Soft capping help rammed soil resists rainfalls: A simulation experiment of consolidation performance of soft capping on rammed soil under precipitation

The importance of soft capping, one preventive conservation method on earthen sites, is increasingly felt, particularly to rammed earth relics, whereas actual resistance abilities of soft-capped soil against short and intensive rains remains unclear. In this research, we used two specific herbaceous plants to soft cap large-scale rammed soil samples. Strength tests and simulation experiments were used to unveil erosion characteristics. Root structures were specifically observed to further reveal their influence on consolidation performances. Results indicate that pulling resistance of soft-capped rammed soil samples increases a lot. Compression by ramming and soil aggregation owing to secretions released by roots lead to significant improvement of the whole stability. When exposed to precipitation, the soil mass of soft-capping samples decreases sharply, whereas diverse root growth patterns impact soil erosion degree. More horizontally extended roots at the early growth stage of herbaceous plants help reduce the occurrence of surface deterioration like cracks, collapses, and gullies to a large extent. By contrast, those grow more fibrous roots in all directions can both decrease sectional deformation and maintain the whole stability. This is the first study concerning how and to what degree soft capping could consolidate rammed soil, which sheds light on prospective application of herbaceous plants with distinct roots to meet diverse conservation needs of rammed soil relics.