Intro In this case study, I will be recommending the contents of a detailed site investigation which is to be undertaken by the relevant contractor(s). Given the proposed site’s ground makeup and historic background, I will also advise which parts of the investigation I consider most significant and applicable. Doing so, I will state the building regulations / codes of practice from which my recommendations are obtained. By the end of my case study, I will choose a suitable foundation based on my preliminary observation with the aid of drawings. Site Details Address - Dunvant Place, Swansea SA1 Latitude - 51.6135 Longitude - 3.9464 The proposed site is located between the Civic Centre and the Marriott Hotel. The land surrounding is currently used as a carpark for both the Civic Centre and the Marriott Hotel. The proposed use of the land is to create a restaurant and ice-cream parlour, with a manager’s apartment. The building is to share parts of the carpark of both existing adjacent facilities and have a GIA at ground floor level of approximately 300 square meters. The ground floor is to contain the restaurant, café bar, ice-cream parlour, kitchen and so on. The manager’s apartment and staff welfare facilities are to be on the second floor. Site History Swansea is historically well known for its supply of copper and coal, especially during the time of the industrial revolution. This provides risk of mines to be present in the ground which would make it liable to subsidence. Attached below are some images taken from the Coal Authority’s interactive map viewer. The first shows that the proposed site is within the highlighted area of the ‘Coal Mining Reporting Area’. The second shows the site is also within the highlighted area of the ‘Surface Coal Resource Areas’. However, as shown in image 3 of the map, the site is not within the ‘Development High Risk Area’. The gov.uk website page on Coal Mining Risk Assessments reassures that if you’re submitting a planning application in a ‘Development Low Risk Area’, then there is no statutory requirement to submit a Coal Mining Risk Assessment. This said, it’s worth noting that the proposed site does in fact lie within a coal mining area which could contain unrecorded coal mining related hazards. It is therefore recommended to immediately report to the Coal Authority if any coal mining feature is encountered during development. They will then advise the appropriate steps moving forward with the groundworks. Ordnance Survey The image below is taken from an Ordnance Survey of Swansea book, and the particular map is dated November 1948. I was able to look in this book at the archival department in the Civic Centre. It shows how the old mumbles train would transport through the area of the proposed site. This would indicate that the soil within the area is disturbed and may well contain remnants of the old train tracks. It’s therefore necessary to take the appropriate precautions when it comes to excavating the ground. It also shows that a wagon repair works was situated within the area, almost exactly where the proposed site is to be. It’s highly likely that remnants of old services, foundations and organics would still be in the ground left behind from such a building. This is something worth noting when investigating the ground for any utilities or contaminations. VOCs Volatile organic compounds (VOCs) are widely used in the industry as chemical manufacturing, solvents and are the by-product of the combustion of gasoline, the burning of coal and diesel fuel. It’s reasonable to assume that there are VOCs present in the soil of the proposed site. I say this as looking at the ordnance survey, it shows that surrounding the area of the proposed site were the following sites: Wagon Repair Works Located almost exactly where the proposed site is. A wagon repair works was the building where repair works for the mumbles train carriages would have taken place. This would involve using many tools, oils and gasses which could have their way into the ground. It’s very likely that this facility would also have contained fumigation chambers. Fumigation chambers would contain a very large cylinder which was set into the ground so rails could run inside. A coach would be moved inside the cylinder, and the cylinder would then be pressurised with the fumigating agent (a gas) and remain under pressure for a while. If such a chamber was used in the wagon repair works, this would be a big factor to consider when investigating VOCs present in the ground. Paint Factory Located just north of the proposed site. A paint factory is self-explanatory when looking at potential contaminants in the ground. The factory would have contained various paints and solvents that could have potentially found their way into the ground causing concern for VOCs in the ground. Timber yards Located just north north/east of the site. Many types of machinery would be used on these sites which would have led to contaminating the ground with oils and diesels, thus again causing concern VOCs in the ground. Site Geology The proposed site is located right on Swansea bay’s shorefront. Being so close the bay indicates that the groundwater table is high and will also be moving with the tide. This is an important factor to take into account when choosing the appropriate foundation, as the groundwater can contribute to excessive settlement if the foundation isn’t adequate. The image below is of a geological map of the surrounding area of the proposed site. The key identifies that the site is within the highlighted area of artificially modified ground, consisting mainly of colliery, mineral smelting spoil and some road and railway embankments. This supports the historical research of potential remnants of the old mumbles train tracks being within the area of the site. It also identifies the site being within the highlighted area of natural superficial deposits identifying as blown sand. This is to be expected, being that the site is a stone’s throw away from Swansea bay. Sandy soil indicates good drainage of the soil. However, sandy soil is classified as a non-cohesive soil, meaning it has no shear strength if not confined. Below is another image taken from a geological map of Swansea. The key for the map identifies the type of bedrock, superficial deposits and artificial ground that is within the area of land. The bedrock within the area of the proposed site is identified as ‘South Wales Middle Coal Measures Formation’, which mainly consists of mudstone, siltstone and sandstones. Borehole Scan The following images show a document of a borehole scan taken from the exact location of the proposed site. This gives a detailed description of the underground strata. The drilling method used was “Open Hole” rotary drilling. The title of the document is “Proposed New County Hall Paxton Street Swansea”, suggesting this investigation took place just before the build of the current Civic Centre which was built in 1982. Analysis of the borehole scan: -At about 8 meters deep the strata is made ground consisting mainly of sand and clay. Between 3 and 5 meters deep there are reportedly brick shale and dense bricks in the soil, likely to have been from the old mumbles train tracks and the wagon repair works building. -From 8 to 18 meters the ground is described as “stiff gravelly boulder clay”. Boulder clay is a geological deposit of clay, usually full of boulders. It’s worth noting that clay soil retains water very well and thus drainage is slow, making it difficult to work with. It has a very low permeability. -The strata changes between 18 to 22 meters deep to grey mudstone, which is fine-grained rock consisting of a mixture of clay and similar silt-sized particles. The borehole ends at 22 meters deep. Recommendations Given the historic background and geological information I have collected of the proposed site, I recommend that the contents of a site investigation include methods suitable for non-cohesive and disturbed soils. Although the borehole scan does show a bedrock consisting of mudstone, the ground largely consists of sandy soils and made ground. Because sand is non-cohesive and has little to no strength unless confined, excavations can be of limited applicability. Therefore, it’s imperative that the investigation takes this into account. Rig Type - I would recommend using a highway rig as the site is easily accessed and, given the fact it’s located in a carpark, the ground is level and solid. Bore Method - The bore method I recommend using for sampling the ground is the ‘Open Hollow Stem Auger’ method. I recommend this method as it’s a suitable method sands and clays, which are the main types of soil present. Given that the soil is weak, this method has a retractable centre bit to allow both undisturbed and disturbed sampling. When investigating the ground on site, it’s important to note that investigation points should be spaced in accordance with BS EN 1997-2:2007 Annex B, I would recommend that a utility investigation take place, as I have discovered from my research that there is a high risk of old utilities being present in the ground. From my findings, I found that there was a wagon repair works building and nearby sites such as paint factories that would require various utilities that may well still be under the ground of the proposed site. It’s also worth noting that the site is located between the Civic Centre and the Marriott Hotel, indicating there’s potential some of their utilities may be travelling under the ground of the site. Should any of these utilities be live, it’s vital they be located before any boring take place. When carrying out such investigation, underground utility detection should be carried out in accordance with PAS 128. Contamination of the ground Looking at my research on potential VOCs in the ground, I highly recommend the investigation be carried out with compliance to BS10175 and BS8576. BS10175 will give appropriate guidance and recommendations on the investigation of land that may be affected by contamination. It allows users to set objectives, develop strategy and identify risks from the contamination for the investigation. It also shows users how to carry out sampling, field testing and laboratory analysis. It will provide guidance on creating an adequate risk assessment of a potentially contaminated site. BS8576 provides guidance on the sampling and monitoring of ground gases such as VOCs and permanent gases like oxygen, methane and carbon dioxide. Foundations Seeing that the proposed building is not a high-rise, it could be argued that a raft foundation would be suitable. However, considering my background research of the condition of the ground surrounding the area of the site, I would highly recommend using pile foundations. Pile foundations are used in situations when the soil at a shallow depth is not suitable to resist excessive settlement. Pile foundations are also used in situations where the groundwater table is high, as we’ve already established the groundwater table is high and varying with the tide at the location of the proposed site. The piles for this foundation should be pre-formed driven piles in my opinion, as they’re capable of densifying loose soils. These piles are introduced into the ground via a percussion driver, using a drop hammer. This particular method is generally used when soft soils overlie a firmer stratum, much like the ground of the proposed site. As these preformed piles come in lengths of up to 10m, it’s likely that a splicing collar would be needed in order to extend a pile to around 20m where the bedrock is located. Given the scale of the proposed building (300m2) I would link the piles together using concrete caps and cap beams. This would be suitable for distributing the weight of the load-bearing walls. The concrete cap is formed at the top of the pile with steel reinforcement, almost like a small pad foundation, which adds stability to the top of the pile. The cap also allows cap beams to interlink between the piles. Below, I have drawn a recommended foundation detail based on my preliminary observations: References Google Maps. (2019). Google Maps. [online] Available at: https://www.google.com/maps/@51.613703,-3.9456457,250m/data=!3m1!1e3 [Accessed 31 Nov. 2019]. Alsenvironmental.co.uk. (2019). BS10175 Investigation of Contaminated Sites - Code of Practice Amendments | Latest News | ALS Environmental. [online] Available at: https://www.alsenvironmental.co.uk/about-us/news/BS10175-Investigation-of-Contaminated-Sites---Code-of-Practice-Amendments_995 [Accessed 7 Dec. 2019]. Thenbs.com. (2019). BS 8576:2013 Guidance on investigations for ground gas - Permanent gases and volatile organic compounds (VOCs), British Standards Institution - Publication Index | NBS. [online] Available at: https://www.thenbs.com/PublicationIndex/documents/details?Pub=BSI&DocID=303538 [Accessed 7 Dec. 2019]. Igg.org.uk. (2019). GANSG - Railway Industries & Works. [online] Available at: https://www.igg.org.uk/gansg/12-linind/railway.htm [Accessed 7 Dec. 2019]. Largeimages.bgs.ac.uk. (2019). British Geological Survey (BGS) | large image viewer | IIPMooViewer 2.0. [online] Available at: http://www.largeimages.bgs.ac.uk/iip/mapsportal.html?id=1004285 [Accessed 8 Dec. 2019]. GOV.UK. (2019). Planning applications: Coal Mining Risk Assessments. [online] Available at: https://www.gov.uk/guidance/planning-applications-coal-mining-risk-assessments [Accessed 8 Dec. 2019]. Flexiblelearning.auckland.ac.nz. (2019). Geology - rocks and minerals. [online] Available at: https://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/mudstone.html [Accessed 8 Dec. 2019]. Norbury, D. (2010). Soil and rock description in engineering practice. Dunbeath, Caithness, Scotland: Whittles Pub. Scans.bgs.ac.uk. (2019). Page 1 | Borehole SS69SE345 | Borehole Logs. [online] Available at: http://scans.bgs.ac.uk/sobi_scans/boreholes/370246/images/10677923.html [Accessed 8 Dec. 2019]. Madabhushi, G., Knappett, J. and Haigh, S. (2010). Design of pile foundations in liquefiable soils. London: Imperial College Press. Means, R. (1961). Soil investigation for building foundations. Stillwater: Oklahoma State University [of Agriculture and Applied Science]. Siegrist, R. and Van Ee, J. (1994). Measuring and interpreting VOCs in soils. Washington, DC: U.S. Environmental Protection Agency, Office of Research and Development. The Stationery Office. (n.d.). Investigation of Potentially Contaminated Sites. Stevenage: Institution of Engineering and Technology. UK Specification for Ground Investigation. (2012). London: ICE Publishing.