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Landslide Research

Tong Qiu, Ph.D., P.E.

My research has been supported by National Science Foundation, U.S. Department of State, Federal Highway Administration, Federal Railroad Administration, PennDOT, Alpine Equipment LLC, Ben Franklin Foundation, and Mid-Atlantic Universities Transportation Center

 

Primary Research Interests

Soil dynamics and geotechnical earthquake engineering

Flow through porous media, fluid-solid interaction

Numerical analysis in geotechnical engineering

Soil-structure interaction

Granular mechanics 

 

Recent Research

 

Topic 1:    Pore Fluid Induced Damping in Saturated Soil during Shear Wave Excitations

 

Topic 2:    SPH Simulation of Geomaterial under Large Deformations

 

Topic 3:    Simulation of Earthquake-Induced Slope Deformation using SPH Method


Topic 1:    Pore Fluid Induced Damping in Saturated Soil during Shear Wave Excitations


In this research, we try to quantify pore fluid induced damping in saturated soil during shear wave excitations through analytical and experimental investigations.  Damping is an important soil property in soil dynamics and geotechnical earthquake engineering.  Figure 1 illustrates the effect of soil damping on site response during an earthquake.  As the earthquake waves travel between the bedrock and ground surface, their energy is dissipated due to soil damping.  Therefore, a higher soil damping would result in a smaller site response (which is beneficial), assuming that everything else stays the same (e.g., soil stiffness, soil profile, and acceleration time history). 

 



Figure 1.  Schematic illustration of the effect of soil damping on site response during an earthquake


When soils deform under dynamic loading, energy loss occurs due to rolling and sliding at particle contacts and the creation and deletion of particle contacts (see Figure 2).  Damping due to these mechanisms is referred to as "skeleton damping" and is the only source of material damping in dry soils.  In saturated soils, additional energy loss occurs due to the relative motion between viscous pore fluid and solid particles.  Therefore, saturated soils exhibit higher damping than the same soils in their dry state.  Although its existence has long been recognized, systematic investigations on pore fluid induced damping have been limited in literature.  The objective of this research is to quantify pore fluid induced damping and provide practical solutions on this phenomenon through combined analytical work and experimental testing.

 


Figure 2
.  Schematic illustration of soil skeleton and individual solid particles

 

Sponsor: National Science Foundation (CMMI-0826097)

 

Status: Currently we are performing resonant column tests on glass beads and sands to validate the analytical solution presented in the following reference.

  

Reference:

 

Qiu, T. (2010). "Analytical Solution for Biot Flow-Induced Damping in Saturated Soils during Shear Wave Excitations," Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 136(11), pp. 1501-1508.

 

Topic 2:    SPH Simulation of Geomaterial under Large Deformations

 

In this work, we try to model solids, particularly granular materials, under large deformations using the Smoothed Particle Hydrodynamics (SPH) method.  Listed below are some results of our simulations of the experiments conducted by Lube et al. (2004) on the collapse of initially vertical 3-D axisymmetric columns of various granular materials.  Simulations and experimental results are compared for granular columns with the same initial radius of 0.1 m but different aspect ratios a=hi/ri , where hi and ri are the initial height and radius of the granular column, respectively.  Typical values of bulk modulus and Poisson's ratio of loose sands, namely 5 MPa and 0.3 are used, respectively. 

 

Fig. 3a                        

 

                  (a)                                                                                             (b)

 

 

                                         (c)

 

Figure 3.    Comparison of experiment and SPH simulation for a sand column with a=0.55 :
                   (a) experimental final profile; (b) simulated final profile; (c) animation of the collapse
                   (experiment image from Lube et al. 2004)





                          
           
                  (a)                                                                                               (b)




                                        (c)

Figure 4.   Comparison of experiment and SPH simulation for a sand column with a=0.9:
                  (a) experimental final profile; (b) simulated final profile; (c) animation of the collapse
                  (experiment image from Lube et al. 2004)


                             
                 
                   (a)                                                                                               (b)




                                        (c)

Figure 5.
  Comparison of experiment and SPH simulation for a sand column with a=2.75:
                  (a) experimental final profile; (b) simulated final profile; (c) animation of the collapse
                  (experiment image from Lube et al. 2004)


Lube et al. (2004) observed that depending on the aspect ratio, different flow patterns exist during the collapse.  For 0<a<0.74 , it was observed that a circular undisturbed area at the top of the column remains at the initial height; for 0.74<a<1.7 , the inner circular region is eroded gradually by outer moving particles, leaving a sharp cone at the center with its tip remaining at the initial height; for a>1.7, the entire upper surface of the column starts to flow and the height of column decreases immediately.  These observations are reproduced by the SPH simulations satisfactorily as demonstrated in Figures 3 to 5.   

 

Status: Currently various constitutive models are being implemented into the developed 3-D SPH model to simulate different phenomena involving large deformations of solids, particularly geomaterials.  

 

References:

 

Chen, W. and Qiu, T. (2012). "Numerical simulations for large deformation of granular materials using smoothed particle hydrodynamics method," International Journal of Geomechanics, ASCE, 12(2), 127-135.

 

Lube, G., Huppert, H.E., Sparks, R.S.J. and Hallworth, M.A. (2004). "Axisymmetric collapses of granular columns," Journal of Fluid Mechanics, 508, 175-199.

 

 

Topic 3: Simulation of Earthquake-Induced Slope Deformation using SPH Method

 

In this research, we aim to develop, calibrate, and validate a SPH model for the simulation of seismically induced slope deformation under undrained condition. A constitutive model that combines the isotropic strain softening plasticity and the modified Kondner and Zelasko rule is developed and implemented into a 3-D SPH model developed by Chen and Qiu (2014). The developed SPH model accounts for the effects of wave propagation in the sliding mass, cyclic nonlinear behavior of soil, and progressive reduction in shear strength during sliding, which are not explicitly considered in the Newmark-type analyses widely used in current research and practice.

The developed SPH model is validated against a readily available and well documented model slope test on a shaking table (Wartman 1999, Wartman et al. 2001, Wartman et al. 2005). The model simulated slope failure mode (Figure 6), acceleration response spectra, and slope deformations are in excellent agreement with experimental data as reported in detail by Chen and Qiu (2014). It is thus suggested that the developed SPH model may be utilized to reliably predict earthquake-induced slope deformations.

 

 

 

Figure 6. Comparison of simulated failure mode and deformed shape with model slope test:

                (a) t=13.4 s;  (b) t=20.2 s;  (c) t=32.0 s;  (d) final deformed profile and sliding surface

                from model slope test (from Wartman et al. 2005).

 

Status: Currently parametric study is being conducted to investigate the effects of boundary condition, slope profile, soil properties, and characteristics of strong ground motion on seismically induced slope deformation. Particular emphasis is being placed on the effect of strain softening behavior on the progressive and total slope deformation.

 

References:

Chen, W. and Qiu, T. (2014). "Simulation of earthquake-induced slope deformation using SPH method." International Journal for Numerical and Analytical Methods in Geomechanics, 38(3), 297-330.

Wartman, J. (1999). "Physical model studies of seismically induced deformation in slopes." Ph.D. Dissertation, The University of California, Berkeley.

Wartman J., Seed R.B. and Bray J.D. (2001) "Physical model studies of seismically induced deformations in slopes." GeoEngineering Report No. UCB/GT/01-01, Department of Civil and Environmental Engineering, University of California, Berkeley.

Wartman, J., Bray, J.D., and Seed, R.B. (2005). "Shaking table modeling of seismically induced deformations in slopes." Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 131(5), 610-622.