冻结黏土−混凝土界面动力剪切特性研究

Study on dynamic shear characteristics of frozen clay-concrete interface

冻土与混凝土接触界面动力剪切特性对于冻土工程的抗震稳定性和长期服役性有直接影响。为了研究动荷载作用下多年冻土地区桩土相互作用及桩侧冻结强度特性,在常规直剪仪的基础上,研制出可同时满足动荷载输出和低温控制条件的动力直剪系统。利用该设备开展不同影响因素条件下的冻结黏土−混凝土桩基界面动力剪切试验,研究了动荷载作用下,试验温度、法向压力、动荷载频率及振次对冻土与混凝土界面冻结强度的影响,同时探讨了界面剪切破坏后的残余强度的变化规律。试验结果表明:动荷载作用下,冻结黏土−混凝土界面力学行为具有应变软化特征,可明显分为线性增长,脆性破坏,强度恢复及残余稳定4个阶段;界面峰值强度和残余强度受温度变化影响最为显著,并且动力荷载特性对界面强度具有一定规律性的影响;温度主要通过冰胶结力作用对剪切强度和残余强度产生影响,随着温度的降低,界面内聚力显著增大,从而表现为冻结强度的增加。通过对动荷载作用下冻土与混凝土接触界面强度特性分析,阐明了界面冻结强度特征及形成机理,可为寒区工程中的冻土与桩基接触面间的剪切特性研究以及结构物抗冻拔病害防治提供参考。

The dynamic shear characteristics of the interface between frozen soil and concrete have a direct impact on the seismic stability and long-term serviceability of frozen soil engineering.In order to study the pile-soil interaction and freezing strength characteristics of pile side in permafrost regions under dynamic load,a dynamic direct shear system was developed based on the conventional direct shear instrument.It could meet the dynamic load output and low temperature control conditions at the same time.Using this equipment,dynamic shear tests of frozen clay-concrete pile foundation interface under different influencing factors were carried out.The effects of test temperature,normal pressure,dynamic load frequency and vibration times on frozen strength of frozen soil-concrete interface under dynamic load were studied.The change law of residual strength after interface shear failure was discussed.The test results show that under dynamic load,the mechanical behavior of frozen clay-concrete interface is characterized by strain softening.It can be obviously divided into four stages,which are linear growth,brittle failure,strength recovery and residual stability.The peak strength and residual strength of the interface are most significantly affected by the temperature change,and the dynamic load characteristics have a certain regularity influence on the interface strength.Temperature mainly affects the shear strength and residual strength through the action of ice cementation force.With the decrease of temperature,the interfacial cohesion significantly increases,thus showing the increase of freezing strength.By analyzing the strength characteristics of the interface between frozen soil and concrete under dynamic load,the characteristics and formation mechanism of the interface freezing strength are clarified.The results can provide reference for the research of shear characteristics between frozen soil and pile foundation interface and the prevention of frost-resistant pullout disease of structures in cold region engineering.