Abstract: Traditional single-sided concrete support servo system used in large foundation pits in soft soil areas exhibits various challenges such as overlarge axial force loss and insufficient deformation coordination of the retaining structures on both sides of the support. Therefore, a case study is conducted on the expansion project of the Taihe Sewage Treatment Plant. Based on real-time axial force monitoring and finite element analysis results, the axial force transmission form of concrete support under the conditions of servo loading points arranged at both ends and servo loading at both ends is studied. A comparison is made between the axial force difference (along the support direction, between the front and rear of the joint) and the coupling beam shear force of the concrete support-coupling beam-column joint. The results indicate that the coupling beam has a limited impact on the axial force loss of the support along the support direction. Furthermore, based on derivation of theoretical formulas and fitting with measured data, a calculation method for the axial force transmission of supports in long-distance servo systems is proposed. The results are as follows: (1) The axial force loss reaches the maximum in the support middle under conditions of servo loading points arranged at both ends and servo loading at both ends. (2) The axial force loss of single-sided servo support is primarily affected by the support length, vertical spacing of supports, and compressive stiffness of the support. (3) The axial force transfer ratio decreases with increasing support length and decreasing support compressive stiffness; whereas it decreases first and then increases with increasing bending stiffness of the column and decreasing vertical support spacing. (4) The ratio between axial force variation at no-servo end to servo force variation is defined to be transferring rate of servo force variation. (5) Under a 50% transferring rate, the length of single-sided servo concrete support should not exceed 38.0 m.

Key words: deep and large foundation pit, concrete support, servo system, axial force transmission