Study On Dynamic Response Of Mudded Intercalations During Cyclic Loading

Weak intercalations are often developed in rock mass engineering,such as foundations of dams,slopes,caverns and so on.Mudded intercalations are the key part of them,for their worst engineering properties and weakest strength.Many construction projects have delayed construction,forced to shutdown or add huge investments.They were all affected by mudded intercalations.Some even caused serious engineering accidents and life or property loss.As the special weak structural surface in layered rock masses,the mudded intercalation is the controlling factor for design and construction of stability against sliding of engineering rock mass.Dynamic response characteristics of mudded intercalations have a significant impact on dynamic instability mechanism of the rock slope under different cyclic dynamic loadings,such as multiple blasting loads,earthquake load,traffic load and wave load.Up to now,the researches on engineering geological characteristics of mudded intercalations have been extensive and in-depth.The research methods were generally field in-situ tests,laboratory direct shear tests,etc.However,only a few researchers have revealed the dynamic response characteristics of mudded intercalations.This paper was financially supported by the National Natural Science Foundation of China(grant number: U1504523): Dynamic instability catastrophic mechanism of rock slope with weak intercalations under cyclic blasting disturbance.The research object was mudded intercalations with different developmental properties.Specimens of mudded intercalations were collected from a geological adit of some large hydro project in the middle reaches of Yellow River.This work aimed at experimentally revealing dynamic response characteristics of mudded intercalations under cyclic dynamic loading.The research method was indoor dynamic triaxial test,theoretical derivation and date analysis.The potential impact factors considered in this work include(i)clay mineral composition,(ii)clay content,(iii)water content,(iv)confining pressure,and(v)cyclic failure time.The main research contents and conclusions are as follows:(1)A theoretical model and its influencing factors were put forward for the cumulative strain description of mudded intercalations according to test results.The results showed that the cumulative strain development law of mudded intercalations have failure characteristics.It is reasonable to describe the characteristics of cumulative strain by the Monismith model.The key impactors have great effects on the cumulative strain,such as cyclic numbers(positive),water content(positive),clay content(positive),and confining pressure(negative)respectively.When main mineral composition is mixed montmorillonite and illite,the cumulative strain of mudded intercalations reaches its maximum.Among them,the influence of each impact factor on the cumulative strain is not much different.(2)The dynamic stress-strain curves of mudded intercalations accord with the Hardin hyperbolic model.It shows significant strain hardening characteristics.The strain hardening characteristic parameter is impacted by water content(strongly,negative)and clay mineral composition(weakly,positive).The dynamic elastic modulus model is attenuated.It is impacted by confining pressure(monotonously positive),cyclic time(monotonously negative),water content(monotonously negative)correspondingly.When the main mineral composition is mixed montmorillonite and illite,the dynamic elastic modulus decreases fastest,and the strain hardening characteristic parameter reaches its minmum.(3)This work aimed at experimentally revealing the impact factors of the strength along with their impacts.The dynamic strength test results showed that the dynamic strength is impacted by water content(strongly,initially positive and then negative),clay mineral composition(moderately),confining pressure(moderately,positive),and cyclic failure time(weakly,initially positive and then negative).The dynamic cohesion is correlated with clay mineral composition(strongly),water content(moderately,initially positive and then negative),and cyclic failure time(weakly,initially positive and then negative).And the dynamic friction angle is correlated with water content(strongly,negative),clay content(moderately,negative),and cyclic failure time(weakly,initially positive and then negative).(4)Based on Ramberg-Osgood hardening law,a fatigue damage variable equation was established,which could be applied to triaxial loading conditions.The results showed that the damage development mechanism can be described by the low cycle fatigue damage evolution model.The fatigue damage variable equation can accurately describe the damage development law of mudded intercalations under cyclic dynamic loading.And the damage development mechanism can be described by the low cycle fatigue damage evolution model.The fatigue damage evolution of mudded intercalations first slows down and then accelerates with the increase of cycle number.And it accelerates with the increase of confining pressure and water content.When main clay mineral composition is mixed montmorillonite and illite,the fatigue damage value is the largest and it evolves most rapidly.