DFI Magazine March/April 2020 - 83

Ischebeck, managing director of Ischebeck, described at the 2019 International
Workshop for Micropiles, the end-bearing
contribution to the external load bearing
capacity is usually neglected.
For five towers on two of the Integration Network lines, a deep foundation
solution using a group of self-drilling
micropiles was designed and implemented. Self-drilling micropiles consisted
of continuously threaded hollow bars
made out of seamless steel pipes. These
micropiles were installed via rotary
percussive drilling. During this process,
the micropiles were continuously grouted
(using dynamic injection), which builds a
rough interlocking of grout and soil where
they interface, increasing the skin friction.

The Blue Line
The Blue Line (Línea Azul) in El Alto is the
longest line in the network at 4.98 km
(3.09 mi) and has 5 stations and 40 towers
(pylons). Along the line, 4 towers (numbers
14 through 17) are located above an existing
canalization vault for a river, making the
standard foundation solution inapplicable.
A deep foundation solution using a
group of eight self-drilling micropiles was
designed and implemented by the
subcontractor, Terra Foundations Bolivia,
for each of the four affected towers. The
TITAN 52/26 self-drilling micropiles were
installed into alluvial deposits (gravels in a
cohesive matrix) using a carbide button
drill bit of 130 mm (5.11 in) diameter. The
micropiles were from 9 m to 10.5 m (29.5 ft
to 34.4 ft) long, and the design resistance
was 520 kN (116.9 kips).
The micropiles were installed in April
2016, and the line officially began operations that November. The line opened for
the public on March 3, 2017. Approximately 770,000 passengers were transported
in the first month of Blue Line operations.

Pale Blue Line
The Pale Blue Line (Línea Celeste) in La Paz
is the fastest line in the network (2.7 km, or
1.7 mi, in 12 min). It has 4 stations and 26
towers. The layout of the line required
installation of a tower in the immediate
vicinity of an existing slope without
interference with another canalization
vault. Construction of the standard shallow

Micropile head connection

foundation would have required a major
intervention of the slope to guarantee the
stability of structures located on its top.
A deep foundation solution using a
group of 14 self-drilling micropiles was designed and implemented by Terra Foundations Bolivia to transfer the loads from this
tower to the ground. This approach reduced
the footprint compared to the traditional
foundation by 40%, thereby minimizing the
intervention area in the slope.
The TITAN 40/16 self-drilling micropiles were installed into alluvial deposits
(gravels in a cohesive matrix) in September
2017. A carbide button bit of 90 mm (3.5 in)
diameter was used for the micropiles of

7.5 m to 9.0 m (24.6 ft to 29.5 ft) length. The
design resistance was 426 kN (95.8 kips).
The Pale Blue Line officially began its
operations on July 9, 2018, and was opened
for the public five days later. It has a transportation capacity of 4,000 passengers/hour.

Conclusion
The increasing density of urban development requires engineers and contractors to
think three-dimensionally: to look skyward
as well as underground. Urban cable car
networks are capable of providing efficient,
environmentally-friendly and sustainable
mobility in locations where other, streetlevel technologies are unworkable.
DEEP FOUNDATIONS * MAR/APR 2020 * 83

DFI Magazine March/April 2020

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