[GEOTECHNICAL SURVEY]

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Winifred Barrett
5 years ago
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1 COMPAGNIE DE BEAU VALLON LIMITEE SUBDIVISION of LAND AT RICHE EN EAU, ST HUBERT [GEOTECHNICAL SURVEY] Rue De La Canelle Ebene City Ebene Tel/Fax No: (230) October 2015

2 2 GEOTECHNICAL INVESTIGATION Client: Compagnie de Beau Vallon Limitée Location: Riche en Eau, St-Hubert Date of investigation: Friday, 16 th October INTRODUCTION The proponent Compagnie de Beau Vallon Limitée is submitting an Environmental Impact Assessment (E.I.A) Report to the Department of Environment in a view to subdivide a plot of land into 73 residential lots at Riche en Eau. We have excavated 3 Nos. trial pits on the proposed site to carry out percolation tests as per BS 6297 in order to determine the onsite disposal system and the soil description of the soil strata in the pits. We, Kaselor Ltd, Civil, Structural and Environmental Engineering Firm, have been appointed by the Promoter to carry out a Geotechnical Survey/Engineering Report for the project. A geotechnical investigation was carried out on Friday, 16 th October The primary goals of the survey are: Description of the soil profile down to a depth of 3 m Percolation test carried out in the pit Level of water table

3 3 2 SITE GEOLOGY Volcanic deposits which formed the Island through a series of three basaltic lava flows, 8 9 million years ago, 200,000 years ago and 20,000 years ago, respectively, dominate the geology of Mauritius. The soil in Riche en Eau, St-Hubert belongs to Low Humic Latosols and Humic Latosols Soils. The geology of Mauritius is mainly composed of basaltic lavas which originate from volcanic origin. The Food and Agriculture Organisation (FAO) and Mauritius Sugar Industry Research Institute (MSIRI) Land Resources and Agricultural Suitability Map of Mauritius identifies the site for proposed development as forming part of the late lavas of the younger volcanic series which erupted from a chain of some 20 vents. The FAO/MSIRI map classifies the different regions into land units. The proposed site consists of Land Unit namely 3.2 as indicated on Figure 1.

4 4 SITE Figure 1: Site Geology 2.1 GEOLOGICAL CHARACTERISTICS The project site falls within the Eastern and Southern Intermediate Lava Plains and Slopes. This type of soil is characterized as moderately deep to deep, dark brown silty clay loam.

A. The project site is partly under cane cultivation and partly under vegetation as shown on the

5 5 3 SITE DESCRIPTION The project area is situated in the District of Grand Port. The location plan of the proposed development site is shown on the accompanying drawing at Annex A. The project site is partly under cane cultivation and partly under vegetation as shown on the plates below: Plate showing project site under sugarcane cultivation Plate showing project site under vegetation

6 6 The project is subdivided into 73 lots of extent 10ha 5,097.07m². All the proposed lots will be developed for residential purposes only with an average daily water consumption of 1.0 m 3 /day. In order to determine the soil profile along with its percolation rate, three (3) trial pits (of depth approximating to 3 metres) have been excavated on the proposed site. The location of the pits is indicated in the accompanying site plan at Annex A. 4 SOIL PROFILING 4.1 TRIAL PITS A typical soil profile for trial pits is provided at Annex B. The soil in Trial Pits is characterized by Horizon A which is 300mm of top soil materials which merges into Horizon B which is 2800mm compacted dark brown clayey soil mixed with weathered basalt. No trace of water was found in the pit. 5 PERCOLATION TEST Each pit has been excavated with the dimensions of 3300mm length, 3200 mm breadth and 3100mm depth. Then below the invert level of each trial pit, a square hole of dimension 300mm with a depth of 300mm has been excavated in the trial pit. On the eve of the test that is the 15 th October 2015, the square holes have been filled with water and the water allowed to seep overnight as shown on the plate below.

7 7 The next day that is on the 16 th October 2015 the test section was filled up again to a depth of 300mm and above. The time taken in seconds for the water to seep away was recorded.

8 8 The results obtained from the percolation tests are tabulated below: Trial Length (m) Breadth (m) Depth (m) Trial Time (Mins) Depth of Water (m) Percolation rate (s/mm) &Infiltration Rate (mm/hr) Vp1 = (10 x 60)/[( ) x 1000] = 19.4 s/mm Infiltration =186 mm/hr Trial Length (m) Breadth (m) Depth (m) Trial Time (Mins) Depth of Water (m) Percolation rate (s/mm) &Infiltration Rate (mm/hr) Vp1 = (10 x 60)/[( ) x 1000] = 20 s/mm Infiltration =180 mm/hr Trial Length (m) Breadth (m) Depth (m) Trial Time (Mins) Depth of Water (m) Percolation rate (s/mm) &Infiltration Rate (mm/hr) Vp1 = (10 x 60)/[( ) x 1000] = 20.7 s/mm Infiltration =174 mm/hr Average percolation rate as per BS 6297 Average percolation rate =180 mm/hr 6 WATER TABLE No trace of water table was found in the excavated pit.

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10 10 Location Plan & Site Plan showing position of trial pits

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12 12 Soil Profile Description

13 13 Location: Riche en Eau, St-Hubert Typical soil profile for Trial Pit A horizon Thickness: mm Color: Dark brown Texture: Silty clay Structure: Top soil B horizon Thickness: mm Color: compacted dark brown clayey soil mixed with weathered basalt Texture: compacted clayey soil No sign of water table

Appendix F Geotechnical Investigation

Appendix F Geotechnical Investigation Cie Sucriere de Bel Ombre Ltee Residential Development at Bel Ombre Environmental Impact Assessment F1 Geotechnical Investigation This appendix includes the Factual