Proposed Spillway Development Oakenholt Reservoir Oakenholt
Total Page:16
File Type:pdf, Size:1020Kb
Geotechnical, Geo-environmental and Earthworks Specification Report: Proposed Spillway Development Oakenholt Reservoir Oakenholt PREPARED FOR: April 2020 Job No: 15861 Esssity UK Ltd REPORT TITLE : Geotechnical, Geo-environmental and Earthworks Specification Report: Proposed Spillway Development, Oakenholt Reservoir, Oakenholt REPORT STATUS : Final JOB NUMBER : 15861 DATE : April 2020 PREPARED BY : REVIEWED BY : APPROVED BY : April 2020 ii 15861 Esssity UK Ltd Executive Summary Site Location Essity UK Ltd is proposing construction of a concrete auxiliary spillway upon the and land east of Oakenholt Reservoir, Oakenholt, Flint. The site is currently used as Proposed open farmland. Development The development site locates 4.5km southwest from Oakenholt, Flint. The site centres on an approximate National Grid Reference of 326300, 371090 occupying a plan area of approximately 1.00 Hectares. Site History The site has remained as open farmland since 1888. Very few changes have been made on-site and off-site since 1888. The current reservoir was built c.1899. Geology The 1:50000 scale geological map of the area (Sheet 108) was consulted for geology underlying the site. The site is shown to be underlain by the Gwespyr Sandstone which is Carboniferous in age. These rocks comprise fine-grained, feldspathic and micaceous sandstones. Made ground may be expected at the site, where earthworks may have taken place during the construction of the overflow pipe from the reservoir. Superficial deposits are not recorded on site. Radon No radon protective measures are required for new developments on the investigation site. Ground Ground Conditions on site were consistent throughout the site. Where the Conditions proposed development situates the following ground conditions were found: G.L. - 0.2/0.4 Soft dark brown silty gravelly CLAY. 0.2/0.4 - 0.5/1.4 Firm reddish brown slightly sandy silty gravelly CLAY. 0.5/1.4 - >2.0 Firm yellowish brown silty sandy gravelly CLAY. Laboratory All contaminant substances tested for were found to be present at concentrations Chemical considerably lower than their respective human health threshold levels for a Testing commercial setting. Earthworks As seen from the classifications of fill, the firm reddish-brown CLAY site won Specification materials are classified as dry/ stony cohesive material (Type 2B/C). Table 6.4 abstracted from Series 600 of the Specification for Earthworks listing the various type of compaction plant suitable for use with type 2B and 2C materials is presented in Annex G. The colliery spoil encountered within TP2 can be classified as a class 6B material. This material can be used as a starting layer, with the firm reddish-brown CLAY being compacted above this. Where this material is to be used, care should be taken to remove any particle size greater than that of the compaction layer i.e. timber, metal etc. Foundation For the proposed development it is recommended that traditional concrete raft and Floor foundations founded within competent in-situ fill material. Slab 2 Solution An allowable bearing pressure of 100kN/m may be used for design purposes. For the given foundation solution and bearing pressure, maximum total settlements of 25mm should result with differential movements of the superstructure not exceeding 1:750. These foundations should be designed as reinforced to avoid differential settlement issues. The foundations should penetrate at least 200mm into the founding horizon and in order to prevent any effects from frost heave the foundations should extend to a minimum depth of 900mm. Floor slabs should be designed as grounded. All foundation formations should be inspected by a suitably qualified Engineer before being concreted. April 2020 iii 15861 Esssity UK Ltd TABLE OF CONTENTS SECTION 1 Introduction and Proposed Development 1 1.1 Introduction 1 1.2 Limitations and Exceptions of Investigation 1 SECTION 2 Review of Existing Data 2 2.1 Physical Setting and Current Site Use 2 2.2 Site History 3 2.3 Geological Setting 4 2.3.1 Geology 4 2.3.2 Coal Mining 5 2.3.3 Radon 5 2.3.4 Natural Hazards 5 2.4 Environmental Setting 5 2.4.1 Hydrogeology and Hydrology 5 2.4.2 Groundwater 6 2.4.3 Flooding 6 2.4.4 Waste 6 2.4.5 Pollution 6 2.4.7 Sensitive Land Use 7 2.4.8 Estimated Soil Chemistry 7 2.4.9 Potentially Infilled Land 7 2.4.10 Industrial Land Use 8 SECTION 3 Preliminary Human Health and Environmental Risk Assessment 9 3.1 General 9 3.2 Preliminary Site Conceptual Model 9 3.2.1 Potential Sources of Contamination and Gas 9 3.2.2 Potential Receptors and Pollution Pathways 10 3.2.3 Preliminary Human Health and Environmental Risk Assessment 11 SECTION 4 Field Investigation 12 4.1 Site Works 12 4.2 Ground Conditions 13 4.3 Water Strikes 13 4.4 Stability and Obstructions 13 4.5 Soil Laboratory Chemical Testing 14 4.5.1 Quality Assurance 14 4.5.2 Sampling Regime 14 4.5.3 Soil Laboratory Analysis 14 4.6 Soil Property Testing 15 4.6.1 Laboratory Geotechnical Testing 15 SECTION 5 Evaluation of Soil Analytical Results 16 5.1 Soil Assessment Methodology 16 5.2 Soil Test Results 16 April 2020 iv 15861 Esssity UK Ltd SECTION 6 Quantitative Risk Assessment 19 6.1 Contaminants of Concern 19 6.1.1 Contaminants of Concern in Soil 19 6.1.2 Gasses of Concern 19 6.2 Potential Receptors and Pathways 19 6.2.1 Human Receptors 19 6.2.2 Aquatic Environment 19 6.3 Mitigation and Remedial Measures 19 6.3.1 Human Health 19 6.3.2 Aquatic Environment 20 SECTION 7 Engineering Recommendations 21 7.1 Preparation of Site 21 7.2 Foundation and Floor Slab Solution 21 7.3.1 Plasticity Testing 22 7.3.2 Material Property Testing 22 7.4 Excavations and Formations 23 7.5 Protection of Buried Concrete 23 SECTION 8 Earthworks/ Compaction Specification 2 8.1 Compaction Specification 2 Tables Table 2.1 Historical Development from Map Information 3 Table 2.3 Water Abstractions 6 Table 2.3 Pollution Incidents 7 Table 2.2 Contemporary Trade Summary 8 Table 3.1 On-Site and Off-Site Potential Sources of Contamination 9 Table 3.2 Preliminary Qualitative Human Health and Environmental Risk Assessment 11 Table 4.1 Summary of Typical Ground Conditions (Area A – TP1, TP3, WS1, WS2, WS3) 13 Table 4.2 Summary of Typical Ground Conditions (Area B – TP2) 13 Table 5.1 Summary of Soil Chemical Test Results - Standard Suite 16 Table 5.2 Summary of Soil Chemical Test Results - Speciated Polycyclic Aromatic Hydrocarbons 17 Table 5.3 Summary of Soil Chemical Test Results: Petroleum Hydrocarbons 18 Table 7.1 Plasticity Test Results 22 Table 7.2 Summary of Ground Conditions (Firm reddish-brown CLAY) 22 Table 8.1 Fill Classification 2 Figures Figure 2.1 Site Location 2 Annexes ANNEX A Envirocheck Report ANNEX B Risk Assessment Definitions ANNEX C Trial Pit Logs ANNEX D Windowless Sampled Borehole Logs ANNEX E Laboratory Chemical Test Results ANNEX F Geotechnical Test Results ANNEX G Table 6.4 Series 600 Specification for Earthworks Drawings Drawing 01 Site Layout April 2020 v 15861 Introduction and Proposed Development SECTION 1 Introduction and Proposed Development 1.1 Introduction Essity UK Ltd is proposing construction of a concrete auxiliary spillway upon the land east of Oakenholt Reservoir, Oakenholt, Flint. The site is currently used as open farmland. Terra Firma (Wales) Limited have been commissioned by Essity UK Ltd to undertake a geo-environmental assessment and geotechnical investigation of the site. The main objectives of the geo-environmental assessment programme were to: Investigate the potential environmental liabilities at the site associated with any soil contamination Provide a summary of the environmental conditions at the site, together with any necessary further intrusive works and / or remediation works to render the site fit for its intended use The main objectives of the geotechnical site investigation were to: Determine the type, strength and bearing characteristics of the shallow superficial and underlying solid geology Provide engineering earthworks specification recommendations for the development Provide recommendations with regard to any other geotechnical aspects pertaining to the development In order to achieve the above objectives, Terra Firma (Wales) Limited carried out an assessment programme including a site walkover, a review of existing data, followed by a field investigation to collect geotechnical and environmental data from selected locations. 1.2 Limitations and Exceptions of Investigation Essity UK Ltd has requested that a Geo-environmental Site Assessment (GSA) and Geotechnical Investigation (GI) be performed in order to determine if contamination is present beneath the site and to provide geotechnical recommendations associated with the proposed scheme. The GSA and GI were conducted, and this report has been prepared for the sole internal reliance of Essity UK Ltd and its design and construction team. This report shall not be relied upon or transferred to any other parties without the express written authorisation of Terra Firma (Wales) Limited. If an unauthorised third party comes into possession of this report, they rely on it at their peril and the authors owe them no duty of care and skill. The report represents the findings and opinions of experienced geo-environmental and geotechnical consultants. Terra Firma (Wales) Limited does not provide legal advice and the advice of lawyers may be required. The subsurface geological profiles, any contamination and other plots are generalised by necessity and have been based on the information found at the locations of the exploratory holes and depths sampled and tested. April 2020 1 15861 Review of Existing Data SECTION 2 Review of Existing Data 2.1 Physical Setting and Current Site Use The development site locates 4.5km southwest from Oakenholt, Flint.