Lec. Dr. Riyadh Abd Al-Abbas<br />Meaning of hilling: It is rearranging the soil particles by expelling air only from the soil voids. This is done using mechanical means, resulting in a decrease in the size of the air voids and an increase in the density of the soil. Reducing hardening differs in that the latter is the gradual expulsion of water from saturated soil using continuous stress, accompanied by a decrease in volume.<br />-The importance of soil grading:<br />1- In the field of earth dams, the thickness of the backfill soil in the dam increases its resistance to water penetration, which reduces the amount of water leaking from it. The shear strength of a well-contoured backfill helps to stabilize this backfill and resist slipping.<br />2- In the field of roads and airports, these engineering works increase their carrying capacity if they are built on a well-planned basis.<br />3-In the field of improving soil properties in replacement operations<br />Reduction is one of the most important operations necessary to stabilize the soil, whether the stabilizing material is added or not.<br />* The effect of humus on soil properties<br />1- The reduction increases the shear resistance of the soil.<br />2- Increases the bearing capacity of the soil.<br />3- It reduces the soil’s ability to compress and subside.<br />4- Reducing the permeability of the soil reduces its ability to seep in water.<br />- Methods of modification on site<br />1) Straightening with vibrators:<br /> 1- Smooth wheel vibrators: These are known as three-wheel vibrators and there are different weights.<br />2- Vibrators with inflated tires under pressure: These are vibrators that contain several small wheels with inflated tires. The heavy ones weigh about 200 tons. The number of passes of these vibrators and the pressure they exert on the soil depends on the required degree of compaction and the thickness of the soil.<br />3- Sheep foot vibrators: They are composed of hollow steel cylinders with prismatic feet distributed over the surface of the cylinders. The weight of the cylinders can be changed by filling them with water.<br />2) Forging with hammers: Forging is done by pounding with hammers, and the weight of the hammer ranges from 30 to 150 kg, including some that weigh up to one ton.<br />3) Vibrating compaction: The soil is compacted using vibration-producing devices. Some of them are manual for small works, and some are huge. One of these devices is what is called vibrating flotation, which contains a vibrating cylinder 2 m long and an outer diameter of 43 cm. The vibrating cylinder is lowered and fills the soil by pushing water from the bottom. The cylinder is then subjected to vibration, causing the soil to move around it. When compaction is completed, more soil is added around the cylinder. Then raise the cylinder by 30 cm and repeat the process again. This type is used to reach depths of up to nine meters.<br />