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 coefficient m 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).