Problem 1: Basic Time for Primary Consolidation (Double Drainage)

A $4\text{ m}$ thick layer of soft clay is subjected to a preloading surcharge. The clay layer is sandwiched between a layer of dense sand above and a gravel layer below. The coefficient of vertical consolidation for the clay is $c_v = 1.2 \times 10^{-3} \text{ m}^2/\text{day}$. Determine the time required to achieve $50\%$ consolidation ($U = 50\%$), given that the vertical time factor $T_v$ for $U = 50\%$ is $0.197$.

Problem 2: Time for Primary Consolidation (Single Drainage)

Re-evaluate the scenario from Problem 1, but assume the soft clay layer is situated directly on top of impermeable bedrock, with sand only on top. Calculate the time required to achieve $90\%$ consolidation ($T_v = 0.848$) under this new condition.

Problem 3: Accelerating Consolidation with PVDs

To solve the $31\text{-year}$ timeline issue from Problem 2, the engineer decides to install PVDs. The drains are installed in a square grid spacing ($S$) of $1.5\text{ m}$. The equivalent diameter of the soil cylinder influenced by each drain ($D_e$) for a square pattern is calculated as $1.13S$. The coefficient of horizontal consolidation is $c_h = 2.5 \times 10^{-3} \text{ m}^2/\text{day}$. The radial time factor ($T_r$) for $90\%$ horizontal consolidation is calculated to be $0.65$. Determine the new time required to reach $90\%$ consolidation.

Problem 4: Optimizing PVD Spacing for a Strict Timeline

A project requires $90\%$ consolidation ($T_r = 0.65$) to be achieved within $180\text{ days}$ ($t = 180$) to meet a strict construction schedule. The soil has a horizontal consolidation coefficient $c_h = 3.0 \times 10^{-3} \text{ m}^2/\text{day}$. Calculate the required equivalent diameter ($D_e$), and determine the required triangular grid spacing ($S$). Note: For a triangular pattern, $D_e = 1.05S$.

Case Study 1: Managing the "Smear Zone" Effect

During the installation of PVDs for a bridge approach embankment, the contractor uses a large, thick steel mandrel to push the drains into the soft, sensitive clay. Subsequent monitoring reveals that consolidation is occurring much slower than the theoretical radial time factor predictions.

Case Study 2: Surcharge combined with Vacuum Preloading

An airport runway extension is being built over exceptionally soft, fluid-like muds. Traditional surcharge preloading (piling up earth) is impossible because the soft mud cannot support the weight of the surcharge soil without experiencing immediate shear failure (mudwaves).