Site Investigation Case Study: Swansea Foreshore Ice Cream Parlour
Fundamentals of Construction Technology
Module: ACBA4001
Daniel Collier
Brief
For this assignment I will be looking at the proposed site on the Swansea foreshore, between the Swansea Civic Centre car park and the Marriot Hotel Premises in SA1. A joint agreement has been made between the Swansea Council and Marriot Hotels, to build an ice-cream parlour and above managers apartment at the location. My aim is to understand the history of the site and from that research, determine the best methods to use to perform a thorough site investigation. I will also be looking at the building regulations and appropriate codes of practice involved in the study. Ultimately, the aim is to determine, given what strata is discovered and other factors are present, a suitable foundation detail for the building.

Location/Site History
Location

The location for the proposed site is on the Swansea foreshore between the Swansea Civic Centre and the Swansea Marriot Hotel in SA1. The site is in very close proximity to Swansea Beach, within 50m. This of course means that large make ups of the ground are likely to be of a sandy make-up. Swansea beach and the Bristol Channel are well known for huge tidal ranges and in wintertime the area can be exposed to heavy wind and high tides. Coupled together there can be a risk of tidal flooding.
History
Having started off with going to the Swansea Civic Centre itself
Historically the site and surrounding areas have been used for a variety of things. Probably most notably, the site of the Civic Centre and car park was used as an Engine Shed and Wagon Repair Works for the Trams that used to operate in Swansea. This will have had many affects to the ground in the area. Trams that were in and out of the area will have been carrying loads of many different types and the probability of things spilling out on to the ground is high. Also, the fact that the site was historically a big site for maintaining the Swansea trams means that there would have been many substances involved in that work, i.e. fuels, oils, greasers and de-greasers and paints. Many of these materials will have had volatile contaminants in their make ups. Raw materials like this left to seep into the ground will have influenced the soil on site and will be a point to look out for when excavating. 
Also close by there was a Cannister works. Coming from the same sort of angle, there was likely to have been waste and raw material that had made its way into the ground. Again, it is a possibility that VOCs (Volatile Organic Compounds) could have penetrated the soil at the site. 
There was a timber shed close by on the site, so again it is a possibility that there will be raw materials found in the ground at the site.
Since the change of use at the site, all historic uses have been demolished and built over. Anthropogenic ground including grass expanses, trees and shrubbery, pathways and pavements, roads, buildings and very close to the spot the site sits upon is the Swansea Civic Centre car park are present in the surrounding areas. There is scope that there will be remnants of old structures still in the ground, also something to consider when looking at safe ways to excavate. 

Ground Make-Up & Formation

Pre-determining the make-up of the ground is a must. This meaning in addition to the top layers of soil, we need to decipher the fundamental architecture of the layers throughout the recommended depths. 
As anticipated, the surface layers indicated in survey maps provided by the British Geological survey show that the substrate and superficial deposits to the area are 
made up of sand/blown sand. The map indicates the beach to be Marine Beach Deposits (Sand). 
So, as part of the desk-top study, we begin to build our picture of the land. We can see that the top layers are likely to be made up of loose ground being made up of mainly sandy deposits that have been deposited by being blown in across the land from the beach. The area is also made up of anthropogenic ground
Referring to other sources of data than the British Geological Survey, another provider of map data (Digimaps UK) has exposed the site to have artificial make up. Being that the parent rock could be many layers down beneath the surface, the land along the expanse of the foreshore is going to have to have been built with layers of fill to create a more stable surface to build upon. 

As we move down underneath the surface layers, we can now understand that the area is going to have some form of artificial layers underneath. This will likely be mixed with blown sand and other organic deposits.
As we move further down, the map indicates the parent rock of the area to be made up of Mudstone, Siltstone and Sandstone. Near the site, there are different layers indicated. Although they are all similar in make up with Sandstone, Mudstone and Siltstone being present in all seams. It is a possibility that all of these different make ups could be encountered on excavation.
Whilst researching for the desk-top study, I managed to uncover a historical borehole report for the actual site of interest. Below is a table included to illustrate the make up of the strata underneath the site. This is data directly take from the borehole report performed. I have included the actual report with assignment for reference.
Site Investigation
Now that the desk-top study has provided us with the relevant data we need, we can start to devise a plan for the methods used for our site investigation. 
We need to work with a few points in mind: Access to site, surrounding working areas, soil shear strength, strength of substrate, Ground water table level, potential contaminants and ordnance, service pipes. All of this is to be kept in mind in order to ultimately provide a build that is going to be safe and economical to build. Feasibility of the build is vital, so bearing capacity, stability under stress and subsidence potential are all to be taken into consideration. Also, so a framework of safe working practices can be set out prior to the build.
The land at the site is fairly open and is of good strength, although best access will be through the Civic Centre car park, so any equipment will have to take into consideration the size of gate into the car park. An area will have to be fenced off to protect the public from potential fallings into boreholes and test pits. As I have been able to uncover no data or maps on underground utilities for the site inspection pits will have to be dug in the area of interest to determine extent. Excavation is to proceed with caution. A borehole has been previously dug in very close proximity, so it may be considered that there were no utilities found at the site.
Observation pits dug by hand will be sufficient for the detail needed for the shallower level foundations to be proposed and shall be carried out in accordance with BS 
5930 -1999.
Our substrate is potentially of a sandy, non-self-supporting make-up. Therefore, sampling boreholes are to be lined with temporary casing until the correct depth is sampled. The frequency is to be determined on site by the geotechnical advisor (BS EN 1997 – 2). Boreholes are to go down to at least 1.5 x deeper than intended foundation and at least 3m into parent rock
A Piezometer is to be used to measure the ground water retention at the site. This method is to be used at methodical times throughout an extended period to establish an average, also a maximum and minimum level.
The method of excavation getting down to depths of 20m + is going to point towards a drilling method to gather our coring samples. 
A Highway Rig or Off-Road Rig are going to be the best rig type to use in this circumstance as the ground on site is strong and access is good. The off-road Rig may be needed because there are some parts of uneven ground i.e. hilly grassy mounds. Either way, dynamic sampling using a Feed-Frame Mounted, Rotary Head Rig will be needed in order to reach sufficient depths. Handheld rigs will not be able to get us to the correct depths. Due to the difference in layers in the sub strata there may need top be different methods of drilling included i.e. percussive hammer to get through the harder rock and soil and rotary head for the softer of the soils. Therefore, a combination rig is advised. Open Hollow Stem Auger Bit excavation to be used for softer soils. Sample logs to be taken at required points, when as excavated, soil colour/make up changes. Photographs to be taken. For sample extraction, Shelby tubes to be used as the substrate is mainly going to be soft enough that the sample tube can be pushed in hydraulically. Once the Bedrock depth has been reached, a coring method is to be used with using a carbide cutting rotary bit to ensure tips stay sharp as coring progresses. 
Summary
The sub strata of the site has indicated to be made up of a range of materials, from shallow depths that are of anthropogenic origins, through mid-level sandy gravel clay, down to a parent rock of Mudstone at a depth of around 18-20m. It is apparent that borehole investigation is to take place with a depth of at least 30m to ensure that bedrock has been fully determined. The site has some historical factors that will need to be taken into consideration when carrying out sampling and correct safety procedures are to be followed at all times to ensure minimisation of risk.

Recommendations
Taking into consideration the granular nature of the soil and anthropogenic make up at the site there is a considerable chance of subsidence and settlement for our structure. 
The recommendation is that a system of Piles and Pile Caps are to be used incorporated into a ground bearing concrete ringbeam. The type of Pile to be used Is an ‘End Bearing Replacement Pile’. This is due to the fact that we need to distribute the load of the structure down to the underlying bedrock. The ‘Toe’ of the piles will sit on the bedrock and act as support columns. Excavation is to be a ‘Drilled’ system, using a Rotary Auger. A casing is to be inserted into the ground in stages as drilling commences to facilitate support of the sides of the borehole. This is also due to the Granular nature of the soil. The close proximity of other facilities to the site rules out a ‘Driven Pile’ approach. This is because the percussive nature of the practice and the displacement of sub soils can create a pressure bulb which could potentially disturb utilities and services in the area, also the Foreshore path and Civic centre car park. 
A reinforced steel cage is to be inserted into the excavation and concrete poured in-situ from the bottom up using a ‘Tremie Pipe’. This is to give the best chance to avoid cavities in our piles, therefore ensuring optimum strength. Steel reinforced concrete pile caps with a 150mm overhang on all sides are to be used to evenly distribute the structure load between the piles. Also, this creates a good flat surface to work from and can help pull any discrepancies out of existing piles. Below is an illustration of the proposed foundation.