Modulus of Subsoil Reaction According to Chinese standards
The calculation of modulus of subsoil reaction according to Chinese standards is based on the JGJ 120-2012 standard (Technical specification for retaining and protection of building foundation excavations) for "m" method.
For "m" method, the modulus of subsoil reaction kh is given by the following formula:
where: | m | - | proportional coefficient of modulus of subsoil reaction [kN/m4] |
z | - | depth of the calculation point from the original ground [m] | |
h | - | depth of the calculation point from the ditch bottom at current stage of construction [m] |
From previous formula it’s obvious that calculation of modulus kh is linear with depth of point during the analysis.
Proportional coefficientm should be determined from pile test with horizontal load. If there are no test data, Chinese standard JGJ 120-2012 suggest an empirical formula to estimate this coefficient:
where: | c | - | cohesion (shear strength) of soil [kPa] |
φ | - | angle of internal friction of soil [°] | |
vb | - | horizontal displacement of sheeting structure at the ditch bottom [mm]; when the displacement is smaller than 10 mm, then vb = 10 mm |
Other methods ("c" method and "k" method) are not published in JGJ 120-2012 standard, but they are based on practical experience and they are used in China profusely. Then the modulus of subsoil reaction kh is given by the following formula:
If exponent n = 0,5, it's "c" method and then a = c (kN/m3.5).
If exponent n = 0, it's "k" method and then, a = K (kN/m3).
It’s obvious that for "m" method, n = 1.
Literature:
JGJ 120-2012 (Technical specification for retaining and protection of building foundation excavations).