湿陷性黄土场地双向螺旋挤土灌注桩成孔挤密效应与极限承载力试验研究

为深入研究大厚度自重湿陷性黄土地区双向螺旋挤土灌注桩成孔前后桩周湿陷性黄土挤密范围和挤密效果,揭示双向螺旋挤土灌注桩破坏特征和极限承载力,在兰州榆中某高阶地开展现场双向螺旋挤土成孔试验与静载试验。基于各地规范中双向螺旋挤土灌注桩桩侧极限阻力修正系数和兰州各典型地层现场实测数据,提出了甘肃地区不同土类桩端极限阻力标准值。结果表明:桩周土体地表隆起量与径向水平位移随距离成孔中心越远呈减小趋势,径向影响范围为3D(D为桩径),竖向影响范围为地表以下25 m; 在2D范围内对桩周土体的物理力学指标有明显改善,桩心距越小,挤土成孔对桩周土体的物理特性影响越明显; 同等工况下双向螺旋挤土灌注桩的单桩极限承载力相比长螺旋灌注桩提高25%,且都呈现缓变型破坏特征。

Test Research on Soil Compaction Effect and Ultimate Bearing Capacity of Bidirectional Soil Displacement Screw Piles in Collapsible Loess Site

In order to deeply study the compaction range and compaction effect of the soil displacement screw pile on the collapsible loess around the pile before and after the hole forming in the large thickness self weight collapsible loess area, and to reveal the failure characteristics and the ultimate bearing capacity of the bidirectional soil displacement screw pile, the on-site bidirectional spiral soil compaction hole forming test and static load test were carried out in a high-order leveling site in Yuzhong of Lanzhou. Based on the correction coefficient of the ultimate resistance of the pile side of the bidirectional soil displacement screw pile in the local codes and standards, and the field measured data of typical strata in Lanzhou, the standard value of pile end ultimate resistance of different soil types in Gansu province was proposed. The results show that the surface heave and radial lateral displacement of the soil around the pile decrease with the distance from the hole forming center. The radial influence range is 3D(D is pile diameter)pile center distance, and the vertical influence range is 25 m below the surface. The physical and mechanical indexes of the soil around the pile are significantly improved in the range of 2D pile center distance. The smaller the pile center distance is, the more obvious influence of soil compaction on the physical properties of the soil around the pile is. Under the same working conditions, the ultimate bearing capacity of single pile of bidirectional soil displacement screw pile is 25% higher than that of long spiral cast-in-place pile, and they all represent the characteristics of slow-moving strength failure.