We are all familiar with soil and how important it is to any kind of construction project. The houses we live in, the offices we work from, the roads we use to move from one point to another etc, just to name a few. All this depend highly on the soil we see and walk on every day. Often, by just using our eyes one can quickly tell whether the soil is sand, clay, gravel, silt, peat, rock or loam. However, we can never tell whether the type of soil we just identified with our eyes can sustain and bring to life a proposed structure from building architects and infrastructure design engineers. And this is where soil testing comes in, the most important procedure to conduct before any construction project commences at a particular site with a particular type of soil identified.
“It is important to check the quality of soil before you build your project (road/pavement/construction etc.). The ground where you are planning to make your project it is important to check the soil quality of it before your construction work begins,” remarks Chris Muya MD at Measurement Systems Ltd.
In David Adede’s view, Director at Rock Link Geological Consultants Ltd, “Soil testing gives the engineering properties of the formation upon which the construction will be based. The construction will therefore be designed based on the properties of the soil or rock as studied through geotechnical investigation. The test result will be very important in deciding the type and depth of foundation, the type of materials to be used during the construction, the height, size and weight of the construction.”
Failure to test site soils adequately and correctly can cause critical levels of financial and safety risks. It is therefore very important to understand the soil properties and make use of the acquired information in the planning and designing of the project phases.
A good example of soil failure is the leaning tower of Pisa located in Italy in the city of Pisa. Originally designed to stand at 60 meters, the current height measurements of the tower stands at 56.67m =highest side; 55,86m =lowest side. The tower has recorded a nearly four-degree lean, as a result of an unstable foundation that could have been caused by poor soil testing analysis or no tests were conducted at all. It was until the 1920s the foundations of the tower were injected with cement grouting that has stabilized the tower to some extent.
“Soil test is very important step before construction begins. If the soil testing is not done, then the project will be exposed to failures/unknown dangers and the end result could be fatal,” emphasized Muya.
He continues that “Soil testing is primarily done to test the bearing capacity on the soil on that ground. The chemical and physical composition of the soil is checked during this process. The soil must have the ability to withstand the weight of the project. Quality of soil not only determines the bearing capacity but it enables to determine the structure stabilization. Quality of Soil depends on various factors such as weather, climate change and for the past years the land was deployed for what purpose and what was there previously.”
“For example, the length and depth of the pillar determined during the foundation depending upon the quality of soil. The water level of the soil only can be determined from soil testing. Based on the soil testing reports quality of material can be decided. For example, if due to moisture the area is prone to corrosion then it is important to choose only corrosion resistant re-bars for the construction or alternatively use necessary additives to inhibit corrosion,” he elaborated.
Some of the different types of Soil Testing for Construction
√ Gravity Test
√ Moisture Test
√ Atterberg’s Limits Test
• Liquid Limit
• Plastic Limit
• Shrinkage Limit
√ Dry Density Test
• Core Cutter Method
• Sand Replacement Method
√ Proctor’s Compaction Test
Factors to consider when conducting soil testing
According to Muya, due to the many geotechnical studies that can be undertaken on soil, there are several guiding factors that inform what test to be undertaken. These include: –
The type & importance of the project one intends to undertake. For example, undertaking soil analysis for purposes of mining is will be different from the analysis of soil where one is to carry out an agricultural project or a construction etc.
The costs for undertaking the analysis. This is basically due to the financial envelope allocated to the project.
General classification of soil based on sieve analysis preliminary tests or sample observation (type of soil/rock,), variation of soil properties/ geological formation in the land on which structure is to be constructed.
Selection of type of foundation (shallow / deep, raft etc.) for a construction project
Depth of compressible layer and its thickness.
Effect of ground water table variation.
Modifications/ improvements in existing soil properties are proposed or not.
Variations in factors which will affect bearing /strength properties and settlement/ deformation of the soil.
Though above mentioned factors makes difficulty in decision in selecting number of lab and field tests to be performed since cost of geotechnical investigation, facilities available, data and experience available on geotechnical investigation on similar type of soil are also important factors need to consider. The prevailing construction codes/standards will give guidelines for number of tests to be performed. However, revisions in codes or standards under development will be of greast help since they will consider research experiences in geotechnical investigations, effect of change in soil conditions and the performance of existing structures.
Adede add’s that other soil testing factors to consider include:-
Location of the project
Nature of the proposed development
Design of the proposed development i. e, depth, size, length, weight, volume etc
All construction projects are made on the soil. The soil has to take the weight of the structures. Soil testing provides important clues about the soil’s bearing capacity, density, compaction, presence of organic matter, sand, and contaminants. Sometimes the existing soil needs to be removed because it is contaminated, which could be harmful to habitat.
For instance, old gas stations often have deteriorating underground gasoline tanks. The gasoline leaks out and contaminates the soil and groundwater over time. In these cases, careful removal and disposal of contaminated soils is necessary. This process is regulated by the EPA and local authorities.
Sometimes we just need to remove organic matter and replace it with an inorganic substitute that is more stable, like gravel. Once the unsuitable soil is replaced with load bearing soil, the foundation can be built.
