Design of a Plastic Concrete Cutoff Wall as a Remediation Plan for an Earth-Fill Dam Subjected to an Internal Erosion

Concrete cutoff walls are usually constructed using a panel-by-panel technique in which primary panels are constructed with space between them and then secondary panels are constructed and inserted in the spaces. A small thickness of residual bentonite cake from the slurry used during excavation usually remains in the construction joints between adjacent primary and secondary panels. The thickness of such bentonite-filled joints should be minimized in terms of the performance of the cutoff wall in controlling seepage. This research experimentally evaluated the effects of a number of design and construction parameters on the thickness of the bentonite cake using data from a case study (the cutoff wall of Karkheh Dam). A physical model test was developed and a number of tests were conducted. The test results showed that parameters such as age of the primary panels, cement content of the slurry, quantity of additives in the slurry, and circulation versus noncirculation of the slurry are responsible for the thickness of the bentonite cake. The results are presented and analyzed.Key words: cutoff wall, plastic concrete, bentonite slurry, bentonite cake, physical model.

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The Seepage Behavior of Composite Geo-Membrane & Cutoff Wall Applied in Three Gorges Project

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.186.146 ◽

2011 ◽

Vol 186 ◽

pp. 146-150

Author(s):

Kai Chang Sun

Keyword(s):

Composite Materials ◽

Primary Objective ◽

Three Gorges ◽

Test Results ◽

Cutoff Wall ◽

Working Mechanism ◽

Second Stage ◽

Plastic Concrete ◽

The Difference ◽

Mechanical Characters

The primary objective of this paper is to study the seepage behavior of the cutoff wall and the working mechanism of the composite geo-membrane applied in the second stage cofferdam of the Three Gorges Dam. The mixture proportion of the plastic concrete applied in the cutoff wall is researched and a recommended proportion is put forward. The difference between the composite geo-membrane and single geo-membrane concerning mechanical strength and permeability is detected and reasons which lead to the difference are found. The test results indicate that the mechanical characters of the composite geo-membrane have been improved remarkably. It is demonstrated that the deformation ratio plays an important role in terms of the permeability by bursting test. The behavior of the composite geo-membrane and the effect of the composite materials in different work-stage are studied and the influence of the elasticity of the composite materials on the practical application of the composite geo-membrane is analyzed. It is found that the strength is not just the superposition of the strength of composite materials and membrane.

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Experimental and Numerical Analysis for Earth-Fill Dam Seepage

Sustainability ◽

10.3390/su12062490 ◽

2020 ◽

Vol 12 (6) ◽

pp. 2490 ◽

Cited By ~ 2

Author(s):

Ahmed Mohammed Sami Al-Janabi ◽

Abdul Halim Ghazali ◽

Yousry Mahmoud Ghazaw ◽

Haitham Abdulmohsin Afan ◽

Nadhir Al-Ansari ◽

...

Keyword(s):

Physical Model ◽

Numerical Models ◽

Seepage Flow ◽

Water Levels ◽

The Body ◽

Silty Sand ◽

Internal Erosion ◽

Dam Failure ◽

Seepage Analysis ◽

Earth Fill

Earth-fill dams are the most common types of dam and the most economical choice. However, they are more vulnerable to internal erosion and piping due to seepage problems that are the main causes of dam failure. In this study, the seepage through earth-fill dams was investigated using physical, mathematical, and numerical models. Results from the three methods revealed that both mathematical calculations using L. Casagrande solutions and the SEEP/W numerical model have a plotted seepage line compatible with the observed seepage line in the physical model. However, when the seepage flow intersected the downstream slope and when piping took place, the use of SEEP/W to calculate the flow rate became useless as it was unable to calculate the volume of water flow in pipes. This was revealed by the big difference in results between physical and numerical models in the first physical model, while the results were compatible in the second physical model when the seepage line stayed within the body of the dam and low compacted soil was adopted. Seepage analysis for seven different configurations of an earth-fill dam was conducted using the SEEP/W model at normal and maximum water levels to find the most appropriate configuration among them. The seven dam configurations consisted of four homogenous dams and three zoned dams. Seepage analysis revealed that if sufficient quantity of silty sand soil is available around the proposed dam location, a homogenous earth-fill dam with a medium drain length of 0.5 m thickness is the best design configuration. Otherwise, a zoned earth-fill dam with a central core and 1:0.5 Horizontal to Vertical ratio (H:V) is preferred.

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Evaluation of Performance of Plastic Concrete Cutoff Wall in Karkheh Dam Using 3-D Seepage Analysis and Actual Measurement

Journal of Applied Sciences ◽

10.3923/jas.2009.724.730 ◽

2009 ◽

Vol 9 (4) ◽

pp. 724-730 ◽

Cited By ~ 6

Author(s):

M.S. Pakbaz ◽

A. Dardaei ◽

J. Salahshoor

Keyword(s):

Cutoff Wall ◽

Seepage Analysis ◽

Actual Measurement ◽

Evaluation Of Performance ◽

Plastic Concrete

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Investigating the Earth Fill Embankment of the Lotsane Dam for Internal Defects Using Time-lapse Resistivity Imaging and Frequency Domain Electromagnetics

Journal of Environmental and Engineering Geophysics ◽

10.32389/jeeg19-057 ◽

2020 ◽

Vol 25 (3) ◽

pp. 325-339

Author(s):

Bokani Nthaba ◽

Elisha M. Shemang ◽

Eliot A. Atekwana ◽

Ame T. Selepeng

Keyword(s):

Frequency Domain ◽

Structural Integrity ◽

Time Lapse ◽

Internal Erosion ◽

Conductive Layer ◽

Dam Foundation ◽

Resistivity Imaging ◽

Resistivity Variation ◽

Earth Fill

We investigated the internal structure of the Lotsane Dam for zones that may be prone to seepage and internal erosion using the electrical resistivity imaging (ERI) and the frequency domain electromagnetic (FDEM) methods. Time-lapse ERI measurements were also made for a period of 8 months in order to monitor the temporal evolution of defective zones. Results from both the FDEM and ERI measurements show two main layers. The first is an upper conductive layer varying in thickness from 10 to 25 m which is related to the clay core embankment. Situated beneath this upper conductive layer is a highly resistive crystalline basement on which the dam was founded. Furthermore, the ERI and FDEM measurements revealed the presence of fractures and possible zones of weakness within the dam foundation. Time-lapse ERI measurements revealed resistivity increases in the observed possible defective zones, including proximal to the spillway and at the embankment-foundation interface. The long-term resistivity variation may be indicating change in material properties in those portions of the dam, and may evolve to destabilize the structural integrity of the dam and or develop into preferential seepage pathways with time. The identified anomalous zones are good indicators that the embankment integrity is at risk and we suggest continuous geophysical monitoring of Lotsane Dam structure in order to ensure dam safety and integrity on the long term.

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Basic Studies on Plastic Concrete (CBC) for Cutoff Wall

Concrete Journal ◽

10.3151/coj1975.21.11_49 ◽

1983 ◽

Vol 21 (11) ◽

pp. 49-60 ◽

Cited By ~ 2

Author(s):

Keizoh Shuttoh ◽

Tadashi Watanabe ◽

Hidehisa Makino

Keyword(s):

Cutoff Wall ◽

Plastic Concrete ◽

Basic Studies

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Critical Hydraulic Gradient of Internal Erosion at the Soil–Structure Interface

Processes ◽

10.3390/pr6070092 ◽

2018 ◽

Vol 6 (7) ◽

pp. 92 ◽

Cited By ~ 8

Author(s):

Quanyi Xie ◽

Jian Liu ◽

Bo Han ◽

Hongtao Li ◽

Yuying Li ◽

...

Keyword(s):

Soil Compaction ◽

Soil Structure ◽

Clay Content ◽

Hydraulic Gradient ◽

Interface Roughness ◽

Internal Erosion ◽

Single Factor ◽

Critical Hydraulic Gradient ◽

Earth Fill ◽

The Impact

Internal erosion at soil–structure interfaces is a dangerous failure pattern in earth-fill water-retaining structures. However, existing studies concentrate on the investigations of internal erosion by assuming homogeneous materials, while ignoring the vulnerable soil–structure-interface internal erosion in realistic cases. Therefore, orthogonal and single-factor tests are carried out with a newly designed apparatus to investigate the critical hydraulic gradient of internal erosion on soil–structure interfaces. The main conclusions can be draw as follows: (1) the impact order of the three factors is: degree of compaction > roughness > clay content; (2) the critical hydraulic gradient increases as the degree of compaction and clay content increases. This effect is found to be more obvious in the higher range of the degree of soil compaction and clay content. However, there exists an optimum interface roughness making the antiseepage strength at the interface reach a maximum; (3) the evolution of the interface internal erosion develops from inside to outside along the interface, and the soil particles at the interface flow as a whole; and (4) the critical hydraulic gradient of interface internal erosion is related to the shear strength at the interface and the severity and porosity of the soil.

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