Geotechnical Engineering Investigation for Proposed Benin River Valve Station (BRVS) BENIN RIVER. OML 40 ONSHORE NIGERIA.
Elcrest Exploration & Production Limited wants to embark on the development of the Benin River Valve Station (BRVS) and other associated facilities at OML-40. This report presents the results of the investigation conducted with the object of determining the litho-stratigraphies at the location by Chattel Associates Nigeria Limited in order to proffer suitable foundations to support the proposed facilities.
The investigations were 5nos each for deep soil boring and Dutch Cone Penetrometer Tests (DCPTs) to refusal. The borings were conducted with Light cable percussion Wayfarer Rig (Mechanical & Manual) and the DCPTs were carried out with a (200kN & 100kN) Thrust Piezo-cone Penetrometer equipment.
The object of the investigation was to ascertain the soil profile in addition to obtaining foundation design parameters for ultimate foundation construction.
From the field investigation, the area is characterized by extensive deposits of very soft peats in all the boreholes. The peats overlie alternating sequences of firm to stiff clayey formations and medium to very dense sandy soil with very high N-values which extends to the terminal depths of the boreholes. The terminal depths of the boreholes were -80.0m or 5.0m band of dense sand formation.
OML-40 lies in the in the Sedimentary Basin of oil-rich Niger Delta Region with approximate distance of 75km northwest of Warri and covers an area of 498km2. The BRVS is located in the shallow and mid-stream within the coastal mangrove swamps. The average water depth of the midstream is approximately 4.50m. Geologically, the area consists of the of the Early Palaeocene resulting from the built up of the grain sediments eroded and transported to the River Nigeria and its tributaries.
To support the proposed structures at the location, consideration of the sub-soil conditions is critical which is the main object of the investigation. Deep foundation is recommended to be terminated in the dense to very dense region for the super-structures.
For light structures, shallow foundations are recommended. However, ground improvement structures that will be founded on shallow foundations, ground improvement is suggested by way of vibro-compaction or stripping the near-surface unstable clayey materials and replacing with sharp sand.
BENIN RIVER VALVE STATION
Client: ELCREST EXPLORATION & PRODUCTION LIMITED
Contractor: CHATTEL ASSOCIATES NIGERIA LIMITED
TABLE OF CONTENT
DEFININTIONS, ABBREVIATIONS & ACRONYMS 4-5
EXECUTIVE SUMMARY 6-7
BRIEF BACKGROUND TO THE STUDY 8
BOREHOLE & CPT FOOTPRINT MAP 8
GEOLOGY OF THE AREA 9-10
1.0 INTRODUCTION 11
1.1 SCOPES OF INVESTIGATION 11-12
2.0 SUB-SOIL CONDITIONS & WATER DEPTH 12-14
2.1 ABSTRACT OF FINDINGS 14
2.2 BOREHOLE & CPT COORDINATES 15
3.0 FIELDWORK 15
3.1 METHOD OF SOIL BORING 15-16
3.2 CONE PENETRATION TEST 16
4.0 LABORATORY TESTS 18
4.1 MOISTURE CONTENT 18
4.2 ATTERBERG LIMITS 18
4.3 PARTICLE SIZE ANALYSIS 19
4.4 UNIT WEIGHT 19
4.5 SPECIFIC GRAVITY 19
4.6 UNDRAINED SHEAR STRENGTH ON CLAY 19-20
4.7 DRAINED SHEAR STRENGTH ON SAND 20
4.8 CONSOLIDATION 20-21
5.0 GEOTECHNICAL DATA 22-26
6.0 FOUNDATION DISCUSSION 27
6.1 PILE FOUNDATIONS 27-31
6.1.1 Deep Foundation Recommendations 31-32
6.2 PROPOSED SHORELINE PROTECTION FACILITY 32-34
7.2.1 Recommendation for Shoreline Protection 32-34
6.3 MOORING DOLPHINS 34
6.3.1 Foundation for Mooring Dolphins 35-36
6.4 SHALLOW FOUNDATION 35-36
6.5 SOIL SETTLEMENT 36
7. SOIL LIQUEFACTION 37
LIST OF APPENDICES
Appendix A: Dutch Cone Penetration Graphs
Appendix B: Borehole Logs
Appendix C: Laboratory Test Results
Appendix D: Borehole Geo-sections
Appendix E: Pile Soil Interaction (PSI) Analysis
Some Site Pictures
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