Mechanical Behavior And Reinforcement Mechanism Of Grout-rock Interface At The Macro- And Micro-scale

As an effective method to strengthen jointed rock masses,grouting has been widely used in geotechnical engineering to prevent the failure of jointed rock masses.Studying the grouting reinforcement mechanism is thus important for controlling the stability of surrounding rocks at both the macro-and micro-scale.This study focuses on the roadway?tunnel?grouting engineering,which was supported by national key research and development plan?2017YFC0603004?.In this dissertation,macro-and micro-mechanical behavior and reinforcement mechanism of the grout-rock interface were investigated combined with macro and micro laboratory tests and numerical test.The following innovative research results have been achieved:?1?Using the designed direct shear test device and electrohydraulic servo-controlled loading system,direct shear tests on cemented specimens were carried out,and the shear mechanical behavior and shear strength parameters of cemented specimens with different cement particle sizes and different nano-SiO₂particle contents were obtained.Combined with the micrographs,the effect of cement particle size and nano-SiO₂ particle contents on the mechanical properties of cemented specimens was revealed.By rheological test,the effects of cement particle size and nano-SiO₂ content on the rheological properties of grout were obtained.?2?Direct shear tests on grout-infilled specimens were carried out.The shear mechanical behavior and strength parameters of grout-infilled joint specimens with different filling matrix,cement particle size and nano-SiO₂ particle contents were obtained.The discrepancy and key control factors of shear mechanical properties of cemented specimens and grout-infilled joint specimens were compared.The bond mechanism between grout and rock was discussed.Combined with high-resolution CCD image and acoustic emission?AE?monitoring technology,the failure process and modes of grout-infilled joint specimens during shearing process were obtained.The characteristic of AE activities during shearing process were analyzed,and the macro-failure mechanism of grout-infilled joint specimens was revealed.?3?The microstructure characteristics of the grout-rock interface of different grout-infilled joint specimens was analyzed by SEM test,and two main bonding modes between the grout and the jointed rock surface were obtained.Using the nanoindentation test,the micro-mechanical properties?indentation load-displacement curve,indentation modulus,and hardness?of different grout-rock interfaces were discussed.Based on qualitative?optical image?and quantitative?indentation modulus?estimations,a method was proposed to distinguish rock,ITZ?Interfacial transition zone?and bulk grout.The ITZ thickness of different grout-infilled joint specimens,the micro-mechanical properties of ITZ and cement stone were further evaluated,and the grout strengthening mechanism was revealed at the micro-scale.?4?Using the PFC numerical simulation software,three types of grout-infilled sandstone specimen models were established by adopting smooth joint model,and direct shear test were counducted.This model can simultaneously achieve the bonding and friction between grout and rock before and after interface failure.Based on this,the crack evolution characteristics of grout-rock interface during the shear simulation process were obtained,and the meso-fracture mechanism of grout-rock interface and filling body was revealed.There are 89 figures,24 tables and 229 references in this dissertation.