Site and Soil Investigations PDF

Site and soil investigations Module Leader: Graham Terry Learning Outcomes understand the need for a site investigation and its relationship to foundation design and construction know typical sources of information and survey techniques understand the basic properties of soils in rela...

Site and soil investigations Module Leader: Graham Terry Learning Outcomes understand the need for a site investigation and its relationship to foundation design and construction know typical sources of information and survey techniques understand the basic properties of soils in relation to foundations and ground movements appreciate the main effects of groundwater movement and how it may be controlled Types of Site Investigation (SI) walk-over site survey desk study survey (site and ground exploration) investigation Site Investigation Objectives of SI to determine the relevant to determine the site engineering properties of all conditions within the region the soils and rocks which of influence of the may influence the design proposed building. and construction of the foundations. Inadequate Site Investigation addition payment and time claims from contractors. examples of inadequate SI presence of ground water no information for design of temporary works. Potential hazards & associated risks Desk Study  A desk study and collection of known data about the site including: ▪ Ordnance Survey maps − historical and modern, note grid reference. ▪ Rights of way. ▪ Geological maps − subsoil types, radon risk. ▪ Site history – green-field/brown-field. ▪ Previous planning applications/approvals of the site. Desk ▪ Current planning applications in the area. ▪ Development restrictions − conservation orders. Study ▪ Utilities − location of services on and near the site and Wayleaves. ▪ Aerial photographs. ▪ Ecology factors − protected wildlife. ▪ Proximity of local land-fill sites − methane risk. ▪ Flood risk and history. ▪ Underground mining and local subsidence history. ▪ Any restrictions made with the deeds of the land. ▪ Archaeological findings Sources of Information: Public Domain British geological survey, maps and information Ordnance survey The Environmental Agency or its equivalent Coastal erosion, landfill sites, details of water extraction The Local Authority Building & Planning control, environmental health, legal search and previous site investigation reports County records offices, libraries, museums and local history sources Utility companies Coal Authority, mining reports – past, present and proposed Soil survey maps Sources of Information: Private Domain local residents the site vendor nearby sites projects of similar sites and type construction – In house information  location, accessibility and space sub-soil nature extent of difficult ground conditions filled or contaminated ground mining shafts & tunnels Information ponds, watercourses, ground water level and risk of flooding Identified utility services previous vegetation landslip natural aggressive chemicals, harmful gases and landfill gases foundations of the adjacent buildings Walk-Over Survey Walk-Over Survey A walk-over survey is a visual check of the site to double check the findings or for deviations from the desk study and to assess the current physical conditions on site, including: ▪ Checking the site boundaries match the deeds. ▪ Looking for potential hazards to health and safety including tipping of hazardous waste. ▪ Assessing the general condition of any existing structures. ▪ Assessing the general surface conditions including ground slope/contours. ▪ Looking for invasive vegetation species such as Japanese Knot Weed. ▪ Confirming Tree Preservation Orders. ▪ Assessing adjacent structures and property that might be adversely affected by any development works  location & accessibility potential hazards size/shape/level of the site Information to position, species, size and condition of be Collected trees position and availability of existing building and utility services signs of ground water and flooding Information to be collected Initial Assessment results The results of the desk study and walk over survey should be recorded and evaluated by a suitable person. The results should be evaluated for suspected hazards and the results recorded, and include the following as appropriate: Site plans, including dates, previous and current uses, proposed site layout Geology of the site, including geological maps, previous site investigations and laboratory reports / test results Photographs, including aerial photographs showing points of interest or concern all photographs to contain dates List of sources of information consulted and copies of the information obtained Site Survey & Ground Investigation Site survey and ground investigation A site survey is a digital measured survey of the land, including ground levels. This is usually necessary at this stage to establish the location of ground investigations. Purpose: to identify the types, properties and depths of subsoil strata on the site and the level of the water table to enable the design of economic foundations to obtain sub-soil samples for identification, classification and ascertaining the sub- soil’s characteristics and properties, depths of sub soil strata on the site to enable design and construction of the proposed economic foundations to establish the presence of geological fault, and level of the water table  Site survey and ground investigation A series of samples extracted at the intersection points of a 10–20m2 grid pattern should be adequate for most cases. Alternatively, representative samples are taken from locations close to, but not interfering with, Source: Kovac, Roy Chudley; Roger Greeno; K. Chudley and Greeno's the proposed works. Building Construction Handbook. Taylor & Francis, 2020. pg.103 https://anglia.primo.exlibrisgroup.com/permalink/44APU_INST/t7lk8a/alma 998908740202051 Site survey and ground investigation Main methods used to obtain soil samples: trial pits; and boreholes. Can be tested on site or in a laboratory. The test results of soil samples are usually shown on a drawing which gives the location of each sample and the test results in the form of a hatched legend or Source: Results of a borehole in the form of a section https://www.rbkc.gov.uk/idoxWAM/doc/Other- section. 1968124.pdf?extension=.pdf&id=1968124&location=VOLUME2&contentType=application/pdf &pageCount=1 21  Site survey and ground investigation Disturbed soil samples These are soil samples obtained from boreholes and trial pits. The method of extraction disturbs the natural structure of the subsoil but such samples are suitable for visual grading, establishing the moisture content and some laboratory tests. Disturbed soil samples should be stored in labelled airtight jars. Undisturbed soil samples "Soil Survey45.tif" by NRCS Montana is licensed under CC PDM 1.0 These are soil samples obtained using coring tools that preserve the natural structure and properties of the subsoil. Reference to regulation: BS EN 1997−2: The extracted undisturbed soil samples are labelled Geotechnical design. and laid in wooden boxes for dispatch to a laboratory for testing. Ground investigation and testing. This method of obtaining soil samples is suitable for rock and clay subsoils, but difficulties can be experienced in trying to obtain undisturbed soil samples in other types of subsoil.  Soil Investigation Methods Methods depend on several factors: size of contract; type of proposed foundation; type of sample required; and types of subsoils encountered The most suitable methods in terms of investigation depth are: trial pits (foundations up to 3.000 mm deep); borings (foundations up to 30.000 mm deep); and deep borings and in-situ examinations from tunnels and/or deep pit (foundations over 30.000 mm deep). Soil Investigation Methods Trial pits are exactions located outside the proposed foundation area and generally be a minimum depth of 3 m. The distance from the edge of the foundation should not be less than the depth of the trail pit. Made by machine in dry ground, which require little or no temporary support to the sides of the excavation. Subsoil can be visually examined in situ by an experienced engineer. Both disturbed and undisturbed samples can be obtained. Source: Kovac, Roy Chudley; Roger Greeno; K. Chudley and Greeno's Building Construction Handbook. Taylor & Francis, 2020. pg.100 https://anglia.primo.exlibrisgroup.com/permalink/44APU_INST/t7lk8a/alma998908740202051  Soil Investigation Methods: Trail Pits Trial pits are generally used for low rise buildings where shallow foundations are deemed adequate. Can be used to: expose and/or locate underground services. to find out the stratum pattern, soil types and thickness, water table level and quantity/flow of ground water. The number and depth of trial pits should be located so they are representative of the site and will depend upon: Proposed development Nature of the site Source: The Constructor, 2020. How to set up proper layout of /trial pits for site investigations? What are the purposes of Trial pits. [online] available at: Inconsistency of the soil and geology provide sufficient information, 25 boreholes will be necessary. Soil Investigation Methods: Bore Holes for proposed foundations up to 30m disturbed soil samples are taken by hand/mechanical auger or power operated drill rod at regular intervals field and laboratory tests to determine the precise grading of particles, shear strength, compression strength, moisture and density, and permeability Soil Investigation Methods: Bore Holes Used for proposed foundations up to 30m. Possible methods to obtain disturbed soil samples are: hand or mechanical auger; mechanical auger; and sampling shells. "Setting up a percussion borehole drill" by "Borehole" by Bryn Pinzgauer is geologicboreholes is licensed under CC BY 2.0 licensed under CC BY 2.0 Social media links https://youtu.be/BhjNXKbxhkk Soil analysis Sieve Analysis a laboratory test for grading/size of soil as determined by sieving % of soil passing through the sieve. Source: http://civilblog.org/2014/02/10/how-to-identify-silt-clay-in-the-field/# Reference to regulation: classification of soil particles is based on BS1377 Particle size and distribution Categories of soil are: solid rock; gravels; sands; silts; clays; and peats. Site soil testing techniques Site soil testing techniques Tests designed to evaluate the bearing capacity, density or shear strength of soils. Do not disturb the soil under test. Reference to regulation - BS 1377: Methods of Test for Soils for Civil Engineering Purposes. Compression Test an on-site or laboratory test to measure the compression strengths of cohesive soil. a clay soil sample is loaded until shear or bulging occurs. Source: Reddy, K., (2015). How to do unconfined compressive strength test of soil?. [online] available at: Exerting pressure on weak stratum Bulb of pressure exerted under a pad and strip foundation Combined stress exerted on subsoil from foundations in close proximity Depth of borehole for pad and raft foundations Depth of borehole for close spaced strip or pad foundations Depth of borehole for friction piles Water Table Water Table ground water is the part of precipitation that seeps down through the soil until it reaches rock material that is saturated with water how the ground is saturated below the water table Problems from Ground Water During construction water flows into the voids created by the excavation. Expensive timbering for earth support may be necessary. stage: After the water table could cause flooding during wet season, and building is an unacceptable humidity around finished buildings and structures. completed: Water Table Piezometers used to measure water pressure in saturated soils are dipped into the boreholes for a long period of time to measure the upper and lower limits of the water table level Recommendations 1 2 3 obtain sufficient site and be aware of the get professional advice ground information for objectives of the works, when it is needed, e.g. design and construction and balance geotechnical engineer, investigation cost against environmental specialist risks in both design and consultants construction 46