山西某电厂黄土地层预应力高强混凝土管桩工程实践

Engineering Practice of PHC Pile in Loess Stratum of a Power Plant in Shanxi

山西某新建2×350 MW低热值煤电厂主要建筑物地段出露地层为第四系上、中更新统黄土(粉土),厚度为40~60 m。其中(3-1)和(3-2)层粉土均匀分布于整个场地且力学性质较好,强度较高,是良好的桩端持力层。但该类地层含丰富的钙质、锰质结核,以往的勘察设计和施工单位大多采用钻孔灌注桩。基于其他工程的成功经验,我们选择采用预应力高强混凝土管桩进行工程试桩,分别采用长螺旋及大型机械洛阳铲进行引孔,通过高应变法检测进行对比检测,再通过静载荷试验最终验证,由此确定了合理的引孔直径和深度,成功总结出一套适合本工程地层的沉桩工艺。与原设计采用直径800 mm钻孔灌注桩方案相比,节省了一半的工程造价。本次实践证明了预应力高强度混凝土桩在黄土地层应用的可行性及可观的经济价值。

The stratum exposed in the main construction area of a newly built 2×350 MW low calorific value coal power plant in Shanxi is quaternary(upper and middle pleistocene series) loess(silty soil), with a thickness of 40 to 60 m. Among it,(3-1) and(3-2) layers of silt are evenly distributed in the whole site and have good mechanical properties as well as high strength. It can be used as a good bearing layer of the main building. But this stratum is rich in calcium and manganese nodules, so most of the survey and design or construction companies used to recommend the use of cast-in-place piles. Based on the successful experience of other projects, we chose PHC pile as the engineering pile testing, using long spiral drill or large mechanical Luoyang shovel respectively to pre-bore the hole. A contrast detection is carried out based on high-strain dynamic testing and then the static load test is also used as final verification, the reasonable diameter and depth of the pre-bored hole are thus determined, and a set of pile sinking technology fit for the stratum of this project is summed up. Compared with the original design of cast-in-place pile with a diameter of 800 mm, half of the project cost is saved. This practice proves the feasibility and considerable economic value of the application of PHC piles in the loess layer.