Soil Nailing for Collapsible Sandy Soil Underpass Construction
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Solution Overview
Problem
The construction of underpasses beneath rail/road traffic poses challenges due to the instability of highly collapsible sandy soil under dynamic loading conditions, requiring a method that maintains uninterrupted traffic and prevents soil collapse without disrupting existing structures.
Innovation Solution
The Soil Nailing Technique involves stepwise de-stabilization and stabilization of vertical cut slopes using grouted and driven nails to reinforce the soil, allowing for the construction of underpasses without alternate routes and minimizing disruptions to rail/road traffic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If shallow depth tunnel construction is performed using cut and cover techniques, then construction speed and cost are improved, but traffic disruption and property demolition increase significantly
Solution Approach 1:
The construction process is divided into sequential stages: first constructing the underpass at a distance from the railway, then progressively pushing precast box sections through the railway embankment in controlled segments. This segmentation allows traffic to remain uninterrupted while construction proceeds in manageable phases.
Solution Approach 2:
The precast box sections are prepared and positioned in advance before the actual pushing operation through the railway embankment. The soil stabilization measures are also performed preliminarily to ensure the embankment can withstand the pushing forces without collapsing during construction.
2Ease of manufacture
If retaining walls are dismantled to create space for box pushing, then underpass construction is enabled, but soil mass stability deteriorates
Solution Approach 1:
Soil nailing is performed in advance before dismantling the retaining walls. The nails are inserted into the soil mass and grouted to provide reinforcement, creating a stabilized soil structure that can withstand the subsequent wall removal and box pushing operations without collapsing.
Solution Approach 2:
The soil nails act as an intermediary reinforcement element between the soil particles and the retaining structure. These nails provide tensile strength and frictional resistance to the soil mass, mediating the stress distribution during wall dismantling and box pushing, thereby preventing soil collapse.
3Strength
If grouted nails are inserted to stabilize soil mass, then shear strength increases, but construction time and complexity increase
Solution Approach 1:
The soil stabilization process is divided into multiple stages corresponding to different sections of the embankment. Nails are inserted and grouted in sequential segments rather than all at once, allowing construction to proceed systematically while maintaining soil stability at each stage without requiring complete stabilization before beginning construction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively stabilizes collapsible sandy soil, enabling the construction of underpasses beneath high-traffic areas with minimal disruption, ensuring safety and cost-effectiveness by increasing shear strength and frictional resistance, thus preventing soil collapse and facilitating box pushing through sandy strata.
Implementation Method 1
The frictional resistance of soil increases due to nails
Implementation Method 2
nailing the soil mass by using grouted nails
Data Source
AI summary
The excavations of side vertical walls for building and underpasses must be shored so that the excavations adjacent to the neighboring properties do not cave in during the constructions. A Soil Nailing system has been used for stabilization of excavations and natural slopes for the last few decades in India and Abroad. Soil Nailing Technique used steel anchor rods inserted directly into the soil mass as a driven nails and when Nails are placed in pre-drilled holes to form grouted nails. In both the cases, it restrained load and the side deformations. In the present study, an innovative technique of ‘Soil Nailing’ has been developed for stepwise vertical de-stabilization and stabilization of compacted collapsible sandy soil for the construction of railway underpasses in live railway loading conditions. This technique is successfully implemented first time in the world for controlled destabilization of vertical cut slope and again stabilization for creating a space for pushing of box for railway underpasses for the length of 22 m and 50 m at two sites, namely Yamuna Bazzar and Apsara border, respectively, in Delhi, India. This Soil Nailing Technique of controlled destabilization of soil and again stabilization in steps has proved a superficial method of stabilization with the other methods for such kind of dynamic loading situations.