Answer:

The unit soil pressure or safe bearing pressure is a term used in geotechnical engineering to refer to the maximum pressure that can be applied to the soil without causing excessive settlement or failure. It is an important consideration in the design of foundations for structures to ensure stability and prevent soil failure.

Net Safe Settlement Pressure:
The term "Net Safe Settlement Pressure" is not a commonly used term in geotechnical engineering. Settlement pressure refers to the pressure exerted by the structure on the soil, which causes the soil to compress and settle. The net settlement pressure is the difference between the applied load and the initial stress in the soil before the load was applied. However, it is not commonly referred to as the safe bearing pressure.

Net Ultimate Bearing Pressure:
The term "Net Ultimate Bearing Pressure" is also not a commonly used term in geotechnical engineering. Ultimate bearing pressure refers to the maximum pressure that can be applied to the soil before it fails in shear. It is a measure of the soil's strength and is determined through laboratory testing. The net ultimate bearing pressure is the difference between the applied load and the ultimate bearing capacity of the soil. However, it is not commonly referred to as the safe bearing pressure.

Gross Safe Bearing Pressure:
The term "Gross Safe Bearing Pressure" refers to the total pressure that can be applied to the soil without causing excessive settlement or failure. It takes into account the weight of the structure and any additional loads applied to it. However, it does not consider any factors of safety or the strength of the soil. Therefore, it may not accurately represent the true safe bearing capacity of the soil.

Net Allowable Bearing Pressure:
The term "Net Allowable Bearing Pressure" is the correct term used to refer to the unit soil pressure or safe bearing pressure. It is the maximum pressure that can be applied to the soil, taking into account factors of safety and the strength of the soil. It considers the weight of the structure, any additional loads applied to it, and any safety factors applied by the engineer. The net allowable bearing pressure is determined through a combination of laboratory testing, soil analysis, and engineering judgment. It ensures that the soil can support the load without excessive settlement or failure. Therefore, option B is the correct answer.