Chapter 11, Problem 11.1P

(a)

To determine

State whether the statement “addition of lime to clays increases the plasticity” is true or false.

Answer to Problem 11.1P

The given statement is $\underset{\_}{\text{False}}$.

Explanation of Solution

Flocculation‑agglomeration is a chemical reaction that occurs when the lime is added to clayey soils and this reaction makes a texture change in the clay soil. In this process, the clay particle clumps together and forms larger particles due to the presence of lime resulting in plasticity reduction.

Therefore, the given statement is $\underset{\_}{\text{False}}$.

(b)

To determine

State whether the statement “fly ash is pozzalanic” is true or false.

Answer to Problem 11.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

Fly ash is a by-product of pulverized coal and is extracted from flue gases through Electrostatic precipitator in dry form. Fly ash is a fine material and possesses good pozzalanic property.

Therefore, the given statement is $\underset{\_}{\text{True}}$.

(c)

To determine

State whether the statement “vibrofoltation is more effective on clays than sands” is true or false.

Answer to Problem 11.1P

The given statement is $\underset{\_}{\text{False}}$.

Explanation of Solution

Vibrofoltation is a construction technique used for the densification of thick layers of loose soils.

Refer Figure 11.3, “Effective range of grain-size distribution of soil for vibration” to identify the grain size in which vibrofloation is effective.

Vibrofoltation is effective for gravel, with 0% to 100% fines and with a grain size of 10 mm to 100 mm.

For coarse and fine sand, with a grain size of 0.1 mm to 10 mm and with 0% to 100% fines, vibrofoltation is effective.

For silts and clay, vibrofoltation is effective for clays with 0% to 40% fines and with a grain size of 0.1 mm to 0.001 mm.

Thus, vibrofoltation is more effective on sands than clays.

Therefore, the given statement is $\underset{\_}{\text{False}}$.

(d)

To determine

State whether the statement “pre-compression is mostly applied on normally consolidated clays” is true or false.

Answer to Problem 11.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

Normally consolidation clays (NCC) are highly compressible. Thus, large constructions over the layer of NCC soils result in large consolidation settlement.

Pre-compression is applied on NCC to prevent the post consolidation settlement.

Ordinary soils generally are not highly compressive and thus less post consolidation settlement.

Thus, pre-compression are mostly applied on NCC.

Therefore, the given statement is $\underset{\_}{\text{True}}$.

(e)

To determine

State whether the statement “duration of pre-compression is shorter, when the surcharge is larger in pre-compression” is true or false.

Answer to Problem 11.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

Show the pre-compression on normally consolidated clay due to structural load $\Delta {\sigma }_{\left(p\right)}$ and due to surcharge load $\left[\Delta {\sigma }_{\left(p\right)}+\Delta {\sigma }_{\left(f\right)}\right]$ as in Figure (1).

Figure 1 shows the settlement-time relationship under the surcharge load of $\left[\Delta {\sigma }_{\left(p\right)}+\Delta {\sigma }_{\left(f\right)}\right]$.

The settlement, $S_{\left(p\right)}$, occurs due to structural load $\Delta {\sigma }_{\left(p\right)}$ and the settlement $S_{\left(p+f\right)}$ occurs due to the surcharge load.

The settlement of the clay layer rises with increase in time in both the cases (settlement due to structural load and surcharge load). Thus, the surcharge increases with the increase in the settlement with respect to time.

$S_{\left(p+f\right)}>S_p$

Therefore, the given statement is $\underset{\_}{\text{True}}$.