Question

1. As an Geotechnical Engineer for a company you have been instructed to handle a project to develop a new Mall. The project currently in construction stage. During process of pile installation, the contractor notices few problems with the site condition:

1. Limited area for work space which might have problem to use conversional method for pile installation.
2. Project site is near with Hospital (contractor must control the sound pollution).

As a consultant you are need to solve these problems and need to suggest (with explanation) suitable method to install the pile.

2. After complete installation of pile, you are need to suggest method/s to conduct pile test (with explanation).

Answer 1

The following design approach is recommended to determine the most appropriate foundation alternative.

1. Determine the foundation loads to be supported, structure layout, limits on total and differential settlements, lateral deformations, lateral loads, scour, seismic and other extreme event loading conditions, and special requirements such as construction phasing and time constraints on construction. A complete knowledge of these issues is of paramount importance.

2. Evaluate the subsurface exploration and laboratory testing data. Ideally, the subsurface exploration and laboratory testing programs were performed with knowledge of the foundation loads and the needed geomaterial resistances. If the subsurface information is insufficient, perform a second subsurface exploration program, laboratory testing program, or in-situ testing program.

3. Prepare a final subsurface profile and critical cross sections. Determine subsurface layers suitable or unsuitable for spread footings, pile foundations, or drilled shaft load transfer. Also consider if ground improvement techniques could modify unsuitable layers into suitable bearing layers.

4. Determine the most feasible foundation alternatives. Both shallow foundations and deep foundations should be considered. Deep foundation alternatives include driven piles, drilled shafts, micropiles, and CFA piles.Proprietary deep foundations systems should not be excluded as they may be the most economical alternative in a given condition. Consideration should be given to the following foundation options.

Shallow Foundations:

a. Spread footings (without ground improvement).

b. Mat foundations.

Deep Foundations:

a. Driven pile foundations.

b. Candidate pile types.

c. Viable pile sections.

d. Drilled shafts.

e. Micropile.

f. Continuous Flight Auger (CFA) piles.

5. Prepare cost estimates for technically feasible alternative foundation designs including all associated substructure and construction control method costs. The foundation support cost should include all associated temporary and permanent substructure costs required for foundation construction (e.g. sheeting or cofferdam requirements, concrete tremie seal, pile cap requirement and size), the effect of environmental or construction limitations (noise, vibration, low overhead, access restrictions), as well as any required mitigation procedures (noise shrouds, predrilling, bubble nets, etc.).

6. Select the most appropriate foundation alternative. Generally, the most economical alternative (lowest foundation support cost) should be selected and recommended. The ability of the local construction force as well as the availability of materials and equipment should also be considered.

A. Limited area for workspace which might have problem using the conversational method for pile installation.

CFA Piles- In groups to transfer heavy loads to suitable geomaterials. Projects with noise and vibration restrictions. Continuous Flight Auger (CFA) or alternatively Auger Cast-in-Place (ACIP) piles are usually installed by turning a continuous-flight hollow-stem auger into the ground to the required depth. As the auger is withdrawn, grout or concrete is pumped under pressure through the hollow stem, filling the hole from the bottom up. Vertical reinforcing steel is pushed down into the grout or concrete column before it hardens. Uplift tension reinforcing can be installed by placing a single high strength steel bar through the hollow stem of the auger before grouting. After reinforcing steel isplaced, the pile head is cleaned of any lumps of soil which may have fallen from the auger.

Continuous flight auger (CFA) piles are drilled and concreted in one continuous operation enabling much faster installation time than for bored piles. Reinforcement is placed into the wet concrete after casting, enabling the pile to resist the full range of structural loading.

Common uses

1. Provide structural support

2. Provide earth retention, especially on site boundaries or close to adjacent buildings

3. Prevent landslides or protect existing buildings and are often combined with other techniques such as ground anchors or soil nails

4. Infrastructure projects such as tunnelling, road or bridge construction as well as flood protection

Process

CFA piles are constructed by rotating a hollow stem continuous flight auger into the soil to a designed depth. Concrete or grout is pumped through the hollow stem, maintaining static head pressure, to fill the cylindrical cavity created as the auger is slowly removed. The reinforcement cage is placed through the freshly placed concrete. Typically, Keller CFA piles are reinforced with a rigid six metre-long cage as a minimum, but it’s possible to install much longer cages as and when required by the design or specification. If required, a specially developed vibrator unit can help accurately locate the reinforcement cages.

Advantages

1. Resists compressive, uplift, and lateral loads

2. A cost efficient foundation solution

3. Can be installed in most soil conditions such as sands, clays, silts, gravels and soft rock

4. Can achieve pile depths up to 32m and with various diameters of 300 mm to 1000mm+

5. Low noise level and no vibration and low noise level so ideal in built-up areas with weak soil conditions and high levels of ground water

6. Compared to bored piles, construction is very quick as temporary casings or support systems are not required

Quality assurance

1. Close control of the installation process is essential to ensure the highest quality pile construction.

2. All CFA rigs are equipped with sensitive state-of-the-art instrumentation that monitors all aspects of CFA piling, including pile depth, auger rotation, penetration rate, concreting pressure, extraction rate and over-break. The instrumentation produces an individual log for each pile that includes element identification, date, time and operator details.

3. This is reinforced by a documented Quality Management System procedure.

4. Quality assurance is achieved through a range of non-destructive testing methods to evaluate both pile integrity and/or load-settlement performance. Selection of verification technique is project and application specific.

B. The project site is near with Hospital (contractor must control the sound pollution).

Consideration of Pile Driving NoiseDriven piles is installed by impact hammers. Noise levels associated with typical impact pile driving activities depend upon the hammer and pile type used. Noise from impact pile driving operations typically ranges from around 80 to 135 dBa. If local ordinances dictate allowable noise levels at or below this level, some driving equipment may not meet these requirements. Manufacturers of a few diesel and hydraulic hammers can provide optional noise suppression devices that may reduce the pile driving generated noise by about 10 dBa. Independently manufactured devices are also available. In noise-sensitive areas, the foundation designer should review any noise ordinances to determine if pile driving noise suppression devices would be necessary and if so, the impact this may have on the contractor’s equipment selection and productivity. If limits on work hours, pile equipment type, or noise suppression equipment are required, costs associated with these limitations should be considered in the foundation selection process.

Pile test;

Soil Boring Methods- Soil borings are the most frequently used soil exploration technique for projects in the public and private sector. Soil borings offer the ability to collect disturbed and undisturbed samples from various depths, as well as to perform in-situ tests. Common boring methods include augered borings, wash borings, and rotary drilling in soil. These methods, as well as sonic drilling. Continuous flight augers are either solid stem or hollow stem and are both used to bore into the subsurface and allow for sampling and/or in-situ testing. A solid stem auger is essentially a solid rod with flights, and must be removed in order to test native soil. They are therefore not useful in soft soils, sands or areas of high groundwater due to the probability of borehole collapse and are best used when soil sampling only at relatively shallow depths is required. Hollow stem augers act as a casing that stays in place during drilling, whereby subsequent sampling and testing is performed through the bottom of the hollow stem. This auger type is therefore practical for a variety of subsurface conditions and utilizes a plug when advancing the auger. Hollow stem auger diameters range from 2.25 inch I.D. up to 12.25 inch I.D with larger sizes reserved for more complex sampling and testing techniques.Rotary drilling may be performed in soil or rock and involves inserting a drill bit to cut and grind the material. Water or drilling mud flushes out the cuttings, and provides borehole stability. Air has also been used to force out cuttings in lieu of drilling mud, however borehole stability issues remain. To sample soil or perform an in situ test, the drill bit is removed and a sampling device is then inserted to collect material. Wash borings are advanced by the chopping action of a light bit in combination with the jetting action of water or drill fluid coming through the bit. Casing may be used to maintain an open bore hole, although typically a bentonite or drilling mud of similar properties is adequate. Drilling mud can contaminate recovered soil samples as well as add difficulty when trying to classify soil stratigraphy from wash cuttings. In addition, heavier particles such as gravel or cobbles may be left at the bottom of the hole if the wash system is undersized. Wash borings are infrequently used in the United States.

Soil Sampling Methods- Soil samples may be collected via disturbed or undisturbed methods. Disturbed soil samples contain representative material that may be used for visual classification and more routine laboratory testing. These soil samples are not suitable for strength or compressibility testing as the sampling disturbance alters their condition. When in-situ particle arrangements, water content and other properties must be preserved for laboratory testing, undisturbed samples are taken. These samples are collected in devices designed to minimize sample disturbance. However, even while using the utmost care for removal and transport, no sample will be completely undisturbed. Disturbed soil samples may be collected with a split barrel sampler, sonic cores, or through test pits. Split barrel samplers typically range from 1.5 to 2.5 inches in diameter and are 18 or 24 inches long. Although multiple sizes exist, the standard split spoon sampler used for the Standard Penetration Test (SPT) has an inner diameter of 1.375 inches and an outer diameter of 2 inches (ASTM D1586). Relatively undisturbed soil samples may be collected with thin-walled tubes (Shelby tubes), a piston sampler or other specialized means. Thin-walled tubes are produced in various sizes and are typically used to collect fine-grained soils. These tubes are pushed into the soil and removed after a brief swelling of the soil occurs. ASTM D1587 provides detailed guidance on this sampling technique. Piston samplers were developed to prevent soil from entering the sampling tube before the sample depth and to reduce sample loss during tube extraction. They are basically a thin wall tube sampler with a piston, rod, and a modified sampler head. There are numerous types of piston samplers; free or semi-fixed piston samplers, fixed-piston samplers, and retractable piston samplers. The Pitcher sampler is a core barrel sampler that may be used for sampling a broad range of materials including undisturbed samples of stiff to hard clays, soft rocks, and cemented sands. This sampler consists of a rotating outer core barrel with an inner thin-walled sampling tube. The sampling tube leads the core barrel when sampling soft soils and the core barrel leads the sampling tube when sampling hard materials. This makes the Pitcher sampler particularly attractive for sampling materials with an alternating hard and soft layer

Dilatometer Test- The dilatometer test (DMT) is an in-situ testing device that was developed in Italy in the early 1970's and first introduced in the U.S. in 1979. Like the CPT, the DMT is generally hydraulically pushed into the ground although it may also be driven. When the DMT can be pushed into the ground with tests conducted at 8 inch increments, 100 to 300 feet of DMT sounding may be completed in a day. The primary utilization of the DMT in pile foundation design is the delineation of subsurface stratigraphy and interpreted soil properties. However, it would appear that the CPT/CPTu is generally better suited to this task than the DMT. The DMT may be a potentially useful test for design of piles subjected to lateral loads. For axially loaded piles, the dilatometer test has limited direct value. The test procedures for DMT are presented in ASTM D6635.

Pressuremeter Tests- The pressuremeter test (PMT) is an in-situ device used to evaluate soil and rock properties, and imparts lateral pressures to the soil, allowing for soil shear strength and compressibility to be determined by interpretation of a pressure-volume relationship. Deposits such as soft clays, fissured clays, sands, gravels and soft rock can be tested with a pressuremeter. A pressuremeter test produces information on the elastic modulus of the soil as well as the at rest horizontal earth pressure, the creep pressure, and the soil limit pressure. For piles subjected to lateral loads, the pressuremeter test is a useful design tool and can be used for determination of p-y curves. However for design of vertically loaded piles, the pressuremeter test has limited value. Pile design procedures using pressuremeter data have been developed and may be found in FHWA-IP-89-008, The Pressuremeter Test for Highway Applications, Briaud (1989). Details on test procedures may be found in ASTM D4719, Standard Test Method for Pressuremeter Testing in Soils.