A Critical Review of Environmental Sampling Methods and Tests and Comparison of Tests
Introduction
Preliminary investigations on a proposed construction site require a geotechnical exploration to ascertain the subsurface conditions and determine the suitability of a given location for a particular project. While constructing permanent structures such as roads, residential houses, retaining walls, landscaping infrastructures, parks, swimming pools, and parking lots, it is essential to conduct a series of environmental tests to determine the chemical and physical properties of the in-situ soils, groundwater, and rock types in a given location. These tests may also include a determination of physical properties, chemical properties, compressibility values, soil structures, soil composition, and rock types to enable constructors to design the best foundations that can provide adequate stability for different structures erected on such soils. Construction projects can take various forms, including new constructions, overlays, reconstruction, rehabilitation, rubbilization, and construction of overlays. The classification of construction projects into different categories points out to the extent and complexity of environmental testing required to determine subsurface conditions.
Problem Definition
Sampling soils on proposed construction sites allows the determination of zonal information on the soil conditions. This is particularly important while determining the suitability of a given location for a construction project. Failure to conduct soil tests and geotechnical investigations on proposed construction sites can have damaging outcomes on a given project. Project managers must work hand in hand with environmentalists and geotechnical consultants while assessing the environmental characteristics of a given construction site. This may encompass the determination of soil conditions, stability of underlying rocks, susceptibility to landslides, and underground water, among other conditions. In the absence of soil sampling and testing, project managers may experience challenges while coming up with designs of the proposed structures. Inadequate soil investigation may translate to over-designed foundations since construction engineers cannot get adequate data to create successful designs for the investigated soils (Albatal, Mohammad, & Elrazik, 2013). In some cases, insufficient soil investigation on proposed construction sites can contribute to under-designed structures, and this may increase the risk of failure. Often, inadequate preliminary soil testing has been termed as one source of project cost overruns, safety risks, project delays, non-conformity with regulatory standards, disputes, and other unexpected problems.
Project Aims and Objectives
This study aims to provide a detailed review of the different environmental sampling methods and tests and their comparisons. This will enable the determination of the most effective ways to investigate subsurface soil characteristics for proposed construction sites.
Objectives
Some of the primary objectives of this research include:
- To critically review the varying scope of different soil sampling and testing methods for construction sites.
- To identify the environmental testing requirements addressed by the different soil testing methods.
- To compare the scope and relative efficacy of the different soil testing methods in conducting soil investigations.
Keywords: construction site, subsurface conditions, soil investigation, soil sampling, and soil testing.
Literature Review
Environmental sampling and testing involve the determination of physical properties, chemical properties, and geophysical characteristics of a given soil type that affect its suitability for the construction of different structures. The development of different analytical methods for soil investigation has enabled the determination of different characteristics and properties that characterize those soils. Soil testing involves the collection of representative soil samples, laboratory tests to determine the different soil characteristics and the interpretation of test results (Walworth, 2006). Analytical results obtained from various tests allows geotechnical engineers to come up with project designs that match with the investigated soils. For example, such data can significantly help while determining the right foundations for different construction projects depending on the soil characteristics of a given site. While deciding on which design to adopt in a construction site, construction engineers must collect geological information about the soil and rock types in the proposed location (Sew & Chin, 2000). The collection of such information allows design engineers to determine the type of structures that can be supported on the construction sites. Besides, soil testing enables construction engineers to assess the stability and movement tolerance and other geotechnical information of different soil types.
Conceptual Framework
A conceptual site model (CSM) presents an effective way to describe the physical, chemical, and geotechnical conditions of a given soil type. CSM allows effective planning and management of soil investigations in construction sites. While planning for environmental sampling and testing for soils in construction sites, engineers should come up with a preliminary conceptual site model and refine the CSM as more data is generated from the different soil tests. The CSM should promote understanding of the geological and geotechnical characteristics of the soils, hydrostatigraphic characteristics, geostratigraphic characteristics, chemical constituents, real and apparent density, groundwater flow, saturation percentage, particle size distribution, compaction, bearing capacity, permeability, dynamic soil resistance, soil strength, shear strength, and sand equivalent value (Ministry of Environment and Climate Change Strategy, 2019). A detailed understanding of the CSM will enable design engineers to advance their construction objectives based on the identified soil characteristics in a selected construction site.
Characterization of Geological and Geotechnical Conditions in Soil Investigation
Heureux and Lunne (2019) establish that soil investigation for a proposed construction test site must include a description of soil classification parameters, soil deformation, geological history, soil strength, and flow parameters. Soil investigations should provide sufficient data on representative soil conditions to determine the suitability for a specific project type. Following the identification of a test site, construction engineers should identify or come up with equipment and soil testing methods for characterization. This may entail in-situ testing on multiple test sites, collection of representative samples, and laboratory testing. Soil investigations allow design engineers to develop methods of testing new foundation solutions to eliminate problems that emanate from under-designed and over-designed structures.
While performing soil testing, it is vital to assess the possible geotechnical hazards or contaminations in the test sites or the surrounding areas (Watts & Charles, 2015). For example, areas with a history of industrial activities such as deep mining or infilling may have buried obstructions or secondary foundations, thus unsuitable for construction of structures. The underlying topography of a selected construction site may indicate the possibility of geotechnical hazards in the event a building or any other structure is constructed on the test site. soil testing should provide information on flood risks and hydrostratigraphy of the test site. With soil investigation, engineers can determine geological and geotechnical parameters considered important in performing engineering analysis and developing designs that represent soil conditions in the test site.
Methodology
The primary aim of this environmental testing is to determine the physical, chemical, geological, hydrostatigraphic characteristics, geostratigraphic characteristics of soils on a construction site. The desk study for this assessment will include site description, sampling procedures, and description of test methods.
Sampling Method
Knowles and Dawson (2018) assert that the limit of accuracy in the test results obtained from soil investigations hinges on the sampling techniques deployed. Walworth (2006) emphasizes that successful analysis depends on the quality of samples available for laboratory testing. While performing soil sampling, it is extremely important to ensure the collection of samples from the same depth and in sufficient amounts. Composite sampling provides an accurate and effective way to collect representative samples from the test sites for laboratory analysis. In composite sampling, sub-sample scores will be collected from multiple locations in the field. The random selection of sampling sites allows the collection of representative soil samples for analysis. All sub-samples collected from the test site are composited at the end and composite samples taken for laboratory analysis.
Environmental Tests
Waste Acceptance Criteria (WAC) Testing
This test allows the determination of how different types of wastes behave after placing them in a landfill. Environmental engineers can sort out potentially hazardous wastes to the right landfill sites and determine the appropriate sites for disposal of non-hazardous and inert wastes. The test involves the determination of the approximate volume of wastes to be transferred from a site to an existing landfill. The characterization of landfill wastes as hazardous, inert, or non-hazardous follows, and a decision is made on the type of landfill that suites the different types of wastes. WAC testing involves s series of chemical analysis of wastes to determine the presence and concentration of leachable compounds and a simulation of how the different types of wastes will behave once buried in the selected landfill.
Proctor Compaction Test
The test allows the determination of compaction characteristics of a given soil type in a test site. The test starts with the air-drying of a 200g composite soil sample and its subsequent division into six sub-samples. The soil moisture content is adjusted by adding 3-5% of water into the samples. The soil samples will be thoroughly mixed with water in polythene bags and left for 30 minutes to attain a moisture equilibrium (Sridharan & Sivapullaiah, 2005). What follows is the arrangement of the samples into three layers in the Proctor compaction mold. While in the mold, each layer will be pounded 25 times using a standard pound hammer for compaction. The samples will then be removed from the mold and air-dried, and their dry density and water content measured. A curve of density versus water content in different soil samples provides an accurate indication of optimum water content in the soil that is required to get the maximum dry density.
Atterberg Limits Test
This test allows the measurement of critical water content in fine-grained soil samples. Some of these measures include liquid limit, shrinkage limit, and plastic limit. The Casagrande device provides an accurate measure of the liquid limit of a soil sample. While measuring the plastic limit, a small amount of water will be mixed with the soil sample and the resulting mixture shaped into a ball. The ball will then be placed in a glass plate and rolled into thin threads (3mm in diameter). The plastic limit of the soil is determined by the ability to maintain its integrity as a single thread without breaking. The procedure will then be repeated multiple times while adding different amounts of water. The shrinkage test involves a mathematical computation of the amount of water required to fill all voids in a given soil sample.
Particle Size Distribution Test
This test allows the classification of soils in test sites by size distribution. The soil samples will be passed through sieves of different pore sizes and their particle size distribution measured. For finer soil samples, the test will include a sedimentation process on a laboratory pipette. The soil solution will be stirred using a mechanical stirrer and placed on a water bath to maintain a constant temperature. The specific gravity of the soil solution will be measured at different stages, and the results will be interpreted on a Namographic chart to determine the relative particle size.
The California Bearing Ratio Test (CBR)
The CBR test provides a measure of the load-bearing capacity of a soil sample relative to that of a ground California limestone. A CBR test machine allows construction engineers to perform on-site tests, laboratory tests and in-situ tests to determine the load-bearing ratios for different soil types in the construction sites. A multiplex CBR machine includes a load cell and displacement transducers that can convert test results into an automatic data acquisition (ADA) system for interpretation. Some of the software that supports ADA functions include ELE’s DataSystem (DS 7.3) and provides improved lab efficiency while performing CBR tests. The use of this software translates to minimal operator errors in CBR measurements.
Moisture Content Test
A geotechnical test that allows the determination of moisture content in undisturbed composite samples from a test site. A Speedy Moisture Tester will be used in the measurement of water content in soil samples. A 10g soil sample will be placed in the Speedy Moisture Tester. The reaction between water and calcium carbide yields calcium hydroxide and carbon dioxide. The moisture content in the soil sample is directly proportional to the volume of carbon dioxide produced during the reaction. A pressure gauge attached to the tester provides an accurate measure of the percentage of moisture content in the soil sample.
References
Albatal, A., Mohammad, H., & Elrazik, M. A. (2013). Effect of inadequate site investigation on the cost and time of a construction project. Geotechnical Safety and Risk IV, 331.
Heureux, J. S., & Lunne, T. (2019). Characterization and Engineering Properties of Natural Soils used for Geo-testing.
Knowles, O., & Dawson, A. (2018). Current soil sampling methods–a review. Farm environmental planning–Science, policy and practice, LD Currie & CL Christensen (Eds). Occasional Report, (31).
Ministry of Environment and Climate Change Strategy (2019). British Columbia Field Sampling Manual
Sew, G. S., & Chin, I. T. Y. (2000). Subsurface investigation and interpretation of test results for foundation design in soft clay. In SOGISC-Seminar on Ground Improvement-Soft Clay.
Sridharan, A., & Sivapullaiah, P. V. (2005). Mini compaction test apparatus for fine-grained soils. Geotechnical Testing Journal, 28(3), 240-246.
Walworth, J. L. (2006). Soil sampling and analysis. The University of Arizona, College of Agricultural and Life Sciences. Retrieved April 19, 2020, from cals.arizona.edu/pubs/crops/az1412.pdf
Watts, K. S., & Charles, J. A. (2015). Building on fill: geotechnical aspects. IHS BRE Press.