加卸荷工况对注浆砂土-混凝土接触面剪切特性影响

Effects of Normal Loading and Unloading on the Post-grouting Sand-Concrete Interface Shear Behavior

土-结构物接触面力学特性是岩土工程领域研究的重点与热点问题之一,揭示其机理有利于促进对桩基础、挡土墙等结构物承载性能的认识。本文采用自主设计研发的注浆设备和室内后注浆试验方法,对3种注浆量和4种加、卸荷工况下,共计28组注浆和未注浆大型接触面进行直剪试验,分析不同加、卸荷工况对注浆砂土-混凝土接触面力学特性和剪切影响范围的影响。结果表明:注浆可逐渐消除加卸荷产生的接触面初始剪切模量和剪切应力差异。未注浆接触面未出现软化;注浆接触面呈现软化现象,并且软化出现在剪切法向应力较小的卸荷接触面剪切过程中。后注浆主要通过提高接触面等效黏聚力,改善接触面力学特性,对接触面等效内摩擦角无明显影响。同一注浆量下,浆液对无卸荷工况接触面等效黏聚力的改善效果优于卸荷工况;卸荷工况的接触面剪切影响范围略大于无卸荷工况;加卸荷和注浆工况下,接触面剪切影响范围与接触面峰值剪切应力呈正相关。同一剪切法向应力下,注入浆液,通过压密注浆形成浆块,增大接触面混凝土板的粗糙度,改善卸荷接触面剪切特性;通过浆液渗透形成浆土混合体,对无卸荷接触面处土体特性进行改善。研究成果可为实际工程中桩基工程后注浆提供指导。

The mechanical properties of the soil-structure interface have always been one of the key and hot issues in the field of geotechnical engineering,and revealing its mechanism is helpful to promote the understanding of the bearing characteristic of structures such as pile foundations and retaining walls.A total of 28 groups of large direct shear tests with the post-grouting sand-concrete interface were conducted under three different grout volumes and four kinds of loading and unloading conditions to analyze the interface mechanical properties and the distribution of shearing influence range.The test results show that grouting can gradually eliminate the difference between the interface’s initial shear modulus and shear stress due to the loading and unloading of the interface.The softening phenomenon doesn’t exist in the un-grouted interface,while the post-grouting interface exhibits softening and the softening occurs in the unloading interface shearing process with low applied normal stress.The grout cement improves the mechanical properties of the interface by increasing the equivalent cohesive force of the interface but has no significant effect on the equivalent internal friction angle of the interface.The improvement of the interface equivalent cohesive force on the loading interface is better than the unloading interface under the same grout volume.The distribution of interface shearing influence range under unloading conditions is slightly larger than that under the loading conditions.Regardless of the loading,unloading,and grouting conditions,the distribution of interface shearing influence range is positively correlated with the interface peak shear stress.Under the same applied normal stress,the mechanical properties of the unloading post-grouting interface were improved due to the formation of the grout bulb by compaction grouting to increase the roughness of the concrete plate,while the mechanical properties of the loading post-grouting interface were improved by penetration grouting to form the soil-cement mixture.The research results can provide guidance for the post-grouting of pile foundations in practical projects.