2.2 Samarco Tailings Dam Breach
21
cation and exhaustive detail in each of these aspects of the Investigation’s evidencebased approach.”
The Fundão Panel was asked not to assign fault or responsibility to any person or
party and because of this it was not able to provide insights as to how the underlying
hazards went unrecognized or were allowed to exist at the time of failure.
2.2.2 Cause of Failure
As reported by the Fundão Panel in its report, “Fundão Tailings Dam Review Panel:
Report on the Immediate Causes of the Failure of the Fundão Dam” (Fundão Report),
the original design was based on employing an unsaturated sand zone for basic dam
support. It was further noted that unsaturated sand is not amenable to liquefaction
and because of this the original design was robust in this regard. In summary, the
dam failed by liquefaction flowsliding as a consequence of a chain of events and
conditions.
The Fundão Panel further reported that:
a change in design brought about an increase in saturation which introduced the potential for
liquefaction. As a result of various developments, soft slimes encroached into unintended
areas on the left abutment of the dam and the embankment alignment was set back from its
originally-planned location. As a result of this setback, slimes existed beneath the embankment and were subjected to the loading its raising imposed. This initiated a mechanism of
extrusion of the slimes and pulling apart of the sands as the embankment height increased.
With only a small additional increment of loading produced by the earthquakes, the triggering
of liquefaction was accelerated and the flowslide initiated.
The Fundão Panel considered the “evolutionary character of the design and operation to be extraordinarily complex” and employed a structured approach to the
examination of a large number of potential failure modes. Its conclusions were that:
1. “The surviving liquefaction trigger mechanism is static load increase …with its
two subsidiary processes: undrained shearing and deformation-related extrusion.
Both of these might be operative either with or without cyclic pore pressure
contribution from the November 5, 2015 earthquake series.”
2. “Also important… are the antecedent events and conditions… that allowed or
promoted static liquefaction at the left abutment. These are: (1) saturation of
the sand; (2) water encroachment that allowed slimes deposition on the tailings
beach; (3) the alignment setback; and (4) the increased height of the setback
resulting from continued raising of the dam.”
21
cation and exhaustive detail in each of these aspects of the Investigation’s evidencebased approach.”
The Fundão Panel was asked not to assign fault or responsibility to any person or
party and because of this it was not able to provide insights as to how the underlying
hazards went unrecognized or were allowed to exist at the time of failure.
2.2.2 Cause of Failure
As reported by the Fundão Panel in its report, “Fundão Tailings Dam Review Panel:
Report on the Immediate Causes of the Failure of the Fundão Dam” (Fundão Report),
the original design was based on employing an unsaturated sand zone for basic dam
support. It was further noted that unsaturated sand is not amenable to liquefaction
and because of this the original design was robust in this regard. In summary, the
dam failed by liquefaction flowsliding as a consequence of a chain of events and
conditions.
The Fundão Panel further reported that:
a change in design brought about an increase in saturation which introduced the potential for
liquefaction. As a result of various developments, soft slimes encroached into unintended
areas on the left abutment of the dam and the embankment alignment was set back from its
originally-planned location. As a result of this setback, slimes existed beneath the embankment and were subjected to the loading its raising imposed. This initiated a mechanism of
extrusion of the slimes and pulling apart of the sands as the embankment height increased.
With only a small additional increment of loading produced by the earthquakes, the triggering
of liquefaction was accelerated and the flowslide initiated.
The Fundão Panel considered the “evolutionary character of the design and operation to be extraordinarily complex” and employed a structured approach to the
examination of a large number of potential failure modes. Its conclusions were that:
1. “The surviving liquefaction trigger mechanism is static load increase …with its
two subsidiary processes: undrained shearing and deformation-related extrusion.
Both of these might be operative either with or without cyclic pore pressure
contribution from the November 5, 2015 earthquake series.”
2. “Also important… are the antecedent events and conditions… that allowed or
promoted static liquefaction at the left abutment. These are: (1) saturation of
the sand; (2) water encroachment that allowed slimes deposition on the tailings
beach; (3) the alignment setback; and (4) the increased height of the setback
resulting from continued raising of the dam.”