Experimental Study On The Cut-Fill Interface Effect And Its Failure Mechanism Of Loess Check Dam

Check dams are important measures for erosion control in the Loess Plateau.The construction of check dam brings development opportunities to the local society,and the same time,the hidden geological disasters cannot be ignored.Among them,the study on the dambreaking along the cut-fill interface is a geological problem that must be highly valued in the construction of check dam project.This paper take the dam-breaking disaster of check dam with cut-fill interface in the site of “Gully Land Consolidation” in Nangou Village,Yan’an City as the engineering background,three groups of indoor physical model test under low compactness,medium compactness and high compactness were carried out to investigated the failure modes,time-dependent deformation laws and hydrological response laws of check dam with cut-fill interface using volumetric water content sensors,pore water pressure sensors and handheld 3D laser scanner,to reveal the interface effect and its failure mechanism of the check dams.The main conclusions are as follows:(1)Different compactness states of the interface results in different failure modes of check dam.For low compactness,the check dam with cut-fill interface presents a complex failure mode consisting of piping,slope collapse and overtopping.For medium compactness,the check dam with cut-fill interface presents a complex failure mode consisting of slope failure and overtopping.For high compactness,the check dam with cut-fill interface has not been damaged,but has slight slope deformation and creep of toe,which can maintain a stable state for a long time.Time-dependent deformation laws of check dam with cut-fill interface.Influenced by the interface effect and the interface compactness state,the time-dependent deformation laws of downstream slope are significantly different.In time,the interface can accelerate the deformation and damage of the dam.In space,the slope deformation is centered on the interface and extend to the whole dam.Moreover,improving the compactness of the filling area can effectively eliminate the interface effect and reduce the risk of dam deformation and damage.(2)Affected by the interface effect and the interface compactness state,the hydrological response characteristics at various locations within the check dam are significantly different.The difference in water content is mainly reflected in the response rate,which is shown as the water content response rate at the cut-fill interface is faster than that at other locations,and the response rate becomes slower as the compactness of the cut-fill interface increases.Compared with the volume water content,the response of pore water pressure has obvious hysteresis effect.Basically,the response of pore water pressure begins after the dam reaches saturation.The rise and fall of pore water pressure are caused by the change of the local seepage field in the dam,which is in good agreement with the deformation and failure process of the dam.the difference in pore water pressure is mainly reflected in the response speed and response degree.The value of pore water pressure at the cut-fill interface is generally greater than the other two positions,and the response speed is also generally greater than the other two positions,indicating the cutfill interface is the dominant seepage channel inside the dam.(3)The cut-fill interface,as a weak interface,plays a key role in the stability of the loess check dam.Under hydraulic action,the cut-fill interface has significant impact on the failure mechanism of the loess check dam.As a dominant seepage channel within the dam,the cut-fill interface will allow water to flow through preferentially,changing the internal seepage field of the dam,causing the interface continuously to soften,leading to preferential seepage deformation at the cut-fill interface,thereby inducing piping failure.The existence of the cutfill interface not only promotes the time of dam failure.but also creates a faster and more easily occurred mode,that is piping.The failure mechanism of the loess check dam with the cut-fill interface is controlled by the interface compactness state,which significantly affects the microstructure of the compacted loess,while the macroscopic physical and mechanical properties of compactness loess are controlled by the microstructure between soil particles.With the improvement of the interface compactness state,the shear strength is improved,and the saturated permeability coefficient becomes smaller,the erodibility of the loess becomes worse,and the dam tends to be stable.