2.2.2. Under Revision

Log – time curve fitting method consists of steps that are used to determine the coefficient of consolidation by analyzing laboratory data.

The log-time curve fitting method is a technique used in soil mechanics to assess how soil undergoes consolidation over time. This method involves creating a log scale graph based on experimental data, where you compare dial gauge readings over time. By doing so, you can estimate how quickly or slowly a soil sample consolidates when subjected to pressure changes.

Imagine a sponge soaking up water. When you put the sponge in water, it slowly absorbs the liquid. The log-time curve helps scientists understand how quickly that absorption happens over time. In the same way, we watch how soil absorbs water under pressure to measure its consolidation.

1. Plot the dial reading of compression for a given pressure increment versus time on a log scale.
2. Plot two points P and Q on the upper portion of the consolidation curve (say compression line) corresponding to time t1 and t2 such that t2=4t1.

The first step involves collecting data on how much the soil compresses at specific time intervals when pressure is applied. Then, you convert this time data to a logarithmic scale, which helps to reveal patterns in the data that are not immediately apparent in a linear scale. By choosing two points, P (t1) and Q (t2), on this graph, we can observe the differences in dial readings, which reflect how much the soil has consolidated at those times.

Think of it like watching the clock while baking a cake. You note how the cake rises every minute compared to how high it is at four minutes. Just as you take those notes to understand the baking process, soil scientists take similar notes to analyze how soil responds to pressure over time.

3. Let x be the difference in dial reading between P and Q. Locate R at a vertical distance x above point P. 4. Draw a horizontal line RS; the dial reading corresponding to this line is d0, which corresponds with 0% consolidation.

Once you plot points P and Q, you find the difference in the dial readings, denoted as x. This difference is crucial because it tells you how much the soil has compressed between those two time intervals. By marking point R at a distance x above P, you can visually determine what the dial reading would represent if no consolidation had occurred (0% consolidation), which is a baseline for comparison.

Imagine using a ruler to measure the height of your sponge before and after soaking it in water. The difference in height tells you how much the sponge absorbed. Similarly, the difference in the dial readings for soil helps scientists measure how much soil has compressed under pressure.

5. Project the straight line portion of primary and secondary consolidation to intersect at point T. The dial reading corresponding to T is d100 and this corresponds to 100% consolidation.

In this last step, you take the lines representing both primary and secondary consolidation and extend them until they meet at a point T. This intersection indicates that the soil has completely consolidated under the applied pressure, marking 100% consolidation. The dial reading at this point provides a final value important for understanding the material's full capacity to settle and stabilize overtime.

Think of filling a container with water until it reaches the brim. When the water becomes completely full, you can think of this as 100% consolidation of the container’s capacity. Similarly, identifying point T in the soil data tells scientists when the soil has completely settled under the pressure and is stable.

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