KVPT’s Patan Darbar Earthquake Response Campaign - Work to Date - September 2016

Part V
Current thoughts on seismic strengthening
As we continue to think and design, ideas evolve. Following
are current thoughts, including lessons learned
over the last 25 years - and since the earthquake:
• Life safety is always a main priority
So much discussion in the field of preservation of historic
monuments delves deep into philosophies and priorities
of the actual preservation of the monuments and
buildings themselves, that sometimes this fundamental
topic is lost in the details. It must always remain in the
forefront of our minds that the buildings we work on are
living heritage and are used daily to serve the people of
the community. Without them, these buildings serve no
purpose, and the safety of those using the buildings must
always be considered at the forefront of any preservation
project.
• Foundations are the critical battleground
Reinforcing foundations is the opportunity and obligation
created by the need to rebuild collapsed structures
after the earthquake! This is a new frontier because earlier
projects have been in situ repairs, which do not lend
themselves to foundation work.
As the foundations are essentially the link between
buildings and the ground, they are the first to experience
seismic motion. If no investigation is allowed, or no
foundation strengthening completed, then any rebuild
runs the risk of damage because of this weak link. After
the earthquake, we have the unique opportunity to easily
access many foundations to study soil composition and
introduce strengthening measures largely invisible upon
completion of construction. Continuity of foundations
to provide a stable base increases safety of the structures
while helping to reduce visible strengthening measures.
Local opposition to the use of concrete - even concealed
in foundations, which is an international preservation
norm - continues to prevent the official acceptance of
this idea and the permitting of projects which include it,
as it has for the last 25 years. After the loss of life and
heritage of the 2015 earthquake, we renew the search
for the way forward.
• Critical distinctions between historic/original, later,
"traditional," and modern materials
So-called “traditional materials” are often misleading.
While they may have been widely used for decades,
many are not original to the historic structures. Our
strategy is to reuse and to return to original materials and
forms wherever possible. With rare exceptions, if traditional
means and materials are not sufficient for durability
and life safety goals, we retain the historic materials
and forms where they are visible and add modern interventions,
usually concealed, to achieve performance.
• Modern materials are sometimes the only solution
(and cement and concrete are not the same).
In keeping with their philosophy, ICOMOS experts
provided an early prohibition of lime-based mortars to
replace traditional mud mortar. This conforms to international
norms; we have removed Portland cement from
traditional structures it has damaged (eg Bhandarkhal
pavilion at Patan Palace). Lime surkhi, although in the
lexicon of traditional materials in Newar architecture,
is not a suitable ‘substitution’ for concrete. Lime mortar
has a much lower compressive strength and much
longer curing time than Portland cement, and is much
more susceptible to water damage. Proposed by others as
a traditional material to be used in foundations instead
of concrete because it was used above grade in Newar
construction for a time in the past, lime mortar is considerably
stronger as a bonding agent than mud mortar,
but is extremely weak in foundations because lime
breaks down over time with exposure to water. Typical
Western guidelines shy away from ever using more than
10-30% lime in concrete mixes below grade, and that is
in the driest, most ideal soil conditions. So soil conditions
in the Kathmandu Valley, in a former lakebed with
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