Micropile testing

06.12.2020 Comments

Arfa Falak. Micropiles are considered a deep foundation system along with drilled piers or driven piles. Geo technical engineers often recommend a deep foundation system over shallow foundation system for important and large buildings. Most notably when the soil conditions are poor or their loads are exceptionally high. Micropile installation is usually a quick process as it uses adaptable mobile drilling equipment to install the piles. They are often an economical alternative to other deep foundation systems.

Usually, due to difficult ground conditions or when site access is restricted, micropiles can be designed to handle lateral loads or bending moments along with axial loads. Design assumptions are often obtained from geotechnical reports and bond values are verified in the field by the use of tension, compression or lateral load tests.

They were invented in response to serious demand for innovative techniques for underlying historic buildings which sustained damage during World War II.

A credible method was needed to support the structural loads with minimal movement. Fondedile then implemented the use of micropiles in North America in Initially, the micropiles technology did not become popular in the United States. The micropiles have been excessively used mainly as an element for foundation support to resist static as well as seismic loading. They have been used for a very long period as foundation elements as driven piles since more than a thousand years — and several European cities are built on thousands of piles.

A micropile is a high-strength, small diameter, non-displacement pile whose dimension is typically less than mm i.

The standard length of a micropile typically ranges from 5 to 30 metre. It consists of a steel casing that is usually between 4 to 12 inches mm to mm in diameter. Even these small elements are able to develop a capacity that ranges between 10 and tons. It is generally constructed by drilling a borehole first and then placing steel reinforcementfollowed by grouting of drilled hole.

Micropiles having the compressive strength of 1, kN or larger are used in the field. The high capacity micropile installation method involves drilling and pressured grout injection technique. Additionally, it uses steel pipes as reinforcements along with the deformed reinforcements in order to construct high capacity micropiles having maximum bearing capacity.

The installation of the micropiles are done by methods that causes the least disruption to adjacent structures, soil, and the environment. They can be installed in soil of any type and places where the ground condition is good.

Since the installation of micropile causes less vibration and noise, they are often used in underpinning the existing structures. For underpinning existing structures, specialized drilling equipment is often required in order to install the micropiles from within the basement or other facilities having limited headroom.A pile is a slender element cast in the ground or driven into it. Since pile construction as well as the final product are mostly invisible, engineers have often questioned their integrity, i.

In fact, experience [1] has shown that in piles, of all kinds flaws may occur. The purpose of integrity testing is to discover such flaws before they can cause any damage. Historically, pile integrity was investigated by direct methods. While excavation may be effective in exposing flaws in the outer part of the pile, it is usually limited to a depth of a few meters.

Core drilling, on the other hand, can be carried out to a large depth provides full information, but only for a very small fraction of the pile volume. Indirect methods, or imaging, were first developed in the early s.

These include three distinct methods:. A pile integrity test also known as low-strain dynamic testsonic echo testand low-strain integrity test is one of the methods for assessing the condition of piles or shafts. It is cost-effective and not very time-consuming. Pile integrity testing using low-strain tests such as the TDR Transient Dynamic Response method, is a rapid way of assessing the continuity and integrity of concrete piled foundations.

The software also produces computer simulations and impedance profiles of the test result, to analyse in detail any intermediate pile shaft responses. The TDR test requires minimal of preparation and is able to find defects corresponding to cracks, reductions in section and zones of poor quality concrete.

Micropiles

The test is based on wave propagation theory. The name "low-strain dynamic test" stems from the fact that when a light impact is applied to a pile it produces a low strain. The impact produces a compression wave that travels down the pile at a constant wave speed similarly to what happens in high strain dynamic testing.

Changes in cross sectional area - such as a reduction in diameter - or material - such as a void in concrete - produce wave reflections. This procedure is performed with a hand held hammer to generate an impact, an accelerometer or geophone placed on top of the pile to be tested to measure the response to the hammer impact, and a data acquisition and interpretation electronic instrument. The test works well in concrete or timber foundations that are not excessively slender.

Usually the method is applied to recently constructed piles that are not yet connected to a structure. However, this method is also used to test the integrity and to determine the length of piles embedded in structures. Widely used in Australia now on existing structures. Rausche, F.

Hussein, M. Likins, G. Massoudi, N. From Wikipedia, the free encyclopedia. These include three distinct methods: Nuclear radiation, or gamma-gamma method [3] Short wave ultrasonic acoustic method [4] Long wave sonic acoustic method [5] A pile integrity test also known as low-strain dynamic testsonic echo testand low-strain integrity test is one of the methods for assessing the condition of piles or shafts.

The test measures: pile length, or depth to anomalies pile head stiffness pile shaft mobility, which is dependent on pile section and concrete properties The software also produces computer simulations and impedance profiles of the test result, to analyse in detail any intermediate pile shaft responses.Soil nail testing is used to establish the bond stress within the stable zone of a slope. Load generated in the wedge retained zone is usually discounted as it does not contribute to the underlying stability of the nailed slope.

Nail load is measured through a pressure gauge incorporated in the jack circuit, with extension recorded by a dial gauge mounted independently. Bearing surfaces for the jack platform should be perpendicular to the angle of installation and have sufficient bearing area to resist settlement as the nail is tested. An alignment load in the jack will ensure correct orientation of the soil nail prior to measuring its elongation. A range of tests are used to establish the settlement characteristics of micropiles.

Compression testing generally falls into two categories, static or dynamic. Static testing employs anchor piles or temporary bearing yoke to provide the reaction against which the micropile is loaded; displacement can then be measured against load.

micropile testing

Tensile pile testing involves loading the micropile with a jack, from a bearing platform that spans outside the cone of influence.

Load is measured through the jack, with extension recorded from an independent reference point. Proof testing is employed to demonstrate the anchor performance, prior to excavation at the front of the face. Following proof loading, anchors are locked-off at working load to provide an active restraint to the structure. Soil Nail Testing Soil nail testing is used to establish the bond stress within the stable zone of a slope.

Tensile test on a temporary anchor pile. Micropile Testing A range of tests are used to establish the settlement characteristics of micropiles. Temporary Ground Anchor Testing Proof testing is employed to demonstrate the anchor performance, prior to excavation at the front of the face.A micropile is a small-diameter commonly less than mmdrilled and grouted replacement pile that is typically reinforced which can either withstand axial or lateral loads or both of these.

A micropile is constructed by drilling a borehole, placing reinforcement and grouting the hole. Based on the definition as described in the principal guides and specifications written about the micropile, here are the various meanings which hold a number of similarities as such:. Presented here is a sample of method statement that can be modified and associated in the preparation of method statement as part of Quality Assurance documentation in a civil construction project.

See also the Method Statement for Bored Piles here. Description of Works 1. Introduction 2. Definitions 3. Reference 4.

Responsibilities 5. Interfacing with Other Operations 6. Duration, Phasing with the Subcontractors 7. List of Subcontractors II.

Resources 1. Plant and Equipment 2. Work Force 3. Light Tools III. Materials IV. Site Planning a. Preparation b. Site Clearance c. Traffic Management d. Pre-construction Safety Meetings V. Methodology V. Risk Assessment VII. Pre-Start Safety Briefing Arrangements 1. Protective and Safety Equipment 2. Information to Personnel 3. Special Safety Requirements 4. Emergency Procedures 5. Emergency Contact Numbers X. Supervision and Monitoring Arrangements XI.

Environment and Quality Issues 1. Precautionary Measure 2. Disposal Requirements 3. Inspection, Test, and Sampling 4. Introduction The purpose of this method statement is to describe the method of installing micropiles as a temporary tie back supports for the temporary shoring of Name of Project here.

The shoring system designed and considered for the project is the contiguous pile wall wherein a series of piles are constructed. To provide lateral support, micropiles will be installed to reduce the bending moment on the contiguous piles.Micropiles are rapidly gaining popularity for foundations in urbanized areas or in locations with low headroom and restricted access.

They are an ideal choice for underpinning or emergency repairs because they can be installed in virtually any ground condition with minimal vibration and disturbance to existing structures. Williams larger diameters of All-Thread Rebar are popular choices for micropile reinforcement. Williams offers right-hand threaded Grade 75 All-Thread Rebar in 14 — 28 along with a selection of reducer couplers that can adapt to splice together any larger size bar to any smaller size.

In larger micropile designs, casing diameter is minimized because the effective net area available for reinforcement is optimized with a single larger bar versus smaller bundled bars see example. There is also an increased rate of production installing a single larger bar versus smaller bundled bars. Through the increased bond stress resultant from the simultaneous drilling and grouting operation, Hollow Bars are the reinforcement bar choice in collapsing soil conditions.

Using sizes from 32 mm to 76 mm, these Hollow Bars offer up to kips of strength, up to 3.

Micropile Bending Test (MP04)

A variety of drill bits promise efficient installation and Williams offers a full line of adaptation equipment and rental grout plants necessary for Hollow Bar anchor installation. Multi-bar elements are often used for attaining ultra-high load carrying capacity in micropiles.

High-rise office buildings and high-rise condominiums are examples where such high load carrying micropiles or sometimes referred to as mini-caissons are used.

Each multi-bar micropile project is uniquely designed by Williams to specific contractor specifications and shipped to the jobsite fabricated in durable cages for quick installation. Williams stands alone in being a customized manufacturer and therefore offers the advantage to the industry of niche accessories to optimize efficiency and costs. Micropiles are often tested in compression and tension for verification and proof tests. Micropiles are more frequently designed to resist large lateral loads, therefore, it is necessary to perform preproduction lateral load tests on single piles or groups of piles as well.

Williams manufactures all products necessary for the reaction piles and offers a full line of testing equipment. Compression testing is accomplished by reacting against the bottom of a test beam that is anchored to the ground with reaction piles.

The reaction piles are installed from the test pile at a minimum distance, so the reaction piles do not influence the loading of the test pile.

On a typical compression test, the reaction beam is crib bed a distance off of the ground to accommodate the test jack and load cell between the test pile and the bottom of the test beam. The compressive load is then applied to the pile through the test jack reacting against the bottom of the beam. The pre-stress force on the reaction piles keep the beam from roll-ing.

micropile testing

Skip to content Search for:. Find a Williams Rep Contact Us. Larger Bar Micropile Cost Saving Advantages In larger micropile designs, casing diameter is minimized because the effective net area available for reinforcement is optimized with a single larger bar versus smaller bundled bars see example.

Deep foundation testing

Bundled 20 Bars Cross Section Area 9. Project Photos.

micropile testing

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Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. I'm working on a relatively small project that is going to require micropiles for no other reason than there is a real lack of real estate to place spread footings. We are trying to minimize the cost associated with this, and my boss believes that there is a pile load capacity threshold in the code, below which load tests do not need to be performed.

I've read thoroughly through chapter 17, but can't find anything that gives a pile capacity that will eliminate the need for load testing. Does anyone know if this exists and where it is located? On another note I know you're in PA I have a friend who is a partner in a firm in Pittsburgh. You seem to be a talented guy Ron- Thanks for the compliment, it is much appreciated.

Micropiles: A Deep Foundation System for Your Home!

Unfortunately, I'm clear on the other side of the state.Low Strain Impact Integrity Testing is a non-destructive pile testing method for integrity assessments of augered cast-in-place piles, drilled shafts or driven concrete or timber piles. If major defects exist, test results may be interpreted to estimate their magnitude and location. Test results may also be used to estimate pile length.

Tests by either method are normally performed after foundation installation and curing, and require minimal pile preparation. In some cases piles in existing foundations can be tested. The GRL engineer hits the top of the foundation with a handheld hammer.

The impact of the hammer generates a compressive stress wave in the pile or shaft, and an accelerometer placed on top monitors the motion associated with this wave. The stress wave propagates down the pile shaft and is reflected when it encounters either the toe or a non-uniformity of the shaft.

Depending on job conditions and requirements, GRL performs the test by the Pulse Echo Method using a non-instrumented handheld hammer or by the Transient Response Method an instrumented hammer is used. Pile Integrity Testing and Assessment Low Strain Impact Integrity Testing is a non-destructive pile testing method for integrity assessments of augered cast-in-place piles, drilled shafts or driven concrete or timber piles. Calculator Enter the capacity you wish to mobilize, in Tons: What type of test do you wish to perform?