Soil spatial variability is a common situation in marine geotechnical engineering, while most studies have primarily focused on evaluating the uniaxial vertical (V), horizontal (H), or moment (M) bearing capacity of foundations in spatially variable clay. Whereas the process of combined bearing capacity analysis by probe method is complex, resulting in low efficiency. As a result, the simplified modified swipe (SMS) method is proposed in this paper, which can represent the capacity in any direction of the load space accurately and takes just 6.5 times the duration of a single probe loading for a half-failure envelope. Based on the established three-dimensional random finite element models, the effectiveness of this method is demonstrated by analyzing the combined bearing capacity of five kinds of foundations in spatially variable clay. Furthermore, Monte Carlo simulations revealed that the spatial variability of the soil cause various failure envelopes, and the response of the combined bearing capacity is not identical in all directions. The VHM failure envelopes with different probabilities are given and could be found that the safety factors recommended by the guidelines are insufficiently conservative for structures susceptible to soil spatial variability. Finally, a strategy for applying different safety factors to both load directions is proposed, which could be helpful for the design of foundations in spatially variable clay.

土壤空间变异是海洋岩土工程中的常见情况，而大多数研究主要集中于评估空间变异粘土基础的单轴垂直（ V）、水平（H）或弯矩（M ）承载能力。而探针法组合承载力分析过程复杂，效率低。因此，本文提出了简化改进的滑动（SMS）方法，该方法可以准确地表示负载空间任意方向的容量，并且对于半失效包络线而言，仅需单探针加载持续时间的6.5倍。基于建立的三维随机有限元模型，通过对空间变化粘土中五种地基的组合承载力分析，验证了该方法的有效性。此外，蒙特卡罗模拟表明，土壤的空间变化会导致各种破坏包络线，并且组合承载力的响应在所有方向上并不相同。给出了不同概率的VHM破坏包络线，可以发现指南推荐的安全系数对于易受土壤空间变异影响的结构来说不够保守。最后，提出了一种在两个载荷方向应用不同安全系数的策略，这有助于空间可变粘土基础的设计。