Papers by Sebastien J N M Martial
Underground Injection Science and Technology
Publisher Summary In regard to the deep-well injection of liquid waste by the Savanna Distillery ... more Publisher Summary In regard to the deep-well injection of liquid waste by the Savanna Distillery that occurred from 1992–2001, lateral and upstream surveys show no evidence of any contamination coming from the injection well. In the case of this distillery, the purpose was to constrain the hydrogeological setting of the aquifer after these 10 years of injection, which should then help determine how different factors explain both the current and future evolution of the waste management methods used. Because of the scarcity of extensive impervious layers, confined aquifers are not common in recently formed volcanic islands. The marine ecological survey describes a slight and progressive enrichment of the sediment at a depth of 120 m. The survey data are consistent with the hypothesis of a slow migration toward the outlet of a confined aquifer, 2 km from the shore, where the effluent that reaches the ocean has been diluted by surrounding native water and degraded by means of underground microbial activity. The numerical simulation of the system must deal simultaneously with the native water, injected effluent, saline intrusion, and gases produced.
Geotechnical Report Feasibility Geotechnical Assessment for a Proposed Multipurpose Development a... more Geotechnical Report Feasibility Geotechnical Assessment for a Proposed Multipurpose Development at Domaine Les Pailles, Mauritius.
On the 26th April 2014 a rock block of approximate volume 15m3 (about 40MT) fell on the B9 Road a... more On the 26th April 2014 a rock block of approximate volume 15m3 (about 40MT) fell on the B9 Road at Macondé, south west of Mauritius. The site is located on the sea shore, in the area of the Rivière du Cap and Baie du Cap.
The consultancy services for Mitigation for Rockfall at Macondé (Procurement MPI/QU 39 of 2014) were awarded by the Ministry of Public Infrastructures, National Development Unit, Land Transport & Shipping (MPI) to GEoTechnical Services Ltd (GETS).
A literature review of rockfall engineering is provided in the report.
The preliminary identification of unstable rocks and boulders has been carried out until 29th May 2014. A first report has been submitted accordingly, estimating about 200MT to be removed from the cliff. The areas to be cleared are 220m on the western slope and 80m on the eastern slope, the height of the cliff varying from 25 to 50m.
Purging works have been carried out by ROCS SARL with an estimate of about 460MT eventually removed.
Following purging, recommended works that remain to get implemented are:
The creation of a rock falls trap at the northern part of the western cliff
- The implementation of a fencing to restrict access to the foot of the western cliff on its southern part, to discourage pedestrian walking and car-parking on this side of the road
- The re-alignment of the B9 road on the eastern side of Macondé
- The implementation of protective netting at the apex of the cliff.
Buffer area on the eastern side to be landscaped accordingly to increase road protection.
- Preventive purging could be considered as the cost effective method to mitigate rock falls, but not providing permanent protection and involving uncertainty regarding required frequency. Preventive purging could be performed off peak hours (10AM-3PM) within 8 working days, with full closure of the road, for a budget estimate of Rs1.5M for each intervention.
- Implementation of permanent protective netting is also considered for a total area covered of 3,100m2, involving at least 9 weeks works with single lane traffic required. Budget estimate for this works is evaluated to Rs8.6M for a lifetime of about 20 years, which therefore becomes also economically favourable on the long term. Purging should however been considered for areas not covered by permanent protective equipment, as a way to monitor the evolution of weathering and fracturation processes.
This Report was commissioned to evaluate additional fresh groundwater potential supply for Villas... more This Report was commissioned to evaluate additional fresh groundwater potential supply for Villas Valriche. A review of available literature and documentation regarding groundwater resources in the area show that there is a global potential for groundwater extraction. Rainfall distribution and soil lithology contributes to provide a significant recharge to the watershed of Chamarel-Bel Ombre-Frederica.
Detailed study from boreholes drilled in the area and field investigations revealed that:
- There is a groundwater potential in some areas (BH2/BH4 ; Biofarms/Belle Riviere) while some other provide less potential (BH1/BH3)
- Understanding the hydrodynamical conditions at the west gate of Villas Valriche is the key to properly assess the groundwater resources in the area.
- The Bel Ombre fault (N163) is most probably acting as a conduit to groundwater flow
- Field investigations showed that groundwater probably springs out in River St Martin, with water table meeting topographical elevation, hydraulic gradient being adjusted accordingly to reach a relative flat pattern as from West Gate area
It is recommended that:
- Future boreholes investigations are focussed upstream from Bel Ombre fault N163, north of West Gate, if possible as closely as possible from the river, which corresponds to the location of the fault N163.
- Extraction of groundwater from a borehole located there will definitely have an impact on flowrate in River St-Martin, and appropriate extraction rate following pumping test will have to be defined accordingly.
- Additional shallow wells are not recommended at the lower part of the domain, unless extraction rate remains very small, as they would be fed with little recharge, mainly from the river nearby, and the risk of inducing salinization is high.
This report was commissioned to evaluate presence of potential cavities (lava tubes) and their im... more This report was commissioned to evaluate presence of potential cavities (lava tubes) and their impacts with regards to design of foundations for the new Discovery Centre at Casela Nature Park, located on the west coast of Mauritius island.
A literature review explained the mechanism of formation of lava tube and its collapse, and where lava tubes have been described in Mauritius.
Presence of cavities was assessed through the analysis of logs of 57 coreholes. Stress analysis calculated at 4m and 8m deep beneath foundations (where minor cavities have been encountered) show that minimal stress will reach the depth of potential deeper (around 6m depth) weak soil or cavities.
The aims of the works are to increase the capacity of a pond and upgrade its water retention perf... more The aims of the works are to increase the capacity of a pond and upgrade its water retention performance by increasing the depth of the reservoir and installing a new impermeable composite geotextile liner. However, water seepage has been encountered upon digging the pond deeper. This report addresses the hydrogeological conditions of the site and bring recommendations to mitigate the detrimental consequence of seepage to integrity of the liner.
Developments in Water Sciences, 2005
ISBN: 9780080457901
L'ÎLE MAURICE FACE À SES NOUVEAUX DÉFIS (Jean Michel Jauze), 2008
ISBN : 978-2-296-05037-2
Thesis Chapters by Sebastien J N M Martial
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Papers by Sebastien J N M Martial
The consultancy services for Mitigation for Rockfall at Macondé (Procurement MPI/QU 39 of 2014) were awarded by the Ministry of Public Infrastructures, National Development Unit, Land Transport & Shipping (MPI) to GEoTechnical Services Ltd (GETS).
A literature review of rockfall engineering is provided in the report.
The preliminary identification of unstable rocks and boulders has been carried out until 29th May 2014. A first report has been submitted accordingly, estimating about 200MT to be removed from the cliff. The areas to be cleared are 220m on the western slope and 80m on the eastern slope, the height of the cliff varying from 25 to 50m.
Purging works have been carried out by ROCS SARL with an estimate of about 460MT eventually removed.
Following purging, recommended works that remain to get implemented are:
The creation of a rock falls trap at the northern part of the western cliff
- The implementation of a fencing to restrict access to the foot of the western cliff on its southern part, to discourage pedestrian walking and car-parking on this side of the road
- The re-alignment of the B9 road on the eastern side of Macondé
- The implementation of protective netting at the apex of the cliff.
Buffer area on the eastern side to be landscaped accordingly to increase road protection.
- Preventive purging could be considered as the cost effective method to mitigate rock falls, but not providing permanent protection and involving uncertainty regarding required frequency. Preventive purging could be performed off peak hours (10AM-3PM) within 8 working days, with full closure of the road, for a budget estimate of Rs1.5M for each intervention.
- Implementation of permanent protective netting is also considered for a total area covered of 3,100m2, involving at least 9 weeks works with single lane traffic required. Budget estimate for this works is evaluated to Rs8.6M for a lifetime of about 20 years, which therefore becomes also economically favourable on the long term. Purging should however been considered for areas not covered by permanent protective equipment, as a way to monitor the evolution of weathering and fracturation processes.
Detailed study from boreholes drilled in the area and field investigations revealed that:
- There is a groundwater potential in some areas (BH2/BH4 ; Biofarms/Belle Riviere) while some other provide less potential (BH1/BH3)
- Understanding the hydrodynamical conditions at the west gate of Villas Valriche is the key to properly assess the groundwater resources in the area.
- The Bel Ombre fault (N163) is most probably acting as a conduit to groundwater flow
- Field investigations showed that groundwater probably springs out in River St Martin, with water table meeting topographical elevation, hydraulic gradient being adjusted accordingly to reach a relative flat pattern as from West Gate area
It is recommended that:
- Future boreholes investigations are focussed upstream from Bel Ombre fault N163, north of West Gate, if possible as closely as possible from the river, which corresponds to the location of the fault N163.
- Extraction of groundwater from a borehole located there will definitely have an impact on flowrate in River St-Martin, and appropriate extraction rate following pumping test will have to be defined accordingly.
- Additional shallow wells are not recommended at the lower part of the domain, unless extraction rate remains very small, as they would be fed with little recharge, mainly from the river nearby, and the risk of inducing salinization is high.
A literature review explained the mechanism of formation of lava tube and its collapse, and where lava tubes have been described in Mauritius.
Presence of cavities was assessed through the analysis of logs of 57 coreholes. Stress analysis calculated at 4m and 8m deep beneath foundations (where minor cavities have been encountered) show that minimal stress will reach the depth of potential deeper (around 6m depth) weak soil or cavities.
Thesis Chapters by Sebastien J N M Martial
The consultancy services for Mitigation for Rockfall at Macondé (Procurement MPI/QU 39 of 2014) were awarded by the Ministry of Public Infrastructures, National Development Unit, Land Transport & Shipping (MPI) to GEoTechnical Services Ltd (GETS).
A literature review of rockfall engineering is provided in the report.
The preliminary identification of unstable rocks and boulders has been carried out until 29th May 2014. A first report has been submitted accordingly, estimating about 200MT to be removed from the cliff. The areas to be cleared are 220m on the western slope and 80m on the eastern slope, the height of the cliff varying from 25 to 50m.
Purging works have been carried out by ROCS SARL with an estimate of about 460MT eventually removed.
Following purging, recommended works that remain to get implemented are:
The creation of a rock falls trap at the northern part of the western cliff
- The implementation of a fencing to restrict access to the foot of the western cliff on its southern part, to discourage pedestrian walking and car-parking on this side of the road
- The re-alignment of the B9 road on the eastern side of Macondé
- The implementation of protective netting at the apex of the cliff.
Buffer area on the eastern side to be landscaped accordingly to increase road protection.
- Preventive purging could be considered as the cost effective method to mitigate rock falls, but not providing permanent protection and involving uncertainty regarding required frequency. Preventive purging could be performed off peak hours (10AM-3PM) within 8 working days, with full closure of the road, for a budget estimate of Rs1.5M for each intervention.
- Implementation of permanent protective netting is also considered for a total area covered of 3,100m2, involving at least 9 weeks works with single lane traffic required. Budget estimate for this works is evaluated to Rs8.6M for a lifetime of about 20 years, which therefore becomes also economically favourable on the long term. Purging should however been considered for areas not covered by permanent protective equipment, as a way to monitor the evolution of weathering and fracturation processes.
Detailed study from boreholes drilled in the area and field investigations revealed that:
- There is a groundwater potential in some areas (BH2/BH4 ; Biofarms/Belle Riviere) while some other provide less potential (BH1/BH3)
- Understanding the hydrodynamical conditions at the west gate of Villas Valriche is the key to properly assess the groundwater resources in the area.
- The Bel Ombre fault (N163) is most probably acting as a conduit to groundwater flow
- Field investigations showed that groundwater probably springs out in River St Martin, with water table meeting topographical elevation, hydraulic gradient being adjusted accordingly to reach a relative flat pattern as from West Gate area
It is recommended that:
- Future boreholes investigations are focussed upstream from Bel Ombre fault N163, north of West Gate, if possible as closely as possible from the river, which corresponds to the location of the fault N163.
- Extraction of groundwater from a borehole located there will definitely have an impact on flowrate in River St-Martin, and appropriate extraction rate following pumping test will have to be defined accordingly.
- Additional shallow wells are not recommended at the lower part of the domain, unless extraction rate remains very small, as they would be fed with little recharge, mainly from the river nearby, and the risk of inducing salinization is high.
A literature review explained the mechanism of formation of lava tube and its collapse, and where lava tubes have been described in Mauritius.
Presence of cavities was assessed through the analysis of logs of 57 coreholes. Stress analysis calculated at 4m and 8m deep beneath foundations (where minor cavities have been encountered) show that minimal stress will reach the depth of potential deeper (around 6m depth) weak soil or cavities.
The detailed analysis, through automated continuous data logging on D8, showed that the rise of water level could be as high as 1m per hour and reflecting a behaviour that could be analogue to those observed in surface water flooding events.
The geometry of the outbreaks from the common recharge zone is suspected to be among the reasons that contributes to this unusual behaviour. However, the permeability contrast between Old Lavas Series and Intermediate Lavas Series is not expressly established in order to draw such conclusion.
The site works were carried out between Monday 18th August 2014 and Wednesday 27th August 2014 and included the implementation of Health and Safety measures and the coordination with the various state holders and security and transport institutions.
A total of about 335MT of unstable rocks and boulders were purged and carted away over the 3No sites, the details per site are:
Chamarel, an estimate of 180 to 200MT
Souillac, an estimate of 50 to 55MT
GRSE, an estimate of 80 to 100MT
These works have decreased the risk of rock falls. However, weathering and fracturation are dynamic process and are expected to continue. Hence, regular monitoring of these sites is recommended, ideally with preventive purging operation to be carried out following summer rainy seasons.
This Report describes the purging activities carried out, the means and methods employed and outcome of the works in terms of weight of removed rocks at each of the three sites. The Report includes extensive photographic records of rock removal, carting away and cleaning operations.
Proposed strategy is:
- The use of surface water should be encouraged instead of groundwater as the potential volume is greater.
- Groundwater should however been considered to ensure minimal supply when surface water quality become inadequate for domestic purpose, relatively frequent intense rainfall events contributing to high turbidity.
- Use water intake from Rivière des Anguilles in order to supply Gros Ruisseau, upgrading system if necessary.
- Drilling of a first backup borehole at Gros Ruisseau and proceed to pumping tests, if possible during dry season (Oct/Nov).
- Use of water from Ruisseau des Chevrettes to supply Bois Sec area (via a pipe crossing Avalon Golf Estate over about 2km)
- Drilling of a second borehole at the northern extremity of Talusseau domain.