Pile load test are usually carried out that one or some of the following reasons are fulfilled:
To obtain back-figured soil data that will enable other piles to be designed.
To confirm pile lengths and hence contract costs before the client is committed to over all job costs.
To counter-check results from geotechnical and pile driving formulae
To determine the load-settlement behaviour of a pile, especially in the region of the anticipated working load that the data can be used in prediction of group settlement.
To verify structural soundness of the pile.
Test loading: There are four types of test loading:
compression test
uplift test
lateral-load test
torsion-load test
the most common types of test loading procedures are Constant rate of penetration (CRP) test and the maintained load test (MLT).
CRP (constant rate of penetration)
In the CRP (constant rate of penetration) method, test pile is jacked into the soil, the load being adjusted to give constant rate of downward movement to the pile. This is maintained until point of failure is reached.
Failure of the pile is defined in to two ways that as the load at which the pile continues to move downward without further increase in load, or according to the BS, the load which the penetration reaches a value equal to one-tenth of the diameter of the pile at the base.
Fig.1 – Test being carried out
Fig.1, In the cases of where compression tests are being carried out, the following methods are usually employed to apply the load or downward force on the pile:
A platform is constructed on the head of the pile on which a mass of heavy material, termed “kentledge” is placed. Or a bridge, carried on temporary supports, is constructed over the test pile and loaded with kentledge. The ram of a hydraulic jack, placed on the pile head, bears on a cross-head beneath the bridge beams, so that a total reaction equal to the weight of the bridge and its load may be obtained.
MLT (the maintained increment load test)
Fig.2, the maintained increment load test, kentledge or adjacent tension piles or soil anchors are used to provide a reaction for the test load applied by jacking(s) placed over the pile being tested. The load is increased in definite steps, and is sustained at each level of loading until all settlements has either stop or does not exceed a specified amount of in a certain given period of time.
Classification of pile with respect to load transmission and functional behaviour
End bearing piles (point bearing piles)
Friction piles (cohesion piles )
Combination of friction and cohesion piles
End bearing piles
These piles transfer their load on to a firm stratum located at a considerable depth below the base of the structure and they derive most of their carrying capacity from the penetration resistance of the soil at the toe of the pile (see figure 1.1).
The pile behaves as an ordinary column and should be designed as such. Even in weak soil a pile will not fail by buckling and this effect need only be considered if part of the pile is unsupported, i.e. if it is in either air or water. Load is transmitted to the soil through friction or cohesion. But sometimes, the soil surrounding the pile may adhere to the surface of the pile and causes “Negative Skin Friction” on the pile.
This, sometimes have considerable effect on the capacity of the pile. Negative skin friction is caused by the drainage of the ground water and consolidation of the soil. The founding depth of the pile is influenced by the results of the site investigate on and soil test.
Fig.1.1 – End Bearing Piles
Friction or cohesion piles
Carrying capacity is derived mainly from the adhesion or friction of the soil in contact with the shaft of the pile (see fig 1.2).
Fig.1.2 – Friction Pile
Cohesion piles
These piles transmit most of their load to the soil through skin friction. This process of driving such piles close to each other in groups greatly reduces the porosity and compressibility of the soil within and around the groups. Therefore piles of this category are some times called compaction piles.
During the process of driving the pile into the ground, the soil becomes moulded and, as a result loses some of its strength. Therefore the pile is not able to transfer the exact amount of load which it is intended to immediately after it has been driven. Usually, the soil regains some of its strength three to five months after it has been driven.
Friction piles
These piles also transfer their load to the ground through skin friction. The process of driving such piles does not compact the soil appreciably. These types of pile foundations are commonly known as floating pile foundations.
Combination of friction piles and cohesion piles
An extension of the end bearing pile when the bearing stratum is not hard, such as a firm clay. The pile is driven far enough into the lower material to develop adequate frictional resistance.
A farther variation of the end bearing pile is piles with enlarged bearing areas. This is achieved by forcing a bulb of concrete into the soft stratum immediately above the firm layer to give an enlarged base.
A similar effect is produced with bored piles by forming a large cone or bell at the bottom with a special reaming tool. Bored piles which are provided with a bell have a high tensile strength and can be used as tension piles (see fig.1.3)
Fig 1.3. Under-reamed base enlargement to a bore-and-cast-in-situ pile
Classification of pile with respect to type of material
Timber
Concrete
Steel
Composite piles
Timber piles
Used from earliest record time and still used for permanent works in regions where timber is plentiful. Timber is most suitable for long cohesion piling and piling beneath embankments. The timber should be in a good condition and should not have been attacked by insects.
For timber piles of length less than 14 meters, the diameter of the tip should be greater than 150 mm. If the length is greater than 18 meters a tip with a diameter of 125 mm is acceptable. It is essential that the timber is driven in the right direction and should not be driven into firm ground.
As this can easily damage the pile. Keeping the timber below the ground water level will protect the timber against decay and putrefaction. To protect and strengthen the tip of the pile, timber piles can be provided with toe cover. Pressure creosoting is the usual method of protecting timber piles.
Concrete pile
Precast concrete Piles or Pre fabricated concrete piles : Usually of square (see fig 1.4 b), triangle, circle or octagonal section, they are produced in short length in one metre intervals between 3 and 13 meters. They are pre-caste so that they can be easily connected together in order to reach to the required length (fig 1.4 a) .
This will not decrease the design load capacity. Reinforcement is necessary within the pile to help withstand both handling and driving stresses. Pre stressed concrete piles are also used and are becoming more popular than the ordinary pre cast as less reinforcement is require.
Fig 1.4a – Concrete pile connecting detail
Fig 1.4b – Squared pre-cast concert pile
The Hercules type of pile joint (Figure 1.5) is easily and accurately cast into the pile and is quickly and safely joined on site. They are made to accurate dimensional tolerances from high grade steels.
Fig 1.5 – Hercules type of pile joint
Driven and cast in place Concrete piles
Two of the main types used in the UK are: West’s shell pile : Pre cast, reinforced concrete tubes, about 1 m long, are threaded on to a steel mandrel and driven into the ground after a concrete shoe has been placed at the front of the shells. Once the shells have been driven to specified depth the mandrel is withdrawn and reinforced concrete inserted in the core. Diameters vary from 325 to 600 mm.
Franki Pile: A steel tube is erected vertically over the place where the pile is to be driven, and about a metre depth of gravel is placed at the end of the tube. A drop hammer, 1500 to 4000kg mass, compacts the aggregate into a solid plug which then penetrates the soil and takes the steel tube down with it. When the required depth has been achieved the tube is raised slightly and the aggregate broken out.
Dry concrete is now added and hammered until a bulb is formed. Reinforcement is placed in position and more dry concrete is placed and rammed until the pile top comes up to ground level.
Steel piles
Steel piles: steel/ Iron piles are suitable for handling and driving in long lengths. Their relatively small cross-sectional area combined with their high strength makes penetration easier in firm soil. They can be easily cut off or joined by welding. If the pile is driven into a soil with low pH value, then there is a risk of corrosion, but risk of corrosion is not as great as one might think. Although tar coating or cathodic protection can be employed in permanent works.
Fig 1.6 – Steel piles cross-sections
It is common to allow for an amount of corrosion in design by simply over dimensioning the cross-sectional area of the steel pile. In this way the corrosion process can be prolonged up to 50 years. Normally the speed of corrosion is 0.2-0.5 mm/year and, in design, this value can be taken as 1mm/year.
Composite piles
Combination of different materials in the same of pile. As indicated earlier, part of a timber pile which is installed above ground water could be vulnerable to insect attack and decay. To avoid this, concrete or steel pile is used above the ground water level, whilst wood pile is installed under the ground water level (see figure 1.7).
Fig 1.7 – Protecting timber piles from decay: a) by pre-cast concrete upper section above water level. b) by extending pile cap below water level
Classification of pile with respect to effect on the soil
A simplified division into driven or bored piles is often employed.
Driven piles
Driven piles are considered to be displacement piles. In the process of driving the pile into the ground, soil is moved radially as the pile shaft enters the ground. There may also be a component of movement of the soil in the vertical direction.
Fig 1.8 – Driven Piles
Bored piles
Bored piles(Replacement piles) are generally considered to be non-displacement piles a void is formed by boring or excavation before piles is produced. Piles can be produced by casting concrete in the void.
Some soils such as stiff clays are particularly amenable to the formation of piles in this way, since the bore hole walls do not requires temporary support except cloth to the ground surface. In unstable ground, such as gravel the ground requires temporary support from casing or bentonite slurry. Alternatively the casing may be permanent, but driven into a hole which is bored as casing is advanced.
A different technique, which is still essentially non-displacement, is to intrude, a grout or a concrete from an auger which is rotated into the granular soil, and hence produced a grouted column of soil.
There are three non-displacement methods: bored cast- in – place piles, particularly pre-formed piles and grout or concrete intruded piles.
Pile foundations have been used as load carrying and load transferring systems for many years.
In the early days of civilisation, from the communication, defence or strategic point of view villages and towns were situated near to rivers and lakes. It was therefore important to strengthen the bearing ground with some form of piling.
Timber piles were driven in to the ground by hand or holes were dug and filled with sand and stones.
In 1740 Christoffoer Polhem invented pile driving equipment which resembled to days pile driving mechanism. Steel piles have been used since 1800 and concrete piles since about 1900.
The industrial revolution brought about important changes to pile driving system through the invention of steam and diesel driven machines.
More recently, the growing need for housing and construction has forced authorities and development agencies to exploit lands with poor soil characteristics. This has led to the development and improved piles and pile driving systems. Today there are many advanced techniques of pile installation.
TYPES OF CONCRETE BLOCKS OR CONCRETE MASONRY UNITS IN CONSTRUCTION
Concrete block masonry which is also known as concrete masonry unit (CMU) have advantages over brick and stone masonry. Concrete blocks are manufactured in required shape and sizes and these may be solid or hollow blocks. The common size of concrete blocks is 39cm x 19cm x (30cm or 20 cm or 10cm) or 2 inch, 4 inch, 6 inch, 8 inch, 10 inch and 12-inch unit configurations.
Cement, aggregate, water is used to prepare concrete blocks. The cement-aggregate ratio in concrete blocks is 1:6. Aggregate used is of 60% fine aggregate and 40% coarse aggregate. Their Minimum strength is about 3N/mm2. ASTM C-90-91 specifies the compressive strength requirements of concrete masonry units.
Types of Concrete Blocks or Concrete Masonry Units
Depending upon the structure, shape, size and manufacturing processes concrete blocks are mainly classified into 2 types and they are
Solid concrete blocks
Hollow concrete Blocks
Solid Concrete Blocks
Solid concrete blocks are commonly used, which are heavy in weight and manufactured from dense aggregate. They are very strong and provides good stability to the structures. So for large work of masonry like for load bearing walls these solid blocks are preferable.
They are available in large sizes compared to bricks. So, it takes less time to construct concrete masonry than brick masonry.
Fig.1 – Solid Concrete Blocks
Hollow Concrete Blocks
Hollow concrete blocks contains void area greater than 25% of gross area. Solid area of hollow bricks should be more than 50%. The hollow part may be divided into several components based on our requirement. They are manufactured from lightweight aggregates. They are light weight blocks and easy to install.
Types of Hollow Concrete Blocks:
Stretcher block
Corner block
Pillar block
Jamb block
Partition block
Lintel block
Frogged brick block
Bull nose block
Concrete Stretcher Blocks
Concrete stretcher blocks are used to join the corner in the masonry. Stretcher blocks are widely used concrete hollow blocks in construction. They are laid with their length parallel to the face of the wall.
Fig.2 – Concrete Stretcher Blocks
Concrete Corner Blocks
Corner blocks are used at the ends or corners of masonry. The ends may be window or door openings etc. they are arranged in a manner that their plane end visible to the outside and other end is locked with the stretcher block.
Fig.3 – Concrete Corner Blocks
Concrete Pillar Blocks
Pillar block is also called as double corner block. Generally these are used when two ends of the corner are visible. In case of piers or pillars these blocks are widely used.
Fig.4 – Concrete Pillar Blocks
Jamb Concrete Blocks
Jamb blocks are used when there is an elaborated window opening in the wall. They are connected to stretcher and corner blocks. For the provision of double hung windows, jamb blocks are very useful to provide space for the casing members of window.
Fig.5 – Jamb Concrete Blocks
Partition Concrete Block
Partition concrete blocks are generally used to build partition walls. Partition blocks have larger height than its breadth. Hollow part is divided into two to three components in case of partition blocks.
Fig.6 – Partition Concrete Block
Lintel Blocks
Lintel block or beam block is used for the purpose of provision of beam or lintel beam. Lintel beam is generally provided on the top portion of doors and windows, which bears the load coming from top. Concrete lintel blocks have deep groove along the length of block as shown in figure. After placing the blocks, this groove is filled with concrete along with reinforcement.
Fig.7 – Lintel Blocks
Frogged Brick Blocks
Frogged brick block contains a frog on its top along with header and stretcher like frogged brick. This frog will helps the block to hold mortar and to develop the strong bond with top laying block.
Fig.8 – Frogged Bricks Blocks
Bullnose Concrete Block
Bullnose blocks are similar to corner blocks. Their duties also same but when we want rounded edges at corner bullnose bricks are preferred.
Concrete Special Structural Wall ACI 318-08 Spreadsheet
The International Building Code (IBC) requires all concrete walls in seismic category D, E, and F, must be designed as a Special Reinforced Concrete Shear Wall. Basically all concrete walls in the West Coast of the US must be designed as a special wall.
The calcs in this spreadsheet are transparent unlike the typical blackbox calculations.
Also the figure of the wall in the spreadsheet changes with the input parameters.
The spreadsheet checks essentially all of the applicable codes in the ACI 318-08. The spreadsheet contains extensive boolean programming to address the convoluted nature of the code provisions for special concrete structural walls.
Anyone who has designed a special concrete structural wall knows how extremely complicated it can be, and will surely appreciate how easy to use and how thorough this spreadsheet is.
IMPORTANT: If upon opening this file, a warning message about circular referencing appears, DO NOT CLICK OK. You must CLICK CANCEL, click on Tools -> Options -> Calculation tab and enable Iteration as shown in the picture to the right. or the spreadsheet will not work properly. The reason for iteration: A vertical axial load P applied eccentrically on the wall will induce a deflection in the wall. The axial load P applied eccentrially on a wall that is deflected will cause it to deflect more. If this iteration was to be calculated by hand, it will take multiple iterations before the numbers converge to an acceptable level.
