METHOD OF STABILIZATING SOIL FOR ROAD CONSTRUCTION

ABSTRACT

There are many types of ground rehabilitation and improvements that can be consider and implement in engineering construction works for soil improvement.

Many factors considering ideal proposal for ground rehabilitation are time, cost, quality, and most importantly practically. It should provide long life span structure in order to reduce

continuous cycle of maintenance. Thus, this paper presents a new technology for ground rehabilitation.

Here, we have used an injection system which consists of polyurethane (PU) chemical. The strong expansion of polyurethane grouting causes significant compression and compacting of the surrounding soil and improve ground properties and uplift sunken structure. It can be applied to any type of soil which needs to be uplifted. The layer of polyurethane is just formed in the soil and no harm is seen in environment as these products has been tested and certified.

It is chemically inert and is stable. Polyurethane is non-hygroscopic in nature i.e. it does not absorb moisture from the air. There is no weathering effect too. It also has symmetrical structure and has adhesive property as it compact itself.

INTRODUCTION

With the existing structure many problem are occurring because of loosely formatted soil. Not soils of all places are fit to be settled down. Some may be loosely format and structure made in these places can be damaged easily. Settlement depression, undulation, sinkhole are some of the types of problems. A greater effect sunken structure, current global climate and many more which requires continuous round of maintenance thus increases the unnecessary budget spending.

In practice conventional method has been applied as a solution for different problem regarding soil stabilization. One of that is cementations grout which provides only short term solutions by addressing the symptoms. But the placement of cement grout is just an additional weight on an already overstressed soil structure, thus will require similar round of maintenance time.

An eco-friendly, sustainable and cost- effective technology is hereby tabled to address the issues of insufficient bearing capacity. Soil stabilization can be defined as an approach or technique in improving the existing ground soil through modification properties of engineering characteristics behavior such as bearing capacity, stiffness, strength, density, compressibility as well as hydraulic conductivity. This is to address long term consolation and settlement, stability and hearing capacities for the foundation. Injecting chemical grout i.e. polyurethane is able to uplift, realign, under seal, fill voids and strengthens ground soil structure which has been implemented with successful outcome at several states. The injected resin within the soil will gain approximately 90% of its maximum compressive strength (of 0.276 N/mm^2) within 15 min.

These chemicals are environmental friendly non-toxic product and indefinite life span. Rigid PU has characteristics of light weight and expansion from ability with high specific strength. Strong in bonding stress with other substances, anti-aging properties and curing in a short time.

As the method of injecting polyurethane has not been implemented in our country we could not find the primary (local) data. However, we went to Lutheran World Relief foundation (LWF) which works for a sustainable development and got to know many more things required and will be required for sustainable development.

The density of polyurethane is 1oo kg/m^3 which seems to much less than that of cement which is 1400kg/m^3.So, from here we can see that the chemical which we will be using will be low in its weight and doesn’t add additional force on sunken soil and just keep holding the soil ,increasing its compressibility. And more importantly if we see on the cost of the maintenance the use of chemical polyurethane is much lower in cost than that of cement.

According to the data of 2016 of Utah State of America, the following costs are seen as the expenditure for cement grouting.

For 4 ft layer with 20% voids, grouting cost=$1,152,000 to $2,880,000 (288,000 ft^3)

For 4 ft layer with 30%voids, grouting cost=$1,728,000 to $4,320,000 (432,000 ft^3)

For 6 ft layer with 20%voids, grouting cost= $1,728,000 to $4,320,000 (432,000 ft^3)

For 6 ft layer with 30%voids, grouting cost=$2,592,000 to $6,480,000 (648,000 ft^3)

Similarly when we see the data of strategic highway research program of USA then the cost of injecting 3,100 lb of polyurethane cost ranged from $4.50-$6.50. Here the average cost came out to be $5.58 for 3,100lb.

From this data we are clear that the cost of injecting polyurethane is little bit higher to that of injecting cement grout. i.e. the cost of cement grouting seemed to be ranged from $4 to $5 and the cost of injecting polyurethane seemed to be $4.5 to $6 . Though the cost of injecting polyurethane seemed to be little higher, the life span of it is much longer than that of cement and does not need time to time repair.

So, our main objective is to stabilize soil which are loosely formatted using polyurethane chemical.

LITERATURE REVIEW

To collect our data and for secondary sources we had to do a quite lot more literature review and from our literature review we got to know that the use of PU form was first invented by prof. Dr Otto Bayer in Germany during world war 2 . They used it as a replacement for rubber. After that it has been used in several places for reconstruction of roads and most importantly for soil stabilization. If we see in the context of Nepal, the use of PU foam has not been seen till now for the stabilization of soil rather cement concrete has been used in place of that.

Polyurethane (PUR and PU) is a polymer composed of organic units joined by urethane links. These are thermosetting polymers which do not melt on heating. Even it takes only small amount of energy to produce the primary ingredients of PU foam, so it even saves energy.

Talking about the polymer, the thing that comes in one’s mind is plastic and toxic for environment and health but polyurethane is certified that it is completely safe for soil as it doesn’t take part in any chemical reaction with soil and remains neutral. Even for drinking water it is completely safe.

Going through the soil reports of Nepal, the cases of sink holes are more common these days. Though the sink holes are increasing day to day and land are being unsafe for the settlement, the way to tackle these problems is just same. But, if we see in the cases of other countries like Malaysia, Qatar, America and many more they are using this method and even doing more research in it .Last time it was used in the road construction in Malaysia and was successfully implemented. In this way it can even be tested in Nepal for the sustainable development and for human safety.

METHODOLOGY

Method of PU grouting is basically identical to the conventional cement grouting whereby the chemical resin is injected into the ground by drilling the hole. Install the pucker with tube and filling up the voids between the ground soils. In addition, with the use of PU foam the bearing capacity of the soil is improved due to the expansion of voids between the soil particles. Furthermore, the light wave characteristics of PU allow a reduction of settlement rate and expansion characteristics of PU foam able to uplift the ground soil.

The methodology for polyurethane grouting is quite simple. We just have to drill small holes in ground of ½ inch to 5/8 inch in diameter. The depth of hole should be 6 inch to 36 inch. Similarly the angle of drilling is 45 degree and the drill hole spacing should be 6 to 36inches apart.

Let us take the estimated area of 51m*45m then the points needed to be drilled will be 621 in each equal area and the blows for injecting the polyurethane is just half, i.e. 150 blows per 300mm for shallow foundation. It is much simple to install and even it can be easily installed with the help of few man power.

For our project we started our work from literature review. From there we got to know more about polyurethane and types of soil. As, we got polyurethane we did two of the test for soil. For finding out the type of soil we did Standard penetration test (SPT test) and for finding standard of soil and polyurethane we did direct shear test.

For receiving more information about sustainable development we went to meet prof.Ashutosh kumar shukla. He gave us around 45 minutes of time and share us more information about development and different new ideas.

After we finished our research we started making reports for final presentation and even started with our prototype. For our prototype we used the thermo coal board of 50*30 cm and have placed the designs of road. One made in stabilized soil and then other one made in unstabilized soil .And for showing the sample we have used the other glass bottle to show how polyurethane works.

PHOTOS COLLECTIONS DURING OUR PROJECT

RESULT

Our research based project finally successes. We got to add our knowledge on soil and its stabilizing properties. From the SPT (standard penetration test) we got to know that the soil we

tested was a loose soil i.e. c-fie soil and from DST (direct shear test) we got result that the value of c and fie was found more for the soil where polyurethane was put.

DISCUSSION/CONCLUSION

It is one of the new technologies which have been introduced for the replacement of cement grouting by the low estimated cost, durability and many more. Even in the type of soil of our country it can be easily used in the places where sinkhole, soil erosion, landslide are more common. The main outcome of our project is to increase the strength of soil and to stabilize with the modern technology.

RECOMMENDATIONS

As the benefits of polyurethane chemical grouting is much more than many other type of grouting, it can be the best alternative in place of other.

For the context of Nepal the areas where it can be implemented are:

- Bhaktapur area near Hanumante River where last week’s flood has affected the road constructions very badly

- Aarmala community of pokhara

And many other places where sink holes and soil erosion are most common.

REFERENCES

Www. Oregon Department of transportation research group.com

www.Federal highway Administration.com

www.Maintenance monitoring Department.com

Book of bio engineering.