Mudstone Softening-swelling Compound Mechanical Model And Its Application

The large deformation of soft rock is one of the most difficult engineering disasters encountered in the construction of deep-buried and long-distance water conveyance tunnels.The stress release effect caused by excavation and unloading in a high ground stress environment and the unique wet expansion and shrinkage characteristics of swelling rock work together,which can easily induce engineering disasters such as large deformation of the tunnel surrounding rock,primary support and second lining damage,resulting in construction delays and investment Adverse consequences such as increased risk of tunnel safety.Therefore,studying the temporal and spatial variation of the moisture field of the rock mass induced by the excavation of the swelling rock tunnel in a water-rich environment,as well as the influence of the time effect of the moisture diffusion inside the rock mass on the stability of the tunnel surrounding rock and supporting structure,has important scientific value and practical significance.In order to explore the swelling performance of mudstone and determine its type,a series of expansions including mineral composition analysis,equilibrium pressure method expansion force measurement,free expansion deformation,lateral constrained swelling deformation,and lateral constrained swelling deformation under overburden load are carried out.Based on the experimental research,combined with the existing swelling rock identification standards,it is determined that the mudstone is a weakmedium swelling rock.Considering the inseparable relationship between rock expansion and deformation and its water absorption characteristics,the water absorption characteristics of mudstone are experimentally studied,and it is found that the water absorption increment of mudstone increases negatively exponentially with time,and gradually tends to a certain stable value;expansion deformation and expansion Forces complement each other,and the development of swelling stress is closely related to the mechanical properties of the rock itself.For this reason,the uniaxial and triaxial compression tests of mudstone with different initial soaking times are used to explore the laws of mudstone damage and deterioration when encountering hydraulic parameters.The effect is obvious.The elastic modulus,uniaxial compressive strength and water content are in a negative exponential relationship,and the mudstone cohesion and water content are in a linear relationship.Based on the time effect of the humidity diffusion,the time-space diffusion law of the internal humidity of the rock mass during the expansion process is obtained.Based on the mudstone softening-expansion composite mechanical model and the indoor test,the influence of the overburden load on the evolution law of the mudstone expansion and deformation is studied: Humidity diffusion coefficient and adsorption-expansion coefficient should be functions related to external load.The load before moisture absorption has a strong limiting effect on the moisture diffusion process and adsorption expansion process of mudstone;by simulating the mudstone under different overburden loads The lateral constrained swelling deformation test verifies the rationality and applicable conditions of the water softening-swelling composite mechanical model of mudstone.The influence characteristics of the moisture diffusion coefficient and the adsorption expansion coefficient on the swelling deformation evolution law of mudstone are studied.The research results show that the humidity diffusion inside the rock mass has a significant temporal and spatial law.The development trend of humidity over time presents a slow,rapid and then gentle process.At the same time point,the humidity decays in a negative exponential trend with the increase of the distance to the humidifying surface;When the adsorption-softening-expansion coefficient is constant,the limit expansion deformation amount and the humidity diffusion coefficient conform to the power exponential function relationship,and when D/D0 is in the(0,1)interval,the limit expansion deformation amount increases more obviously;the limit expansion deformation amount is one Timing,the adsorptionsoftening-expansion coefficient has a negative exponential relationship with the humidity diffusion coefficient,and when D/D0>2,the humidity diffusion coefficient has almost no effect on the adsorption-softening-expansion coefficient.Based on the moisture diffusion coefficient and the adsorption-softeningexpansion coefficient obtained from the lateral constrained expansion test,combined with the actual engineering background and the characteristics of mudstone,the main incentives for the moisture diffusion in the surrounding rock after the tunnel excavation are analyzed,and the humidity field is determined Boundary conditions,study the influence of the time effect of humidity diffusion on the spatial variation law of the surrounding rock humidity field,and the influence of the time effect of humidity diffusion on the stability of the tunnel surrounding rock and supporting structure.Through numerical simulation research,it is found that the spatial change law of the humidity field has obvious time effect.At the initial stage of diffusion,the spatial change law of the humidity field is greatly affected by the accumulation of water at the bottom of the tunnel.As the diffusion time increases,the humidity diffusion outside the disturbance zone has a significant effect.The spatial variation of the humidity field plays a leading role;based on the obtained spatial variation of the humidity field at different times,combined with the mudstone softening-expansion composite mechanical model,the influence of humidity diffusion on the deformation of the tunnel surrounding rock is obtained,the roof subsidence and the floor uplift It is a continuous development,and it is easy to cause gradual cumulative damage to the tunnel structure;the maximum principal stress of the tunnel lining structure increases with the increase of the humidity diffusion time,but due to the influence of the softening characteristics of mudstone in contact with water,the maximum principal stress in a short period of time The value fluctuates,and the position of the maximum principal stress will change with the increase of diffusion time.The arch toe position of the lining structure at the initial stage of diffusion is very prone to damage,and as the diffusion time increases,the bottom heave of the tunnel is prone to damage.