PILES FOUNDATION

Bored Piles

Bored and cast-in place piles ranging from 600mm to 3000mm in diameter and depth up to 80 meters. Bored piles are formed by removing first the soil by special drilling technology method, and then constructing the pile by placing the reinforcement and concrete or other structural element into the bore hole. Bored pile is drilled using latest hydraulic drilling rig equipment and with the use of short temporary steel casing for stable ground and using long temporary casing driven and remove by vibratory hammer or a combination of short temporary casing and drilling fluids slurry (Bentonite or Polymer) for unstable ground. Bored Piles are most suitable for Bridges, High Rise Buildings, Industrial tanks and other Heavy Structures.

 

Continuous Flight Auger

Generally known as CFA Piles, are cast-in place piles with varying diameter from 300mm to 1000mm and depth up to 20 meters. They are installed by drilling with a rotary continuous-flight auger to the required depth. This type of pile is suitable for unstable ground or water bearing soils. CFA piles are carried out using a flight auger with a hollow stem closed at the bottom by the plug. After reaching the final level a fairly cement-sand mortar or concrete made with a course aggregate of not more than 20mm, is pumped down the stem and fills the void as the auger is slowly withdrawn with or without rotation. Thus the wall of the borehole is continually supported by the spiral auger and soil within them, and by the mortar as it is pump in, the resulting pile having a cylindrical shaft. Reinforcement steel then be installed with the assistance of vibrator.

  

Minipiles and Micropiles

Are piles having a diameter from 50mm to 300mm, with the working loads in the range of 50 kn to 500 Kn. The term of “Micro-pile” is given to those in lower range diameter. The principal use of minipiles and micropiles is for installation in condition of low headroom, such as underpinning works or replacement of floors of buildings. They can be installed by a variety of methods as follows:

  • Driving small-diameter steel tubes followed by injection of grout with or without withdrawal of the tubes,
  • Driving thin wall shells in steel or reinforced concrete which are filled with concrete and left in place,
  • Drilling holes by rotary auger, continuous flight auger, or percussion equipment followed by placing a reinforcing cage and in-situ concrete in a manner similar to conventional bored pile construction.
  • Lacking-down steel tubes, steel box-sections, or precast concrete sections. The sections may be joined by sleeving or dowelling.

 

 

Piles Testing:

  1. Static Load testing (Compression or Tension)
  2. High Strain Dynamic Load Testing
  3. Caliper Logging Testing of Pile Bore
  4. Koden Testing of Pile Bore
  5. Cross-hole Sonic Logging Testing
  6. Low Strain Integrity Testing

 

Static Load Testing (Compression or Tension)

Static Load test on a pile is made for the purpose of finding the settlement to be expected at the estimated working load, or some multiple thereof, determining the ultimate bearing capacity, or checking the structural soundness of the pile. Generally, static load testing is carried on 1% of Preliminary and 1% working piles and tested in accordance to project specification and relevant international standards, such as ASTM D1143-81 Standard Test Method for Piles under Static Axial Compressive Load, BS 8004-1986 British Standard Code of Practice for Foundation and ICE Specification for Piling and Embedded Retaining Wall. Static load testing can be carried out by either of the following method:

  • Reaction Piles System
  • Reaction Anchors System
  • Kentledge System
  • Bi-directional (O-cell) System

Reaction Piles System in this method, reaction piles were used for either compression or tension static load testing, all reaction piles should be at least three test pile shaft diameter from the test pile, center to center, and in no case less than 2m.

Reaction Anchor System in this method, reaction ground anchors were used for compression static load testing, the reaction ground anchors should be at least three test pile shaft diameter from the test pile, center to center, and in no case less than 2m.

Kentledge System in this method, concrete blocks were used for compression static load testing, the center of gravity of the kentledge is on the axis of the pile. The nearest of the crib supporting the kenledge stack should not be closer than 1.3 m to the surface of the test pile.

Bi-directional (O-cell) System in this method, sacrificial hydraulic jacks are fixed in the intermediate part of the test pile for compression static load testing. For tension test pile, extension pile length will be provided below the design toe level and the hydraulic jack will be fixed at the design toe level of the test pile.

 

High Strain Dynamic Testing

This load test method is much quicker to complete than static pile testing since it will not require any pre-installed reaction system. This test method covers the procedure for testing vertical or batter piles individually to determine the force and velocity response of the pile to an impact force applied axially by a pile driving hammer or similar device that will cause a large strain impact to the top of the pile. This test method is used to provide data on strain or force and acceleration, velocity or displacement of a pile under impact force. The data are used to estimate the bearing capacity and the integrity of the pile, as well as hammer performance, pile stresses, and soil dynamics characteristics, such as soil damping coefficients and quake values. The resulting forces and motions recorded by gauges fixed at 1.5 x the test pile section below the top of the test pile. Generally, dynamic testing is carried out on 5% of working piles and to be tested in accordance to project specification and relevant international standards, such as ASTM D4945-00 Standard Test Method for High Strain Dynamic Testing of Piles, BS 8004-1986 British Standard Code of Practice for Foundation and ICE Specification for Piling and Embedded Retaining Wall. This testing is to be conducted by independent laboratory piles testing agency.

 

Caliper Logging Test of Pile Bore

This test is used to measure the borehole diameter and depth, and provide information on drilled borehole. This test is to be conducted by independent laboratory piles testing agency.

 

Koden testing of Pile Bore

The Koden is an apparatus for checking verticality of an excavation (diaphragm wall, barrettes or circular piles). Based on an ultrasonic transducer, it allows measurement of the distance between the transducer and the wall of the excavation. This testing is to be conducted by independent laboratory piles testing agency.

 

Cross-hole sonic logging testing of Piles

This method uses data from ultrasonic probes lowered into parallel access tubes in the pile or structure to assess the homogeneity and integrity of concrete between the probes. The data are used to confirm adequate concrete quality or identify zones of poor quality. The basic principle of the test is that the velocity of an ultrasonic pulse through concrete is directly proportional to the density of the concrete. By measuring the travel times of a pulse along a known distance, a measure of the density, and, hence, quality of concrete can be determined. This method does not give the exact type of defect, but rather only that a defect exists. Non uniformities such as contamination, soft concrete, honeycombing. This testing is to be conducted by independent laboratory piles testing agency.

 

Low Strain Integrity Testing

This test method covers the procedure for determining the integrity of individual vertical or inclined piles by measuring and analyzing the velocity (required) and force (optional) response of the pile induced by an (hand held hammer or other similar type) impact device usually applied axially and perpendicularly to the pile head surface. The test can be tested by either Pulse Echo Method (PEM) or Transient Response Method (TRM). This testing is to be conducted by independent laboratory piles testing agency.

 

 

SHORING WORKS

Secant Piles Wall

Consist of primary and secondary interlocking bored and cast-in place piles, are constructed at center to center spacing less than the diameter of the casing. These piles are interlocked to prevent the entry of water, generally the overlapping is 150mm, is achieved by first installing the primary piles, followed by boring for the secondary piles in the intermediate spaces between the first stage piling. A boring tool is used to cut grooves down the sides of these first stage piles, and after completion of drilling each intermediate pile, reinforcement is fixed and concrete is placed to fill the borehole including the groves cut in the first stage piles. The diameter of secant piles varies from 500mm upwards depending on the resistance that they have to provide against hydrostatic and active earth pressures on the sides of the excavation supported by the interlocked piles. Secant bored piles can be used as a permanent cantilever retaining wall or with support of either by ground anchors or metallic struts.

 

Contiguous Piles Wall

Is bored and cast-in place piles, are constructed in a single or double row on a line in plan at center to center spacing equal to or slightly greater than the external diameter of the casing or lining. The diameter of piles varies from 500mm upwards depending on the resistance that they have to provide against active earth pressures on the sides of the excavation supported by contiguous piles. It can be used as a permanent cantilever retaining wall or with support of either by ground anchors or metallic struts. This type of shoring wall is unsuitable for retaining water-bearing granular soils which are liable to bleed through the gaps between the piles, unless special measures are taken to provide a seal between adjacent piles.

 

Soldier / King Piles Wall

These consist of vertical members built at suitable center to center spacing with a system of ground support spanning between them. The piles are installed first along the perimeter of the proposed excavation. Sheeting, supporting the ground, is placed in position as excavation proceeds. The sheeting spans either horizontally between the soldier/king piles or vertically between horizontal waling. H-section piles are commonly used. This type of shoring may be used to support deep, narrow, shallow or wide excavation in various soil materials including sands and clays. This type of shoring can either cantilever retaining wall or with support of either by ground anchors or metallic struts. Excavation in water-bearing ground may require special attention; this method is unsuitable for the inclusion of water and if soil is washout from behind the sheeting unacceptable settlement may be caused to adjacent structures or services.

 

Diaphragm Wall

Formed of reinforced concrete panel, cast or placed in the ground using a bentonite or polymer suspension, can be used economically in situations where they combine the functions of a barrier to water entering the excavation and a permanent retaining wall to an underground structure. Excavation is carried out in the suspension to a width equal to the thickness of wall required. Excavation for the trench is performed in alternate panels each about 4 m to 6 m long, depending upon the length of the grab. The excavation equipment uses either rope suspended grabs, grabs mounted Kelly bars, or reverse-circulation excavating equipment. The bentonite or polymer suspension is designed to maintain the stability of the slit trench during digging and until the diaphragm wall has been concreted. Diaphragm wall is either cantilever retaining wall or with support of either by ground anchors or metallic struts.

 

Steel Sheet Piles Wall

Used in many types of temporary and permanent retaining structures, it can be drive in almost any soil except rock. Steel Sheet Piles wall is either cantilever retaining wall or with support of either by ground anchors or metallic struts.

 

 

GROUND IMPROVEMENT

These techniques used to meet temporary requirements, such as reducing the water flow towards excavations, or to provide a permanent improvement such as increasing the strength of the soil under a foundation. The methods used to improve the ground are preloading compaction, installation of vertical drains, injection of grouts and electrochemical and thermal hardening of the ground. Ground improvements methods are:

  • Shallow Compaction
  • Deep Compaction by Vibration
  • Ground improvements by Vibro-displacement and vibro-replacement
  • Deep Compaction by heavy tamping
  • Uses of vertical drains
  • Electro-osmosis

 

 

GROUND INVESTIGATION

The ground investigation are mainly concerned with establishing the nature and general stratification of soils underlying the site. The purpose of ground investigation is to assess the suitability for the construction of civil engineering and building works and of acquiring knowledge of the characteristics of a site that affect the design and construction of such works and the security of neighboring land and property.

 

 

DEWATERING

Dewatering is the method of lowering the groundwater level to keep the excavation bottom dry, to prevent leakage of water or sand, to avoid sand boiling or upheaval failure, and to forestall the occurrence of floating basements. Commonly used methods of dewatering in excavations include the open sump or ditch method, the deep well method, and the well point method.

 

 

GROUND ANCHORING

Ground anchors are cement grouted, pre-stressed tendons that are installed in soil or rock. Anchored systems include excavation anchored shoring wall, flexible anchored walls, slopes supported using ground anchors, slope and landslide stabilization systems, and structures that incorporate tie down anchors. The installation consists basically of an anchor head, free length and fixed anchor. The construction of ground anchorages should be carried out in such a manner that the validity of the design assumptions is maintained. Ground anchor is designed and constructed in accordance with project specification, BS 8081-1989 British Standard Code of Practice for Anchorages and other relevant international standard.

 

 

GROUTING

Grouting method of ground treatment is to inject suitable grouts, being fluids with or without fillers which, in their ultimate position in the ground, will be stable and, in combination with the ground, will meet specific engineering requirements. These fluids are required to travel through the ground to controllable limits and, in so doing, should not be affected by the ground or the groundwater to the final detriment of the work.

 

 

MICRO TUNNELING / PIPE JACKING