Characteristics of sub-grade soils

 

Characteristics of sub-grade soils

Hi guys, Today we learn about Characteristics of sub-grade soils.

What is Sub-grade Soils?

Pavement, along with the subdivision and other components placed on the subdivision, are the two most important and essential parts of the road structure. Subgrade is the layer of soil that serves as the foundation of the upper road structure at a depth equal to the sum of the thickness of the pavement, base course and subbase course from the top surface of the preparation floor.

Since the substation carries all the loads on the road structure and the structure built on it, any defect of the subgrade after the construction of the road will be rectified. There is no chance. So for a good road, the subgrade design has to be done in advance.

Subgrade carrying capacity:

Pavement, along with the subdivision and other components placed on the subdivision, are the two most important and essential parts of the road structure. A sub-grade is a layer of soil that serves as the foundation of an overhead road structure at a depth equal to the sum of the thickness of the pavement, base course and subbase course from the top surface of the preparation floor. 

Since the substation carries all the loads on the road structure and the structure built on it, any defect of the subgrade after the construction of the road will be rectified. There is no chance. So for a good road, the subgrade design has to be done in advance. The type, thickness and quality of the road depends on the carrying capacity and characteristics of the subgrade. Depending on the type, thickness and quality etc.

Bituminous road surface damage, surface corrosion, broken concrete road plumbing, surface cracks, pumping action, etc. are usually due to weak subgrades. Therefore, while constructing road embankments, special attention should be paid to the subgrade soil and sub-graded soil should be constructed in uncompressible soil.

Road subgrade soils are affected by gravitational water, capillary molsture and absorbed water. As a result the subgrade sits down, the road fails. Therefore, soil should be selected for subgrade keeping in view the Soil index properties and other properties of subgrade soil.

Characteristics of different sub-grade soil:

Soil characteristics are not the same in all places and in all situations a particular soil exhibits the same behavior = as a result the soil characteristics in different regions differ in different places. The presence and amount of water affects the release properties. A small amount of water acts as a lubricant. 

The behavior of soil also depends on the size, arrangement and quantity of soil particles, which are called index properties of soil. Soil index is one of the following spices.

(A) Grain size distribution and

(B) Consistency limit & indices

(A) Grain size distribution and

(A) Soil Particle Size Arrangement Particle layout and soil particle size play an important role in soil religion and behavior. Soil particle size is determined by sieve analysis in clay grain soils and fine particle soil particle size is analyzed by sedimentation process. Different institutes of road research follow different classifications based on the size of soil particles to determine both the properties of the soil. Although there is not much difference between them. Depending on the size of the particle, pearls are divided into gravel, sand, silt, mud and colloid. Below is a brief introduction to .

Gravel: These are usually rock particles with a diameter of more than 2 mm. These tend to be eroded in the water flow or due to natural causes. Less eroded particles of quartz, niss, cyst, basalt or limestone are angled.

Maeta Bali:

These are less than 2 mm in size. These are also round or angular according to the gravel. Polly. They are angular in shape and composed of the same chemical elements as sand, but they are formed as a result of chemical decomposition.

Mud and chemical weathering usually cause mud to form, and in the presence of water the colloids are so fine that they can float. Under the influence of gravity, they behave quite complexly in the presence of water as sediment. When viewed under a microscope, they can be seen in an uncontrolled state of motion.

(B) Consistency limits and indicators:

 The characteristics and behavior of coarse-grained soils largely depend on the particle size format but the characteristics of fine-grained soils. And behavior largely depends on the amount of water in the soil. 

That is, the amount of water in a fine-grained soil decreases with increasing amount of energy, and gradually becomes soft and liquid with increasing amount of water. In 1991, Mr. Etterberg, the eminent liberation scientist, invented the method of testing the consistency and flexibility of fine-grained clay.

These are known by their names as Atterberg Boundary and Index. These are briefly discussed below

Liquid limit, LL:

The minimum amount of water in a soil is the amount of water that flows in the Otterberg machine in 25 shakes, the amount of water is called the liquid limit of that soil (L.L.). In this condition the release has internal friction, the shear resistance level is zero and the ability to take pressure is lost. 

The amount of clay in the soil is known indirectly from the liquidity limit. The liquidity limit of sandy soils is usually around 20 and in silty and clay soils it is more than 40. If the presence of water increases with the release of more silt or mud, their carrying capacity will be reduced.

Plastic limit, P.L:

The amount of water in which the humility of the muktika ends is called the amount of water in the soil. Simply put, it is common knowledge that any mud release in water can be turned into a three millimeter diameter yarn without cracks and without cracks. The amount of water in the release is the amount of water. The average readiness limit of silt, black and colloid is 20, 45 and 46 respectively.

Plasticity index, P.I or Ip:

The extent of water content in the soil within which the soil exhibits flexibility behavior

Is called the flexibility index. Simply put, the difference between liquidity limit (LL) and flexibility limit (P.L) is called flexibility indicator.

 I.e. the flexibility index, P. = LL- L.

Shrinkage limit, S.L.:

As the water level decreases from the clay soil mixed with water, its volume also decreases. But there is no change in the volume even if the water level decreases within a certain limit of the oily part. But the sixty voids begin to become airy. The amount of water in the soil does not change the volume of the soil even after the water is reduced. This amount of water is called the soil compaction limit.

Suitable sub-grade for various types of highway construction :

Subgrade of the following qualities is required for construction of different types of roads.

(1) Any adverse conditions will not interfere with its stability.

(2) In no case shall its power be altered, i.e. it shall have permanent power.

(3) It will not be incompressible under any circumstances.

(4) It will have good drainage qualities.

(5) It shall not swell in the presence or adverse reaction of any kind of water.

(6) The stability of frost action will not be affected.

 (7) It can be easily compacted during construction.

(8) Its maximum density can be obtained at a certain amount of compaction during construction.

 (9) Soil particles of different sizes will be formed in its structure in a balanced arrangement.

Procedure of improving sub-grade soil far road construction :

All work prior to placement and reinforcement in the vault structure is associated with subgrade soil preparation. So road erosion Cleaning, earthworks (excavation or filling), soil consolidation, etc.

The task of preparing the sub-glade release depends. The position of the subgrade is on the normal mucous membrane or filled clay

After excavation the surface may be liberated. In all the above cases, all kinds of impurities (slaves, herbs, tree roots and other organic matter) have to be removed from the surface of the substrate and the design camber has to be applied according to the vertical profile design of the subgrade and the subgrade soil has to be compacted well . If there is any unsuitable soil (organic soil, clay, loose soil etc.) in any part of the road, it should be removed and filled with suitable soil and compacted properly. 

If suitable soil is not available, a small amount of fine granular soil (85% - 90%) mixed with a small amount of fine grained soil (10 # - 15%) should be spread in multiple layers and subgraded by railing every 6 to 12 ton smooth wheel roller. In order to multiply the subgrade to withstand the pressure as per the design, the quality of the subgrade soil needs to be improved by stabilization. 

The amount of pressure tolerance can be increased by compacting the mucus at moderate humidity. Bituminous material or bitumen coated paper can be used on the surface to keep the subgrade free from the infiltration layer or bituminous membrane under the subgrade and to keep the road surface free from water absorption.

Construction of road in water logged aréa:

Water lagged aren is the position of groundwater or standing water within the capillary fringe of subgrade i.e. within 1.5 m.

Waterlogged areas can be divided into three categories. Such 

(1) Flood-free waterlogged areas.

(2) Waterlogged areas with prolonged flood status and

(3) Waterlogged areas with the presence of harmful salts in groundwater and surface water.

(A) Lowering the ground water table through proper drainage:

Cut a 1.5 m to 3 m deep canal along the road embankment as far as possible and connect it with a suitable low-lying canal or stream for quick drainage or by digging a properly designed deep ditch along the side of the pavement to connect with the drainage ditch.

(B) Increasing the height of embankment or road embankment:

If the cost of digging deep ditches is higher, at least above the maximum water table. Road embankments can be constructed at a height of more than 5 m. (C) Capillary cut off with capillary cut off and capillary cut off at least 15 cm above the surface or at the height of the standing water level. However, in no case should this height exceed the height of 60 cm below the top floor of the subshred and a cut off under drain must be given.

Use bituminous primer, felt or polythene sheet as capillary resistant layer to be 10 cm above it. Sand or similar materials are used in cm thickness. It must be given that the water is drained from the surface of the road. Resistive layers do not cut or rupture at the edges of the edges of the filled material.

(D) With sufficient thickness pavement:

Adequate thickness of pavement should be applied in case of subgrade being saturated and if subbase of stabilized soil of at least 10 cm thickness is used, the subgrade will not get wet or saturated.

E) Withdrawal of sand layer and vertical sand drain and some distance away drainage of ground soil.

(F) In the case of waterlogged areas with prolonged flood status, successive vertical sand drains and interstitial sand levels.

(A) In this case, after performing the tasks described in (i), the following tasks should be performed as an additional step: (b) Cement concrete or bitumen concrete pavement should be provided for heavy and medium vehicles.

(C) Bituminous surfacing with silk coat should be applied on light moving roads. (ii) In case of waterlogged areas with presence of harmful salts in groundwater and surface water

(A) In this case, after taking the steps described in (i) and (ii), the following additional steps should be taken: Prevent harmful salts and water penetration in the pavement and solder and capillary cut off below subgrade.

(B) Harmful salt resistant materials should be selected for road construction.

(D) If the above mentioned works are not considered sufficient for the road of special importance, it is too expensive.