What is Plate Load Test?
The plate load test is a site investigation technique used to determine the ultimate bearing capacity of soil and the settlement of the foundation under different loads for both clayey and sandy soils. The results of this test are used to assist in selecting and designing the foundation. To ensure safety, a suitable factor of safety is applied in calculating the safe bearing capacity.
In essence, the plate load test involves applying a load to a steel plate placed on the soil surface and then measuring the resulting settlement. By analyzing the data collected from the test, engineers can accurately determine the strength of the soil and its ability to support the foundation of a structure.
In addition to providing information on the bearing capacity of the soil, the plate load test also helps engineers to identify any potential issues that may arise during construction. By conducting this test prior to the construction of a building, engineers can develop a more effective foundation design that takes into account any weaknesses in the soil.
Overall, the plate load test is an essential tool in the construction industry, as it provides valuable information on the strength of the soil and helps engineers to design foundations that are safe and effective. By applying a factor of safety to the results of the test, engineers can ensure that the foundation will be able to support the weight of the structure without any risk of failure.
Apparatus for Plate Load Test on Soil
There are five items listed: mild steel plate, hydraulic jack, reaction beam or reaction truss, dial gauges, and excavating tools.
A mild steel plate is a type of metal plate that is often used in construction and manufacturing due to its strength and durability. It is commonly used in applications where high stress and heavy loads are expected.
A hydraulic jack is a type of mechanical device used to lift heavy objects or apply pressure to a material. Hydraulic jacks work by applying force through the use of hydraulic fluid, which allows for a relatively small force to be used to lift a heavy object.
A reaction beam or reaction truss is a type of support structure used in engineering and construction projects. It is designed to provide a stable foundation or reaction point for other structures or equipment. Reaction beams and trusses are often used in conjunction with other types of support structures, such as columns or walls.
Dial gauges are precision instruments used to measure small distances or changes in position. They are commonly used in manufacturing and engineering to ensure precise measurements and to monitor changes in position over time.
Excavating tools are a group of tools used for digging and moving earth, rocks, and other materials. They include tools such as shovels, pickaxes, and bulldozers. Excavating tools are commonly used in construction and mining, as well as other types of excavation projects.
Procedure of Plate Load Test on Soil
A pit is dug in the ground for the purpose of laying a foundation, and its size is typically five times the size of the plate that will be used. The depth of the pit should be equal to the proposed depth of the foundation. The plate used for this purpose is made of mild steel and can either be square with dimensions of 0.3m x 0.3m or circular with a diameter of 0.3m, and it has a thickness of 25mm. Once the pit is excavated, a hole is dug at the center of the pit with a thickness of “Dp” as calculated by the given formula, and the steel plate is arranged in this hole.
The plate is first arranged in the central hole, and then a hydraulic jack is placed on top of the plate to apply load. To take up the reaction, a reaction beam or reaction trusses are provided for the hydraulic jack. Alternatively, a loaded platform can be created using sand bags or other means to provide the necessary reaction. Once the hydraulic jack is set, a seating load of 7kN/m2 is applied to the plate and then released after a certain amount of time. Settlement values are recorded using dial gauges placed at the bottom of the plate at specific time intervals, such as 1 minute, 5 minutes, 10 minutes, 20 minutes, 40 minutes, and 60 minutes, and then at one-hour intervals thereafter. This process continues until a total settlement of 25mm has occurred.
A truss is arranged on jacks, with both sides of the truss anchored to the ground with strong supports. The two ends of the truss are loaded uniformly, and the load is transformed into the plate, causing settlement to occur. The load is incrementally increased by 2kN at regular intervals, and observations are made of the settlement at each interval. This process continues until the rate of settlement is reduced to 0.2mm per hour. These observations are specifically made for clayey soils, and the testing is done until the desired settlement rate is achieved.
Calculation of Bearing Capacity from Plate Load Test
A logarithmic graph is created using the results obtained from a plate load test, with the loads applied plotted on the x-axis and the corresponding settlements plotted on the y-axis. By examining the graph, we can determine the value of the ultimate load for the plate, which is equivalent to the settlement at a point that is 1/5th of the plate width. This information allows us to understand the load-bearing capacity of the plate and its ability to withstand applied loads without excessive settlements. By analyzing the graph, we can obtain valuable insights into the behavior of the plate under different load conditions, helping us make informed decisions about its suitability for specific engineering applications.
The ultimate load for a plate is determined by the point at which the curve breaks. This load is considered as the ultimate bearing capacity of the soil for foundation design. By analyzing the behavior of the plate under increasing loads, we can identify the load at which the plate fails, resulting in the curve breaking. This ultimate load value serves as a key parameter in determining the safe bearing capacity of the soil for designing foundations. Understanding the ultimate load for a plate helps engineers assess the stability and load-carrying capacity of the soil, providing crucial information for foundation design and ensuring the safety and durability of structures.
Bearing Capacity Calculation for Clayey Soils
The ultimate bearing capacity of a plate is equivalent to the ultimate load that the plate can bear without collapsing. This relationship can be expressed mathematically as qu(f) = qu(p), where qu(f) represents the ultimate bearing capacity and qu(p) represents the ultimate load for the plate. In other words, the maximum amount of load that a plate can withstand before it fails is the same as the ultimate bearing capacity of that plate. This relationship is an important factor to consider when designing structures that involve the use of plates, as it helps to ensure that the plates are able to withstand the expected loads without collapsing or failing. By understanding the relationship between the ultimate bearing capacity and the ultimate load for a plate, engineers and designers can make informed decisions about the size and thickness of the plate needed for a particular application.
Bearing Capacity Calculation for Sandy Soils
The given context provides formulas for calculating the ultimate bearing capacity and safe bearing capacity of a plate. The ultimate bearing capacity is determined by multiplying the ultimate load for the plate by the ratio of the width of the pit to the size of the plate. The resulting equation is: ultimate bearing capacity = ultimate load for plate x {Width of pit (Bf) / Size of Plate (Bp)}.
Another formula provided is for calculating the safe bearing capacity, which is the ultimate bearing capacity divided by a factor of safety. The factor of safety typically ranges from 2 to 3. The equation for safe bearing capacity is: safe bearing capacity = ultimate bearing capacity / factor of safety.
Overall, these formulas provide a way to calculate the maximum load that a plate can bear, as well as a safety factor to ensure that the load does not exceed the plate’s capabilities. By using these equations, engineers and builders can design structures and equipment that are safe and efficient.
Calculation of Foundation Settlement from Plate Load Test
We can also calculate settlement for given load from plate load test as follows
Foundation Settlement Calculation on Clayey Soils
The expression “Settlement of foundation (sf) = sp x Bf/Bp” relates to the calculation of the settlement of a foundation. Settlement refers to the sinking of a foundation into the soil over time. This sinking can cause structural damage to a building, so it is important to calculate the expected settlement in order to design a foundation that can withstand it.
The settlement of a foundation is determined by the soil’s ability to support the weight of the building. The soil’s ability to support weight is affected by a number of factors, including its composition, moisture content, and density. These factors can vary depending on the location of the building, so it is important to conduct soil tests in order to accurately determine the settlement.
The expression “Settlement of foundation (sf) = sp x Bf/Bp” is a formula that is used to calculate the settlement of a foundation. The variables in the formula represent different factors that can affect settlement. “Sp” represents the pressure that the building exerts on the soil, “Bf” represents the width of the foundation, and “Bp” represents the width of the loaded area of the foundation. By plugging these variables into the formula, engineers can determine the expected settlement of the foundation and design it accordingly.
It is important to note that settlement is not always predictable, and unexpected settlement can occur due to factors such as changes in soil moisture or temperature. However, by using formulas such as “Settlement of foundation (sf) = sp x Bf/Bp” and conducting thorough soil tests, engineers can design foundations that are better equipped to withstand settlement and minimize the risk of structural damage to the building.
Foundation Settlement Calculation on Sandy Soils
The provided equation relates to the settlement of a foundation, which can be calculated using the dimensions of the foundation and plate. The settlement of a foundation refers to the amount of vertical displacement or sinking that occurs in the soil supporting the foundation, which can lead to structural damage if it exceeds certain limits.
The equation uses two variables, Bf and Bp, which represent the widths of the foundation and plate, respectively. The equation also includes a constant value of 0.3, which is added to both Bf and Bp.
To calculate the settlement of the foundation, the equation requires the values of sp and sf. These values are related to the soil properties and the load applied to the foundation. In practical applications, these values are determined through testing and analysis of soil samples.
By substituting the values of Bf, Bp, sp, and sf into the equation, one can calculate the settlement of the foundation. The result will provide valuable information for engineers and builders to ensure the stability and safety of the structure built on the foundation.