How to make the week soil stabilized, i.e. what is soil stabilization?
Soil stabilization is a method to improve the quality of interior soil with respect to strength, density, stability, bearing capacity etc.
Here is a soil stabilization technique that can build Road and Building to long last, building them at low costs. Roads for trucks and tourists, for produce and pleasure, ferrying the country’s people need.
Stabilization of Pavement subgrade soil
Roads are the primary link in the transportation system, and good roads are vital arteries for a country’s lifeblood. While the safety and comfort of a high-class highway are plain to see, it is what lies beneath the surface that determines how long this smooth safe surface will last anew.
The bituminous surface does not carry the traffic loads. This is borne by the whole thickness of the road and the soil beneath, down to a considerable depth. The base course is the layer of hard stable material, whose function is to spread these loads so that the soil does not deform or move.
The object of the surfacing is to prevent dust and skidding and reduce wear and damage to the pavement.
Base materials are many and varied, but the crushed stone is most commonly used. Here, however, instead of quarrying rock, surface limestone has been collected and is being stockpiled at the crusher site. This limestone is common in certain parts of “Rocky terrain as well as Himalayan Region or mountainous area” and crushed makes a good base for roads.
Nearby the crushing plant is being erected. Involves the use of heavy machinery which causes high cost, and because of the large quantities of base material used a six-inchlayer total over two thousand tones per mile.
Costs of material can become staggering. That is why construction men are always searching for good rubble or gravel pits. Little or no blasting, no crushing, easy loading and one handling from the pit to the road is all that is required. The cost is often less than half that of crushed rock.
Cartage costs increase alarmingly if the trucking distance is long, and pits like these close to the road, mean big savings. But here where there is neither stone nor rubble, but just miles of drift sand and some sand mixed with clay, what can be used for base material?
What can be used for base material?
I am telling you the solution to just such a problem near a Border town. The natural and won’t do, although it makes the earthworks easy.
Dry sand is loose and unstable, hard to walk on and useless for traffic.
Yet it only needs to be damp to make it more stable. As witnessed, car racing on wet beaches.
Clay reacts to water, in the opposite way to sand, when wet it is soft and plastic.
This plasticity is a peculiar state lying between the solid and the liquid.
It means the ability to be deformed into any shape without cracking or rebound, at all glaze of plastic in the right range of water content. And dry clay can be might hard.
So just the right amount of clay added to sand will set it hard when it is dry. Giving a stable pavement, in all weathers.
Yet we don’t want the mixture to have excess clay and soften when wet. And For this reason careful control is essential and this is done by precipitate tests on the mixture.
Here in the pictures is a highways department laboratory, all materials used in road making are tested, and processes such as mixers are controlled.
As water is added to dry clay, it changes gradually from a solid to a liquid.Passing through that peculiar in-between stage of plasticity.
Again consider the sand and clay mixture, dry it is a rigid solid. Pressure does not permanently deform it, but under heavy blow, it shatters. A solid When rather wetter, the block can be deformed and doesn’t return, but cracks, not yet fully plastic. Now the material is truly plastic.
Rather on the wet end of the plastic range, a soft cohesive mess. And finally, cohesion went it flows as a true liquid.
The actual tests are done on a fraction of the material which passes a 36 mesh sieve.
Measure of Plastic-limit
These tests determine the moisture content of which a degree of plasticity is reached, and more clay present, the more water needed to bring it to that state.
The wetter a clay is the thinner it can be rolled before it crumbles and breaks. Either the hand or a glass plate may be used. When it is just plastic enough, to roll into a cylinder, one-eighth of an inch in diameter, and then breaks into beads it is defined to be at its lower plastic limit. This is measured by the percentage of moisture it then contains.
Measure of water content
To find the water content of the clay, it is placed in an aluminum drying tin whose weight is known. The tin and contents are weighed.
Then the soil is thoroughly dried in the oven. Taken out, and the tin and dry soil re-weighed.
When clay is wet beyond the plastic limit, it becomes more and more like a liquid, and the percentage of water at which it just flows, when jarred, determines the upper end of the plastic range.
A special device is used to make this test more accurate. Although it can be done by hand in an evaporating dish.
A groove is cut in the wet clay, and the pan dropped into a rubber base.
The moisture content, at which 25 blows caused enough flowing to close half an inch of this groove, measured the lower liquid limit.
This being found as before, by weighing and drying. Clay shrinks as it dries and this property forms the basis of a simpler test of the activity of the clay present in the soil. The material passing the 36 mesh sieve is weathered to the liquid limits and the mould is filled.
As it dries, a clay soil shrinks. Then the soil as freshly placed in the mold, then mold showed the same soil partly and fully dried.
The actual shrinkage in length expressed as a percentage is a linear shrinkage.
Application on the Road
On the new road, the cuttings have exposed deposits of sand containing a fair percentage of clay. Too much for the base material, but it is still soft enough to part easily when dry. Which is important as hard clay cannot be parted with construction equipment.
All the deposits of sand clay are thoroughly sampled and tested.
And the conclusion is, that two parts of sand clay mixed with one part of sand, will give a stable pavement, whether wet or dry.
So at suitable sites, pits are opened and bulldozers push up great heaps of sand clay ready for the loader to lift and dump into trucks. Despite the varying colors, the sand-clay is fairly uniform in clay content.
Any wide variations could make it difficult, impossible to obtain a sufficiently uniform mixture. The bulldozer by taking a long cut from top to bottom is mixing and making the sand clay more uniform.
On the road, the material is tipped at measured intervals, sufficient to give and even thickness of four inches throughout. The grader spreads the loads and levels the surface until this thickness is obtained. Construction and ordinary traffic and rain have set the sand-clay hard. So before mixing, it is broken up, by ploughing.
Tests on soil stabilization
The disc harrows chop and pulverize until the pile is fine and ready to mix. Mixing is done with a plough, set six inches deep. Bringing up two inches of sand into the four of sand clay. This is worked with disc harrows until the sand is thoroughly mixed with the sand clay. Rotary hoes are good for this work if no large stones are present.
Development of the rotary hoe is this pulverizer, designed to break up hard lumps and make the intimate mix. The back of the cover levels and smooths the mixed material. Here it is stabilizing an over plastic stony river gravel by mixing in the sand. It’s tynes are spring loaded on a revolving shaft and so can strip under heavy impact avoiding damage to the machine.
As a smooth mix is obtained the length is ready for sampling and testing the pavement. The testing closely follows the mixing so that a stretch of road with the wrong percentage of clay can be corrected before the construction equipment has moved too far ahead.
Back at the construction camp, a field laboratory has been setup in one of the huts. Then the samples are tested, checking that the mix is within the proper limits. Each morning, the tester technician have to give the list of the results. Showing where the mix is right and where corrections are needed.
Sometimes this is done by adding sand clay. Others by ploughing up more sand. That time the foreman is supervising the adding of sand clay to a stretch which is too sandy, and would crumble when dry. The grader follows to spread the material evenly over the right area.
Then follows the usual sequence of mixing, sampling, and testing. Until the whole stretch is right.
The mix is then given the right shape and a smooth surface by the grader. Finally, the length of road is watered until it reaches the moisture content at which compaction is most easy.
The mix may be compacted by various types of rollers, and one of the theme is solid tyre compactor is working its motor other mixture of local sand and clay in waste mine residues. This waste is a crushed rock which has lost its fine during the extraction of copper.
So in places like these, without a local stone, a stable base can be built by the methods shown. At a far lower cost than by bringing stone over long distances.
There are many other materials which are not naturally satisfactory for road making, but with modification, make excellent base courses. Often the change of plasticity is all that is needed. For example, such a material is an ironstone gravel. Lacking in a binder, it travels and corrugates easily. This can be corrected by the addition of sand clay.
But when tackling these stabilization jobs you must remember these main four points. You must be able to pulverize the clay material. All the material to be used must be tested.
The right mix must be calculated and checked. And you must have proper testing right with the construction gang to ensure the results.
So using many materials and methods we can build roads most reliable. Building them to last, building them at low costs. Roads for trucks and tourists, for produce and pleasure, ferrying the country’s people and they’re goods, serving you daily in an endless variety of ways.
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