西安北至机场城际铁路黄土塬段现场试坑浸水试验研究

Experimental Study on Site Test Pit Immersion in Loess Tableland Section of Xi’an North-airport Intercity Railway

为准确确定城际铁路跨黄土塬的场地湿陷类型和自重湿陷下限深度,推动该地区湿陷性评价体系发展,在分析西安北至机场城际铁路黄土塬段黄土分布特征的基础上,选取代表性场地进行原位大型浸水试验。试验研究结果表明,该场地处于Q_(3)黄土层中,其自重湿陷性土层下限深度位于Q_(3)古土壤层的顶界面位置,远小于通过室内试验获得的下限深度;确定了自重湿陷地区土质修正系数β_(0)为1.036,大于规范推荐值0.9;浸湿区与饱和区的影响范围随深度的增加而逐渐增大;每个浅标点日沉降速率基本符合“小→大→小→大→小→稳定”的特征,地表累计沉降以中心浅标点为中心大致呈对称发展,总的变化趋势为距离试坑中心越远,湿陷量越小;各深标点单日沉降速率特征与浅标点相同,深标点的最终沉降随深度增加而逐渐减小;试坑浸水后地面裂缝在湿陷产生后才出现,且裂缝范围小于试坑沉降范围。该试验研究可使西安北至机场城际铁路黄土塬段地基处理深度更加合理,使桩基深度设计更加规范,路基排水性能更好,可为该地区其他建设工程提供借鉴和指导。

In order to accurately determine the type of site subsidence and the lower limit depth of the self-gravity collapsing zone of the inter-city railway across the loess plateau,and to promote the development of the collapsible evaluation system in this area,based on the analysis of the distribution characteristics of loess in the loess section of the intercity railway from Xi’an North to the airport,representative sites were selected for large-scale in-situ immersion tests.The test results show that the site is located in the Q_(3) loess layer,and the lower limit depth of the self-weight collapsible loess of the site is taken from the top interface position of the Q_(3) paleosol layer,which is far less than the lower limit depth obtained through indoor tests.The soil quality correction coefficientβ_(0) in the area of gravity subsidence is determined to be 1.036,which is greater than the recommended value of 0.9.The range of influence of wet and saturated areas increases with depth.The single-day settlement rate of each shallow mark point has the characteristics of“small→large→small→large→small→stable”.The cumulative settlement of the ground surface develops symmetrically with the central shallow mark point as the center.The farther away from the center of the test pit,the smaller the amount collapsible.The characteristics of the single-day settlement rate of each deep punctuation point are the same as those of the shallow mark point.The final settlement of the deep mark point gradually decreases with increasing depth.After the immersion of the test pit in water,the ground cracks appear after the collapse,and the range of the cracks is smaller than the settlement range of the test pit.The results give technical guidance and theoretical application value in the optimization of the ground treatment depth,the negative friction design depth of the pile foundation,and the optimization of the subgrade water-proof and drainage width in the loess section of the Xi’an North to Airport Intercity Railway,as well as provide reference for other construction projects in the area.