The Resistivity technique is a useful method for characterising the sub-surface materials in terms of their electrical properties. Variations in electrical resistivity (or conductivity) typically correlate with variations in lithology, water saturation, fluid conductivity, porosity and permeability, which may be used to map stratigraphic units, geological structure, sinkholes, fractures and groundwater.

The acquisition of resistivity data involves the injection of current into the ground via a pair of electrodes and then the resulting potential field is measured by a corresponding pair of potential electrodes. The field set-up requires the deployment of an array of regularly spaced electrodes, which are connected to a central control unit via multi-core cables. Resistivity data are then recorded via complex combinations of current and potential electrode pairs to build up a pseudo cross-section of apparent resistivity beneath the survey line. The depth of investigation depends on the electrode separation and geometry, with greater electrode separations yielding bulk resistivity measurements from greater depths.

The recorded data are transferred to a PC for processing. In order to derive a cross-sectional model of true ground resistivity, the measured data are subject to a finite-difference inversion process via RES2DINV (ver 5.1) software.

Data processing is based on an iterative routine involving determination of a two-dimensional (2D) simulated model of the subsurface, which is then compared to the observed data and revised. Convergence between theoretical and observed data is achieved by non-linear least squares optimisation. The extent to which the observed and calculated theoretical models agree is an indication of the validity of the true resistivity model (indicated by the final root-mean-squared (RMS) error).

The true resistivity models are presented as colour contour sections revealing spatial variation in subsurface resistivity. The 2D method of presenting resistivity data is limited where highly irregular or complex geological features are present and a 3D survey maybe required. Geological materials have characteristic resistivity values that enable identification of boundaries between distinct lithologies on resistivity cross-sections. At some sites, however, there are overlaps between the ranges of possible resistivity values for the targeted materials which therefore necessitates use of other geophysical surveys and/or drilling to confirm the nature of identified features.

Constraints: Readings can be affected by poor electrical contact at the surface. An increased electrode array length is required to locate increased depths of interest therefore the site layout must permit long arrays. Resolution of target features decreases with increased depth of burial.

As part of a hydrological study, a series of resistivity tomography profile lines were acquired to map variations within the overburden thickness. The example section above displays an extensive erosional channel feature together with more subtle overburden thickness variations.

A 3D resistivity survey was carried out to map the lateral and vertical extent of buried foundations. The grey zones represent noisy data due to buried services and the high resistivity values (red) reflect the foundation material. The resistivity suggest that the foundations extend to a maximum depth of 2m.

 Two 22-metre-wide road tunnels, touted to be one of the longest four-lane tunnels in the world, would connect Mumbai and Pune by 2021, according to Maharashtra State Road Development Corporation (MSRDC). The 8.9-km tunnel would be built to decrease the time taken to commute between the two cities through the existing Mumbai Pune Expressway (MPEW).

The tunnel will be a part of the Missing Link Project, a 19.8-km stretch of eight-laned roads on the MPEW which will reduce distance by 6 km and the time taken by 20-25 minutes. “Though there are tunnels longer than these, there are none of this length with four lanes. They would be the widest tunnels at this length,” explained a senior MSRDC official.

Connecting Kusgaon village to Chavani village on the Pune side, these would be twin tunnels constructed for travelling in opposite directions. Each four-lane tunnel will be 22-metre wide and separated by a distance of 50 metres. Composed of two tunnels and two viaducts alternately, the project will also include the construction of a cable-stayed bridge in a valley in Khopoli. To be constructed at a height of 130 metre, it will be a 700-metre long bridge with eight lanes. “Constructing cable-stayed bridges in valley areas is known to be a challenge,” he added.

Expected to cost Rs 4,800 crore, one of the tunnels will also be passing 150 metre below a lake in Lonavala.

(Source: https://indianexpress.com/article/cities/mumbai/coming-up-22-metre-wide-road-tunnels-on-mumbai-pune-route-5098278/)

 Mechanization is the process of changing from working largely or exclusively by hand to doing that work with machinery. The mechanization has several advantages. The work can be done speedily due to large output of machines, deployment of machinery is cost effective, can be deployed in difficult areas, the work can be done in time, large quantity of materials can be handled and effective quality control can be exercised so the size of the project can be increased. Optimum use of material, man power and finance can be achieved by deploying appropriate machinery.

Earlier smooth three-wheel roller 8-10 tonnes were used for compaction of earthwork, sub-base and base courses. In the year 1994 vibratory rollers were introduced in specifications. Drum type hot mix plant was used in bituminous works for preparation of mix for bituminous macadam, semi dense bituminous concrete and bituminous concrete. In the nineties Slip form paver and Batch type hot mix plant were provided in the specifications. Now a days full width pavers up to 11m width are being used in bituminous paving.

The Highway Sector in India is poised for rapid growth, due to launching of project Bharatmala by NHAI, PMGSY by Ministry of Rural Development and projects by other agencies such as NHIDCL and various state Govts. Most of the projects have become time-bound and have to be completed within the stipulated period. Due to this, expectation from the equipment market has also changed. The current trends in the market are going towards more mechanization and higher capacity machines. The speed of execution is the essence and the quality expectations of the end customer are constantly increasing. The customers want from their suppliers not only a machine but also support on the job site, to take care of the fleet of machinery. Machine operator interface will become a must. The electronic adaptation in machinery is improving their usefulness.

Generally road and bridge projects comprise of various activities of diverse nature. Execution of each activity should be planned meticulously to ensure sequential execution in time. There is no alternative to adopting mechanized construction methods to achieve more in less time. Once a decision of deployment of construction equipment is taken, requirement of construction equipment in a project needs to be identified. Selecting an appropriate equipment for a job ideally forms part of the construction planning process and should be chosen for performing any particular task only after analysis of many interrelated factors. The important points for consideration are: function to be performed, capacity of the equipment, method of operation, limitations of the method, costs of the method, cost comparison with other methods, possible modification in earlier acquired machine etc. The capacity of machine to be deployed on any activity is related to the size of activity and overall cost of the project. In the revision of Ministry’s Data Book for analysis of rates, this aspect of machinery selection is being considered.

The cost of construction is a major factor in all projects. There are many factors influencing the construction cost such as labour, material, construction equipment and profit etc. Costs of construction equipment ranges from 25% to 40% of total project cost.

Deployment of machinery allows manual efforts to be more productive. Large output can be maintained even if there is a shortage of skilled and semi-skilled manpower (as operators of construction equipment are of different category). Sophisticated road/bridge design may require precision in implementation which can be achieved by using modern construction equipment equipped with software controls.

Construction equipment and machineries could be rented as and when required for a calculated period of time. Hiring agencies are responsible for their repair, replacement, and even operation depending on the contractual period. On completion of the hiring period, the executing agency would be liability free of the rented items.

Information about machinery can be obtained from the internet or market survey even then a reference hand book with working output of machine and specifications of machinery is required for making assessment of the requirement of machinery for road project. To support the construction industry and the highway departments, need for such a reference document for machinery was being felt for quite same time.

“Pocket book on Road Construction Equipment”, comprising salient features of various equipments, their output, other supporting machinery in relation to various activities in road, bridges and tunnels has been recently published by the IRC. Machinery required for complete execution of any activity of a project and description of usage/working of machinery gives useful information to field engineers. For placing order for any equipment, specifications for the same are required. In the document, specifications for various equipment’s have been given. Machinery description have been given for latest machinery such as Track mounted crushing station, Sand preparation plant, Sand classifier, Bucket wheel Sand washer and Road sweepers, etc.

Description of essential equipment for all bridge construction activities such as concrete placement, concrete pumps, pneumatic sinking, bored/driven pile, prestressing, shotcreting, drilling, etc has been explained.

Tunnels are becoming part of hill and urban road projects. Essential equipment required for various tunneling activities such as Excavation, Steel lining, Concrete lining, Shotcreting/Guniting, Grouting and Lifting application have been given. Different tunneling methods including difficulties involved in each method and limitation of the methods, machinery involved in each method and tunnel ventilation system have also been given in the pocket book. The pocket book also includes various equipment required for quality control tests as well as for restoration work in disaster management.

The construction activities in the country are set to take a faster pace in the coming days with the present government drawing its road map of long-term infrastructure development. This has opened up new growth avenues for the construction equipment market in the country. Construction equipment manufacturers are exploring new technologies that provide productivity and fuel efficiency to the machines. They need to adopt clean energy sources and methods to stay in the market.

Reader are requested to make use of the recently released Pocket Book for Road Construction Equipment by IRC and send their valuable feedback for its further improvement.

Written by: Sanjay Kumar Nirmal,Secretary General,Indian Road Congress |

 Reference : Indian Highways, September-2019

The concept of green encompasses the mechanism of conserving, enhancing and managing the quality and quantity of natural resources. Getting green in other words is getting conducive to nature. Green highway is the one which is designed, constructed and maintained with the ultimate aim of conserving, enhancing and managing the quality and quantity of natural resources. The degree of green interventions, however may differ from project to project as technologies required depend on their economic feasibility, technical knowhow and availability of means to make use of a technology.

Green rating of highways refers to rating of various components of highways in terms of their environment friendliness. The rating is being introduced to encourage a qualitative assessment of environmental sustainability of highways.

Our country has voluntarily committed in Conference of Parties (COP-21) to reduce the carbon emission intensity of its GDP by 30 to 35 percent by 2030 from 2005 level. Road Transportation is one amongst the major carbon emission contributing sectors. Our country has more than 2.5 lakhs km of NH’s, and SH’s network spread all over the country that leaves behind its environmental footprint (including carbon footprint) during construction, maintenance and operation.

USA has established a number of green rating systems including “Green Roads” developed in 2010 for Green rating of Highways. At present, there is no such system in India that can quantify the environmental footprint of upcoming and ongoing projects.

The Guidelines for Green Rating of Highways has been recently formulated by Indian Roads Congress to help all stakeholders in identifying the degree of greener interventions to be made oralready made in a green field or existing road project. These guidelines will help produce a rating forthe reductions in environmental footprint of highway projects and hence enable the road authorities towards assessing the contribution of the main highways in achieving the commitment in COP-21.

All the stakeholders can use the rating system in making scientific and qualitative assessmentof various alternatives studied for a particular highway project in terms of their environmentalfriendliness. The rating system will provide a scale for determining the index of environmentfriendliness of a highway project also leading to adoption of environment friendly practices inroad projects. Apart from financial and technical feasibility, environmental feasibility should alsobecome an integral part of decision making. Highway projects should be evaluated based on theirown project specific conditions.

These green rating guidelines for highways have been developed with an attempt to overcome the major limitations of the present rating systems, which lack objectiveness in the criteria selection and weighting process considering existing environmental legislations in India and overall Indianperspective.

Green rating takes account of environment friendly, innovative techniques such as recycling ofmaterials, use of renewable resources use of soil stabilizers for stabilizing in situ soils, warm mixtechnology, construction and demolition waste etc. that have just started to come into practice in the country. The system has 13 mandatory Qualifying Criteria (QC) and 7 Evaluating Criteria (EC) with 24 sub-criteria. Mandatory qualifying criteria are the bare minimum requirements for rating a project while Evaluation Criteria are based on various parameters related to environment that needsto be quantified for all the alternatives of a particular project.

IRC is shortly going to release this document as IRC:SP: 122-2019 entitled “Guidelines for Green Rating of Highways”. These guidelines will mark the beginning of adopting the green rating approach for evaluating roads and highways. Green ratings once provided to projects can be used for greenfinancing by floating green bonds in the market. It can also be used for providing various incentivesfor projects using sustainable/environment friendly / low carbon technology in the project.

IRC would welcome any feedback/ difficulties faced in use of these Guidelines so that furtherimprovements in Guidelines can be carried out.

Written by : Sanjay Kumar Nirmal, Secretary General, IRC, Reference : Indian Highways - August,2019