Erosion

Erosion refers to the process of weathering and transporting the materials around the earth like soil and rock. The erosion force usually occurs by the wind, water and natural slopes or some chemicals like acid rain


Although the erosion process is from the nature but lately it has been increased because the wrong behaving of human in dealing with nature resources, these like deforestation and the huge industrial revolution



One of the main causes of erosion is the gravity effect, on edged or creep sloped areas, the particles leave its places from higher levels to lower land due to gravity. The obvious example for erosion caused by the force of water is the shores erosion, it happens because of the tides effect. On very huge scale, erosion can happen by the movement of crust (the outer layer of the earth), in this case, erosion is caused by Tectonic effects

Soil Testing

foundation types

Soil testing means the analysis of soil samples to determine its composition and other characteristics like its behavior under different loading circumstances and the nature of its formation. Soil characteristics can vary from one spot to another in the same place

So, in soil testing many samples from different places should be taken and tested to have aright judgment on the soil.Soil tests is preliminary and very important step in construction projects. Depending on the soil results that came from commercial lab, engineers make their decision about the foundation type

Not only the construction projects that  need the soil testing, but there are also farmers or gardeners, they use soil testing to know minerals percentage and pH balance in the soil. Also some environmental agencies do soil tests to monitor problem areas for pollution and released contaminants, and to check environmental remediation programs. 

look retaining walls

Deep Foundation:: Piles

PILES  is a type of deep foundations that are driven into the ground. They are usually used in water constructions and poor soil that is opposed to heavy loads that any other foundation types can handle. Foundations pile can be made out of timber, steel, reinforced concrete and precast concrete 

Deep foundations can be installed by either driving them into the ground by pile drivers or drilling a shaft and filling it with concrete, mass or reinforced. Foundations relying on driven piles have groups of piles headed by a pile cap which is a large concrete block embeds the heads of piles into it. That is to distribute loads which are larger than one pile can bear. Pile foundations often are driven into place by a pile driver (a piece of heavy equipment that raises a weight to a certain height and drops it forcefully onto the top of the pile 

The weight forces the pile into the ground until the desired depth is reached. Steel piles' driving is easy, but the concrete ones have to be especially reinforced to withstand the hammer drop over it. In areas where pile driving may not be possible, piles can be drilled and poured in place. Drilling also allows for pile foundations to be used in areas where soil is very dense or hard. Often, drilled piles are formed by using permanent casings, which can then be filled with concrete

.

Diesel Hammer

The diesel hammer is a very large two-cycle diesel engines and one of the most common pile drivers. It consists of the piston which represents the weight and the cylinder mounted on the head of the pile

The process of pile driving here starts with raising the weight by cables attached to some crane for larger heights. When the weight is dropped, it compresses the air which forces this air to ignition point and at the moment a diesel fuel is injected in mechanically way to the pile hammer

This quick process generates force like small explosion acts In two ways, one forces the weight piston up and the other sends the pile down into the ground. This cycle keeps repeated until pile is inserted or fuel is out. In diesel hammer, Impact energy depending on driving resistance and there is limited possibility to control impact energy but still the most popular impact hammers in the world

Pile Driver

Pile driver is one of the construction equipment used to install piles in soil to provide more support and stability, and also to form the core strength of a structure. The weight of the structure is transferred to the soil through the piles. 

This piling here is not common in all construction projects; it is only used in some cases like large structures and structures on poor soil. An example for poor soil is the soil of sea bed. In water construction piling is always used. Piles can be made of wood, steel ( H shaped or steel tubes) or reinforced concrete.

The pile driver use a heavy weight, lift it for big height and then releases it over the pile top. This impact force forces the pile to go into the soil. In case of concrete piles, they have to be especially reinforced to withstand the impact power. There are many types of pile driver developed with the time. These types such as

• Diesel Hammer Pile Driver.
• Hydraulic Hammer Pile Driver.
• Vibrator Pile Driver.

 

 And the sizes of these pile drivers vary from small to medium to large. near this equipment, some cautions are necessary like covering ears because of the noise, standing away from it while operating and other routine Maintenance must be done

Hydraulic Hammer

The hydraulic hammer is the more quiet pile driver and it is modern type. From the name we can tell that it works by hydraulic power. Hydraulic power is generated by pushing hydraulic fluid through the rotary type hammer

As a result for that, a huge hydraulic power is generated that force the hammer down in high speed to hit the pile top sending it down into ground. Hydraulic hammer is used for piling steel piles, timber and pre-cast concrete in soft or unsteady ground as no other type of piling hammers will be suitable or leads to work collapse

In hydraulic hammer pile driver, Operator can accurately control hammer operation and optimize it according to soil conditions and pile size. in this type of pile drivers, there is no smoke, low noise and low vibration unlike the diesel hammer pile driver

look sheet piling

Vibrator Hammer

Vibrator hammer is the quietest and most efficient pile driver as it doesn’t make noise while working. It uses vibrating system that moves the soil particles from their places, which allow the piles to be easily driven into the soil. But this type is different from the others, that it can also extract the pile from the soil




The driving or extraction process begins with putting the vibrator hammer on the pile's top with the aid of excavator arm or crane and fastened by bolts or series of clamps. Vibrator pile drivers are perfect in some cases. Like when the construction is very close to residence or office buildings, or when there is not enough vertical clearance above the foundation to permit use of a conventional pile hammer



They are also effective in a variety of different types of soil, like clay, sand, and granular. Vibratory hammers commonly used to drive piles for such projects as ports and in highway construction

Sheet Piling

Sheet piling is one of the retaining walls' methods and it is used for soft soil like pure sand or soft clay. For piling in this method, piles used are made of steel or planked wood. They are used for offshore protection some times, supporting  excavating sides, ‎trenches and permanent use as retaining walls
 

At the site, these piles are driven into the ground by a pile driver or crane and 2/3 of the total length must be under the ground. They are put together and interlock in each other to make stable wall. Behind the sheet piles, there is the main soil which causes the active pressure. Also there is soil in front of the wall which cause a small pressure compared to the active called passive
 

Due to these two pressures, a shear force can be exerted on down third of the sheet piles wall. If this problem was covered by good reinforcement, the wall can take high loads. The disadvantage of this type is weak resist for overturning. It is perfect for small spaces because it can be totally vertical

Retaining Walls

Retaining walls are structures used to hold the lateral pressure of sloped soil and to prevent its motion. These walls are made of stone, concrete, steel piles and also modern interlocking blocks. Retaining walls must be designed to resist sliding, uplifting and overturning. For increasing the stability and performance of these structures, they have to contain draining system to allow the water seepage. 

This cancels the thrust of hydrostatic pressure caused by water on the walls. 

The lateral earth pressure behind the wall is called active pressure and on the other side called passive pressure. In the past, the retaining walls were large stones and big wood logs. Now there are many types and shapes depending on the cost, the nature of soil and on the place of the walls. The typical types of the retaining walls are four;

                                                                                    

2- Anchored retaining walls.

3- Sheet Piling retaining walls.

4- Gravity retaining walls.

4- Cantilevered retaining walls.

And for more stability, some techniques are used such as Soil nailing which is used to reinforce soil.

Anchored Retaining Walls

 Anchored Retaining Walls are very commonly used and are not different in their construction about the others. They are used in moderate height (up to 12.0 m) depending upon the site and soil conditions.


This type of retaining walls is supported by (1) horizontal steel tie rods with isolated anchorage or deadman (fig a), (2) steeply raking tie rods connected to soil anchors or driven steel H piles (fig b). (3) Horizontal tie rods connected to A- frame anchorages with backward and frontward raking bearing piles (fig c).




One end of the cable is attached to the wall and the other is anchored in stable structure like  deadman. As the other types, anchored walls should be designed to resist bearing capacity failure as they are often thin walls. The way of driving the piles on the soil depends on its condition, as example if the soil was rock it needs driller and if it was clay the piles can be shot in position by such equipment like air compressor.

Gravity Retaining Walls

Gravity retaining walls are a type of retaining walls, they are mostly trapezoidal-shaped but they may be with broken back. That was the shape, but about the material, the gravity walls are often made off stone, concrete and other heavy materials.

The gravity walls depend in its work on their heavy weight to resist the lateral earth pressure and the horizontal forces of the soil. As the other walls, the resultant of forces acting on the back of the wall must not exceeds the bottom third for avoiding the overturning, for that gravity walls can have leaning back embedded into the retained soil.

The gravity retaining walls need rigid footing to support the massive weight and ensure the required stability. In frost areas this is not an issue, no rigid footing is necessary as we can use Dry-stacked gravity walls which have a good flexibility. The similar wall here is the gabion which is a basket of steel filled with stones.

In the past, the retaining walls can get longer with the increase of massive concrete or stone weight, but now they can get longer by other ways such as soil nailing and crib walls. These walls can be strengthen with reinforcement bars or counterfort at the back

Cantilevered Retaining Walls

Cantilevered walls are a type of retaining walls that are used for resisting soil steep slopes. They are named with cantilevered because they are
constructed in such a fashion that the wall behaves as cantilever beam. Cantilever walls or stem walls or reinforced concrete walls are the commonest type or retaining wall

They are composed of a vertical or inclined slab placed with a slab base. Simple forms ofcantilever walls utilize the weight of the earth or backfill on the heel. This weight is added to the concrete to provide resistance against active thrust

The base of the stem should be large enough to resist the shear without any reinforcement. Some times for more stability and strength to the wall, we use "Buttresses" which are short wing walls at right angles to the main trend of the wall. This type of wall uses much less material than a traditional gravity wall

Before constructing this wall, a lot of calculations are made to ensure the safety of the wall. These calculations such as lateral earth pressure, bearing capacity, normal weight of the soil and also must be checked for overturning, sliding and uplifting

Soil Nailing

Soil nailing is a technique which inserts reinforcement bars into soil and into retaining walls for more stability. These bars are driven into the soil slopes in drilled holes and then grouted with concrete or be already in grouted drills



This technique was first appeared in France in year 1972 and after that it was widely spread around the world. After the bars are inserted in its place and have its reinforcement attached to the retaining wall, the heads of them and the walls too are covered by shotcrete (pumping the liquid concrete at high speeds through thin pipes).



The process of soil nailing is not easy, as it need professional soil engineer to determine the perfect places for nailing and also  trained workers because this technique is used for more stability ensuring, and if it doesn’t done perfectly, it will be money and time loss. Not only concrete walls and sloped soil are secured by this method, but also the steel sheet piles

Gabions

Gabion word is from Italian word, gabbione which means big cage. Gabions are boxes or cages filled with soil and used as retaining walls in civil engineering. Also they are used in military and road building. The materials of the gabion is different depending on the application, such as wick gabions and canvas gabions.

Gabions are known since the medieval times, and still used in some purposes. They are commonly used in protecting shores from erosion and soil from washing away under heavy rains. They are also effective in the case of floods, as they are temporary and quick solution which can be removed after the flood water is controlled.

In civil engineering they are used as retaining walls which are metal or other materials sack filled with stones. Gabions are also used in roads in supporting the sides of the road and to keep small rocks from  falling from the cliffs on the road.

In military, soldiers were using gabions in the field of battle for protecting the artillery gunners from enemy attacks. These gabions at that time (medieval times) were made from light material like wicker so they can be easily carried on the ammunition carts