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CE 566 Deep Excavations and Retaining Structures Department of Civil Engineering
Middle East Technical University, Ankara,Turkey Prof. Dr. K. Önder Çetin
ASSIGNMENT 3: The Assessment of Flow into an Open Pit with RocScience RS2 Software
Solution 3: The Assessment of Flow into an Open Pit with RocScience RS2 Software
1. For a highway cut, a sloped excavation is to be performed. Figure 1 shows a schematic view
of the proposed excavation along with some soil data. Estimate the amount of flow into the
open cut by using either RS2 or Slide soft wares.
Figure 1: Planned excavation
Slide software enables user to make a Steady State FEM Analysis (Under Project Settings –
Groundwater – Method -- Steady State FEM Analysis. Half part of the geometry was
modelled (symmetric geometry advantage). Sınce we are only ınterested with the flow
amount, the soil layers above the water table were ignored. Total head values of the geometry
were shown below. The green line (discharge section) in the model is established to fınd the
flow amount through the slope. (one discharge section also added on the slope surface,
because program calculates flow between higher head and lower heads and these lower value
is not only 10m , shortly program calculates flow between upper 16 m and slope surface
whıch has a linearly varying head of 10-16 m )
Figure 2: Total head values of the boundary
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CE 566 Deep Excavations and Retaining Structures Department of Civil Engineering
Middle East Technical University, Ankara,Turkey Prof. Dr. K. Önder Çetin
ASSIGNMENT 3: The Assessment of Flow into an Open Pit with RocScience RS2 Software
Results of the analysis is shown below.
Figure 3: Interpretation of Analysis (flow lines, flow direction and discharge section values)
As seen on figure, discharge section calculated as 2.413 m3/day flow through the section.
However as seen on figure, program also calculates a 0.350 m3/day flow through the sloped
surface. As a conservative approach, better to assume that this flow will be through the
excavation site. (actually it is not known what percent of this 2.413 m3/day flow is also
responsible for this 0.350 m3/day, so considering them as independent will be conservative).
Therefore, estimated amount of flow that will go into the excavation site will be
Flow estimated = 2 * (2.413+0.350) m3/day = 5.326 m3/day
2. Figure 2 shows the excavation plan for a construction. Considering the project plan;
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CE 566 Deep Excavations and Retaining Structures Department of Civil Engineering
Middle East Technical University, Ankara,Turkey Prof. Dr. K. Önder Çetin
ASSIGNMENT 3: The Assessment of Flow into an Open Pit with RocScience RS2 Software
i. Estimate the amount of flow into the deep excavation
Slide programs was used to model the problem. For the sheet pile wall a very low
permeability value, k=10-50 m/day was assigned. Also in boundary conditions, total flow on
the wall boundaries are assigned as 0 m3/day. Geometry is shown below.
Figure 4: Geometry of the Problem and Total head values with Boundary Cond.
Half part of the geometry used, symmetry of geometry benefitted. Green line shows the
discharge section. Below figure shows the vertical hydraulic gradient line (for part 2) and
discharge section amount.
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CE 566 Deep Excavations and Retaining Structures Department of Civil Engineering
Middle East Technical University, Ankara,Turkey Prof. Dr. K. Önder Çetin
ASSIGNMENT 3: The Assessment of Flow into an Open Pit with RocScience RS2 Software
Figure 5: Flow lines, flow directions, vertical hyd. Gradient and discharge section
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CE 566 Deep Excavations and Retaining Structures Department of Civil Engineering
Middle East Technical University, Ankara,Turkey Prof. Dr. K. Önder Çetin
ASSIGNMENT 3: The Assessment of Flow into an Open Pit with RocScience RS2 Software
Total estimated flow will be 0.01405 m3/day from only one side of excavation. Therefore,
total estimated flow through excavation site is 0.0281 m3/day
ii. Check if boiling is of concern (assume icr=1.0)
Slide program enables the user to check the hydraulic gradient values, too. As seen in the
output, the highest amount of the vertical hydraulic gradient, imax is 0.410 (notice that
hydraulic gradient values are higher close to the wall as seen in Figure 5
𝐹𝑆𝑏𝑜𝑖𝑙𝑖𝑛𝑔 =𝑖𝑐
𝑖𝑚𝑎𝑥=
1
0.410= 2.44
iii. Check if base heave is expected by using Slide or RS2 softwares
Base heave is likely to occur if pore pressure is higher than the total pressure at a point.
Therefore, pore pressures of the downstream part should be checked.
Below the excavation site, Pore pressures were calculated for every 2 intervals, i.e. 2-4-6 so
on. Results are shown in figure 6.
𝐹𝑆ℎ𝑒𝑎𝑣𝑒 =𝑇𝑜𝑡𝑎𝑙 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒
𝑃𝑜𝑟𝑒 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒=
39
26.18= 1.49
Depth Below, m
Pore Pressure, kPa
Total Pressure, kPa FS
2 26.18 39 1.49
4 52.36 78 1.49
6 78.56 117 1.49
8 104.77 156 1.49
10 130.98 195 1.49
12 157.21 234 1.49
14 183.15 273 1.49
16 208.26 312 1.50
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CE 566 Deep Excavations and Retaining Structures Department of Civil Engineering
Middle East Technical University, Ankara,Turkey Prof. Dr. K. Önder Çetin
ASSIGNMENT 3: The Assessment of Flow into an Open Pit with RocScience RS2 Software
Figure 6: Pore Pressure Output of the Problem