A Plate Load Test is a valuable method to determine the strength of the soil beneath the surface. It's akin to gently pushing the ground to gauge its capacity to withstand the weight. In this post, we'll walk you through the straightforward procedure of this test:
Step 1: At a specified depth (D), create a pit measuring 5 times the size of the plate (Bp) in both length and width. The plate load test is conducted by drilling a hole of dimensions Bp x Bp within the pit, as depicted in the figure below.
Step 2: Insert a sizable flat plate into the hole. The plate is connected to a machine capable of applying weight. Begin by applying and releasing an initial load of 7 kN/m².
Step 3: Slowly increment the weight on the plate. The plate can be loaded using Kentledge or through a truss/beam reaction.
Step 4: Apply loads in increments of 20% of the safe load or 1/10th of the ultimate load.
Step 5: Record the settlement at intervals of 1, 5, 10, 20, and 60 minutes, and subsequently at 2-hour intervals.
Step 6: Increase Load When the settlement rate reaches 2 mm per minute, apply a higher load.
Step 7: Repeat the test until failure occurs or a 20 mm settlement is reached.
Analyzing the Results: Pay close attention to the results. Consider the amount of weight added before the soil's compression. This weight offers insights into the soil's strength. If the soil compresses significantly, it may not be very strong. Conversely, minimal compression indicates greater strength.
Bearing Capacity:
Bearing capacity mirrors ground strength. It signifies the weight the soil can bear before sinking or collapsing.
Calculation of Bearing Capacity from Plate Load Test:
The load-settlement curve is drawn after collecting field data. It is a logarithmic graph with the applied load on the X-axis and the settlement on the Y-axis. The ultimate load for the plate is obtained from the graph, which is the corresponding load for one-fifth of the plate width settlement.
The curve is broken at one point when the points are plotted on the graph. The ultimate load on the plate is the appropriate load to that breakpoint. The ultimate bearing capacity can be estimated using the plate's ultimate load. To estimate the safe bearing capacity of soil from the foundation, the ultimate bearing capacity is divided by a suitable factor of safety.
Bearing Capacity for Clay: For clayey soil, calculate the ultimate bearing capacity using the equation:
Ultimate Bearing Capacity = Ultimate Load for the Plate
Bearing Capacity for Sand: For sandy soil, the equation is slightly differs:
Ultimate Bearing Capacity = Ultimate Load for the Plate * (Width of pit/Size of pit)
Safe Bearing Capacity = Ultimate Bearing Capacity/Factor of Safety
Typically, the range for the factor of safety varies from 2 to 3
You can calculate the ultimate bearing capacity by inputting values for cohesion, unit weight, plate width, and soil factors. This reveals how much weight the soil can support per unit area. The Plate Load Test and understanding bearing capacity are fundamental tools in engineering, ensuring that the ground beneath us is sturdy and reliable.
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