study of slope stability

Introduction:

• To determine the ideal position of the piles in an unstable slope (position in the transverse direction) we will study this behavior using PLAXIS 8.2 modeling software;
  First, we will take a soil sample characterized by an embankment with the dimensions shown in Figure 3-10, the geotechnical characteristics are of a soil sensitive to slippage and a load applied at the head of the distributed slope of 10KN / ML .
  Lx: is the position of the pile with respect to the foot of the slope is variable between 0 and L = 19m.
  We will study the slope stability in five pile positions for Lx = 0, 5, 10, 15 and 19 (1 / 4.1 / 2.3 / 4 and L) using PLAXIS 8.2 software compared to each times the results obtained by themselves and with respect to the results obtained for the sample before putting the pile stabilization device.

• The geotechnical characteristics of the soil sample:
  γ=18 KN/M3
  γSAT=19,63 KN/M3
  E=2000 KPA
  C=23 KPA
  φ=10°
  Rinter=0.75
  ϑ =0.35

• The physical and mechanical characteristics of concrete materials:
  γ=24 KN/M3
  E=4960 KPA
  ϑ =0.2

Figure 1-1: Stake positioning study model designed by me.

Modeling of the soil sample without piling stabilization with head loading:

Figure 1-2: Modeling slope with loading in Plaxis 8.2 taken of my computer capture of my modeling on software.

The behavior of the embankment alone without the installation of the pile as shown in the following figure:

Figure 1-3 : Comportement talus avec chargement en Plaxis 8.2 prise de mon ordinateur capture de ma modélisation sur logiciel.

The safety factor value obtained is Fs = 0 .851.

First pile position Lx = 0 (pile position at the foot of the slope).

Figure 1-4: Modeling slope with pile at the foot of the slope in Plaxis 8.2 taken from my computer captures my modeling on software.

The pile-reinforced slope behavior for the first pile position LX = 0 (at the foot of the slope)

Figure 1-5: Behavior slope with loading with pile in foot taken from my computer capture of my modeling on software.

The safety factor value obtained for the first slope position Lx = 0 (at the bottom of the slope) Fs = 1.499.

Second pile position Lx = 5m (pile position in 1 / 4L foot of slope).

Figure 1-6: Modeling slope with pile located at 1 / 4L in Plaxis 8.2 taken from my computer captures my modeling on software.

The pile-reinforced slope behavior for the second pile position LX = 5m (pile position in 1 / 4L foot of slope)

Figure 1-7: Behavior with a pile located at 1 / 4L in Plaxis 8.2 taken from my computer captures my modeling on software.

The safety factor value obtained for the second slope position Lx = 5m (pile position in 1 / 4L foot of slope) is Fs = 1.498.

Third position of the pile Lx = 10 m (pile position in ½ L of slope foot).

Figure 1-8: Modeling of slope with pile located at 1 / 2L in Plaxis 8.2 taken of my computer capture of my modeling on software.

The pile-reinforced slope behavior for the third pile position LX = 10m (pile position in 1 / 2L foot of slope)

Figure 1-9: Behavior with a stake located at 1 / 2L in Plaxis 8.2 taken from my computer captures my modeling on software.

The safety factor value obtained for the third slope position Lx = 10m (pile position in 1 / 2L foot of slope) is Fs = 1.481.

Fourth pile position Lx = 15 m (pile position 3/4 L foot slope).

Figure 1-10: Modeling with pile located at 3 / 4L in Plaxis 8.2 taken from my computer captures my modeling on software.

The pile-reinforced slope behavior for the fourth pile position LX = 15m (pile position in ¾ L foot slope).

Figure 1-11: Behavior with pile located at 3 / 4L in Plaxis 8.2 taken from my computer captures my modeling on software.

The safety factor value obtained for the fourth slope position Lx = 10m (pile position in 1 / 2L foot of slope) is Fs = 2.208.

Fifth position of the pile Lx = 19 m (pile position at head of slope).

Figure 1-12: Modeling with pile at the head of slope in Plaxis 8.2 taken from my computer captures my modeling software.

The pile-reinforced slope behavior for the fifth pile position LX = 19m (pile position at head of slope).

Figure 1-13: Behavior with pile at the head of slope in Plaxis 8.2 taken from my computer captures my modeling on software.

The safety factor value obtained for the third slope position Lx = 10m (pile position in 1 / 2L foot of slope) is Fs = 1.42.

7-Discusions:

• On the basis of the results obtained during the modeling of an embankment subjected to a load distributed at the head of embankment without any retaining device which gave a result of safety factor = 0.85 this value which was considered insufficient to ensure slope stability for this, reinforcement by pile was deemed necessary.

• Five simulations have been studied for the ideal location of the pile to give the best security to know:
  First case: positioning of the pile at the foot of the slope.
  Second case: pile position at 0.25 L (L: cross-sectional width).
  Third case: pile position at 0.5 L.
  Fourth case: stake position at 0.75 L.
  Fifth case: position of the pile at the head of the slope.

The safety factor values were variable for each case:
Table 3-1: Safety factor values as a function of pile position change.
Position of the pile in relation to the foot of the slope Lx / Lt Foot slope 0.25 L 0.5L 0.75L Head of embankment
Safety factor obtained by modeling (PLAXIS 8.2) FS 1.49 1.50 1.48 2.20 1.42

Figure 1-14: Graph of safety factor values ​​according to pile positions.

• We note that the 0.75L value gave the best safety factor hence the better stability of the slope.

• All other positions of the piles have given values ​​of safety coefficient greater than 1, hence the slope stability is ensured.

8-Conclusion

• Following the study of an ideal positioning of the piles in an unstable slope by calculating the value of safety coefficient of an embankment for five locations of the piles between the foot of slope and the head of the same slope (foot of slope, ¼ L, ½ L, ¾ L, head slope) using soil modeling software (PLAXIS 8.2) we can see that the position of piles for better stability of a slope is near the head slope exactly ¾ L (L is the transverse width of the slope).

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