Pseudo dynamic analysis of soil nailed slope


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Pseudo dynamic analysis of soil nailed slope

  1. 1. Thesis Advisor : Dr.P.Ghosh By: Piyush Sarangi 12103045 Geotechnical Engg
  2. 2.  Soil nailing is the most popular method of in situ ground improvement technique which is used to stabilize the vertical cuts and slopes by offering passive resistance.  It offer resistance to shearing through tension, bending and shear.  Divide the slopes into two zones i.e. active and resistive zone  As the slope deforms due to external load it exerts a drag force(Pull out) on nail in active zone which is balanced by the frictional resistance mobilized between nail and surrounding soil in the resistive zone.  The interaction length behind the slip surface in resistive zone is known as bond length. Active and resistive zone
  3. 3.  Stability analysis of soil nailed slope has been studied by several researchers among them Stocker et al(1979) was the first to study about the stability of soil nailed slope which is know as the famous GERMAN METHOD.  But the main concern was how the soil nailed slope behave under seismic conditions, several studies were performed by several researchers on the stability analysis of reinforced soil subjected to seismic loading and several interpretations were made . Sakaguchi M(1996) was the first to study about the reinforced soil.  As seismic stability analysis of the of the nailed slopes was a very rigorous and costly issue and could not performed by all . To overcome these drawbacks pseudo static and dynamic methods were come into picture.
  4. 4. Name Contribution Okabe(1926) Reported earth quake lateral earth pressure behind retaining wall using limit Equilibrium and pseudo static method considering failure surface to be linear and passing through toe Monobe and Matsuo(1929) Studied seismic lateral earth pressure behind the retaining wall in active and passive conditions using pseudo static method similar to above method but wall and ground inclinations were also considered Steedman and zeng(1990) First to propose pseudo dynamic method behind the vertical cantilever retaining wall considering finite shear wave velocity in the backfill .The amplification of acceleration and non uniform shear modulus was considered. Choudhury and Nimbalkar(2005) First to modify the pseudo dynamic method of steedman and zeng by considering horizontal as well as vertical accelerations which were dependent on the shear and p-wave velocity with in the backfill
  5. 5. SOIL NAILING Stocker et al.(1979) First to study about the stability analysis of nailed slope by large scale field tests and model tests measured the deformation within the reinforced soil and observed two failure mechanisms based on position of load on the slope. Sakaguchi M(1996) Studied different design methods like limit equilibrium, limit analysis and FEM method as well as proposed optimum design of nailed slope by sequential unconstrained minimization technique Patra and Basudhar(2005) Here computer based optimum design of soil nailed slope was reported .A limit equilibrium formulation satisfying overall and internal stability and considering tensile resistance of reinforcement was used for the computation of stability of nailed slopes Meenal Here seismic stability analysis of the soil nailed embankment was performed by pseudo static analysis. The failure surface assumed to be log spiral and internal stability analysis was done by means of moment equilibrium method Choudhury Used pseudo dynamic method for determination of internal stability of RE wall by horizontal slices method. Results were presented in graphical and tabular form to show the required tensile force and length of geosynthetic to maintain stability. The effects of variation of parameter such as friction angle of soil, horizontal and vertical acceleration on stability of RE wall was also investigated
  6. 6. Reddy Used the pseudo dynamic method to determine the seismic stability of the reinforced wall subjected to pullout and oblique force by sliding of soil masses. The seismic stability analysis was carried out considering the kinematics of oblique pull. The parametric studies quantify the effects of different parameters on F.O.S considering increase in tension due to oblique pull and pseudo dynamic forces. Sengupta and Giri (2011) Here stability analyses of the nailed soil slopes were presented by kinematic limit approach. Here earthquake forces were incorporated by means of pseudo static method. Two types of failure surfaces i.e. planar and circular were considered. The F.O.S and nailed forces were found out to be good agreement with publishes results
  7. 7.  Max no. of studies till now performed are based on reinforced earth structures and very Less no. of studies based on seismic performance of the soil nailed slopes.  The available studies of soil nailed slopes have been performed based on Pseudo static method which is very less realistic  Studies are yet to performed on seismic stability analysis of soil nailed slopes based on pseudo-dynamic method
  8. 8. PSEUDO-STATIC PSEUDO –DYNAMIC  Proposed by Monobe-Okabe(1926)  Horizontal and vertical accelerations considered to be time independent  Here the shear wave velocity is assumed to be infinity as soil wedge is considered to be rigid.  Does not consider the shear modulus variation  Magnitude and phase of acceleration are considered uniform throughout the backfill  Less realistic  Proposed by Steedman & zeng(1990)  Time dependent  Finite shear and P-wave velocity through out the backfilled  Non uniform shear modulus variation through out the backfill  Magnitude same as pseudo static analysis but phase changes with respect to time.  More realistic
  9. 9.  Pseudo-dynamic analysis of soil nailed slope Soil Nailed Slope Pseudo dynamic method
  10. 10.  Pseudo-dynamic formulation  Max force determination in the nails by incorporating the skin friction between nail and surrounding soil or bond resistance of soil nail.  Stability check by performing slope stability analysis under static and dynamic loads.  Variation of coefficient of horizontal and vertical acceleration cofficient with respect to different parameters
  11. 11.  Okabe, S. (1926) General Theory of Earth Pressure, Journal of the Japanese Society of Civil Engineers, Tokyo, Japan,12(1).  Mononobe, N. and Matsuo, H. (1929) On the determination of earth pressure during earthquakes, Proceedings, World Engineering Conference, Vol. 9, 176 p.  Steedman, R.S. and Zeng, X. (1990) The influence of phase on the calculation of pseudo-static earth pressure on a retaining wall, Geotechnique, 40(1), 103–112  Kramer, S.L. (1996)Geotechnical Earthquake Engineering, New Jersey, Prentice Hall  Choudhury D, Nimbalkar S. Seismic passive resistance by pseudo dynamic method. Geotechnique 2005; 55 (9):699–702  Choudhury, D., Nimbalkar, S. S. & Mandal, J. N. (2007). External stability of reinforced soil-walls under seismic condition.Geosynthetics International, 14, No. 4, 211–218.  Nimbalkar, S. S., Choudhury, D. & Mandal, J. N. (2006a). Seismic stability of reinforced soil wall by pseudo-dynamic method. Geosynthetics International, 13, No. 3, 111–119  Shahgholi, M., Fakher, A. & Jones, C. J. F. P. (2001).Horizontal slice method of analysis.Ge´otechnique, 51, No. 10, 881–885  Ahmad, S. M. & Choudhury, D. (2008).Pseudo-dynamic approach of seismic design for waterfront reinforced soil wall. Geotextiles and Geomembranes, 26, No. 4, 291–301  Saran S, Mittal S, Gosavi M (2005) Pseudo static analysis of nailed vertical excavations in sands. Indian Geotech J 35(4):401–417  Patra CR, Basudhar PK (2001) Nailed soil structure: an overview. Indian Geotech Journal 31(4):322–362  Giri D and Sengupta A (2009) Dynamic behavior of small scale nailed soil slopes. International Journal of Geotechnical and Geological Engineering 27(6): 687–698  Sengupta A and Giri D (2011) Dynamic analysis of soil nailed slope. Ground Improvement 164(GI4) 225-234