Groundwater WJ Dr Toby Roberts FRENG of WJ GROUNDWATER LTD Depressurisation strategies in the PropertyLambeth Group River Terrace Deposits Terrace Gravels Upper Aquifer London Clay Aquiclude Thames Group Harwich Forma:on Upper MoDled Beds Intermediate Aquifer Cohesive + granular Laminated Beds Lambeth Group laminaons to channels Lower Shelly Beds Mid-Lambeth Hiatus Lower MoDled Beds + occ sand channels Upnor Lower Aquifer Thanet Sand Thanet Sand Formaon Bullhead Beds Chalk Chalk London basin typical soil profile Lambeth Group/ Upper Mottled Beds Intermediate Aquifer Depth: 5 to 60 m to top Laminated Beds: Stiff Clay Thickness: 15 to 20 m Predominantly cohesive Channel Sands Granular horizons range Groundwater Reduced from laminaons to MLH sand channels: WJ Oxidised width: 2 to 300 m length: ? of correlaon with lost Rivers Lower Mottled Beds: Stiff Clay Thickness: mms to 12 m Property Crossrail: Stepney Grn EB Groundwater WB WJ Caverns of 100 m long 40 m apart 8 to 17 m wide Property 62 installaons Groundwater WJ of Property Non-hydrostac Recharge required to sustain profile Boundary Condions: Source of recharge? • Seepage from London Clay Very low permeability • Leakage via fissures or scour features Scour features relavely rare, lile evidence Groundwater • Seepage via ungrouted wells or boreholes WJ Plenty of them but not much evidence of • Horizontal flow from areas with higher groundwater Significant distances involved Property Wellpoint Groundwater pumps WJ of Access constrained in an advancing SCLProperty cavern 45 Surface ejectors EB WB 105 tunnel wellpoints Crossrail: Stepney Grn Crossrail: East London Stepney Grn Cross passage CP6 Groundwater WJ of Works impacted by Lambeth Group Property mTD LW9 Made Ground 110 River Terrace Deposits Cross Passage CP6 A3 LW9 approximately 10 m away 100 Lambeth soils above MLH cohesive London Clay Sump extends below MLH: 90 A2 Ejector dewatering required Groundwater WJ 80 Eastof Bound West Bound UMB 71.21 71.21 70 LTB MLH LMB 67.12 LambethGroup PropertyUF 60 Thanet Sand Groundwater WJ of Property Sump ejector system mTD As built: Combined probe holes and wells 80 WU2/4 WU1/3 PR4/9 PR1 EB WB PR6 WP2 UMB WP3 PR3/8 71.21 Groundwater 71.21 LTB NW19 NW13/14 70 NW18 NW1/2 EJ3 WJNW16 MLH NW7 NW15 PR10 LMB NW6 67.12 NW17 PR5 NW8/11 ofWP7/14 WP8/13 WP19/22 WP18/23 Lambeth Group NW3/5 NW9 NW4 UF EJ2 P1 NW10 EJ4 EJ5 60 Thanet Sand EJ1/6 LW9 Property Groundwater WJ of Property Groundwater WJ of Property Groundwater WJ of Property mTD LONDON CLAY 80 EB WB UMB SAND CHANNEL 73.150 UPPER MOTTLEDGroundwater BEDS LEVEL OF CONCRETE LTB 70.64 mTD 70 WJ LAMINATED BEDS LMB of 67.12 mTD LOWER MOTTLEED BEDS 65.95 mTD UPNOR FORMATION UF 60 Thanet Sand LW9 Property NW7 NW6 NW5 NW8 NW13 NW14 NW4 NW9 EJ6 PR6 NW15 EJ5 NW3 EJ4 PR10 As built: NW2 NW16 NW1 NW10EJ2 EJ3 P1 NW11 EJ1 WP3 NW12 East Bound PR1 NW17 WU2 Plan View PR5 NW18 NW19 NW20 WP2 EJ8 LW9 PR8 TCBs WP15A WP16 GroundwaterWP14A WP15 WP14 PR3 WU2B WP13 WP12PR9 WP28 WP11 WU1 WP26 WP25 WJ WU4 WP10 WP27 WP24 WP24a EJ7 WU3 PR4 WP9 WP23 WP7 WP8 WP22 of WP30 WP21 WP6 WP29 WP5 WP20 West Bound WP19 WP17 WP18 Key: Sump ejectors Downwards probes/wellponts Property0 5m Upwards probes/wellpoints Scale not installed Groundwater WJ of Property Technique Site Notes Passive relief wells Whitechapel Shas, Limmo Pressure relief Surface deepwells Valence Gardens Extensive channel sands Surface ejectors Stepney Grn, Cross passages Extensive channel sands Groundwater Tunnel wellpoints LIV/WHI, Cross passages Overbleed WJ Tunnel ejectors VD4, Cross passage sumps of >5 m drawdown Under drainage Some cross passages Proven Lower Aquifer link Crossrail dewatering: Techniques used to target Lambeth Group Property Groundwater WJ Lambeth Groupof CIRIA: C515 LambethProperty Group: Permeability range Excess pore pressure? Channel sands Laminated beds Lithology: Laminaons Layer Sand Channel Unknown? Groundwater Elevaon: Pressure relief WJ Dewatering of Overbleed Access: Constraints Opportunies Dewatering scheme drivers: Lithology and Geometry Property Dr Toby Roberts FRENG WJ GROUNDWATER LTD Dewatering strategies GroundwaterIn the Lambeth Group WJ of Crossrail Liverpool Stn: VD4 inclined SCL tunnel: tunnel ejector system Property .