ABP Southampton. Environmental Statement for Port of Southampton: Berth 201/202 Works. Appendix B. Dredge Material Characterisation

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1 ABP Southampton Environmental Statement for Port of Southampton: Berth 201/202 Works Appendix B Dredge Material Characterisation

3 Appendix B Dredge Material Characterisation

5 Environmental Statement for Port of Southampton: Berth 201/202 Works Appendices Appendix B. Dredge Material Characterisation Introduction A literature review and search for geotechnical and geophysical data has been undertaken to develop an understanding of the geological structure of the Berth 201/202 pocket and help characterise the material that requires to be dredged. Geographical Information System (GIS) presentation of the main data sets was used to identify locations where further information was required with the aim of completing the determination of: Volumes of different material types to be dredged; The soil's properties for dredge, disposal and beneficial use purposes; Parameters on inputs to the modelling investigations; Possible contamination within the dredged sediments; and Probable stability of side slopes. This information was used to define a project specific site investigation to integrate with the existing data. This was undertaken by Fugro Alluvial Offshore Ltd between February and April The geotechnical site investigation provided additional data at Berth 201/202 from nine boreholes. In addition, laboratory testing was undertaken on borehole samples to determine the engineering, rheological and chemical properties of the materials. A further benthic grab survey obtained surface sediment quality data following the latest maintenance dredge campaign in September The samples for chemical analysis were distributed throughout all areas to be dredged in the berth pocket and with depth, following the principles of OSPAR guidelines for the characterisation of dredge material for possible disposal within the marine environment. The results of this analysis are presented and discussed in the Sediment Quality Chapter of the main Environmental Statement (ES). In addition, separate sampling for benthic invertebrate analysis, which included particle size distribution analysis, was undertaken from the areas to be dredged and locations where sediments may disperse to during the dredging works, as well as in and around the Nab licensed deposit ground, where the dredged material is likely to be deposited. These data sets are reported in the Sediment Quality and, Marine and Coastal Ecology Chapters of the main ES. From these datasets, a detailed analysis of the geological strata encountered in the berth pocket was undertaken, in the form of an interpreted profile, along with a general description of the material characteristics that are to be dredged. This analysis is presented in the following sections and forms the core data that defines the likely dredge methodology and timescale to undertake the dredge of Berths 201/202. The characteristics of the disturbed sediment and character of the material at the point of disposal/use is also used to inform the numerical modelling (Appendix C). The following sections describe the material types that need to be dredged, the sediment structure within Berth 201/202, the general characteristics of the different material types to enable their dredgeability and the likely character of the material at the time of disposal to be determined. R/3754/1 B.1 R.1494

6 Environmental Statement for Port of Southampton: Berth 201/202 Works Appendices Material Types and Volumes Table B.1 summarises the volumes of each material type at Berth 201/202 that need to be dredged. Table B.1 Volumes of different sediment types to be dredged at Berth 201/202 Material Type Volume to be Dredged (m 3 in situ) Very stiff (in places hard) silty sandy CLAY 35,800 Very dense silty SAND (Greensand) 101,200 Stiff silty/sandy CLAY 45,300 Total 182,300 The geotechnical site investigation data has been used to construct a geological section parallel to the Berth 201/202 Quay line, showing the material to be dredged from the berth pocket (Figure B.1). Figure B.1 shows that the centre section of the deepened berth will be dredged into green/grey stiff laminated sand/silty clay. This material appears as a former channel within the Greensand, which requires dredging from either end of the berth. On top of these undisturbed sediments a transient veneer of very soft silt/clay, of the order of <0.3m thick could exist, particularly at the corner of the quays. Physical Characteristics of Material to be Dredged In broad terms, three types of material will require to be dredged. Whilst some have similar general descriptions they come from different geological strata with different physical characteristics. Eocene - Bracklesham Beds Very stiff (in places hard) silty/sandy CLAY): This material is typically described as stiff to very stiff (sometimes hard) greenish grey laminated slightly sandy clay, sometimes with organic matter. The particle size envelope is shown on Figure B.2 and shows the median size (D 50) to be 5-9µm, nearly all material being less than 200µm. Bulk densities are generally in the range of t/m³. The clays are generally fissured and the clay mineralogy changes in different beds. Undrained shear strengths have been measured in the range kpa with moisture contents of %. Laboratory testing to determine the Atterberg limits show a liquid limit for the clay in the range of 59-66%, a plastic limit of 24-29% and a plasticity index in the range 35-37%. Very dense silty SAND (Greensand): Is typically described as very dense grey green becoming green clayey glauconitic fine and medium sand, often interbedded with stiff grey clay sometimes with shell fragments. Typically the particle size distribution comprises 75-85% > 63µm with up to 25 % in the silt and clay fractions. The median particle size (D 50 ) is generally in the range of µm with a D 90 of µm. A typical particle size distribution is shown on Figure B.3. The bulk density is generally in the range of t/m 3 with a moisture content ranging from 20-40% at different locations. The relatively high proportion of clay means the material has Atterberg limits with the liquid limit in the range of 27-31%, plastic limit of 16-17% and a plasticity index between %. An undrained shear strength in excess of R/3754/1 B.2 R.1494

7 Environmental Statement for Port of Southampton: Berth 201/202 Works Appendices 300 kpa has been measured for the material, with typical SPT penetration being mm for 50 blows. Stiff silty/sandy CLAY: The sediment is generally described as firm to stiff light brown/olive grey sandy clay, often thinly laminated sand/silt partings. The bulk density has been measured in the range of t/m³ with a moisture content 25-37% and an undrained shear strength about 100 kpa increasing with depth. The Atterberg limits have been recorded as % for the liquid limit, 17-23% for the plastic limit and 40-42% for the plasticity index. The median particle size is around 12-50µm and a D 90 of µm. Dredgeability Summary The stiff to very stiff clays and silts and dense Greensand although from different geological times are generally similar with respect to their dredgeability. Whilst some could be dredged by a trailer suction hopper dredger this would be inefficient. All these materials can be dredged by a cutter suction or bucket wheel dredger, or large backhoe dredger, however for predominantly environmental reasons the latter is likely to be used. The different layers will not be easily separated and little benefit is likely to be derived from doing so. R/3754/1 B.3 R.1494

D C B A 0 1 2 3 4 0.5 km A B C D 10.0 Bi Bd Bh Bc Bg Bb Bf Ba? DEPTH (METRES) BELOW CHART DATUM 11.0 12.0 13.0 14.0 15.0 JDN57 Channel Depth 16.0 Depth of Berth Pocket 17.0 18.

4 km Date Sep 08 Scale ABPmer, All rights reserved, 2008 HO1095/070712/18 NOT TO BE USED FOR NAVIGATION By MCE Size A3 Version 1A Projection OSGB 1936 QA 1:12,000 DP 3754 -

8 D C B A km A B C D 10.0 Bi Bd Bh Bc Bg Bb Bf Ba? DEPTH (METRES) BELOW CHART DATUM JDN57 Channel Depth 16.0 Depth of Berth Pocket A West DISTANCE FROM A (METRES) D East km Date Sep 08 Scale ABPmer, All rights reserved, 2008 HO1095/070712/18 NOT TO BE USED FOR NAVIGATION By MCE Size A3 Version 1A Projection OSGB 1936 QA 1:12,000 DP Fig_Profile_Lines_1.mxd Produced by ABPmer Ltd Very soft to soft CLAY Firm to Stiff Sandy CLAY Grey green clayey SAND Stiff to Very Stiff CLAY Made Ground GREENSAND Predominantly stiff-very stiff sandy CLAY Predominantly firm-stiff sandy CLAY Greensand Geological Profile Along Berth 201/202 Figure B1

Very stiff clay and stiff silty sandy clay of Bracklesham and Barton Beds Date By Size Version Oct 2008 SNH A4 1 Reference 3754

9 Very stiff clay and stiff silty sandy clay of Bracklesham and Barton Beds Date By Size Version Oct 2008 SNH A4 1 Reference Fig.B.2.xls Produced by ABPmer Ltd. ABPmer, All rights reserved, 2008 Particle size envelope Stiff Clay/Sandy Clay Figure B.2

Greensand Date By Size Version Oct 2008 SNH A4 1 Reference 3754 - Fig.B.3.xls Produced by ABPmer Ltd.

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