Geomechanics magnetic model test is a new test method that simulates gravity field with electromagnetic force field to study geomechanical engineering problems. In geomechanics magnetic model test

the magnetic field is achieved by solenoid and the similar material is made from the mixture of ferromagnetic material and rock-soil mass. The magnetic force

which is decided by the magnetic flux density gradient

will act on ferromagnetic material when it is put in a gradient magnetic field. In order to simulate the uniform gravitational field

a magnetic field with same magnitude and unidirection is needed in a certain space. According to the principle of magnetic circuit design and from different perspectives

three different kinds of magnetic circuit are presented to obtain the requisite magnet field to load the ferromagnetic material. In the optimum test space

the open type magnetic circuit can make full use of the magnetic field so that its magnetic flux density gradient can reach a larger quantity when the current is same; but the uniformity is not as good as expected. Taking advantage of the assumption of no magnetic dispersion

the closed type magnetic circuit has a better performance than the open ones. Comparing with the other two magnetic circuits

though the semi-open type is slightly inferior in terms of weight and efficiency

the uniformity of magnetic flux density gradient is the best of all; whose error is within 5%. In addition

because of the distribution of the coils and the test space

it is more convenient to arrange the testing instruments and loading device. Therefore

the semi-open type magnetic circuit is the optimal choice as the magnetic field generator for geomechanics magnetic model test.