Geotechnical Study Area G20 Roquevaire, near Marseille, France
GEOTECHNICAL STUDY AREA G20
ROQUEVAIRE, NEAR MARSEILLE, FRANCE
Plate G20 In the mines at Roquevaire, near arseille, France
SUMMARY
Within the framework of the LIFE project, the site at Roquevaire has been selected to illustrate the interaction of ground instability with local and regional development plans.
Situated 15km to the north-west of Marseille, Roquevaire has nearly 7,000 inhabitants. Gypsum from the district of Roquevaire was extracted from 1800 until 1960. Roquevaire is now facing collapse of the old mines and must deal with the resulting instability problem.
This study comprises three parts:
· Part One is an introduction to the problem. · Part Two succinctly presents the physical characteristics of Roquevaire as well as the responsibilities of all those involved.
1 Geotechnical Study Area G20 Roquevaire, near Marseille, France
· Part Three reviews the instability in Roquevaire, the various causes of collapses and risk situations, the way the problem is perceived by the inhabitants and how it is being addressed and resolved.
1. INTRODUCTION
Hundreds of derelict underground mining cavities have existed beneath French soil for decades, and in some cases for centuries. These cavities were exploited until stability limits were reached and the mines were subsequently abandoned. Today they pose a threat to development that has taken place over these sites. The gypsum found in the district of Roquevaire was exploited between 1800 and 1960. The town of Roquevaire (Plate G20) must now face the progressive collapse of the old mines and must deal with this serious problem. Situated 15km north west of Marseille (see location plan - Figure G20.1), Roquevaire has a resident population of 7,000. The study area is located at Est between the village and the motorway and comprises an area of 60 hectares (Plate G20a).
From a geological point of view the zone being studied for this LIFE project is located in the gypsum formation of the Trias. The gypsum’s origin is linked to tectonic deformation. Located at the front of the overlapping of the Sainte Baume block, the gypsum, an incompetent deposit, was strongly folded and has developed a diapyr-type structure, with abnormal thicknesses reaching 100 m (see Figure G20.2).
Extraction was carried out in the past from the Triassic formation of gypsum in order to make plaster. This extraction was carried out by different operators who have not left reliable documents that enable the precise location of the old mining galleries to be identified. Though mining has now stopped, some galleries remain accessible, others were used for growing mushrooms in the past whilst parts of the mine are underwater. All the galleries show signs of weakness resulting from a poorly planned extraction programme with worn out pillars supporting the gallery vaults.
Visible collapses from the ground surface have taken place in numerous locations without any harmful consequences. However buildings have also been destroyed or have been seriously damaged. Pillars have been observed which are indicating signs of surcharge and are seriously affected by natural fracturing. They are in a state of imminent failure showing all the signs of a steady deterioration in stability.
Periodic falls from the roofs of the caverns have been observed with some natural fractures being karstified over a considerable thickness; openings of more than a metre can be found at some points. Pockets of dissolution are full of glaze and can lead to severe instability as they unload.
The galleries are completely underwater from the second level with percolating rainwater from the watershed of the Basseron draining into the galleries. In addition vibration generated by human activity undoubtedly also has an adverse affect on stability in the area.
Collapse following the spontaneous fracturing of one or several pillars is the most important instability event but other problems include the collapse of swallow holes when they reach ground level, roof falls, and the opening up of karstic pockets. Indications of failure of the exploration support walls in the northern part of the site near the highway CD45 can also be found.
Facing a proven crisis situation, emergency action has been taken involving the relocation of seven families and the closing of the mushroom growing business that was accommodated in the mine. The road CD45 has been reduced to a single lane to prevent excessive loading. In the first instance compensation would normally be paid but as the Barnier Law (which authorises the government to ex-appropriate and pay compensation for property threatened by natural risks) cannot be applied, legal action is being taken against the last operator of the mine.
2 Geotechnical Study Area G20 Roquevaire, near Marseille, France
The risk zone has been delineated by risk studies, first in the area of the mine, then in surrounding areas. The mine is to be stabilized by using a gravel fill, this being the chosen solution for both technical and economic reasons.
2. THE STUDY AREA
2.1 Geology and Geomorphology
Located at the front of the over thrust Sainte Baume block, the structure of the area accounts for its tectonic complexity. The gypsum, as an incompetent deposit, was strongly folded and has a developed diapyr-type structure, with an abnormal thickness ranging up to 100 metres.
The structural plan for Roquevaire (see Figure G20.3) shows a concentric distribution of discontinuities, centred on a sub-circular depressed area. This kind of distribution seems to indicate a phenomenon of halocinese : the gypsum, deformed and folded, develops a positive structure with tectonic thickening in the axial part; this explains the abnormal thicknesses of the gypsum.
2.2 Morphology
The depressions to which discontinuities converge is the axial part, which has been subsequently eroded. On the north flank, at the level of gypsum extraction, except for severe collapses the circular structures could result from slope collapses due to the dissolution of gypsum. The zone being investigated for this study is located in the gypsum formation. This formation is made of Gaudy clay, marl limestone and lenses or banks of gypsum. The stratification is chaotic and caused by severe structural movement and in this situation there are lenses of gypsum; the geology of the whole area is folded.
Under “Les Plâtrières” (see location plan - Figure G20.1) the geological sequence comprises: alluvial deposits of Huveaune in the town centre, limestone of the Urgonien at the west end of Les Plâtrières, marl and gypsum visible to the east, keuper with gypsum in the central zone, limestone of the mulschelkalk to the east and limestone of the Jurassic to the south-west.
2.3 Chronological Account of Events
A brief history of instability at the Roquevaire study area is as follows:
1. Collapses of 10-12 m diameter recorded in the years 1892 and 1940. 2. The collapse of 20 January 1946 “with a shape of a bell”, 5 m diameter and 5 metres deep. 3. Old collapses to the north of the study area. Two collapses have a diameter of 10-20 m and a depth of 7-10 m (1960). 4. A collapse over 30 years ago on Land Parcel 64. 5. In January 1970 a collapse of about 20 m in the south-west part of the study area near the path, the collapse filled up Les Plâtrières. 6. 15 December 1971 at 2130 hours - collapse to the north-west of the site affecting an area of about 2,000-2,500 sq m. 7. 1970 - a collapse near Parcel 73, reactivated in 1973 with a small event to the south. 8. 1974 - collapse of an old building. According to a witness the event affected an area 40- 50 m in diameter. 9. 28 November 1990 at about 1400 hours : emergence of a swallow hole on Parcel 207. According to a study by BRGM a house was 1.8 m from it. The swallow hole was 5.9 m long and 4.8 m wide with a depth of 2.5 m. This event had serious repercussions for the Commune, which decided to begin a programme of risk management.
4 Geotechnical Study Area G20 Roquevaire, near Marseille, France
2.4 Operation of the Gypsum Mine : 1800-1960
Extraction was carried out in the past on the Triassic formation of gypsum in order to make plaster (Plate G20c). The map in Appendix G20.1 illustrates land use at the scale of 1:10,000 and provides the available information concerning : land use (plots and construction), identified drifts, swallow holes and shafts.
On the geological section the different levels of drift are marked. The earliest extraction dates from 1800 when many owners manufactured their own plaster. From 1865 two companies industrially exploited the gypsum, the firm Rancurel extracting from a site north of the highway CD45 and the firm Pontet in the south. Les Plâtrières de Vaucluse (later known as Plâtrières Lafarges), became proprietor of these firms in the years of 1912 and 1926 respectively. Extraction was carried out until 1960 when the work was stopped because properties were being threatened.
The Extraction Process
Drifts were excavated at the boundaries of the gypsum deposit; the deposit being compact without any stratification and dip and often including nodules of Anhydrite. Overburden (of unsuitable ground) had variable thicknesses, with extraction being entirely underground and supported by pillars. According to local records between 1 and 3 floor levels of workings were used. The gallery grid is not uniform and the levels are not regular.
Drifts generally have a section of 7 m wide and 7 m high. They were excavated with a concave roof and have no support. Some drifts were re-excavated during a second phase of mining at a height of 4-5 m, so some excavated cavities have a height of between 11-12 m. The extraction of gypsum was carried out by means of shafts or headways. The shafts have a narrow section (2 m) and a depth below 25 m; they were used until 1905. Headways were in the centre of the extraction area and extended to 2 - 3 levels. Collapses occurred during extraction and sometimes major support filling was required, particularly in the north. However this work of infilling and support was often not carried out or completed correctly.
2.5 Development Activity (1960-1995)
In 1957 a mushroom farm occupied the central part of the mine. Farming stopped in the year 1995, the year of the legal intervention, because of serious risk of collapse. Aerial photographs shows the spread of residential development over sites which were exploited underground in the past. There is a contradiction between the concerns of the mine operators who had stopped the mining activity because buildings were nearby and the ignorance or lack of awareness of private owners. The perception of risk was imprecise although collapses had been catalogued during this period. This can be partly explained by the fact that there were never any human casualties.
2.6 Condition of the Mine
Photographic and other techniques illustrate three types of problem within the mine area:
· Pillars scaling · Sheeting of the floor · Swallow holes and collapses
Condition of Support Pillars
Pillars have been observed presenting:
· Signs of surcharge and serious effects of natural fracturing. · Serious degradation with, for example, mechanical fracturing of the axial part, scaling, collapses etc.
5 Geotechnical Study Area G20 Roquevaire, near Marseille, France
· A steady overall deterioration as time progresses.
The fact that extraction was carried out with the use of explosives has also led to serious fissuring.
Condition of the Mine Roof
Sporadic falls from the roof have been observed, sometimes reaching the clay covering, when swallow holes can then be formed.
Fracturing
Natural fracturing of the site is not a key factor although planes of sub-vertical joints are especially visible in a ring in the pillar surfaces and in the roof. Also some important continuous fractures affect the roof and pillars. Some natural fractures are karstified over a considerable depth and openings of more than a metre can be found. Pockets of dissolution are full of glaze and can lead to severe problems when they open up.
However the most serious problem is general collapse following the spontaneous failure of one or more pillars. This kind of event is particularly evident for the pillars in the deepest sector when they are affected by the natural/fracturing. The most exposed sectors are under Chemin du Baou, where this evolving problem has been in existence for the last five years, as well as to the north-east of the mine. Another problem is linked to the risk of local collapse. This kind of collapse follows the sudden appearance of swallow holes on reaching ground level, or roof falls or the opening up of karstic pockets. Near the highway CD45 and Maison Blanche signs of roof failure can be seen.
3. ADDRESSING THE PROBLEM AT ROQUEVAIRE
3.1 Factors Aggravating the Instability Problem
Hydrogeological conditions
Taking into consideration the topography and the level of the Huveaune, water may saturate the deposit of gypsum, reaching the level of the river, and the galleries may be completely underwater if no pumping is undertaken. This aquifer flows out from the east to the west and is fed from Saint Baume and from rainwater run off from the adjacent highway; the galleries are completely underwater from the second level.
Water enters the galleries from numerous sources including fractures and swallow holes, flowing out from the old mining area to the north and from the south eastern workings. Surface water comes from the watershed of Basseron, which is largely uncontrolled and can percolate through to the galleries. This water may dissolve gypsum and generate some changes in the temperature and humidity which may decrease pillar resistance. Circulation or condensation of water generates karstification, also swelling the clay layers and encouraging movement, as well as opening filled fractures.
Water has been pumped at the second gallery level since the beginning of the mining operation (see Figure G20.4). The pumping system was installed by Les Plâtrières Lafarges, used by the mushroom grower and now the system is maintained by the Commune. The system currently pumps 350-400 cu m per day (per 8 hours). Water analysis shows a complete saturation at 2 grams of sulphate per litre.
The pumping system is helpful because it decreases the saturation of pillars (the resistence decreasing with saturation), but it may have an erosive action because it generates flows of unsaturated water which may in turn dissolve gypsum. In 1974, nearby highway construction work was completed. In 1975, the mushroom grower lodged a complaint against the motorway company (Escota) because the ingress of water in the galleries had increased; rainwater from the highway percolating into the galleries of the mine.
6 Geotechnical Study Area G20 Roquevaire, near Marseille, France
The impact of human activity on ground stability
Vibration generated by human activity undoubtedly plays an important role at this location.
Hydrological conditions
There are between 60 and 80 days of rain a year in this part of France, which are irregularly distributed throughout the season. On some days rainfall is concentrated over a few hours (see figure 5) but the quantity of water per year is usually small - of the order of 70 cm per year, frosts occur on an average of 60 days a year. Regular piezometric measurement (see Figure G20.5) shows that the level of the aquifer remains constant. The decrease during the summer months is caused by the low water level of the River Huveaune and by irrigation.
Socio-economic impacts
The closure of the mushroom farm resulted in 15 redundancies and the loss of an entire harvesting. The operator also had to maintain the pumps, which was a supplementary cost (today the Commune undertakes the maintenance). The highway CD45, which passes directly through the mining area had an average frequency of 980 vehicles per day. The Department for Equipment (DDE) managed to reroute some traffic to reduce the risk. This was not without consequences to the local economy, because the amount of traffic passing through Roquevaire was reduced.
There are other risks in the Commune (flooding and earthquake) which reduce opportunities for development. The topography is very steep and so there is not an easy solution in terms of town planning in this area. The gypsum mine is located quite near the centre of the town, its stabilization will have a major economic impact for the benefit of the Commune.
Impact on the local population and their perception of the problem
Residents of Roquevaire and particularly those living in the vicinity of the old mine were very concerned about the legal situation as set out in the letter from the Mayor (see Appendix G20.2). Seven families had to vacate their homes and to fund the cost of renting premises while their compensation claims were being considered. The mushroom grower had to dismiss 15 employees and still no compensation has been given because the complex legal proceedings are still in progress.
In response to the problem two resident action groups were formed:
1. The group “Zone A” was formed at the end of the year 1994 with the aim of contesting boundaries of the risk area and to highlight to the authorities and to others the fact that authorisation to build in this area should not have been given.
2. The group RADHEE (Roquevaire Association de Défence de L’Habitat de L’Economie et de L’Environnement) was formed in December 1995. Better organised and more active than the group Zone A its aims are to prove the responsibility of the firm Plâtres Lafarges and to restore the mine to a stable condition. This society has been received by the Ministry of the Environment, its actions no doubt influenced the choice of the Ministry not to apply the Law Barnier (see below).
The group has raised funds for a study that has been commissioned from a geologist with respect to the possibility of restoration of the site. In the beginning the problem at Roquevaire was accepted but the slow pace of legal proceedings and the lack of remedial measures has irritated the local population. Two of the families who were required to leave their homes have now returned. Risk studies now proved that two other families have to be moved from their homes but they do not want to leave. Three
7 Geotechnical Study Area G20 Roquevaire, near Marseille, France
affected residents are not allowing access to their properties and this means that remedial works in connection with stabilization of highway CD45 cannot commence.
3.2 Role of Key Agencies
The authority concerned is the Commune of Roquevaire which is located 15km north-west of Marseille.
According to public security (Article L131-2-6 of the Commune’s Statute Book), “the Mayor is responsible for management and all measures required to prevent dangerous situations arising from natural risks. The Mayor of Roquevaire is, therefore, responsible for the on-going management of the risk of this location.
The Prefect of the Département has to make arrangements to enable risks to be understood with the aim of ensuring civilian safety and civil security. He has to follow certain proceedings and can be represented or helped by the following Prefectoral services:
· SDIS (Services in Charge of Fire and Rescue Management) · SIRACED-PC (Service responsible for Civil and Economic Management for Defence and Protection)
The Departmental Road, number 45, which passes through Roquevaire is partly damaged. Therefore the Département through its General Council (Conseil Général), which is in charge of its maintenance, is also a Responsible Authority.
Local Authorities are helped by Local Government services such as:
· DRIRE (Regional Director for Industry Research and Environment) within the Ministry of Industry which is in charge of management of mining activities. · DIREN (Directorate for the Environment) within the Ministry of the Environment which manages the scientific studies for the Plan de Prévention des Risques (PPR). · DDE (Department for Equipment) and DRTE (Directorate of Roads, Transport and Equipment) within the Ministry for Equipment is in charge of maintenance of the road network. This service is helped by a specific laboratory (CETE) for the scientific studies.
Other Organisations Involved
“Les Plâtres Lafarges was the last operator of the mine back in 1960; their activities appear to have been in adherence with the law. The motorway company Escota, has a responsibility because the highway surface water runoff appears to have aggravated the problem. Arguments about the study findings and the return of families to properties at risk show that the perception of risk is not good at this location.
3.3 Role of the Responsible Authorities
Role of The Mayor:
The Mayor is responsible for safety of the public in his Commune. He is in charge of everyday management of risks in three ways by:
· Providing information to the public; according to the law of the 22 July 1987, citizens have a right to information about major risks which may threaten them. · Town planning and construction; The Mayor can refuse permission to build for safety reasons. He can demarcate areas where construction is forbidden or controlled. He can take risks into consideration as part of Town planning.
8 Geotechnical Study Area G20 Roquevaire, near Marseille, France
· Risk management; The Mayor is the permanent administrator for risk in his Commune. To manage risk he has administrative support (see Appendix G20.4) including: - Les Pouvoirs De Police - Police General, and Special Police with respect to derelict buildings. - Proceedings for natural risks; according to the law of 2 February 1995 (Law Barnier) he can evacuate people threatened by natural risk; - Les Procédures De Péril and La Procédure De Catastrophes Naturelles.
The Prefect of the Departement
He is in charge in the Departement for the control and enforcement of Government policy. He is also in charge of the Pouvoir De Police and is the only Authority who can take the place of The Mayor where it is not possible to otherwise afford the management of risks (for example, in the case of a small Commune). The Prefect will keep track of proceedings and is responsible for the demarcation of vulnerable areas (see Appendix G20.5). The Prefect is, therefore, an important mediator during proceedings.
Services of the Government
Ministers are represented at Departement level by local services. The DRIRE, for the Ministry of Industry, keeps record of the control of classified installations such as mines. This service is consulted for consents to build on vulnerable areas because it has in its Record Office maps produced by the Operators. The Prefect has chosen to keep track of PPR proceedings.
The DDE for the Ministry of Equipment; provides support for studying and for demarcating vulnerable zones. The CETE is the Laboratory for this service and undertakes studies and gives advise for demarcation of vulnerable areas. DDE may give authorisation to build on this zone. The DIREN for the Ministry of Environment provides help with dissemination of information and manages Government finances for the study of risks.
Other Assistance
The Conseil Général and the Conseil Régional financially support scientific studies. Roquevaire belongs to the Communauté De Villes De Garlaban-Huveaune-Sainte Baume, which has funded various technical studies.
Remedial Works (from 1991 to the present day)
After the swallow hole appeared on the 28 November 1990, the Mayor commenced procedures to put in place a system for management of risks. A succession of long and difficult proceedings followed with a wide range of studies being commenced to assess the problem. The proposed solutions were aimed to assist the administrative proceedings that would in turn assist compensation payments. In order to do this there were many technical initiatives required in terms of mitigation.
The Course of Events
1. 28 November 1990; a swallow hole appeared resulting in damage to a house in the neighbourhood of Les Plâtrières. 2. 7 March 1991; the Town Council voted to ask the Prefect to envoke proceedings of Article 311/3 of the Town Planning Code. 3. 9 April 1991; report by Mr Deschamps (an independent geologist) with a map of the area of vulnerability (a study commissioned by The Mayor). 4. 1991 - 1993; on-going proceedings for the enforcement of Article R111/3 (public investigation, vote of the Town Council). 5. 13 January 1994; enforcement of the Article with a Prefectoral Order which formally demarcated the vulnerable area (see Appendix G20.5).
9 Geotechnical Study Area G20 Roquevaire, near Marseille, France
6. July 1995; the owner of the mushroom farm commissioned a study from the geologist Mr Deschamps to investigate the technical problem. The results of this study were alarming and the Mayor was informed. 7. August 1995; the Mayor commissioned from Mr Deschamps a study of the area in the vicinity of the highway CD45 and the path Chemin Du Baou. Key findings included: - Imminent risk of collapse for the Chemin Du Baou. - Risk for La Maison Blanche inhabited by five families (Plate G20b). - The threat from an extension of the instability in the mushroom growing area. - The threat of collapse of part of the CD45 highway. 8. 7 August 1995; The Mayor provided the Prefect and the DDE with a copy of the studies. 9. 9 August 1995; by the order of the Town Council, closed the Chemin Du Baou and on the 4 October an order was made to close the highway CD45. 10. 5 October 1995; a meeting was held between the concerned services of the Préfecture, the DDE, the Prefect and The Mayor of Roquevaire. They decided to: - Annul the order of the 4 October 1995 and replace it with an order which would reduce traffic on CD45 to single lane. - To ask for the proceedings of the Law Barnier to be implemented. 11. 8 November 1995; the Prefect formed an action Committee involving the Commune, the Region, the Departement and local services of Government (DRIRE, DIREN, DDE, SDIS, SIRACED-PC). It was decided; that the Mayor should order the closure of all accesses to galleries on private sites and issue a “Mesure De Péril” for the Maison Blanche. The Mayor would also ask for the enforcement of the Law Barnier to start studies for a PPR (Plan de Prévention des Risques) and to obtain compensation for the residents. 12. 15 November 1995; a report of an expert from the tribunal identified the imminent risk to the Maison Blanche and to the mushroom bed. Actions were put in place to enable an order of “Péril grave et imminent” for the Maison Blanche (immediate evacuation of five families), and order of peril for the mushroom growing area (an obligation to stop the mushroom farming). 13. 23 November 1995; distribution of an information note to the inhabitants by the Commune. 14. 9 September 1996; an order of “Péril grave et imminent” is placed on two other properties near the Chemin du Baou because of the results of the studies. 15. 5 August 1997; an order to change the town planning regulations. Until final results of the PPR (Plan de Prévention des Risques) were published, applications on an area where construction would be regulated (see Appendix G20.5). 16. 1996 to September 1998; proceedings for the enforcement of the Law Barnier were in progress. The three Ministries concerned had given a favourable opinion. On 6 March 1998, the Ministry of Environment, which was co-ordinating the Government’s response asked for a legal opinion to define the responsibilities of the Plâtres Lafarges. The Ministry is awaiting the results of this before deciding on the Déclaration d’Utilité Publique (DUP).
This description does not provide every detail of the legal and administrative procedures but summarises the courses of action that have taken place.
3.4 Risk Assessment
Facing a proven crisis situation the responsible authorities have had to manage a day to day problem and so they created a management board to assist this process. The commencement of proceedings for PPR studies requires the creation of a Works Committee and this has been established to assist the development of the follow-up actions at Roquevaire.
3.5 Management of the Crisis
10 Geotechnical Study Area G20 Roquevaire, near Marseille, France
The Management Board is responsible for following-up and the management of technical studies and mitigation measures. Its tasks consist of providing support for the Commune and the demarcation of the vulnerable area and the definition of mitigation measures.
Arising from this a general study has been provided by the Commune to the design office ANTEA (March 1996), this study provides a map of the instability problem. The CETE undertook a study of the Highway CD45 for the Conseil Général and a study on the property Maison Blanche for the government (Ministry of the Environment). In July 1996 CETE completed their study which assessed precisely the risk for every property located in the vulnerable area. This study provided the required information for the property owners concerned. In addition to this the Management Board is responsible for the protection of citizens and mitigation of risk. The Pouvoir de Police, under the instructions of the Mayor, was able to take appropriate enforcement action. The Conseil Général controlled the traffic on the CD45 following implementation of the PPR.
Assistance to residents relocated as a result of hazardous situations has included:
· Re-housing with the assistance of the Prefect and the Mayor. · Intervention to obtain agreement to delay payment of their mortgages to the bank. · Help and advice to the mushroom growing business and its employees. Completion of the PPR
PPR proceedings require the completion of appropriate studies, in particular preparation of a risk map. DRIRE was chosen by the Prefect to manage these proceedings, a Board of Labour defining and supervising the studies. In this case the Board comprised BRGM, SIRIACEDPC, CETE, DRIRE, DDE, INERIS and DIREN.
Natural risks which are mapped, including flooding, earthquakes and ground movements are quantified through resources being made available by the Ministry of the Environment when the Prefecture asks for them, studies are carried out by BRGM, CETE and INERIS.
3.6 Mitigation Measures
Preliminary Investigations
In terms of historical research it was necessary to map the mine galleries in order to provide a history and description of the collapses since 1920, the date of commencement of mining. This involved research at the Municipal Offices, in the Public Records Offices, interviews with local residents and with the mine operator. The Society RADHEE has, in order to try and prove liability of the Plâtres Lafarges assembled a considerable amount of information.
Study of aerial photographs : seven flights of stereoscopic aerial photographs in black and white cover the period from 1932 to 1992. They show the evolution of collapses and have enabled these to be mapped. Inspection of the Mine Galleries : visits to the mine galleries were necessary for this study. They showed the gradual degradation of the mine pillars. This study consisted only of a visual analysis without any quantitive measurement.
Evaluation of the Risk
This work resulted in the definition of those people and properties which were at risk and comprised:
· A small central zone where risk is imminent; Maison Blanche, Chemin de La Baou, highway CD45. · A more important zone where risk is called “major risk” (19 properties). · A peripheral zone affecting between 80 and 100 properties.
The evaluation of the risk has emerged from two studies:
11 Geotechnical Study Area G20 Roquevaire, near Marseille, France
· The study by ANTEA (March 1996) “Secteur des Plâtrières et du Coteau du Nègre-Etude préliminaire de risque”. · A study by CETE and INERIS (July 1997) “Carrières Souterraines de Roquevaire- Niveaux de risque sous les constructions”.
Preliminary Study of Risks (ANTEA)
The aim of this study was to provide a risk map, identifying threatened properties, and an indication of safe areas for people and property (Appendix G20.1). The map consisted of:
· A map of the problem comprising information from various sources, four levels of vulnerability depending on the accuracy of the information. A safety zone of 50 m is applied to high risk areas in order to take account of the possible forms of collapse. When several problems are superimposed it is most important that these are identified on the Land Registry records. · A map illustrating the vulnerability zones. Classes of property are defined each being given a vulnerability index. This index is related to a defined chart established by the Mayor taking account of specific criteria (see Table 1 (a) and (b)). · The publication of a risk map based on the map of Enjeuxl (see Table 1 (a) and (b)).
Assessment of Risks Beneath Buildings (Study by CETE INERIS 1996)
This report comprised a study of every house which is located in Zone A (vulnerable area). For each house a technical brief describes its situation, information about the owners, sub-surface conditions and the potential for evolution of instability as well as giving advice on safety and strength of construction. The risk is qualified by two parameters:
· The intensity perceived taking account of the proximity to the collapse hazard and its consequences. · The probability of an event defined by estimation of time probability based on the state of the galleries and their predicted deterioration.
3.7 Public Works in Progress or Planned
Pumping of Water
This is the major engineering work that is in progress at the present time.
Construction of Pillars
The mushroom grower constructed a number of support pillars, their effectiveness is yet to be proven.
Prevention of Water Leakage and Removal of Surface/Rain Water Run-off
The DDE on behalf of the Commune defined and calculated the necessary work which comprised addressing the question of the fluvial system for highway drainage from the CD45, the drainage system along the CD45 and repairs to leaking pipes. The estimated cost of the work is 9 million francs and tenders are now being sought.
Stability Conditions Beneath Highway 45
Gravel infilling could be possible in some areas. For the time being the Conseil Général has decided to provide support for the CD45 by gravel infilling and has made available the sum of 10 million francs for this purpose. The support of the Chemin du Baou is estimated to cost
12 Geotechnical Study Area G20 Roquevaire, near Marseille, France
between 11 and 15 million francs but at the present time funds have not been allocated. Highway stabilization beneath Maison Blanche is too expensive to be considered. For the other sites a hydrological study must be completed (estimated cost 300,000 FF which will be financed by the Ministry of the Environment).
For the stabilization scheme three methods were considered :
· Caving with controlled collapse of cavities. · Strengthening of the support structures (pillars, cavity roofs etc). · Infilling.
A study by the CETE (January 1996 “RD45 Roquevaire - Recherche de Cavités Minières- Confortement”) concluded that the only reasonable option was infilling. This can be undertaken by injection or gravel filling at an estimated cost of 2,170,000 to 2,730,000 TTC. The gravel infilling is, therefore, the preferred solution for technical and economic reasons and will start shortly for the affected length of the CD45. The study of rehabilitation ordered by the group RADHEE suggests the use of mud baths from the mine of the Gardanne to infill the whole area.
Public Information
Two types of notice are applicable - Orders or Decrees and information to people who are living in the zone or who may wish to build on it.
3.8 The Different Orders Taken Out as Part of Mitigation
Municipal Order
The most important are:
· Imminent peril arising from a building after partial collapse (11.12.90), imminent serious risk and evacuation from the Maison Blanche (17.11.95). · Prevention of access along the Chemin du Baou (9.8.95), closure of the mushroom farming area (17.11.95), continuation of water pumping in the galleries (20.11.95), diagnosis and maintenance of the pumping system (1.7.96, 22.7.96, 24.1.97), publication of the new POS (24.4.95).
Prefectoral Order
This order concerns proceedings of “enquête publique”; “Declaration d’Utilité Publique” necessary to the enforcement of the law:
· “Enquête publique” (for the proceedings to apply article R113-5) 10.2.92. · Demarcation of the vulnerable areas - 13.1.94 (see Appendix G20.5). · Authorisation to occupy temporary parcels necessary for the support of highway CD45 (22.1.97). · Application of a new zone of town planning regulation pending the results of PPR - 5.8.97 (see Appendix G20.5).
Departmental Order (Conseil Général): Regulation of the traffic on highway CD45 (7.6.95)
Information for Residents
The reference document is the POS (Plan of Ground Occupation). The POS for Roquevaire was published on 14.12.97 and formerly agreed on 6.10.98. It contains two references about the mine. The POS ordered “advice from the DRIRE as necessary” with a map which was produced by “Les Plâtrières du Vaucluse”. The POS rule defined “zones with natural risks” which are marked on a map. Authorisation to occupy a parcel of land would be allowed if a
13 Geotechnical Study Area G20 Roquevaire, near Marseille, France
geotechnical study demonstrated that the proposed construction is possible. Furthermore the zones in B, and MD were bounded by controls on rainwater run-off. All these regulations were applied under the order R111/3 in April 1994 (see Appendix G20.5).
Today the Commune indicates that in the vulnerable area, according to legal regulations, every construction is covered by an authorisation which is given by the DDE. Between the year 1993 and 1994 all construction work was forbidden because of the Proceedings R111/3. The POS published on 24.4.95 (agreed formerly on 11.4.96) has the same regulations but the vulnerable area is the zone A of Prefectoral Order 13.1.94, the zone B was not included. The POS was changed by another Prefectoral Order on 5.8.97, to apply in advance of the PPR. The PPR for Roquevaire will be implemented at the beginning of the year 1999.
Communication Measures
During the first events (1995) the Mayor alerted the population and the authorities by a press statement and TV interview on channel FR3. To inform the citizens, a letter was sent to every inhabitant of Roquevaire (see letter in Appendix G20.2). In waiting for the publication of the PPR, the DIREN is organising a publicity campaign.
3.9 Ex-appropriation and Compensation Measures
Law Barnier
The Implementation Board chose to apply the Law Barnier (2 February 1995). This law authorises the ex-appropriation and compensation by the Government of all property threatened by natural risks when the remedial works are too expensive to undertake (see Appendix G20.4).
However, proceedings which started in June 1996, are halted at the level of “Déclaration d’Utilité Publique”, the Ministry of Environment is waiting for the results of a judicial study in relation to this problem. The aims of this study are to identify any liability of the Plâtres Lafarges as the group RADHEE believe. In essence the compensation arising from the implementation of the Law Barnier can only be applied if the occurrence has resulted from natural hazards rather than the activities of the mining company.
Investigation of Liability
The operator of the mine left the site in 1960 and taking account of the law at that time his responsibility may not be limited. However, the provisory conclusion of the DRIRE is covered by the advice of the Ministry of Industry since May 1996 for a judicial review. An investigation of liability is the solution being requested by the group RADHEE. This group has undertaken an important investigation to try and prove the responsibilities of the last operator. The question of liability of the mine owner is governed by the act of the Civil Code. So the administration are not able to deal with this and only the courts will be able to decide on any liability as far as the operator is concerned.
Control of Town Planning in the Vulnerable Zone
For the period from October 1988 (date of the application of the regulation on the risk) to the year 1993, and from April 1994 (date of the application of article R111/3) to the present day, the Mayor agreed 16 planning approvals to build (construction, extension and modifications). According to the Prefectoral Order of 13.1.93 (see Appendix G20.5), this authorisation must be accompanied by a geological study of the underground cavities to a depth of 50 m in the vicinity. Five authorisations over the intervening period have been given by mistake within the vulnerable zone and a further five were not accompanied by a geological study. Six authorisations did have a geological study provided by private design offices. These studies concluded that construction was possible; two of these did not mention the existence of the mine. To confirm the absence of any risk, this local study is not adequate but a regional study
14 Geotechnical Study Area G20 Roquevaire, near Marseille, France
is required which of course is difficult to undertake and very expensive but would bring more reliable results.
For the 1988 to 1993 period and since 1996, the Mines Services of the DRIRE checked 26 files of which 22 received a favourable opinion. These opinions were given based upon maps on which the extent of investigations has not wholly been confirmed. The CETE has identified that there is further information required in relation to the galleries and the thicknesses of covering in the area and, therefore, there is the requirement to assess the risks of the ratio of the height covering/galleries as a first parameter.
3.10 Studies of Demarcation and Evaluation of Risk, and Lessons Leant
Vulnerable Zone
The first demarcation of the vulnerable zone is the one which is in the POS of 1998. Criteria chosen by the DDE are unknown. For a long time this zone was retained for safety reasons even when studies suggested that a smaller more limited zone would be appropriate. Questions about the covering thickness and the cavities showed the subjectivity of estimation of the boundaries. On each occasion it was the technical service of DDE that reflected the boundaries with the help of studies. Therefore the demarcation is a personal interpretation by its author.
Risk Evaluation
The report of the CETE and INERIS presents for each case a situation underground and the risks. 19 houses over an area representing 80% of zone A of the site Les Plâtrières are described (see Prefectoral Order of 13.1.94, Appendix G20.5).
The advantages of this report lie in the fact that it provides a global and systematic study of every house, based on the shared findings of Land Registry plans and mine plans (this information coming from the ANTEA study. Unknown information for example from inaccessible mine galleries, hydrogeology and the thicknesses of cover are still to be investigated.
A form (see Appendix G20.3) is provided for each house with:
· The classification of risk from the study by ANTEA. Classification being based only on the existence of swallow holes or galleries. · A description of the underground conditions. · An evaluation of risk. · Cost of mitigation.
Gravel infilling is most often proposed as mitigation. It is a good solution for roads but for houses more refined operating procedures are usually required (eg. injections, micropiles etc).
Monitoring
Today monitoring is a difficult problem because the support pillars have many structural defects thus posing safety issues. Further investigations are necessary in order that a more co- ordinated approach for monitoring and management of the land parcels is possible. This co- ordination will define parameters, monitoring needs, means and result in terms of a regional solution of mitigation.
Rescue Measures
A particular remedial plan was never defined and is a serious shortcoming which does not improve the perception of risk by the public.
15 Geotechnical Study Area G20 Roquevaire, near Marseille, France
Enforcement of the Law Barnier
Timescale is the major problem with this process. Since its commencement the Minister concerned, the DIREN representative and the Prefect have changed. The expropriated owners have still not been compensated. Though the “Déclaration d’Utilité Publique” should have been proclaimed, a new judicial study has been requested by the Ministry of the Environment. This difficulty with proceedings requires considerable exchange of information between Department level and the Ministries. It does not appear to be a suitable procedure for this problem and creates a number of serious misunderstandings for local government who do not know how to adequately inform the public. The case as Roquevaire will without doubt be the first of its kind in France which considers the management of instability due to mining activities underground. The enforcement of the Barnier Law will be defined as a result of this case.
Information and Communication
In the case of Roquevaire, this is a major problem. The lack of information exists at all levels and this has always been the case. A loss of trust and a negative viewpoint of government actions has caused an angry reaction by the RADHEE group and has led to the return by owners to their properties. This misunderstanding also exists within the Technical Services Department of the Mayor which faces difficulties in applying the risk zones and how to manage the problem. Notwithstanding this the Mayor is very worried by the legal implications and the numerous unanswered questions. Facing a long and difficult proceedings the reaction of those directly affected was not surprising due to the difficulty in comprehending the risks. The Prefect has also faced numerous difficulties in trying to explain why the necessary legal and administrative procedures have taken so long but on the other hand he does not have the power to address adequately the social problems faced by the families who have been requested to leave their homes.
3.11 Action Required
Addressing the Social Problem - A priority
If the Barnier Law is not enforced there are no proceedings other than through the courts to compensate the families and the mushroom growing business affected by the problem. Compensation and remedial solutions will not be dealt with rapidly without negotiations between government services who would be able to help but who are awaiting the results of various legal and other procedures.
Organising an Information Campaign to Address the Risk Problems
Although some stabilization measures have been undertaken at Roquevaire there is still a lack of knowledge of the risks and a range of administrative difficulties faced by the Town Hall. Public information is necessary but needs to be complemented by an education programme for those involved with civil risks. One option would be to develop procedures whereby the Mayor is allowed to make local decisions on the most appropriate action to take in risk situations of this kind.
Risk Mitigation
The lack of co-ordination between the different studies and the individual actions of the groups concerned create a major organisational problem. The Committee charged with remedial works requires reorganisation. The RADHEE group have complained that they have not been adequately consulted or involved. This group commissioned and owns a study which comprises the mapping of the mine galleries and a review of various legal aspects that was not made available to the local government. In order to ensure efficiency a reorganised structure must consider technical competences but also the judicial and social implications.
3.12 Medium-term and Long-term Actions
16
The ANTEA study established the necessity for a better knowledge of the site. In other words a global hydrogeological study is required by the different local interest groups but funding of course remains a problem. In addition to hydrogeological aspects the overall strategic problem must be considered. Local stabilization solutions such as those required for the highway CD45 will not be effective if the overall problem has not been ascertained. In the long term a detailed study of the options for stabilization of the mining area needs to be undertaken. At the present time the law states that for the closure of a mine a study is necessary. These studies, however, take a long time and are expensive to undertake. The issue of payment is outstanding and a modification is, therefore, required to the proceedings of the Barnier Law. In modifying the proceedings of the Barnier Law it will be interesting to develop a productive tool to help those involved with decision-making in the area. The local authority should be the people most capable of leading coherent actions where a risk problem of this kind occurs in the future.
4. CONCLUSIONS
This study shows that the assessment of a risk situation in town planning is essential and this should be undertaken as early as possible after the discovery of the hazard. The problems at Roquevaire have arisen from a series of misunderstandings and as a result of the sudden physical appearance of the cavitation problem although the hazard has existed for many years. The mitigation proceedings initiated by the government (like the PPR) require adaptation and must be changed as soon as possible.
The Mayor and technical staff are not involved closely enough and they often feel that official documents are imposed upon them without proper input leaving many questions remaining unanswered. The mitigation of risk is not only a technical issue for the case at Roquevaire but requires a delicate public relations exercise and information campaign in order that all those in the vicinity are aware of the risks and to ensure that this can be taken into consideration in town planning.
5. BIBLIOGRAPHY
Cairon D., Boennec J.M. Mars 1996. “Secteur des Platrières et du Coteau du Nègre- Etude préliminaire des risques”, Rapport ANTEA Marseille. Lyon G. (CETE), Watelet J.M. (INERIS). Juillet 1996. “Carrières souterraines de Roquevaire, quartier des Platrières-Niveaux de risques sous les contructions”, Rapport CETE Aix En Provence et INERIS. Poteur M. Février 1997. “Rapport d’expertise-Constat Ste Lafarge Platres exploitation carrières”. Pothérat P. Février 1996. “Anciennes carrières de gypse de Roquevaire (13) - Risques d’effondrements associé”, Rapport du LCPC Paris.
17 Figure G20.1 Roquevaire location map. Figure G20.2 Geological situation of Roquevaire. Figure G20.3 Structural plan, Roquevaire. A Est A52 A Ouest
Huveaune RN96 185m 150m 149m 140m 145m 127m Niveau de pompage 115m
10m Echelle : 0m 100m Alluvion de l'huveaune
Formation remaniee (Trias et Oligocene)
Cone torrentiel Wurmien
Urgonien
Kimeridgien
Keuper
Muschelkalk
Figure G20.4 Geological section, Roquevaire. Figure G20.5 Piezometric levels, Roquevaire.
Plate G20a General view of the Roquevaire study area
Plate G20b Maison Blanche (evacuated)
18
Plate G20c Entrance to the gympsum mine at Roquevaire
19
HAZARD Criteria STAKES Criteria RISK Very high Sub-mined and listed High All land units where there is Very fontis zones any building. high
Gypsum zones Public areas, car parks
National or district roads, highly used routes.
Important or strategic networks High Medium Low use roads and sign- posted pedestrian pathways Medium Low Zones not included in the to Low preceding classifications (undeveloped land units and zones outside of roads and pathways) Strong Suspect zones with a This hazard category has not been found. presumption of an exploited or fontis zone. Medium Sub-mined and listed High All land units where there is Quite fontis zones. any building high
Gypsum zones Public areas, car parks
National or district roads, highly used routes.
Important or strategic routes
Medium Low use roads and sign- posted pedestrian pathways Medium
Medium Dubious zones Low Zones not included in the corresponding to zones preceding classifications Medium to which no exploitation (undeveloped land units and to low rights are apparent. zones outside of roads and (archives, direct pathways) inquiries) but where former uses or spaces where things have crumbled away could potentially exist with regard to the geology. Weak Zones in which gypsum This category of risk has not been found. structures are assumed to be absent.
Table 1a Definition of the criteria chosen for the hazards, stakes and risk.
1 Table G20.1 Definition of criteria for risk. Appendix G20.1a Report of the ANTEA study area (see following pages b, c, d and e for sections 1 to 4 of the map). Appendix G20.1b Report of the ANTEA study area. 2
Appendix G20.1c Report of the ANTEA study area. Appendix G20.1d Report of the ANTEA study area. Appendix G20.1e Report of the ANTEA study area. Appendix G20.2a Letter of the Mayor. Appendix G20.2b Map accompanying the Mayor's letter.
Dear Sir/Madam
Following the news given in the press and on TF1 about the zone at risk at Platrières, I was contacted by a number of residents of Roquevaire who were worried about their land or their property. In addition, I was able to record that completely outlandish news is circulating, which will only increase this feeling of unease.
Also, I am keen to put an end to these stories and inform you personally of the reality of the risks and of the real area concerned.
A Prefectoral Order taken on 13 January 1994 delimits a risk zone as a result of the possibility of earth flows in the subsoil during the years when clay was extracted. There is a high risk zone A, where there should be no construction, and a zone B of lower risk for which it is necessary to undertake certain geological studies before obtaining a building permit. The map of these two zones is provided on the reverse of this letter.
With regard to the departmental highway, which is one of the most exposed areas, the General Council, which is competent in this area, has had a number of studies undertaken and, following a meeting in the Prefecture on 8 November has commissioned the DDE to undertake strengthening works. This will cause certain disruptions over several weeks but will be the price of the safety of this highway.
The properties in zones A and B are now the subject of a more detailed analysis of risks which will allow the Prefect to take the necessary safety and legal decisions. You should also know that these studies are expensive as they are long and difficult to undertake. The complete results that will determine the action to take will only be known during the second quarter of 1996. At the current state of investigations, the most exposed property is the White House which, moreover, has just become the subject of a risk order and whose occupants are going to be evacuated and re-housed.
Also, the Baou crossing, which is also situated in this sensitive zone, had to be closed to all traffic. The Commune had a study undertaken to provide a car park at Saint Dominique.
A further serious consequence : the Inspector of Works took the decision to ban all activity in the mushroom factory/shops resulting in the unemployment of 15 people and serious difficulties for this use. There will also be a risk order for this zone which will be hit if there is subsidence by a devastating collapse.
On the request of the Prefect an order was taken to ban access to the factory/shops and all the entrances and exits will be blocked up.
We are doing everything in our power to help the people affected by this drama.
I will keep you informed about how the situation evolves.
Yours sincerely
Henri GANTAU Mayor of ROQUEVAIRE
Appendix G20.2c English translation of the Mayor’s letter.
APPENDIX G20.3
EXAMPLE OF A FORM ISSUED BY THE CETE STUDY
DEPARTMENTAL OFFICE FOR FACILITIES OF BOUCHES-DU-RHÔNE
COMMUNE OF ROQUEVAIRE
Delimitation of zones exposed to ground movements (subsidence) (Article R 111.3 of the urban planning code)
NOVEMBER 1993
1. PRESENTATION REPORT 2. DELIMITATION MAP (as shown in Appendix G20.2(b)) 3. EXAMPLE TECHNICAL SHEET (Appendix G20.3 (a), (b), (c))
DEPARTMENT FOR URBAN PLANNING LAW AND -State Initiatives- 7, avenue du General Leclerc 13332 MARSEILLE - Telephone 91.28.40.40 Commune of Roquevaire Delimitation of zones exposed to ground movements (subsidence) Application of article R111.3 of the urban planning law
PRESENTATION REPORT
For a long time in the Commune of ROQUEVAIRE (Bouches du Rhône) gypsum extraction has taken place, for making plaster. These underground extractions were undertaken by successive owners who have not left trustworthy documents which would allow the tunnels, some of which are really old, to be placed with precision. Although extraction was stopped a while ago, some of these tunnels are still accessible and are used most notably for growing mushrooms; others, of which there are more, are flooded; all show signs of weakness due to the bad organisation of the extraction works, the dilapidated state of the pillars supporting the tunnel roofs, and the natural erosion of the gypsum. Subsidence is already visible on the surface: even if there has not been accidents involving people, buildings have been destroyed or seriously damaged. In the Commune's local development plan (plan d'occupation des sols), certain empty mines have been shown on the maps and it is indicated in the regulation that planning permission can only be granted if it is proven, by a geological study, that the ground can support the planned building. Taking into account certain subsidence, the Municipal Council wanted a better definition of the sectors where this hazard could occur: it commissioned a geologist Mr. DESCHAMPS to undertake a research task. After having analysed a large part of the Commune (320 hectares), he decided on five zones that showed definite subsidence hazard, zones 1 to 4 being the most dangerous. Furthermore, in its sitting on 7th March 1991, the Municipal Council of Roquevaire asked the Prefect, to delimit these hazard zones through application of article R111.3 of the urban planning code. This report was then developed on the basis of the study of the geologist Mr. DESCHAMPS, in which two types of zones were differentiated: - Zone A, within which the hazard is major: no technique can be implemented by the local authority or by a developer: these zones have to be declared as areas where building is not permitted: they correspond to zones 1 and 4 as defined by the geologist; - Zone B, within which the hazard may exist: before all building, a special study must be carried out in order to define the nature of the hazard and the measures to take for protection against it: these zones correspond to zones 2,3 and 5 as defined by the geologist, as well as a band of 50 metres surrounding all the zones (1 to 5) to take into account the depth of the mining works and the morphology in the "inverted cone shape" of the subsidence, of which the angular value is around 45°. The document was subjected to a public inquiry during which the following observations were put forward: The Public Inquirer in his report and his conclusions gave a favourable opinion and proposed that a number of amendments should be made to the document. ROQUEVAIRE Municipal Council, in its sitting on 22nd October 1992, also put forward some suggestions for the definition of the zones and how they should be regulated. All these observations and suggestions were analysed resulting in a reduction of the major hazard zone A1 to classify part of the area in a probable hazard zone B1. These zones A and B are defined in the delimiting plan (item no. 4) and, for each of these zones, special conditions of ground use for building have been set (item no. 5). After approval of the document, these regulations will be added to those contained in the Commune's local development plan (plan d'occupation des sols).
Ph.1 Appendix G20.3 (a) Example of a form issued by the CETE study. Ph.2
Piliers de grande hauteur (8/10m) en limite de l'éboulement de 1971. Zone partiellement l'nondée.
Ph.3
Appendix G20.3 (b) Example of a form issued by the CETE study.
TECHNICAL SHEET NO. (ENGLISH TRANSLATION) 1
Plot Identification No. CS 472 CETE MEDITERRANEE - INERIS
Owner: MILLIARD Denise née HOARAU Date: June 1996
- Technical commentary: geometry: correct archive map isolated tunnel, H _ 5 to 5 m covering _ 40 m geological details: a lot of water coming from a diaclass karst (N 120_) with immediate infiltration across the embankments, probably towards the S.E.
- State of underground works: to the right of the house: good general condition. at the edge: towards the S.E. limit of fallen material from slide in 1971, with pillars in very bad condition and very high (8 - 10 m ) - partially flooded area.
- Opinion on possible development: Development of the subsidence towards the house and possibly eventually up to the road St. Dominique. For the house: low risk of development of a karst towards the surface.
- Proposal for safety procedures: Install water drainage in the entire tunnel up to St. Dominique. Monitor the site. Estimate for works: (15 x 15 x 6) + (15 x 8 x 7) x 450 = 985500 _ 1000000 francs
- Observations: problem already noted in 1941 by the Mines Department taking into account the proximity of the tunnels under the house; water already stated at that time. Seems stable since that date.
Medium hazard. Low degree of uncertainty.
Appendix G20.3 (c) Example of a form issued by the CETE study (English translation of text).
APPENDIX G20.4:
MANAGEMENT OF HAZARDS / PROCEDURES AND REGULATIONS
PREVENTIVE INFORMATION
The public have a right to information about the major hazards which impact upon them in certain zones of the area and about the safety measures that affect them.
Preventive information was established by decree no. 90-918 of 11th October 1990, completed by circulars from 13th December 1993 and 21st April 1994. This decree defines the tasks of those with the responsibility of bringing preventive information to the public: namely, the prefect, the mayor, owners of certain buildings and industry.
1. FIELD OF APPLICATION
These measures affect Communes that have a PPI, a PER, a PSS or R111-3 areas and the Communes exposed to hazards designated by State or prefectorial order.
2. CONTENTS OF THE PREVENTIVE INFORMATION: THE ROLE OF THE PREFECT
Constitution of the CARIP
The regulatory documents for implementing preventive information are established by the Prefect or by a devolved State section designated by the Prefect.
To facilitate the work, the Prefect constitutes a centre for the analysis of hazard and preventive information (CARIP), bringing together the main players within the department (the devolved services, the local partnerships, the associations etc.).
Aim of the CARIP
It will establish: - the list of the Communes affected by a hazard - the hazard and risk maps (in general these are developed by the DDE) - the Departmental Major Hazards Document (DDRM) and the Commune Summary Document (DCS) which comprises information on the hazard and the safety measures at the département and Commune level.
It increasingly plays an advisory role to the Mayor by prefectorial order.
3. DISSEMINATION OF PREVENTIVE INFORMATION: THE ROLE OF THE MAYOR
On the basis of the DCS, the Mayor establishes the DICRIM (Commune Information Document of Major Hazards). The two documents are made available to the public in the town hall.
Furthermore, in order to inform residents living within the hazard zones the mayor establishes a plan for communication and disseminating posters.
In a more general way, he must organise a plan for displaying posters.
4. DISPLAYING INFORMATION ON SITE: THE ROLE OF THE OWNER
The posters, which conform to models ordered by the State, within the framework of the plan established by the mayor are put up by the managers or owners.
COMPULSORY PURCHASE OF AFFECTED PROPERTY
In application of the law of 2nd February 1995, decree no. 95-1115 of 17th October 1995 sets out the regulations relating to the compulsory purchase of property affected by certain major natural hazards threatening human life. It is completed by the inter-ministerial circular of 10th July 1996.
1. FIELD OF APPLICATION
The only hazards concerned are foreseeable ones of ground movements, avalanches or torrential floods, which gravely threaten human life. Furthermore, compulsory purchase is only used provided that measures for the safety and protection of people prove to be more expensive than the cost of compulsory purchase.
2. THE PROCEDURE AND ITS CHARACTERISTICS
This procedure passes through several phases: (i) an administrative phase driving towards the declaration of public use and unlocking the necessary funds, and (ii) a legal phase concerning the compulsory purchase itself (this phase is not developed because it does not interest us).
Initiative for compulsory purchase:
1. The Prefect receives the compulsory purchase proposals from the Mayors, accompanied by evidence brought forward to justify them. They can equally take the initiative themselves. 2. The Prefect proceeds to a first analysis on the basis of which he forms an opinion. 3. The Prefect then sends each compulsory purchase proposal, accompanied by his detailed opinion and the first analysis document, to the minister responsible for the prevention of major hazards. 4. The minister responsible for hazard prevention then decides on the course of action to take in agreement with the ministers responsible for public safety and the economy. 5. In the case of a favourable course of action, the Prefect, at the request of these ministers, undertakes the compulsory purchase (Decree 1995, Art. 2). 6. To this effect he establishes a public inquiry document. In parallel to the development of this document he prescribes the development of a PPR and ensures that the necessary conservation measures are taken, danger orders, refusal of planning permission etc. 7. The public inquiry document is sent to the ministers concerned who will decide on the courses of action to take. If the course of action is pursued, the Prefect initiates the procedure of declaring public benefit.
Preliminary inquiry, Declaration of Public Use (DUP1):
A file subject to public inquiry is opened with an analysis defining the circumstances of time and place which characterise the hazard, the evaluation of the timescale for warning and evacuation of the population, the confirmation that the cost of compensation for compulsory purchase is less than the measures for the protection and safety of the population.
The document is subjected to the opinion of the Commune which has two months to respond. The prefect designates an inquiry commissioner or inquiry commission which opens the preliminary inquiry. If this commission responds favourably, the compulsory purchase and compensation are authorised and managed by the prevention of major hazards funds within the "limit of the resources of the funds".
From the beginning of the public inquiry, no planning permission, nor any administrative authorisation likely to increase the value of the property can be given, when this is not the
1 Déclaration d'Utilité Publique case, the department responsible will be liable for the additional costs resulting from its decision. THE DANGER PROCEDURES
1. EMERGENCY PROCEDURE
This involves an emergency procedure in the event of imminent danger threatening public safety.
The Mayor should (in the absence of a mayor, the prefect ensures the procedure):
- Take the emergency measures to safeguard public safety (closure of roads, evacuation of people etc.); - Warn the owner by registered letter with acknowledgement of receipt and possibly the architect for French buildings (art. R430-26 of the urban planning code); - Make an appeal to the judge of the magistrate's court in order to nominate an expert responsible for examining the problem within 24 hours (art. L511-3 of the code for construction and housing). To forward a copy of the advertisement to the owner with acknowledgement of receipt by post; - If the expert concludes that the danger is not imminent, follow the usual procedure; - If the expert concludes that the danger is imminent, establish an order to take all provisional measures to guarantee safety within a certain timescale fixed from the notification. The verbal process of notification should be drawn up by an officially designated agent.
If the owner does not comply and is responsible, the mayor can automatically carry out the works at the cost of the owner.
ORDINARY PROCEDURE
This concerns a procedure in the event of a non-imminent danger.
The Mayor should (in the absence of the Mayor, the prefect ensures the procedure):
- Visit the houses affected (right of visit of the mayor - art. L511-1-2 of the construction and housing code). - Take out an order to instruct the owner to have the danger stopped on a determined date, by indicating to him the measures to take. (depending on the zone, to possibly take advice from the architect for French buildings). The verbal process of notification should be draw up by an officially designated agent. - If the works are not carried out by the set date, have an expert report drawn up and send it to the magistrates court. - The magistrates court gives a ruling and can authorise the Mayor or the Prefect to automatically undertake the works. The charges are lent by the town council and recuperated from the owner in the form of direct taxes.
THE POWERS OF THE MAYORAL POLICY
Certain judicial techniques allow human losses to be avoided and often material damages to be limited. These techniques are those of general powers to maintain law and order available to the mayor, it is also a question of the policy for buildings threatening to collapse. The coexistence of these two policies, poses a certain number of difficulties in terms of underground hazards.
THE GENERAL POLICY
Insofar as the authority of general powers the mayor can intervene when an underground hazard seems to be on the point of happening. This results from the former article L131/2 of the Commune code, today article 2212/5 of the general code of the code of local authorities. According to this article, the local policy includes care of prevention through appropriate precautions and to stop, through distribution of necessary assistance, accidents and disasters such as mud or rock slides, to urgently provide for all assistance measures and if necessary, to prompt the intervention of a higher department. This general text will apply such that another more precise text such as that of buildings threatening to collapse does not apply. Furthermore this article 2212/5 should be applicable to undeveloped areas. In this way, when the danger emanates from the threat of a talus or hill slide and even if the threat is on buildings downslope, this is the article that applies. The mayor can intervene under the general powers.
The mayor would therefore be bound to prescribe that safety measures be carried out which would comprise the following depending on circumstances, and case law provides a certain number of examples:
- in raising ground to form an embankment, - in the construction of a supporting wall, - or in a general way in the adoption of appropriate measures.
All the same when it is the ground itself that presents a hazard, the general policy applies. These powers of the general policy also apply when the hazard directly threatens a building. In order for this article to apply, the hazard must be outside the building.
The cause of the hazard should not result:
- in a building fault - in a construction fault - or in a fault in the foundations.
So, for example, this could be ground movement outside a building consisting of a landslide, an earthquake, subsidence attributable to underground watercourses or floods. The interest of this general policy is that it gives extended powers to the mayor. The mayor could order the demolition of the building or prescribe works on private properties.
But if these works have a collective interest, they must be undertaken on behalf of the community and it should pay.
The owners are bound to accept the works being undertaken but it is not up to them to undertake them nor to cover the cost of them. In reality, the real difficulty, from a legal point of view, comes from working out the origin of the danger. The general policy only applies if the cause of the risk is exclusively natural and yet, it is not difficult to work out the origin of the danger in the majority of natural disaster or natural hazard cases. On the contrary, in terms of underground risks, the difficulty comes from the labyrinth of possible causes be they natural causes or human causes which cause a ground movement. When the cause of danger is not exclusively natural, the special policy of buildings threatening to collapse applies.
2. THE SPECIAL POLICY OF BUILDINGS THREATENING TO COLLAPSE
This policy first and foremost, gives the mayor under article L511/1 of the construction code the possibility of prescribing the repair or demolition of the walls, buildings or structures such that when they are threatening to collapse and that they could, if they collapsed, compromise safety. The powers of the mayor in this regard, are extended but this procedure is inconvenient in that it takes quite a long time to bring about. In addition to this article, there is article L511/3 of the construction code which allows the mayor through an accelerated procedure, in cases of imminent danger, to order the necessary measures to guarantee the safety and notably the evacuation of the building.
In terms of this emergency procedure, the powers of the mayor are less extensive than in the case of the general policy. He can, however, order for a building to be evacuated and strengthened. However, he cannot order either the restoration of the building, or its demolition, except in exceptional circumstances.
Case law will consider that the policy for buildings threatening to collapse can be used when the cause of the risk is inside the building. Such is the case, for example, when a collapse is due to a fault in the water drainage system or a fault in the foundations. But this procedure for buildings threatening to collapse would also be used in cases where the causes are both natural and human.
Some examples from case law:
- in the case of disorder due to subsidence of the earth on which the building was constructed such as a lack of special foundations in an area situated above an old non consolidated quarry. - in the case of the collapse of a building not adapted to a ground stratum composed mainly of gypsum and rendered fragile and unstable by the presence of old underground tunnels of a disused gypsum quarry. - in cases where ground movement is due to mining installations.
However, if natural causes are mixed with human causes, the human cause does not have to be the act of the owner concerned or even his predecessors. Likewise, any human activity which leads to a hazard enables use of the policy of buildings threatening to collapse, and in extreme cases, if the cause of collapse can be tracked down to seepage from the drains of the Commune or even in works undertaken by the Commune itself, this procedure applies.
This case law which makes the owner responsible for the cost of the repairs will present serious disadvantages in terms of underground hazards. It could be justified or at least explained by article 552 of the civil code which states that the owner of the ground takes ownership of what is below. Consequently, an owner is supposed to buy his subsoil at the same time as his property whether he knows or not. The local elected members, when they have to make a decision, can largely be ignorant, as can the owners, of what the causes of collapse hazards are. There is some uncertainty in terms of the legal course to follow and, this uncertainty is all the more regrettable as the error of the choice in procedure, and therefore the error in the choice of policy, leads to it being cancelled by administrative tribunals.
Faced with this uncertainty, the appeal court in Lyons in an order in 1991, city of Lyons, proposed a quite innovative solution. The hazard of buildings collapsing was due in this case neither to a construction fault nor a fault in the maintenance of the building but stated torrential rain, as the natural cause and the collapse of underground tunnels. The court considered that the great depth of the said tunnels, as well as their age, meant that their collapse should be regarded as a natural accident, regardless of who the owners were.
THE HAZARD PREVENTION PLANS (P.P.R.2)
The PPR instituted by law no. 95-101 of 2nd February 1995, modifying the law of 22nd July 1987, delimits the zones exposed to foreseeable natural hazards. They also set out the preventive measures to be implemented by the owners and local authorities or public bodies.
1. FIELD OF APPLICATION AND AIMS OF THE PPR
This procedure applies to foreseeable natural hazards such as floods, ground movements, avalanches, forest fires, earthquakes, volcanic eruptions, storms or cyclones.
The PPR can prohibit or subject to special conditions, within delimited areas, buildings, works, property or activities either because they would be exposed to hazards, or because they could aggravate them nor cause them to start again.
The aims are:
- to no longer increase the number of buildings and new developments built in vulnerable areas; - to reduce the vulnerability of those that are already in exposed areas; - to neither aggravate the hazards or cause them to start again.
The PPR can also define or impose on the local authorities and private individuals other measures such as measures to facilitate the intervention of assistance, to impose the prescriptions on private individuals.
Certain measures can apply to buildings already constructed such that the cost of the works does not exceed 10% of the value of the building.
2. DEVELOPMENT AND IMPLEMENTATION OF THE PPR
It comes from decree no. 95-1089. The State is responsible for the development and implementation of the PPR. The prefect prescribes the consideration of the PPR, he defines the area considered, the nature of the hazards taken into account and the decentralised State department responsible for preparing the PPR.
The draft plan is subjected to a public inquiry and circulated to the Communes for comment (the public inquiry procedure is the same as that for compulsory purchase).
After consulting the general and regional councils and the Communes the plan is approved by prefectoral order. It may have been modified to take into account the views expressed.
Anticipated application of certain measures
During its development and if urgent enough, the Prefect can immediately challenge certain clauses of the draft PPR.
Contents of the PPR
The plan comprises three documents: - a presentation note indicating the geographic area concerned, the nature of the natural phenomena taken into account and their possible consequences given the state of knowledge.
2 Plans de Prévention des Risques - graphical documents, showing the zones where the PPR regulations apply. - the regulation that determines the rules for prohibition and prevention, which are applicable in the zones under consideration.
Implementation of the PPR
The PPR is a constraint on public use which must be appended to the POS and applies to all public or private individuals:
- who want to undertake building works or new developments - who, as existing owners or managers of property or activities installed before the PPR, must conform to what is prescribed within it.
In all cases, the provisions of the PPR should be respected when granting planning permission.
The provisions of the PPR should figure in annexe to the POS, if the mayor fails to do this, the prefect appends them to the POS without consultation.
COMPENSATION FOR NATURAL DISASTERS
Law no. 82-600 of 13th July 1982 set as an objective the compensation of victims of natural disasters founded on the principle of national solidarity.
1. AIM OF THE LAW
Insurance contracts which cover fire damage or damage to property located in France as well as damage to the body of terrestrial motor vehicles opens up the right for cover against natural disasters.
In order for the threat to be covered under "natural disasters", the natural cause has to be the determining cause and of an abnormal intensity.
2. FIELD OF APPLICATION
The risks covered are those that are not usually covered by classical insurance rules (floods, water seepage, mud slips, slides, collapses etc.)
The property covered are furniture, buildings etc. insured against fire damage or all other damage, belonging to physical or mental people different from the State and being subject to direct material damage.
3. THE PROCEDURE FOR DECLARING A STATE OF NATURAL DISASTER
The state of natural disaster, which opens up the right for cover is declared by an inter- ministerial order which determines the zones and the timescales where the disaster is located, as well as the nature of the damages resulting from it and covered by insurance.
Development of the document
When a event happens that is likely to be a natural disaster, the prefect of the department warns the Direction de la Sécurité Civile (DSC) (civil safety department) by telex, then he sends him a written report within one month.
The inter-ministerial commission
This brings together representatives from the ministry of the interior and the economy, who form a consultative opinion about the abnormal intensity of the natural cause before an order is made.
4. REGULATION OF THE DAMAGES
Insured persons should declare their damages within 10 days following the publication in the Official Journal of the inter-ministerial order, and within 30 days for loss of use.
The amount and conditions of the regulation come from the clauses of the "basic contract".
APPENDIX G20.5
PREFECTORAL ORDER TO ENFORCE ARTICLE R 111/3
PREFECTORAL ORDER TO ENFORCE BY ADVANCE PPR DEMARCATION
PREFECTURE OF BOUCHES DE RHONE FRENCH REPUBLIC
Office for Decentralised Affairs
Departmental Office for Facilities
ORDER DELIMITING THE AREAS EXPOSED TO GROUND MOVEMENTS (SUBSIDENCE), WITHIN THE TERRITORY OF THE COMMUNE OF ROQUEVAIRE
The Prefect of the Provence, Alpes, Côte d'Azur Region Prefect of the Bouches du Rhône Officer of the Legion of Honour
WITH REGARD TO the urban planning code and, notably, article R-111.3,
WITH REGARD TO the prefectorial order dated 19th February 1992 prescribing on the territory of the Commune of ROQUEVAIRE a public inquiry prior to the delimitation of a ground subsidence hazard zone,
WITH REGARD TO the observations presented during the course of the inquiry,
WITH REGARD TO the deliberation on 22nd October 1992, by which the Municipal Council of ROQUEVAIRE gave its opinion on the provisions to take in the subsidence area,
WITH REGARD TO the favourable decision of the Departmental Director for Facilities, on 23rd November 1993,
CONSIDERING that a party within the area of the Commune of ROQUEVAIRE is exposed to natural hazards in terms of hazards of ground subsidence,
CONSIDERING that it is agreed as a result to prohibit buildings or subject them to special conditions when they are authorised,
ON the proposition of the Secretary General of the Prefecture of Bouches de Rhône,
ORDER
ARTICLE 1: the grounds of the Commune of ROQUEVAIRE exposed to natural hazards (subsidence) are delimited conforming to the plans appended to this order,
ARTICLE 2: The level of hazard taken into consideration corresponds to zones A (major hazard) and B (probable hazard),
ARTICLE 3: Appended to this order are the special conditions of ground use for building within zones A and B,
ARTICLE 4: This order will be inserted in the appendix to the plan d'occupation des sols (detailed local plan) of the Commune of ROQUEVAIRE; it will be made available to the public during office opening hours:
- at the ROQUEVAIRE town hall, - at the Prefecture of Bouches de Rhône, Place F, Baret, - at the Departmental Office for Facilities, Planning Law and Litigation Office in Marseilles, 7, avenue du General Leclerc,
ARTICLE 5: The secretary general of the Prefecture of the Bouches de Rhône, The mayor of the Commune of ROQUEVAIRE, The Departmental Director of Facilities of the Bouches de Rhône, are responsible, to each person it may concern, for the enforcement of this order, which will be published in the compendium of the official proceedings of the State and mention of which will be made in large print in the newspapers "Le Provencal" and "Le Meridional".
PREFECTURE OF BOUCHES DE RHONE FRENCH REPUBLIC
Office for Local Authorities and Environment Marseilles, 5th August 1997
ORDER PRESCRIBING THE MODIFICATION OF A FORESEEABLE NATURAL HAZARD PREVENTION PLAN WITHIN THE COMMUNE OF ROQUEVAIRE
The Prefect of the Provence, Alpes, Côte d'Azur Region Prefect of the Bouches du Rhône Officer of the Legion of Honour
WITH REGARD TO the law no. 87.565 of 22nd July 1987 relating to the organisation of civil safety, to the protection of forests and the prevention of major hazards, notably its articles 40.1 to 40.7 resulting from the law no. 95.101 of 2nd February 1995 relating to the reinforcement of the protection of the environment;
WITH REGARD TO the prefectorial order dated 13th January 1994 delimiting the areas exposed to the ground movement hazards (subsidence) within the Commune of ROQUEVAIRE;
WITH REGARD TO decree no. 95.1089 of 5th October 1995 relating to the foreseeable natural hazard prevention plans;
CONSIDERING that the plan annexed to the order of 13th January 1994 should be rectified to take into account the complementary geological studies recently undertaken;
ON the proposition of the Secretary General of the Prefecture of Bouches de Rhône,
ORDER
ARTICLE 1: the modification of areas exposed to known subsidence conforming to article R111-3 of the urban planning code and validating the foreseeable natural hazards plan, is stipulated within the territory of the Commune of ROQUEVAIRE
ARTICLE 2: the area under consideration is delimited on a 1:25 000 map appended to this order.
ARTICLE 3: the Departmental Office for Facilities of the Bouche du Rhône is responsible for initiating and developing the plan.
ARTICLE 4: This order will be published in the compendium of the official proceedings of the State in the Département and mention will be made in large print in the following two newspapers: - Le PROVENCAL - Le MARSEILLAISE
ARTICLE 5: certified copies of this order will be sent to: - the Mayor of the Commune of Roquevaire, - the Director for the Prevention of Pollution and Hazards, - the Regional Director for Industry, Research and the Environment, - the Regional Director for the Environment, - the Departmental Director for Agriculture and Forestry, - the Departmental Director for Facilities, - the Departmental Director for Civil Safety.
ARTICLE 6: This order and the map that is attached to it are made available to the public in the following offices: - Roquevaire town hall - the Prefecture of the Bouches du Rhône, Place Félix Baret.
ARTICLE 7: The secretary general of the Prefecture of the Bouches de Rhône, The mayor of the Commune of ROQUEVAIRE, The Departmental Director of Facilities of the Bouches de Rhône, are responsible, to whom it may concern, for the enforcement of this order.