71 Sleep incline down to tunnels /
for mines and listening posts
-.......... Steep incline down 10 deep ~........... defensive laterals and "''..:-.:-flghting tunnels
FORWARD DEFENCE LINE Former entrance. now blocked
..,
)-
CROSS SECTION
;:
"'"
en w
C!J
.., Z
a:
C!J
LINE OF CROSS-SECTION
x
Approximate Scale Rooms
In
Brigade Headquarters
A Signals office B C o E F
Sleeping quarters Commanders offIce Operations Room Officers Mess First Aid Post and DreSSing Station
x=gnU or 9,,/1 door (no through access)
To support trenches
Fig. 3. A sketch map of the military underground mines, excavations and principal trenches connected with the Grange Subway which are accessible as part of the Canadian Vimy Memorial Park. The map is based in part on the field survey conducted by Lt. Col. G. P. G. Robinson RE on 14 Nov, 87 and on the authors own observations. IMPORTANT NOTE: There is no access beyond the grills and grill doors marked on the site plan. The tunnels beyond are known to contain major hazards, particularly unstable rock in the tunnel roof and poisonous gases. On no account should these tunnels be entered.
TUNNEL GEOLOGY UNDER THE WESTERN FRONT
139
There were also connections, partly for ventilation and partly for access, along "laterals" (deep tunnels) to some of the eleven other similar subways along Vimy Ridge which together contributed substantially to the many tens of kilometres of excavation achieved dUring the years of attrition. Each of these subways had access from the rear areas allowing reserves to reach the front line with reasonable protection and out of sight of enemy observers. They not only provided covered approaches but also incorporated command posts, first aid dressing stations, water supply points (some with wells), electricity power stations, magazines and accommodation. Many had tramlines (often wooden so as to minimise the noise) for assisting removal of spoil and the supply of munitions, and the main subways also had light railways established within them. After the war an area of Vimy Ridge, including the Grange Subway, was donated in perpetuity by France to the Canadians as a memorial to commemorate both the Canadian contribution to the struggle on the Western Front and to the storming of Vimy Ridge which had been a major component.
beyond the fault was considered to be a major threat and an extensive system of air lines was installed within the deeper workings. Carbon monoxide was also given off in considerable quantities from mine and camouflet explosions. The release and absorption of carbon monoxide into the porous chalk and associated joints was a particularly difficult phenomenon to predict, depending greatly on the prevailing atmospheric pressure, the moisture content of the exposed chalk rock, and the degree of air circulation within the tunnel workings. In addition, the use of gas by the enemy proved to be a very dangerous problem. To the north of the Memorial Park on Hill 145, around the area known as The Pimple, the Ridge is capped with Tertiary sediments, essentially sands overlying the Louvil sediments which unconformably overly the chalk. The sands are similar in composition to the Thanet Beds of southeast England and the clays to the London Clay, although the stratigraphy is not directly comparable. The lower part of the Louvil sediments are sands similar to those of the Thanet Beds above but between them lies a continuous bed of overconsolidated clay.
3. GEOLOGY OF VlMY RIDGE
4. INFLUENCE OF GEOLOGY ON UNDERGROUND WARTIME WORKS
The Ridge is an extensive feature which stands about 60 m above the Douai Plain to the northeast. It is effectively a scarp slope developed in the upper part of the Upper Cretaceous chalk, with the more marly Middle Chalk outcropping at the foot of the slope. The ground drops away to the southwest at a much gentler angle, following the dip of the Upper Chalk. The presence of the Ridge is largely due to the major disturbance known as the Marqueffles Fault which runs in a north westerly direction. This disturbance has thrown the north eastern side down by over 100 m, partly by faulting and partly by folding. This has also brought the underlying Hercynian basement close to the surface and is responsible for the extensive coalfield centred on Lens that extends as far north as Lille and east towards Mons. The excavations for the Grange Subway lie for the most part in the Upper Chalk, the near surface zones of which are considerably weakened by periglacial frost shattering and solifluction. This chalk is similar to that outcropping in southeast England around Dover, a weak rock with numerous flint nodules mostly forming bands sub-parallel to bedding. A 1 to I! m thick mantle of loess blankets the area and this is also found up to 15 m below ground level along solution cavities within the chalk. Additional shattering of the chalk accompanies minor normal faults which are thought to be associated with the Marqueffles Fault. During the tunnelling of 1916 the presence of gas, particularly methane and carbon monoxide, passing into the workings through the fracture system from these Carboniferous rocks
During the wartime offensive mmmg, it was imperative that silence by maintained in the forward advancement of each tunnel and much effort was expended in trying to predict the position of the Louvil Clay. Tunnelling within this stratum not only proved easier due to the longer stand-up time before the need to apply support, but also benefitted from the clay acting as an effective sound baffle. Indeed, the early development of geophones already noted had arisen from the need to detect enemy excavation in order to predict the direction and depth of mining activity and to determine the likely onset of an underground attack. Uncontrollable collapse of the excavations needed to be avoided and the chalk fracture spacing was a major control in determining the detailed design of the tunnels. However, it was also important to minimise the tunnel size in order to keep spoil removal to a minimum and to achieve the greatest possible rate of advance. The predominant joint orientations are subvertical and subhorizontal (both tectonic and exhumation stress relief, the subhorizontal joints often taking advantage of clay or marl seams within the chalk). This gave rise to slabs of rock which could fall directly from the roof, thus the tunnel width was limited to 0.8 m in order to provide sufficient bridging maintained by the friction along the joint surfaces. As a matter of standard procedure, the tunnels were supported by timbers for every 1 m of advance, consisting of two pillars driven into small recesses in the wall supporting a roof beam, the whole
140
M. S. ROSENBAUM
being driven home by wooden wedges. The tunnels were 1.3 m high and so working conditions were very cramped. Most of the mine timbers were salvaged after a successful attack due to the chronic shortage of wood in the war zone. Those mine timbers which were left behind have now rotted completely but the tunnel profile has survived largely intact through the succeeding 70 years. However, the standard tunnel size was too small for the assaulting infantry to pass through rapidly so the main access subways were built to the larger profile of 1 m width and 2 m height. This has been too great for long term stability of the roof and 10 years after the War concrete beams had to be installed in order to maintain the roof against further collapse. The other major hazard in tunnelling was caused by the inflow of water. Indeed the water table rose and fell by as much as 10 m between the winter and summer months. This would be a particular problem if a sand channel or bed were intersected. The remedy was to excavate all tunnels at a slope of at least 1 in 100 and to provide sumps in side passages capable of storing excess water until it could be either pumped out or carried away. The need to maintain as dry conditions as possible underfoot need not be elaborated in view of the well known conditions of the trenches at that time! Knowledge of the underground geological structure was not altogether lacking, but much was located in university libraries or behind enemy lines. A general understanding of the regional geology could therefore be compiled but this required a considerable input
from geological advisers able to access and interpret the diverse records and maps. At the local level the geology was insufficiently well defined for practical purposes and so field mapping, particularly of new craters(!), supplemented by shallow borings was undertaken. Within the tunnels further detailed mapping and section drawing could be undertaken by the military geologist. Once the tunnelling commenced, there was an ongoing requirement to check on the excavation progress and in particular to warn of likely hazards which had not hitherto been anticipated. Limited use was made of advance boring to supplement geological measurements within the tunnels, but the presence of sedimentary sand channels within the Louvil Clay and the close proximity to the ground surface, not to mention the enemy counter-mining activities, made this a hazardous task.
5. VIMY RIDGE TODAY Anyone who would like to visit the old tunnels and defences of the Western Front at Vimy may do so by visiting the Canadian Vimy Memorial Park which is open daily from 1 April to 15 November. Guides (English and French speaking) are available to escort visitors around the 250 m of the Grange Subway which has been preserved, starting from the Information Kiosk near the car park at the southern end of the Park. A sketch map of the military excavations accessible as a part of the Memorial Park is presented in Fig. 3. However the fighting tunnels are barred to public access but may be viewed at one point in the tour.
References INSTITUTION OF ROYAL ENGINEERS. 1922a. The Work of the Royal Engineers in the European War, 1914-19: Geological Work on the Western Front. Institution of Royal Engineers, Chatham, 71pp. - - , 1922b. The Work of the Royal Engineers in the
European War, 1914-19: Military Mining. Institution of Royal Engineers, Chatham, 148pp. ROBINSON, E., 1988. Geologists at War. Geologists' Association Circular, 867,30-31.