| With the Three Gorges hydropower generation and the development and construction of a large number of hydropower projects in western China,how to accurately establish the damage evolution model of rock under the action of water-rock is the key to determine the rock deformation and mechanical state and important support for safety and stability evaluation of water slopes.Based on this,this article carried out repeated loading tests on single specimens,physical and mechanical tests on unloading damaged sandstone,physical and mechanical tests on unloading damaged sandstone under water-rock interaction,and obtained the critical value of sandstone damage based on self-organized critical theory and renormalization group theory.In this article,I have established a damage evolution model with clear physical meaning that can accurately describe the entire damage evolution law of unloading damage sandstone,and further according to the related theory of critical damage criteria for unloading damaged sandstone is proposed.Finally,based on the critical damage value proposed in this paper,two exponential laws of critical displacement of avalanche hazards are modified,and typical slopes are analyzed and predicted.Unloading is widespread in geological processes and human engineering activities.Engineering rock mass deformation and destruction due to unloading are common.With the Three Gorges hydropower generation and the development and construction of a large number of hydropower projects in western China,a large amount of manual excavation unloading are inevitable.The deterioration effect under water-rock interaction will directly affect the long-term deformation stability of the wading slope.So,how to accurately establish the damage evolution model of rock and theoretically obtain the critical state of rock damage under the water-rock interaction is the key to determine the rock deformation and mechanical state and important support for safety and stability evaluation of water slopes.However,as far as the current research results of water-rock interaction on wading slopes are concerned,the main focus is on the degradation effects of the physical and mechanical properties and mechanism analysis of various types of "intact" rocks,and less attention is paid to the effect of initial unloading damage.Based on this,this article carried out repeated loading tests on single specimens,physical and mechanical tests on unloading damaged sandstone,physical and mechanical tests on unloading damaged sandstone under water-rock interaction,and obtained the critical value of sandstone damage based on self-organized critical theory and renormalization group theory.In this article,I have established a damage evolution model with clear physical meaning that can accurately describe the entire damage evolution law of unloading damage sandstone,and further according to the related theory of critical damage criteria for unloading damaged sandstone is proposed.Finally,based on the critical damage value proposed in this paper,two exponential laws of critical displacement of avalanche hazards are modified,and typical slopes are analyzed and predicted.The research shows that:(1)Based on the angle of compressive strength,shear strength and energy,the critical damage value is determined by single specimen repeated loading method,and the critical damage value based on axial strain energy is relatively low.From the perspective of engineering safety,it is recommended to use a single specimen repeated compression test to determine the critical damage value of the rock with compressive strength as the damage variable.(2)The degradation law of the shear strength parameters of sandstone with different unloading damage is basically the same,but there are a little differences.That is,cohesion and internal friction angle gradually decrease with the increase of unloading amount.However,when the unloading amount reaches 90%,a rebound of the internal friction angle occurred.That is to say,when the unloading amount is low,the internal cracks caused by unloading damage are not developed,and the confining pressure effect is obvious.Under the initial confining pressure,the internal cracks are closed.However,when the unloading amount is more than 80%,especially 90%,the internal cracks of rock samples begin to derive from the initial disordered state to the orderly unstable state,cluster and accumulate to nucleate.At this time,even if there is confining pressure,the internal cracks can not be completely closed.The existence of internal unloading cracks leads to the increase of friction contact area,and the increase of friction strength leads to a rebound of internal friction angle.However,the cohesion is mainly determined by the cementation strength of particles and cements.The larger the unloading amount is,the greater the damage is,and the cementation strength will inevitably decrease.(3)The rate of sodium ion formation is greatest in the three typical types of ion during the water-rock interaction process of unloading damaged sandstone.On the one hand,sodium ion is more active than potassium ion and calcium ion,and plays a leading role in ion competition.As a result,albite reacts fastest in water and precipitates the most ions.On the other hand,when feldspar minerals undergo hydration reaction,Silicon hydroxide will be generated.The potential energy of Silicon hydroxide is high,which is extremely unstable and easy to decompose into Si O2 colloid,while Si O2 colloid with negative charge will absorb with positive charge The ability of cations to be adsorbed and exchanged increases with the increase of their electrovalence.When cations electrovalence is equal,their adsorption and exchange capacity increase with the increase of their atomic radius.Therefore,according to their exchange capacity and the order of adsorption,Ca2+ > K+ > Na+,the sodium ion is the least adsorbed,and the calcium ion is the most adsorbed.Sodium feldspar is the easiest to dissolve,followed by potassium feldspar and calcareous feldspar.(4)Through the comprehensive analysis of natural climate system,regional landslide system,single landslide system in reservoir area and indoor test angle,it is found that there are a large number of self-organized critical phenomena in complex systems in nature.When a complex system crosses its critical point,it will increase the risk of other systems crossing the critical point.The process in which the acting system evolves towards a critical state by itself under the complex and highly nonlinear coupling(feedback).(5)A critical damage constant C that reflects the critical damage state of the rock is proposed,and then the critical damage criterion of unloading damaged sandstone under water-rock interaction is obtained.Based on the renormalization group theory,the range of the critical damage value is obtained by considering the density between particles,introducing the densest filling mode and the loosest filling mode of particles,which is verified by relevant literature the damage constant is in their range.The critical damage constant C and the critical criterion for reflecting the critical damage state of sandstone are reasonable.(6)The critical displacement criterion of avalanche disaster is proposed based on the modification of critical damage constant.Through the analysis of typical collapse and slide cases,it is found that the displacement prediction value of the characteristic points are more closer to the actual monitoring displacement,and the error is within 8%.It is proved that the critical displacement criterion of collapse and slide disaster based on the correction of the critical damage constant proposed in this paper is feasible and reasonable,and the critical damage constant proposed in this paper is also verified from the side.Relevant research results have certain enlightenment and guiding significance for further revealing the damage mechanism of unloading damage sandstone under water-rock interactions and establishing the criteria for determining the critical damage state of sandstone.It can also provide corresponding theoretical basis for the support timing of wading slopes. |
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