Experimental Investigation of the Arching Effect and Joint Optimization of a Timber-Pile-Supported Mulberry Branch Bundle Arch Revetment

Conventional rigid revetments provide limited ecological functions, while flexible biomass-based systems often lack adequate load-bearing stability. This study developed a timber-pile-supported mulberry branch bundle arch revetment and investigated the effects of bundle arrangement, joint restraint, and rise-to-span ratio on structural deformation, load transfer, and load-bearing performance. Staged model-box loading tests, rise-direction compression tests, joint-optimization validation tests, and rise-to-span ratio tests were conducted, and the support-transmitted forces and equivalent eccentric-compression characteristics were analyzed. Among the four basic configurations tested using scaled specimens, the horizontal mulberry branch bundle arch configuration (HA) exhibited the smallest horizontal deformation. In the rise-direction compression tests, the combined horizontal-vertical mulberry branch bundle arch configuration (CA) reached a mean peak load of 5.384 kN, which was 12.0% higher than that of HA (4.807 kN), whereas HA exhibited a more stable post-peak response. The combined joint optimization scheme, comprising solid trapezoidal timber joints, contact surface flattening, geotextile interfaces, and restraining nails, reduced the cumulative horizontal displacement of HA by 14.3–16.7% and increased its mean peak load by 26.96%, without separately evaluating the contribution of each modification. The support-force measurements and equivalent eccentric-compression analysis provided support-level evidence of relatively balanced bilateral compressive support and arch-type load transfer in the optimized HA. For rise-to-span ratios of 0.2, 0.3, and 0.4, the corresponding mean peak loads were 4.487, 6.917, and 2.260 kN, respectively, with 0.3 showing the most favorable overall mechanical response among the three tested ratios under the present experimental conditions. These results highlight the combined influence of bundle arrangement, joint configuration, and rise-to-span ratio on the mechanical response under the tested conditions.