An Overview of Soil nailing technique and it's implementation in India

Soil nailing is an in-situ technique used in slope stabilisation and excavation with the use of passive inclusions which can withstand tensile forces, shearing forces and bending moments. In-situ reinforcement refers to inclusions placed in the soil to maintain equilibrium under the soil self-weight loading and surcharge loading on the soil. Soil nails develop their reinforcing action through soil-nail interaction due to the ground deformation which results in the development of tensile forces in soil nail. Direct shear test and Pull-out test were conducted to understand the effect of soil properties and soil-nail interaction mechanism. The effect of soil nailing is to improve the stability of slope or excavation through A, Increasing the normal force on shear plane and hence increase the shear resistance along slip plane in friction soil. B, Reducing the driving force along slip plane both in friction and cohesive soil.

History of Soil nailing technique

The soil nailing technique was developed in the early 1960s, partly from the techniques for rock bolting and multi-anchorage systems, and partly from reinforced fill technique. The New Austrian Tunneling method introduced in the early 1960s was the premier prototype to use the steel bars and shotcrete to reinforce the ground. With the increasing use of the technique, semi-empirical designs for soil nailing began to evolve in the early 1970s. One of the first applications of soil nailing was in 1972 for a railroad widening project at 18 m high near Versailes, France. In Germany, the first use of a soil nail wall was in 1975. The United States first used soil nailing in 1976 for the support of a 13.7 m deep foundation excavation in dense silty sands. The excavation for the foundation of the extension to the Good Samaritan hospital in Portland, Oregon was executed in 1976. The next significant development was the excavation for the foundations of the PPG Industries headquarters in Pittsburgh, executed by Nicholson construction was completed in 1982. The remedial construction for repair of a reinforced earth retaining wall and repair of anchored wall in Frejus Tunnel, France was conducted. The restoration of a drystone masonry retaining wall at Denholme Clough near Brandford was done by repairing wall facing. The stabilisation of a failed soil slope at Herbouville, Lyons, France was done. Soil nailing technique is applicable for the protection and preservation of the historical buildings, examples include repairing a dam in the historic hydroelectric power plant in Rutki, Poland and slope stabilisation of castle hill in Sandomierz, Poland. Clouterre project, France in 1991 led to the widespread interest and application of soil nailing. Following the same, various other projects were launched in different countries like Bhutan, Vietnam, Hong Kong and others. In India use of soil nailing technology is gradually increasing and guidelines have been made by IRC with the help of Indian Institute of Science, Bangalore.

Soil nailing with Box Jacking technique

Rapid growing population with increase in vehicular traffic in metropolitan cities have urged the expansion of flyovers and underpass construction. Box Jacking technique is a non-disruptive technique for the underpass construction without disturbing the live traffic ensures safety and enables speed construction. Box Jacking involves the fabrication of a series of large size of precast RCC box segments. The box segments are pushed with the help of jacking force applied through hydraulic jacks installed at the rear end of the segment. When the precast box tunnel is pushed to create an underpass beneath any existing structure, the overburdened soil experiences increase in pressure which may lead to differential settlements or collapses. It is necessary to stabilise the soil at the box face during the box pushing operation. It has been observed that the soil slope in front of the box suddenly collapses and workmen get buried during the operation.

To avoid such situations, CSIR-CRRI invented a technique called 'Soil nailing with Box Jacking’ for strengthening the soil at the box face during box jacking operations. The team conducted the laboratory test model consists of model tank representing the embankment, box tunnel was inserted through the front wall of the model tank, loading frame has loading plate placed at the centre of the model embankment and load cell was attached on the top of it. Linear Vertical Displacement Transformer (LVDT) is used to measure the displacement. The box tunnel is pushed into the model tank at vertical and horizontal offset ratios and their corresponding load carrying capacity and percentage increase in load carrying capacity of soil are noted. The poorly graded fine sand (SP-SM) was used for the model embankment. The test was conducted in the overburdened soil without nails and then with the nails. The numerical study of box jacking with soil nailing technique was done using PLAXIS-3D software. This shows that the lateral and vertical displacement are reduced when nails are applied at inside and top of the box tunnel.

The technique was used for the first time in the world to construct underpass below two rail tracks at Yamuna Bazaar, Delhi. Similar projects including Apsara Border (Delhi), Sahibabad (Ghaziabad), Pragati maidan (Delhi), road underpass at Mahipal Pur, New Delhi and Seemapuri to Anand vihar are constructed.

Soil nailing for landslides

Due to climate change and rising temperatures, that triggers landslides in mountainous areas affected 4.8 million people between 1998-2017 said by World Health Organisation (WHO). The first half of 2024 has seen 310 fatal landslides, which have killed 2,315 people. A total of 83 fatal landslides that was occurred in June alone, written in EoS by AGU. The majority of landslides occur in Asia due to monsoonal rainfall in countries China, Nepal, India, Bangladesh and Pakistan but also extending across to Afghanistan and Kyrgyzstan. Recently, Papua New Guinea which is in Southwestern Pacific has faced a massive landslide that destroyed most villages and more than 2000 people were buried alive under the debris said by Reuters.

India is considered among the top five landslide-prone countries globally, where atleast one death per 100 sq km is reported in a year due to a landslide event. Soil nailing has been implemented in many parts of India such as National Highway Authority of India (NHAI) used soil nailing technique for road work at Kazhakootam - Karode national highway, Kerala. The State highways department of Tamilnadu, implemented soil nailing and hydroseeding in hilly areas such as Yercaud, Kodaikanal and Nilgiris. The tunnel project on Shiradi Ghat that connects Mangaluru - Bengaluru highway is constructed using soil nailing and micro filling technology. The technology has been implemented in northeast states such as Arunachal Pradesh for slope stabilisation and soil strengthening. It's important to preserve our mother earth and people lives without causing any harm to both the perspectives. Soil nailing technique does this job really good and the scientists invention and their repeated tests after every failure are truly commendable for creating a safe and secure environment.