Photographs of Bishop Monkton Borehole1
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Ground Stability Assessment: Proposed Development - Church Farm, Bishop Monkton HG3 3RA G20280 Table of Contents Introduction ...................................................................................................... 3 Historical Subsidence Features ........................................................................... 4 The Pond ........................................................................................................... 4 Borehole Site Investigations ............................................................................... 7 Site Geology ...................................................................................................... 8 Field Pattern, Topography & Ground Stability .................................................... 9 Drift Condition & Ground Stability ..................................................................... 9 Bedrock Condition and Ground Stability ............................................................. 10 Comparative Instability Risk – Zone C Ripon ....................................................... 12 Foundation Design ............................................................................................. 13 Other Mitigation ................................................................................................ 13 Ground Stability Declaration .............................................................................. 13 TM Units 3a and 4 Terry Dicken Industrial Estate Ellerbeck Way Stokesley North Yorkshire TS9 7AE Tel. 01642 713779 Fax 01642713923 Email [email protected] www.geoinvestigate.co.uk 2 April 2021 Ground Stability Assessment: Proposed Development - Church Farm, Bishop Monkton HG3 3RA G20280 Introduction Phase Site Investigations provided Kebbell Homes with a geophysical survey report (Project ref GEO/2722/1023) for the site in November 2019. The Phase report is available from Kebbell Homes. It is not included in this report as it is assumed it will form part of the planning application for the Church Farm site by Kebbell Homes. The Phase report identifies two possible broadly liea iogait aoalies A ad B at the site. Anomaly A located in the north is larger and stronger, while B along the southeast site boundary is weaker and perhaps smaller. The geophysical report is uncertain whether the anomalies are gypsum related dissolution features speculating that they might instead arise from variations in geology, soil compaction or possibly even anthropogenic activity i.e., human activity concluding that the only way the uncertainty could be resolved was by intrusive investigation. Encouragingly the Phase SI report mentions that EM geophysical survey indicated that that there are no infilled troughs or peat deposits at the Church Farm site which are known to be associated with much older sinkhole activity in the Ripon area. The anomalies are indicated as BLUE areas in the subsequent desk study ground stability report carried out by Geoinvestigate, emailed to Mr Mike Mulligan of Kebbell Homes on 29 January 2020 and provided in Appendix A As part of the desk study the tentative rough historical subsidence hollow map provided in Appendix B was generated for the site and the surrounding area based on the OS map record dating from 1854. This base map was not included in the email of 29 January 2020 to Kebbell Homes. The map of 1891 is the first map showing a small circular water feature/spring or perhaps even a small embryonic sinkhole to the southeast of the site. Sometime after 1957 and by 1975 the feature is shown as a larger recognisable pond. The origin of the pond feature is discussed in Geoinvestigates early 2020 ground stability report and subsequently with Dr Tony Cooper in several informal email exchanges. Dr Cooper of the Natural Environment Research Council and the British Geological Survey, Emeritus is the UKs recognised leading authority on the egieeig geolog of ‘ipos gypsum dissolution problem. Subsequently, Dr Cooper was engaged late 2020 as a specialist consultant by Geoinvestigate to provide advice on the engineering geology of the gypsum beneath the Church Farm site and specifically to provide a report on two 45m and 50m deep rotary cored boreholes sunk at geophysical anomalies A & B in September 2020. Initially Geoinvestigate suggested that owing to the COVID pandemic and Dr Cooper shielding during this period that the core boxes were delivered to his home address to be logged by him. However, rather than receive core boxes it was felt safer for Dr Cooper to evaluate photographs of the core both in its original condition and split open (to remove surface smearing) and these were sent to him in April 2021. Subsequently Dr Cooper called for the core samples themselves to be delivered to his home for further preparation and detailed logging by him which was done in March 2021. www.geoinvestigate.co.uk 3 April 2021 Ground Stability Assessment: Proposed Development - Church Farm, Bishop Monkton HG3 3RA G20280 Dr Coopers detailed report on the borehole cores issued March is presented in Appendix C together his high- resolution core photographs. Dr Cooper is an accomplished amateur photographer. Folloig D Coopes loggig, the cores were picked-up and returned to Geoinvestigates Stokesley Head Office in April 2021 for longer term storage. Subsequently Geoinvestigate compiled logs of the cores incorporating Dr Coopers logging information. Geoiestigates logs ‘C ad ‘C at geophsial aoalies B ad A espetiel ae peseted i Appendix D Historical Subsidence Features The draft base map provided in Appendix B shows subsidence hollows, ponds, sinkhole collapse events, speculative ground water movement direction and other features of interest with respect to understanding the ground stability and gypsum dissolution situation local to the Village of Bishop Monkton and the Church Farm site. Following discussions with Dr Cooper two features, a pond which appeared sometime between 1851 – 1910, and a ground collapse c. 1830 occurring well to the west and east of the site respectively were added to the map. The appearances of the features or the first recording of them date mostly to the mid to late 1800s and early 1900s. Four ground water pumps (shown yellow circles) believed to be perhaps two wind and two hand pumps located in farmland and at a farmstead to the east of the site are shown on the map. It was speculated in Geoinvestigates desk study report that the formation of some of the subsidence hollows and ponds might be connected to ground water pumping in the late 1800s and early 1900s. As far as Geoinvestigate has been able to ascertain, few significant recent (within the last 80 years and probably longer) subsidence events/features have been reported/documented within and around the Village of Bishop Monkton and its immediate surrounding area. The Pond The ospiuous lage pepetual pond to the southeast of the site lies at a rim height of 34m AOD while the development area is at 37m to 38m rising locally to 39m AOD. Ground level rises gradually from the pond to the site. The pond occupies a wider depression/bowl crossed to the northwest by an ancient/old hawthorn hedge and the caravan park access track which may be slightly embanked. According to the site owner the pond outflows to the southwest onto lower lying ground where a second pond is formed intermittently. Recent 2020 images of the pond are shown in Appendix E On 26 April 2021 Ross Nicolson spoke to Emma Oates the landowner and the caravan site manager. According to her recollections the land was acquired some 23 years ago (1998) by her family/partners family. She grazes her horses in the pond field but had no recollection of the pond enlarging during this period or any excavation or infilling of it or raising of its banks. Her family had moved to Bishop Monkton in the 1950s and she was not aware of any ground instability event within the site or the pond or the village during this period. www.geoinvestigate.co.uk 4 April 2021 Ground Stability Assessment: Proposed Development - Church Farm, Bishop Monkton HG3 3RA G20280 With respect to the pond depth, she didt ko ut guessed it might be 2m or so placing its bottom at perhaps 32m AOD. Her horses didt ade ito the middle of it. Selected historical maps used to illustrate this section of the report are presented in Appendix F together with a recent Google satellite image of the pond. A full set of larger and smaller scale historical maps dating from 1852 are provided as part of the Phase 1 Desk Study reference materials in Appendix 1. The pond is first recorded as a small circular feature (perhaps a spring) on the OS map of 1891 and remains a small map feature up to 1957. By 1974/1975 it is shown as a larger feature of some 24m width x 29m length and 0.049ha area remaining the same size on the later map of 1989 – 1994 when it is shown some 62m from the southern site boundary. By 2003 the pond is much larger 35m x 55m, 0.197ha, and 4 times its previous surface area and now some 42m to 45m from the site boundary. The most recent Google satellite image suggests that the pond has not increased noticeably in surface area since 2003 though the northeast margin adjacent to Knaresborough Road and the east field line have perhaps been infilled in recent years. An image of possible infill material on its roadside rim is shown in the Appendix G. Much of the change in size of the pond and the subsidence arising from dissolution of the underlying gypsiferous bedrock may date from around 1960s perhaps slowing in recent