Development Of 3D Deformation Monitoring Method For Centrifuge Model Test Of Embankment On Soft Foundation

As an effective physical simulation test method,geotechnical centrifuge model test has been widely used to solve various geotechnique problems,such as the deformation and stability of dam and slope,shallow foundation and deep foundation,retaining structure,soil dynamic engineering,foundation and so on.In geotechnical centrifuge model test,deformation monitoring plays an important role and is most commonly used.At present,the traditional deformation measurement technologies mainly include linear variable differential transformer(LVDT)and laser displacement sensor.LVDT has the advantages of long mechanical life,high separation rate,and durability.However,LVDT requires a rigorous contact with model surface,which has a certain influence on the physical properties of the model.Meanwhile,LVDT has a limited measuring distance and range.The laser displacement sensor has the advantages of non-contact and high measurement accuracy.However,it also has a very strict requirement on measuring range.Most of the above mentioned traditional deformation transducers can only measure one fixed point deformation each at one time.Photogrammetry is a technology based on image analysis processing.Compared with traditional displacement measurement methods,it has many advantages such as non-contact,visual interface,large measuring distance,wide measuring range and convenient layout.It has been obtained some applications in geotechnical centrifuge model test,but only for the measurement of the internal deformation of one side of the model.In this paper,a new set of 3D photogrammetry technology is developed and applied to the centrifuge model test of embankment on soft foundation.The soft foundation has the characteristics of high water content,high compressibility and large natural porosity.Therefore,the embankment on soft foundation is prone to large deformation and sliding failure.The 3D photogrammetry technology developed in this paper can measure the three-dimensional deformation on the surface of the embankment model,with large measuring distance and wide measuring range.The monitoring results can provide basis for structure design and ensure project safety.Using the principle of lens imaging,3D photogrammetry can calibrate the camera parameters through model images taken simultaneously by two cameras,and further calculate the spatial position of each measurement point in the image to infer the deformation of the model during the test.In this paper,the object of the centrifuge model test is the embankment on soft foundation.Compared with the laser displacement sensor,results from this study indicate that the 3D photogrammetry has high accuracy and is suitable for large deformation monitoring of the centrifuge models.During the centrifuge testing,along with the increase of centrifuge acceleration,it was obvious that the embankment model gradually sunk.The settlement was the most obvious at the top of the dam,which gradually decreased downward along the model slope.At the bottom of the dam,the settlement became small,and the local uplift occurred.At the same time,the embankment model encountered transverse deformation,which increased with the increase of centrifuge acceleration.The largest horizontal displacement was observed on the bottom of the model,and the displacement decreased upward along the model slope.During the centrifuge acceleration loading process,a transverse crack appeared on the centrifuge model of the embankment on soft foundation,indicating that the uneven deformation of the embankment in both vertical and horizontal directions caused the ultimate cracking damage.In order to study the influence of centrifuge acceleration on the sliding stability of the centrifuge model,this paper uses the simulation analysis software GeoStudio to analyze the sliding stability of the model under different centrifuge accelerations.Results show that the stability of the model decreases with the increase of centrifuge acceleration.The sliding failure surface of the embankment is in an arc shape,and extents deep into the soft soil foundation.The observed deep failure indicates that the stability of the embankment model mainly depends on the bearing capacity of the soft soil foundation.Finally,the limitations of the current study and implications are discussed for future research.