Advanced Geotechnical Engineering
Earth Dam Design Project
Rationale
Earth dams are very critical and important geotechnical engineering structures when storing
water for different purposes such as drinking, irrigation, hydropower generation, etc. These
dams should be engineered designed for slope stability failures under different conditions,
seepage control, and settlement. The manual assessments of stability and seepage of an earth
dam are not easy when the dam structure is complex. Therefore, the computer aided tools are
widely used in the practice.
Objectives
Understand key features of an earth dam and its design
Learn how to use SEEP/W to analyse seepage in an earth dam
Lean how to use SLOPE/W to calculate the stability of earth dam slopes under
different conditions
Verification of results obtained from numerical software
Give experience on team work in designing geotechnical engineering structures
Task
Compose a report following the CRA provided
Things to know
Every student should submit the pdf version of the report through BB by
11.59 Am on the 2nd April 2018 (It is your responsibility to upload the correct file by
due date, the version of the report last submitted before the due date is used to grade)
Earth Dam Design Problem
In the tropical and subtropical climates, dry season agriculture cannot be commenced using
only the streamflow. Evaporation and high temperature increase the uncertainty of
continuous water supply for the commercial crops. Considering primarily for irrigation, local
council in the Queensland state is proposed to construct a 200 m long earth dam for
increasing the security of domestic water supply and flood amelioration. Figure 1 illustrates
the proposed site for the earth dam.
Figure 1 Proposed site for the new earth dam
Accounting the generic representatives of existing earth dams in Queensland, the dam
configuration shown in Figure 2 was selected for this proposed dam. According to the
guidelines, this dam is required to achieve very low hazard potential in stability as it is
proposed in highly populated area. Your design group was selected in this purpose to check
the stability of the dam at four design conditions: 1) during the construction period, 2) at
service level, 3) at overtopping level, and 4) during rapid drawdown events. The dimensions
and material properties of the dam are illustrated in Table 1. The client has requested from
your design to provide your recommendations on the following points:
1) Model the earth dam in SEEP/W (GeoStudio software) and assign relevant material
properties and boundary conditions. Analyse the earth dam for steady-state seepage
conditions when the upstream water is at the service level. Using SEEP/W results,
calculate the total seepage loss through the dam and foundation per year in m3.
2) Using the results of steady-state seepage analysis (SEEP/W), determine the total head
and pore-water pressure at Points “A” and “B” under steady-state seepage conditions
with upstream water at the service level. Use following relationships to define the
locations of points “A” and “B”.
=3+ =5 x =2 + `=8(1+ )
where, M: mean of the final two digits of all group figures
Ex: figure 01: d ××××56, figure 02: d ××××04, and figure 03: d ××××00, M = 20
3) Obtain two different flow nets from the above steady-state seepage analysis using
SEEP/W (service water level). Using Darcy’s equation for 2-D seepage and Bernoulli’s
equation, calculate the total seepage loss through the dam and foundation per year in
m3 and the total head and pore-water pressure at Points “A” and “B” for each flow net.
Use only the permeability of embankment soil to estimate the total seepage loss through
the dam and foundation. Compare the calculated total seepage loss, total head at A & B,
and Pore-water pressure at A & B with the values obtained from SEEP/W ((1) and
(2)).and provide three possible reasons for any deviation
4) The council expects to minimise the seepage through the dam by selecting the best
material properties for the core of the dam. Using at least four different saturated
permeability values for the core of the dam, select optimal saturated permeability for
the core of the dam considering the steady-state seepage loss under serviceability
conditions (service water level). Typical values of the permeability of core materials are
between 1 10-9 m/S and 1 10-14 m/S.
5) Using SEEP/W, re-analysis the dam for steady-state seepage when the reservoir water is
at the overtopping level. Calculate the total seepage loss per year in m3, total head and
pore-water pressure at A & B. Compare these values when the reservoir water is at the
service level and give the reasons for differences.
6) Model the earth dam in SLOPE/W and assign the relevant material properties and boundary
conditions. Analyse both the upstream and downstream slopes of the dam for stability after
the construction by using Morgenstern-Price, Bishop’s simplified, Janbu’s simplified,
Spencer, and Fellenious (Ordinary) methods. Briefly describes the reasons for different
factor of safety (FOS) values obtained from different method of analysis for a
given slope. Further, provide three recommendations to increase the stability of the dam
during/after construction.
7) Using SEEP/W & SLOPE/W, calculate the stability (FOS) of the downstream slope of
the dam under steady-state conditions at both service and overtopping water levels by
using Morgenstern-Price, Bishop’s simplified, Janbu’s simplified, Spencer, and
Fellenious (Ordinary) methods. Provide three recommendations to increase the stability
of the downstream slope of an earth dam during steady-state seepage condition.
8) To satisfy the peak water demand of a dry season, water in the reservoir is proposed to
release to the water treatment plant in very short time (sudden drawdown). Calculating
the stability of upstream slope during drawdown using SEEP/W and SLOPE/W,
estimate the safest rapid drawdown level of the reservoir using at least four drawdown
levels to ensure the stability of the dam during this operation using Morgenstern-Price
method. Assume that 30 days are required to dissipate the excess pore-water pressure
from the dam after the rapid-drawdown operation.
HC-E | |||
S1 | S2 | ||
1 | |||
1 |
|||
L4 | B | Core | |
L3 | α | αEmbankment | 3 m |
L1 | Hfilter | ||
L2 | A | 4+Ltop |
|
Foundation |
Figure 2 Dam configuration
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- Assignment status: Resolved by our Writing Team
- Source@PrimeWritersBay.com
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