加筋对桩承式路堤变形模式与土拱效应影响试验

对于桩承式加筋路堤,加筋改变了路堤底面的变形形态,不可避免地将对路堤变形模式与土拱效应产生影响。为了深入分析加筋的影响,利用开发的多沉陷门(Multi-trapdoor)试验装置和椭圆钢棒相似土填料,开展未加筋桩承式路堤试验并得到不同参数组合下存在的3种变形模式,选取3种变形模式的代表性试验,开展相同参数条件下的加筋试验以及4种不同填料高度和3种不同加筋刚度的桩承式加筋路堤试验。通过粒子图像测速技术(PIV)和自制三点式载荷计准确测试得到全场位移及桩顶和桩间土压力。结果表明:加筋后,未加筋桩承式路堤的三角扩展型和塔形升高型变形模式转化为同心椭圆扩展模式,等沉面模式转化为同心圆等沉模式;2种变形模式之间转化的临界高度为1.5倍桩间净距,但等沉面的高度仅为67%的桩间净距;加筋对土拱效应发挥起到了双重作用,一方面,加筋减小了差异沉降,导致土拱效应发挥程度降低,另一方面,加筋改变了路堤变形模式,为同心圆土拱提供了稳定的拱脚,使得土拱效应发挥程度提高;在填料高度低,加筋刚度高的情况下,土拱效应发挥程度进一步降低;而填料高度高,加筋刚度低时,土拱效应达到了充分发挥所需的差异沉降,加筋对土拱效应有提高作用;张拉膜效应发挥程度随加筋刚度增大而提高,且随着桩间土下沉而提高,导致土拱效应减弱。

Experimental Investigation on Influences of Geosynthetic Reinforcement on Deformation Pattern and Soil Arching in Piled Embankments

In geosynthetic-reinforced pile-supported embankments, geosynthetic reinforcements change the deformation patterns at the bottom of the embankment, which inevitably affects soil arching. In order to investigate the influence of geosynthetic reinforcements, a multi-trapdoor test apparatus and elliptical steel rod analogical soil, were used. For different parameters, three developed deformation patterns were observed in the unreinforced piled embankment tests. Three typical tests of these different deformation patterns were selected. Three tests were performed for the embankments with geosynthetic reinforcements, considering the same geometric parameters, i.e., filling height, pile net spacing, and pile width. The influence of the fill height and geosynthetic stiffness were tested by performing four tests considering different fill heights and three tests considering different stiffness values. The overall displacement was measured using particle image velocimetry (PIV), and the pressures applied on the piles and the soil between the piles were measured using three-point load cells. The test results show that the triangular expanding and tower-shaped evolution patterns of the unreinforced piled embankment transform into concentric ellipse expansion patterns. Additionally, equal settlement pattern with the triangular arch transform into equal settlement pattern with concentric circles in the case of geosynthetic-reinforced embankments. The critical height between the two deformation patterns is 1.5 times that of the pile net spacing. Meanwhile, the height of the equal settlement plane is only 0.67 times that of the pile net spacing. Geosynthetic reinforcements play a dual role in the soil arching effect. On the one hand, geosynthetic reinforcements reduce the differential settlement, resulting in a reduction of the soil arching effect. On the other hand, geosynthetic reinforcements change the deformation patterns of the embankments, providing a stable arch foot for the concentric circular soil arch and improving the soil arching effect. For the condition of low filling height and high geosynthetic stiffness, the soil arching effect is low. However, when the filling height is high and the stiffness of reinforcements is low, soil arching can be fully mobilized by the required differential settlement, and the reinforcements can improve the soil arching effect. High stiffness values result in a higher degree of membrane effect. As the soil settles between the piles, the membrane effect becomes more significant. This causes the soil arching effect to weaken.