Location: Noida

What: Brief of the Problem: Upliftment problem due to high pressure (buoyancy) beneath the ground surface

The problem of uplift due to buoyant force was observed at the commercial building development site. The site location is near to Yamuna River. The presence of the water table was very close to the ground surface created the development of high pressure beneath the ground surface. HCL wanted to make a commercial building, but the high-pressure buoyant force acting vertically upwards, leading to upliftment of the ground surface, created obstruction due to its stability problem.

“Buoyant force is an upward force that fluid exerts on any object that is placed in them. Buoyant force occurs because the fluid below an object exerts greater pressure on the object than the fluid above it.”

How: Engineered Solution: Arresting Ground Upliftment Using Vertical Anchor Systems

There was a need for some anchoring system that will hold the upward movement. The use of a passive cable anchor was selected to serve the purpose of the anchoring system. Fixed length (grouted length) will act as a rigid system, and stress transfer will occur through its free length (which is in tension). Stressing of the anchor will restrict and arrest the upliftment of structure, which was occurring due to buoyant force.

The designed anchors for the project were of 18 meters length out of which 12 meters was bonded length (fixed length), and 6 meters were a free length. The capacity of the anchor was 60 tons, and the spacing of the anchor was kept 3×3 (grid) meters.

Difficulties Faced during Execution:

The groundwater table was present at the -2 Mtrs, and we had to install anchors at -14 Mtrs. So, the process of de-watering was continuous to draw down the water table. The machinery movement was also difficult in this scenario. Apart from this, to get the required capacity of anchors, it was necessary to make grout bulbs for which high precision was required.

The technology used for Execution:

Grouting of the anchor was done by using new innovative technology known as Tube-A-Manchette grouting was used. This was used to achieve high strength/load-bearing by taking advantage of more frictional resistance.

“Application of TAM grouting is that where the sleeved grouting pipe allows to carry out first the primary injection followed by high-pressure injection, granting perfect cementation (well packed bonded arrangement) of the anchors in the bond length.”

Achievements:

The installation of anchors in a vertically downward direction along with proper grouting technique minimized the chance of uplift of the ground, and zero magnitude of uplift is observed after completion of the commercial project up to the present.

The post Uplift Ground Anchor Project, Noida 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.