Is it good practice to use soils with T-times greater than 20 min/cm, even though they are allowed in the Building Code?

Is it good practice to use soils with T-times greater than 20 min/cm, even though they are allowed in the Building Code?

• A. Yes, it is acceptable
• B. No, they are often difficult to handle during construction, especially in wet weather
• C. Only in dry weather
• D. Never under any circumstances

Answer: (B)

The key idea here is that T-time tells you how quickly wastewater infiltrates into the soil. A T-time greater than 20 minutes per centimeter means very slow infiltration, which is typical of heavy, clayey soils. Even if the Building Code allows using such soils, they create practical problems during installation, especially in wet weather. Wet, slow-draining soils are difficult to excavate, keep dry, and backfill properly; trenches can stay muddy, walls may cave in, equipment can get stuck, and overall construction becomes unreliable and slow. Because of these handling and installation challenges, soils with long T-times are not considered good practice to rely on, despite code allowances.

The key idea here is that T-time tells you how quickly wastewater infiltrates into the soil. A T-time greater than 20 minutes per centimeter means very slow infiltration, which is typical of heavy, clayey soils. Even if the Building Code allows using such soils, they create practical problems during installation, especially in wet weather. Wet, slow-draining soils are difficult to excavate, keep dry, and backfill properly; trenches can stay muddy, walls may cave in, equipment can get stuck, and overall construction becomes unreliable and slow. Because of these handling and installation challenges, soils with long T-times are not considered good practice to rely on, despite code allowances.