Bearing capacity of gravel road with and without geogrid. What are the theories involved with determining bearing capacity of a gravel road. How do you determine its ability to carry heavy trucks without deforming?

            Gravel road is a road which is formed using the mixture of sand, fine stones and sand. This mixture supports the base of the paved passage. Geogrid is a synthetic material formed from soils and similar materials. It acts as a support material for walls and can be used as sub-soil or sub-bases component in formation of roads. They are formed from synthetic materials such as polyester, polyvinyl alcohol, polyethylene or polypropylene (Skorseth and Selim). It is a great support material therefore the road with geogrid will be with increased bearing capacity and can tolerate heavy vehicles passing through it as well as different environmental conditions.

            Many people attempted to perform research on bearing capacity of road. Most recent attempts show utilized bearing capacity theory in order to understand the effect of materials used on the unpaved road. There are few roads which have a surface layer and some does not and the purpose of the surface layer is to protect the materials present within. Its presence results in shear strength characteristics (Koerner). Depending upon bearing capacity theory, pavements are designed on a fixed level of traffic approach. In this theory contact area and pressure is determined, single axle with single tires, single axle with double tires, and estimation of matric suction and includes effect of matric suction on bearing capacity.

The ability of bearing capacity of gravel road can be determined by performing tire tests. If the road is not paved properly then excessive deformation takes place. The pavement methods depend upon capacity theory in order to adopt a variety of recommendations and provide the factor of safety and load factor. The thickness and strength of the road depends upon the shear strength and unit weight of base layer in addition to subgrade layer and the one with geogrid in it is well sustained.

Over turning stability check of a wall, consists of footing and concrete block wall. What theories are applied to determine its stability?

        Curbs, short retaining walls and tall retaining walls are features required for well-established retaining wall components. The stability check of a wall consists of footing and concrete block wall comprises of different steps which also include overturning stability check. Boussinesq approach is utilized to check the stability of a wall road way parallel which can be modeled with a strip road.  If the wall is exposed to environmental pressures such as wind sometimes the stem extends to the backfill and wall is located in seismic pressure then Mononobe-Obake approach is considered. The Mononobe-Obake approach is based upon coulomb theory (Ghosh and Sengupta).

Overall stability is checked in four instability modes. Sliding, overturning, soil bearing and global instability.

 Boussinesq approach

This approach is applied to Reynolds stresses to mean velocity gradient. The Reynolds stress is related to mean gradient of velocity by means of Boussinesq approach. There are several cases in which Boussinesq approach can perform well (Parmar and Steinmanis).

Mononobe-Obake approach

It is a method which is utilized to check the pressure of lateral earth by geotechnical engineers. It is the closed form of method.

When burying electrical cables in the earth in a trench, a thermal fill is usually used so thermal energy from the cables can be expelled, thermal rho of thermal fill is used, how is this calculated? What theories are at play to determine the effectiveness of the thermal fill?

            The systems are usually laid open which makes the detection of the faults and flaws easy and facilitate the installation. When the cables are dug deep inside, this makes the problems undetectable. They are kept in a hospitable environment such as within rich thermal fill. The correct way to install electrical cables in thermal fills includes the intelligent design in order to appreciate the release of heat and allow optimum area to function underground (Yazdani, Azad and Farshi). If the correct thermal backfill is chosen then heat flux is reduced and energy is transported in better way possible. Normally the thermal backfill is filled up till 300mm, above the electrical cables. If the land condition is poor then width of backfill is increased to some folds in order to maintain a low thermal rho (Encinas). The good backfill comprises of the quality to resist complete dry out and in conditions of complete dry out has the possibility of low thermal rho to avoid dead dry conditions. Thermal rho is the thermal resistivity and fluidized thermal fill provide best quality cable backfill.

            The thermal resistivity or rho of a backfill can be calculated by equations developed by Fink and Smerke. Different thermal resistivities of backfills are compared with that of earth. The following equation can calculate the effective resistivity for an effective backfill (Brocchini).

                        Peff = Pf + (Pe – Pf)/ log 4L/De X Gb

Gb is the geometric factor which is equal to .0024 {307-2.5W-Y} {1+ .69/Pe/Pf}

W= width of trench (inches)

Y= depth of trench (inches)

Pe= initial earth resistivity (°C- cm /watt)

Pf = backfill earth resistivity (°C- cm /watt)

De= diameter at the start of the earth portion of the thermal circuit (inches)

L= depth of the cable below earth surface (inches)

There are few points which should be noted in order to determine the effectiveness of the thermal fill.

1.Properties of the soil and the backfill should be well known in order to ensure better and effective electrical cable installation.

2.Thermal resistivity can be measured with the help of determination of water and soil density. This will ensure safety and appropriate management and balanced water content.

3.Fertile soil always possesses high electrical resistivity because of lower value of densities and variable. It might contain low water table.

4.Backfill materials which are manipulated and engineered can be made available which in turn produce adequate thermal performance.

5.Thermal conductivity is a phenomenon which is straight forward and can be part of design cable and installation projects (Mckee).

References of Bearing capacity of gravel road with and without geogrid. What are the theories involved with determining bearing capacity of a gravel road.  How do you determine its ability to carry heavy trucks without deforming?

Brocchini, Maurizio. "A reasoned overview on Boussinesq-type models: the interplay between physics, mathematics and numerics." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469.2160 (2013).

Encinas, Javier. Restrained Retaining Walls: A Design Overview. 2016. <https://www.asdipsoft.com/restrained-retaining-walls-a-design-overview/>.

Ghosh, Sima and Satarupa Sengupta. "Extension of Mononobe-Okabe theory to evaluate seismic active earth pressure supporting c-φ backfill." Electronic Journal of Geotechnical Engineering 17 (2012): 495-504.

Koerner, Robert M. Designing with Geosynthetics - 6Th Edition. Xlibris Corporation, 2012.

Mckee, Smith Jane. Coastal Engineering 2006 - Proceedings Of The 30th International Conference (In 5 Volumes). World Scientific, 2007.

Parmar, Deepak and Jan Steinmanis. INTELLIGENT UNDERGROUNDING Underground Cables Need a Proper Burial. 2003. <https://www.tdworld.com/underground-tampd/underground-cables-need-proper-burial>.

Skorseth, Ken and Ali A. Selim. Gravel roads: maintenance and design manual. U.S. Dept. of Transportation, Federal Highway Administration, 2000.

Yazdani, Mahmoud, et al. "Extended “Mononobe-Okabe” Method for Seismic Design of Retaining Walls." Journal of Applied Mathematics 2013 (2013): 10. <https://www.hindawi.com/journals/jam/2013/136132/>.