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Nagasaki University

題目. Centrifugal Model Experiment and Stability Analysis of Geosynthetics-Reinforced Cohesive Earth Fill. R.Katoh Y.Tanabashi Y.Jiang. Nagasaki University. Adoption of Reinforced earth method. Positive use of excavated surplus soil. Rapid ascent earth fill. Reinforced material.

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Nagasaki University

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  1. 題目 Centrifugal Model Experiment and Stability Analysis of Geosynthetics-Reinforced Cohesive Earth Fill R.Katoh Y.Tanabashi Y.Jiang Nagasaki University

  2. Adoption of Reinforced earth method • Positive use of excavated surplus soil • Rapid ascent earth fill Reinforced material Past Division method Development of Geocomposite The mechanism of drainage and reinforcement functions has not been clearly examined • High rigidity and high intensity • Strength decreases as the rise of saturation degree • Both functions of drainage and reinforcement Not considered • Seepage surface that acts under the seepage surface Background of Research

  3. Examining the drainage and reinforcement functions of Geocomposite by experiment Change of seepage surface and seepage force with time Saturated-Unsaturated seepage analysis Calculation of seepage force Evaluation of drainage and reinforcement function of Geocomposite Non-reinforced earth fill Calculation result Comparison Development of new division method program Geocomposite reinforced earth fill (Considering both the cohesion decrease and the seepage force) Purpose of the Research Centrifugal model experiment

  4. Characteristic of Geocomposite Non woven fabric Non woven fabric Woven fabric

  5. Fill model with seepage surface Experimental examination in drainage and reinforcement functions of Geocomposite Non-reinforced earth fill Comparison Reinforced earth fill Centrifugal model experiment Fill material:Kanto loam (One kind of volcanic cohesive soil)

  6. 25cm 22cm 11cm 31.4cm 45cm Outline of examination fill 18.2cm w =80.0% ρd =0.825g/cm3 Slope gradient 1:0.6 Geocomposite 59° 14.5cm

  7. Arrangement of measuring points 18.2cm 9.1cm 0.7cm Slope gradient 1:0.6 ② ② 22cm 2.0cm ③ ① ③ ① 11cm 5.5cm 2.0 cm Earth pressure gauge Pore water pressure gauge

  8. Increasing process of centrifugal acceleration

  9. ② ③ ① Gauge ② slope failure at about 35G Gauge ① Keep constant from 35G to 40G Gauge ③ keep constant from 35G Initial seepage surface moves Result of non-reinforced earth fill Influence the strength decrease of the earth fill

  10. Non-reinforced gauge① Non-reinforced gauge① Non-reinforced gauge② Gauge①decreases by the effect of reinforcement It can be confirmed that the fill is steady from this Gauge①decreases because of drainage function The fill is steady Rises smoothly in Gauge②,③ Result of Geocomposite reinforced earth fill ② ③ ①

  11. Comparison of displacement vectors Non-reinforced Geocomposite reinforced The effect of the Geocomposite as a drainage and reinforcement material could be confirmed

  12. Equivalent to the earth fill of 8.8m high Calculated seepage force 1:0.6 Earth fill stability calculation b Geocomposite element Analytical model Saturated-unsaturated seepage analysis The same point of contact h

  13. Analytical parameters

  14. Total head is the sum of pressure head and potential head Saturated area Pressure head is positive Pressure head is negative Unsaturated area Linking the points where the pressure head is 0 Seepage surface Outline of Saturated-Unsaturated seepage analysis① Considers upper partial saturation area from free surface of water Understand the behavior of seepage surface as time passed by

  15. Outline of Saturated-Unsaturated seepage analysis② Using these results Calculate seepage force {ix}e Seepage force in the direction of X and Y ：Hydraulic gradient of factor e in X direction { } { } e e = g × × i dvol Px {i y}e w x ：Hydraulic gradient of factor e in Y direction { } e { } e = g × × Py i dvol w y γw：Unit weight of water dvol：Volume of factor e ② Understand the behavior of seepage surface as time passed by

  16. 0 40 ×9.8 (kPa) Non-reinforced Geocomposite reinforced Change of seepage surface and seepage force with time In 30 minutes (It corresponds to acceleration 40G) Initial seepage Seepage surface at 30minutes Seepage force Scale of seepage Seepage surface at 30 Seepage surface at 30 Geocomposite Initial seepage Initial seepage

  17. Image chart in division method O x O j m j y R m R PX k Px m PY θ k k θ Py k m (a) Seepage force in each element (b) Seepage force in each block Moment given by seepage force Resisting moment Sliding moment Pxm･ym ‐PXksinθk ･R Pym･xm PYkcosθk ･R

  18. Expression used for fill stability calculation The seepage forces in horizontal direction and vertical direction acting on the blocks are considered depend on the saturation degree of this slip surface The seepage forces acting on each elements are considered Σ{ c’k(Sr)･Lk+(Wkcosθk‐PXksinθk +PYkcosθk‐ukLk)･tanφ’(Sr)}･R Fs = ΣWksinθk･R +Σ(Pxm･ym＋Pym･xm)

  19. Initial Cohesion c’=43.9kPa Cohesion c’=10.98kPa Initial saturation degree Sｒ=77.4% Sｒ=100% Change of strength constants with saturation degree Angle of shear resistanceφ’ Cohesion c’ K.Hisaraku 1983 Collapse of fill structure and research on measures Academic dissertation of Kyushu University

  20. The safety factor would be expected to exceed 1.0 The shear resistance of the Geocompositewas not considered Could be considered Greatly influenced by the decrease of cohesion Higher than the result of Non-reinforced earth fill Calculation result of each division method Earth fill type No seepage surface Have seepage surface Past division method ① ② Proposed division method Both ① and ②are omitted Both ① and② are considered Decrease of cohesion is considered Seepage force is considered Non-reinforced Geocomposite reinforced

  21. Seepage analysis The seepage surface in the upper part of the fill decreases. The safety factor has increased The seepage force has decreased Water in the fill drained by the Geocomposite. Conclusions① Experiment Both functions of drainage and the reinforcement of the Geocomposite are confirmed The effect of drainage of the Geocomposite is confirmed

  22. Conclusions② Proposed division method Decrease of cohesion and seepage force are considered The influence on the safety factor is small It greatly contributes to a decrease of the safety factor Proposed fill stability calculation method It is useful for evaluating the safety factor of actual fill with seepage surface Past division method The seepage surface is made

  23. Future study Clarifying the effect of reinforcement by numerical analysis Developing the program that considers the shearing resistance of reinforcement Establishing stability analysis method Based on all of these, reexamination of the fill stability analysis Developing the program to satisfying various cases The program could be used properly according to the condition

  24. The End

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