含水率对湛江组结构性黏土触变强度恢复的影响OA

[Objective]This study focuses on water content as the key controlling factor to clarify the time-depend-ent patterns of thixotropic strength recovery of Zhanjiang Formation structural clay under different initial water con-tents.The microscopic mechanism is interpreted through three pathways:pore structure evolution,particle reorgani-zation,and water action.The findings are expected to provide experimental evidence and theoretical support for pre-dicting strength recovery and evaluating the stability of thixotropic clay foundations.[Methods]Remolded Zhan-jiang Formation structural clay specimens were prepared and subjected to a 150-day thixotropy test.Specimens at different thixotropic durations were investigated using macroscopic and microscopic tests.For macromechanical tes-ting,unconfined compressive strength(UCS)tests were conducted on cylindrical specimens.Direct shear tests were conducted on ring-knife specimens to obtain UCS,cohesion(c),and internal friction angle(φ),which were used to evaluate thixotropic evolution.A thixotropic strength ratio was defined as A,=m,/m0,and two indicators-At(q)(based on UCS)and At(τ)(based on cohesion)—were used to compare recovery characteristics among different strength parameters.For microstructure,fabric evolution was observed using an SEM.Pore parameters,including porosity(M)and abundance(C),were extracted to quantitatively analyze pore structure evolution.Particle pa-rameters,namely probability entropy(H)and distribution fractal dimension(D),were used to quantitatively char-acterize particle orientation/orderliness and aggregation degree,respectively.[Results](1)Stage-dependent re-covery:Both UCS and cohesion(c)increased with thixotropic duration and showed two stages:a rapid and signifi-cant recovery phase during 0-30 d,followed by a slower,stable phase during 30-150 d.The increment during 100-150 d was small,indicating near-stabilization,after which the test was terminated.(2)Dual effect of water con-tent:At the same thixotropic duration,UCS generally decreased with increasing water content,reflecting weakened particle contacts and bonding and thus reduced instantaneous strength.However,higher water content resulted in a faster strength recovery rate,especially at early stage,indicating that water promoted the kinetics of self-adaptive structural adjustment during thixotropic process.(3)Indicator-dependent differences:Cohesion exhibited a higher thixotropic strength ratio and faster recovery within 1 d,suggesting that shearing promoted directional particle align-ment and optimized the friction-bonding interface,making c more sensitive to structural rebuilding than UCS.(4)Coordinated micro-parameter evolution:As thixotropic duration increased,M and c decreased continuously.Pores shifted from"large and numerous inter-aggregate pores"to"small and fewer intra-aggregate pores",while the o-verall pore shapes remained mainly quasi-equant but became denser.Additionally,H and D decreased synchronous-ly,indicating enhanced particle orientation/orderliness and increased aggregation.These changes were most signifi-cant within the first 30 d,consistent with the rapid macroscopic recovery stage.SEM observations revealed a transi-tion from an"open flocculated-dispersed"fabric to a"closed flocculated-aggregated"fabric.Pores between and within aggregates decreased,while particle contacts and continuity of force-transfer paths improved,thereby sup-porting strength recovery.[Conclusion]The thixotropic strength recovery of Zhanjiang Formation structural clay exhibits distinct time-stage characteristics and strong sensitivity to water content.Recovery generally progresses through a rapid phase(0-30 d)and a stable phase(30-150 d).Higher water content reduces the strength level but significantly accelerates the strength recovery rate.Cohesion exhibits a higher thixotropic strength ratio than UCS because shear-induced particle orientation facilitates more effective structural reconstruction.Microscopically,syn-chronous decreases in M/C and H/D indicate pore reduction,particle ordering,and aggregation densification.Wa-ter enhances particle activity by altering relative particle positions and expanding migration pathways,thereby accel-erating self-adaptive adjustment and strength recovery during thixotropic process.Innovations included:(1)parallel comparison of UCS and rapid direct shear parameters within a single thixotropic framework,revealing the cohesion recovery advantage caused by shear-induced particle orientation;(2)linking the macroscopic two-stage recovery pattern with the coordinated evolution of M,c,H,and D,forming an evidence chain of"structural rearrange-ment-aggregation densification-strength recovery";and(3)demonstrating that higher water content,while re-ducing instantaneous strength,accelerates recovery by enhancing particle mobility/activity.