This study have taken Nanning Ronghe East Railway Station City Plaza as the engineering background, the O-cell method for static load testing of foundation piles were adopted to systematically carry out the effect of combination grouted in the strongly weathered mudstone stratum. A comparative experiment was conducted using two sets of six test piles to analyze the bearing capacity and internal force differences between grouted and ungrouted piles. The results show that the load-settlement curves of test piles were slow-variation type, with obvious mutation characteristics, which confirms that the pile-soil interaction exhibits the friction-type pile characteristics in the mudstone layer. In the mudstone layer, a very small relative pile-soil displacement could trigger a significant change in the lateral resistive force of the pile, and the greater the difference in the weathering strength of the mudstone, the more pronounced is the difference in the lateral resistive performance of the foundation pile. Under the same working conditions, significantly enhance the lateral resistance and end resistance of the pile, and then improve the stability of the pile foundation bearing performance. The bearing capacity of post-grouted piles was increased by 1.71, 1.75, and 1.72 times compared with the design values, and the ultimate lateral resistance of strongly weathered mudstone and strongly weathered sandstone was increased by 43.4% and 44.3% compared with the test values of ungrouted piles, respectively. The ultimate end resistance of post grouting for strongly weathered mudstone and strongly weathered sandstone was improved by 39.5% and 46.9% respectively compared with the surveyed values. This method can meet the design requirements under the condition of shortening the pile length, and the results can provide an important reference basis for similar projects in strongly weathered mudstone strata.