Location: Terminal 1D, New Delhi

Brief of the Problem: Slope Protection work having Variable Strata for Construction of Metro Station and Interchange Section of Train

Metro Station was proposed near Domestic Airport Terminal 1D, and the station has to pass under the main road leading to the airport. For the construction of the station, the cut and cover technique was adapted. The cut and cover method need to be executed with precision so as not to affect the adjoining structures and necessitate proper support for the stability of the slope.

Engineered Solution: Supporting System for Safe Deep Excavation Works

To complete the station with minimum impact on adjoining facilities and structures and to not cause much hindrance to the moving traffic, the excavation work was proposed and executed.

Slope protection work was a temporary solution, and later on, permanent retaining walls were constructed. The protection systems used included soldier piles, timber lagging with cable anchors in soil strata, and rock bolts with shotcrete in rocky strata.

The retaining structure using a row of soldier pile was installed at the first stage as the soldier piles are vertical elements for the temporary protection wall. Soldier piles were made of H-shaped steel beams that are drilled deep into the strata before excavation commences.

The excavation started from the ground level to reach up to the bottom slab of the station box. Support to the soldier piles was given using timber lagging in between the soldier piles and by installing tie back cable anchors at different elevations with Waller Beam on the soldier piles. In some areas strut with king posts were also installed to support the soldier pile wall, which in turn supported the soil at the sides.

Rock bolts with shotcrete were used for supporting the sides of the rock surface. The choice of installation of places with anchor and rock bolt was made according to active earth pressure through earth pressure analysis. The anchors were used for temporary support, which was retrieved after the construction of concrete retaining walls. The anchor of capacity 68 and 45 tons were installed.

King post piles were installed beneath the steel platform. The steel platform was placed to keep traffic moving since the road is the main access road.

Difficulties Faced during Execution:

The geological strata in the area were of mixed geology. It included soil and rock. It created many difficulties to adhere to the H design of the work as the length of the pile, cable anchors, and king posts varied because of strata at different locations. Also, coordination was required between the excavation agency and us.

Achievements:

We are proud to have completed the work within the time frame despite many difficulties. The metro has started working on that Magenta line, and we are happy to be a part of making that possible.

The post Deep Excavation Using Retrievable Anchor at Terminal 1D Metro Station appeared first on Spar Geo Infra.

What: Brief of the Problem: Global Instability Issue of Deep Excavation of 3 Stored Basement.

Geology: – Peninsular gneiss covers a significant portion of the study area and is highly
migmatitic in nature. Their composition varies from tonalite and trondhjemite to granodiorite
and has fine to medium-grained texture. They are fine to medium-grained and generally grey
in color. In some places, they are regularly banded with alternate bands of felsic and mafic
minerals, and at places, the banding is irregular.

Granitic Gneisses and Granites were noticed under the study area. These gneisses and granites
are intruded by basic dykes, quartz and pegmatite veins. The average thickness of the weathered
zone is 3 to 20 m, whereas the thickness in low lying areas ranges from 10 to 70 m. The granitic
gneisses are intruded by numerous east-west running dolerite dykes of varying dimensions. The major
top layer of soil types found in are clayey, clayey mixed, red loamy soil, red gravelly soil were observed.

Disturbing factors::

Metropolitan cities were facing land scarcity, and out of which Bengaluru (Bangalore) called
to be a cyber-hub of India is the main victim. As it was a huge commercial project with three-storied
basements. So they decided to have a deep excavation to have increase basement number to 3 number.
But the geotechnical conditions present over there were not feasible to have an unsupported excavation
cut because, beside high raised building loads, the presence of commercial projects behind the plot
area made the deep excavation much riskier. The options were minimized due to account for higher loads using
conventional methods such as retaining wall, which in turn decrease the working space.

How: Strategy to Resolve the Issue: 

Preliminary site survey and reconnaissance in terms of geological-geotechnical assessment
made by Client. Data collection was done and recorded in a data sheet based on the
assessment of site conditions. Based on borehole data analysis of the geological slope profile,
it was proposed that due to the fragile geology of the project location. Two-dimensional soil
modeling for numerical analysis was performed to check the adequacy of deep excavation
was anchored pile wall to accommodate for the higher loads. Based on the site constraints
and geotechnical conditions, the cable anchor provided with a contiguous pile wall on the
sides where commercial complexes reside. The contiguous pile wall can be used as a
basement wall or helps in reducing the loads on the basement wall, which helps in reduction
in thickness.

The other sides, where loads were on the minimal side, was proposed for soil
nailing. As the solution was found to be optimal and the client was satisfied, we proceeded
for the design with our method mentioned where the diameter of the contiguous pile is
around 600mm (M30), and Fe500 steel and active cable anchor of 60-ton capacity was fixed
with a spacing of 3m*3m of free length varied from 8.5m to 10.5m and fixed length of 6m.
The grout material used of w/c ratio 0.4 attaining M30 grade. Soil nailed wall of 1.0m *1.0m
c/c spacing with an inclination of 10 degrees of 75mm thick shotcrete (M25) was provided
for the anchored wall facing criteria.
Our execution team is enriched with professionals having vast experience and with highly
advanced machines. This enabled the Geo Spar to carry out protection work on time without
fail.

Difficulties faced during Execution:

Contiguous pile wall driving is a difficult task in case of rock strata as for socketing of rock is
a major task which requires hard bucket tool for the depth of embed and even that the
maintaining the perfect spacing among the piles to have uniform c/c spacing for the
installation of anchors with limited tolerance in vertical alignment.

The technology used for Execution::

The strata present in the site was Granitic Gneisses rock strata, in which drilling of the casing
was a big task. Casagrande machine was imported for drilling of the casing operation. Special
admixtures used for the fixed-length portion to gain faster strength and accelerated setting
time for the anchorage system.

The post Contiguous Anchored Pile Wall Project for Cyber-hub, Bengaluru appeared first on Spar Geo Infra.

What: Brief of the Problem: To Provide Foundation System for 70 R Bridge at Challenging Terrain:

In Leh- Ladakh area, there is one important road leading to china’s border in which there crosses the Shyok
river width around 500 meters, and there was an urgent requirement of class 70 R Bridge. The site at KM
150.00 has desert terrain located at an elevation of 14700 feet above MSL with glacier valleys and during
summer season glacier melts, which increases the water level of Shyok River and damages the road which
ultimately leads to difficulty in transportation. The terrain in such areas is up to very high altitudinous and
deficient in oxygen in the atmosphere. The temperature touches minus 30 degrees centigrade, and
consequently, snowbound areas, including frozen river beds, are frequently encountered. There are a number
of glacial deposits leading to the worst environmental condition allowing hardly three to four working hours
daily. Site remoteness was the issue.

The approach to this location is connected by a single road axis, which
was 300 Km away from the nearest habitat of Leh city. The river flows through the difficult terrain of
Ladakh valley, and this area is prone to ‘Glacial Lake Outburst Floods’. These constraints demand the
construction of permanent structure for inland road connectivity across the Shyok River. The bridge piers
constantly remain in the threat of bed erosion due to the turbulence effect around the pier periphery.
Mountainous terrain possesses vital challenges, maximum difficulty at the site due to difficult approaches,
limited accessibility, larger time for deployment of resources, long movement across a number of high
mountain passes, which ultimately affect the logistics and communication hampering both the sustenance
and maintenance efforts.

Morphology of River Bed:

The site conditions comprises of varying thickness of glacial overburden soil
with cobbles and boulders. It has a huge quaternary deposit predominantly. The general strata comprised of
sand mixed with boulders of size 40mm to 200mm. Borehole investigation showed that at only one
abutment bedrock was at 12m and at two piers the bedrock encountered below the 20m, remaining having
almost river sand with gravel, soil classification of SW- well-graded sands, gravelly sand, little or no fines
and GP- poorly graded gravels, gravel-sand mixtures, little or no fines. The entire site soil condition was the
river born material (RBM) with glaciers (ice).

How: Strategy to Resolve the Issue:

A detailed discussion about the feasibility of the appropriate foundation type for this challenging region was
made with BRO officials. Several options were deliberated for the possibility of the foundation for the
proposed bridge. At the first stage for the foundation purpose of the bridge, such as deep (well, pile, etc.)
and shallow foundations (open cast foundation). Suitability of well foundation was not suitable due to the
higher water level, which restricts the accessibility for execution. In the case of pile, the requirement of
mobilization of heavy machinery, which is not possible because mobilization of these heavy machines will
contribute to further stresses. In the case of a shallow foundation, the concrete is not setting due to the
presence of a high water table; dewatering is required continuously, which is not considered to be a good
option.

The new technique was proposed to transfer of superstructure load to the desired firm bed level using
vertical and battered micro piles. To take advantage of Micropile and strengthen its surrounding area of
Micropile periphery, feasibility and design of TAM grouted Micropile was then investigated.
Design and analysis were carried out to achieve the axial capacity and lateral load-carrying capacity.
TAM grouted micropile constructed by drilling a borehole using Pneumatic Machine, placing steel
reinforcement, and grouting the hole. Tam grouting having various benefits such as injections can be carried
out in various stages, and different mixtures can be injected for each grouting stage. This permits better
penetration of the fine voids after the big ones have been closed.

More permeable soil layers can be sealed first regardless of the order of injection level, which prevents
loss of high-cost, low-viscosity grouts The abutments were designed with 69 piles. Out of these 69 piles,
25 piles at the center were vertical piles, and at the outer 44 piles were raker piles. The design for each
pier has been finalized with a pile group of 49 piles. Out of these 49 piles, 25 piles at the center are
vertical piles, and at the outer 24 piles are of raker piles. Each micropile of 273 mm diameter socketed
deep 21 meters into bed soil. Grouting was carried out using cement (53 grade OPC) with an addition of
1% special admixture of the total weight of cement to increase the strength of grout mix with the help of
double packer for 1.5 m section which helped to maintain almost a uniform thickness of grout along the length.

Pile Load Test:

The finalization of the project has to be done by verification of field tests.
Pile Load Tests as per are: 2911- part four were conducted for this purpose
Vertical piles – 8 no’s
Lateral load tests on vertical piles – 6 no’s
Group Pile one battered & vertical Pile – 2 no’s
Axial Load Test was conducted for Depth of Pile: 21m
Applied Axial load: 80tonnes, Rate of loading: 20% of Ultimate load
For lateral load test, Initial Pile load test for Ultimate Load: 2.5 ton

Difficulties faced during Execution:

Since the site was located in the region where climatic conditions are extreme and due to temperature
variation causes health issues to the workers. While carrying out the plate load test, sometimes the test was
aborted because of floods. The regular machines were not capable of executing work in such a climate, so
machines capable of working in low temperatures were imported by us. While grouting the grout setting was
also tough to achieve due to the presence of a water table.

Special Technology used for Execution:

For grouting of micropile Spar Geo suggested Tube-A-Manchette technology. A Manchette tube is a PVC or
metal pipe in which rubber sleeves cover holes that are drilled in the pipe at specific intervals. The sleeves
open when pressure is applied, which allows the spreading of grout outside of the tube; these sleeve doesn’t
allow grout to come inside. The grouted area got increased by using a double packer. This technology helps
to reduce the magnitude of settlement due to increased confinement and friction with the surrounding soil.

Achievement:

We were successful in carrying out grouting by using TAM technology effectively on the site where harsh
climatic conditions prevail. Our machines and workers adapted to the climatic conditions and carried out the
execution work for the bridge foundation efficiently. With a limited working period available, the bridge
was completed in 18months. The project was inaugurated by our Honourable Defence Minister, Mr.
Rajnath Sigh Ji, on 21st October 2019 and is dedicated to the nation.

The post Micropile Foundation Project at KM 150.00 D-S-DBO Road appeared first on Spar Geo Infra.