Abstract：In order to calculate the ultimate bearing capacity of subgrade above the stratum with multiple karst caves, based on the upper bound and the lower bound theorems of the limit analysis as well as finite element method, the computational program was coded in MATLAB. The modified Hoek-Brown criterion was adopted to describe the non-liner characteristic of the rock mass, and then was incorporated into the computational program. On this basis, a dimensionless parameter N? and a reduction factor ξ were defined to estimate the effects of single cave and two caves on the bearing capacity of subgrade, respectively. The numerical results were presented in the form of tables, and the impacts of different parameters on the bearing capacity of subgrade were investigated. The results reveal that N? may increase non-linearly with the increase of the values of H/R (thickness of rock/radius of cave) and geological strength index (GSI), and it has a roughly linear relation with rock type parameter mi. The influence of the rock mass weight on N? could be neglected. The value of ξ increases with the increase of H/R, when X (horizontal distance between two caves)/R≤2. The value of ξ increases with the decrease of H/R, when X/R≥3. ξ has the minimum value at X/R=2, when Y (vertical distance between two caves)/R<3. ξ approaches to 1 when X/R≥3, and in this case it is only necessary to consider the effect of one single cave on bearing capacity. The ultimate failure mechanism of single cave is related to the value of H/R. With the increase of H/R, the failure surface may extend from the top to the bottom of the cave, and the influence range may gradually extend. When the burial depths of two caves are the same, the arching effect may occur if X/R is small, X-shaped rupture planes may occur if X/R is relatively large. When the burial depths of two caves are different, the running-through rupture planes between two caves may gradually disappear with the increase of Y/R. The results for bearing capacity of strip footing located on a rock stratum are compared with those in the previous study, and the difference is within 4%, validating the correctness of the method proposed in this work. Meanwhile, for the convenience of design in engineering practice, the design steps and instructions are provided, which basically meet the requirements in most projects.
