Each natural object is modeled via properties. To avoid the misunderstanding during communication, scientists often use terms (short names) for properties instead of their full names. Those terms are standardized in the national or global scale. However, in Vietnamese reports on geotechnical investigation, terms and their symbols and measurement units are not used consistently.
Each natural object is modeled via properties. To avoid the misunderstanding during communication, scientists often use terms (short names) for properties instead of their full names. Those terms are standardized in the national or global scale. However, in Vietnamese reports on geotechnical investigation, terms and their symbols and measurement units are not used consistently.Density – Unit weight
The term of “density” means ‘mass per unit volume’ and symbolized by a Greek character ρ (rho). Its dimension is [mass]/[volume].
Measurement units of mass are g, kg, ton… and those of volume are mm³, cm³, m³… Therefore, the measurement units of density are g/cm³, T/m³…
The term of “unit weight” means ‘weight per unit volume’ and symbolized by a Greek character γ (gamma). Its dimension is [weight]/[volume]. Measurement units of weight are N, kN… and those of weight should be N/m³, kN/m³…
In order to guarantee the consistency in using terms-symbols-units, the term ‘density’ should be accompanied with the symbol ρ and measurement unit of g/cm³ or kg/m³ or T/m³… Meanwhile, the term ‘unit weight’ should be accompanied with the symbol γ and measurement unit of kN/m³ or N/m³…
In Vietnamese reports on geotechnical investigation, there are common misuses as:
- Term of ‘unit weight’ is accompanied with symbol γ and measurement unit of g/cm³. In this case, the unit of kN/m³ is prefered.
- Term of ‘density’ is accompanied with symbol γ and measurement unit of g/cm³. In this case, the symbol ρ should be used.
- Term of ‘wet unit weight’ is noted by a symbol γw (w means ‘wet’ in English) but dry unit weight is noted by γk (k means ‘dry’ in Vietnamese) and submerged unit weight is noted by γđn (đn means ‘submerged’ in Vietnamese): this is a situation of ‘English-Vietnamese harmony’!
Atterberg limits
The term of ‘liquid limit’ is noted by wch (ch means ‘liquid’ in Vietnamese) but plastic limit is noted by wp (p means ‘plastic’ in English): this is a situation of ‘English-Vietnamese harmony’ once again!
kG/cm² - Kg/cm² - kgf/cm² - KG/cm²
According to Decree No. 65/2001/NĐ-CP and No. 134/2007/NĐ-CP issued by Government about Vietnamese legal units of measurement, measurement unit of pressure is pascal (Pa). Therefore, in the field of geotechnical engineering, pressure or stress will be expressed in kilopascal (kPa) or kG/cm² in the update or old version of units of measurement respectively. However, people use randomly different symbols of units: kG/cm² or Kg/cm² or kgf/cm² or KG/cm²… Which one is the correct writing?
Because the dimension of pressure is [force]/[area] and ‘kg’ is the measurement unit of mass so ‘kg’ could not be used in the dimensional formula of pressure. Therefore, kg/cm² or KG/cm² or Kg/cm² are not correct writing. The correct ones are kG/cm² or kgf/cm². In some documents, unit of kgf/cm² is also written as ksc (kilogram-force per square centimeter).
Q: Why is an uppercase character 'K' in ‘KG/cm²’ a wrong writing?
A: The character 'k' in kG/cm²' is a unit prefix and means 'kilo' so it must not be written in uppercase.
Q: Why is a character 'G' written in uppercase in ‘kG/cm²’?
A: Character 'G' is written in uppercase to emphasize that ‘kG’ is kilogram-force (force value), not kilogram (mass value).
Q: Why a character f is needed in kgf/cm²?
A: Similarly, the character ‘f’ is used to emphasize that ‘kgf’ is measurement unit of force (kilogram-force) not the measurement unit of mass (kilogram).
Q: Does the unit of ‘kg/cm²’ exist ?
A: Yes, it does but it is used to express the concept of ‘a surface density measurement unit’