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Dynamic Load Testing and Static Load Testing

Dynamic Load Testing is a method of measuring the bearing capacity of foundations. Dynamic Load Testing has been found to be a quick test with a low cost associated with running the test. Dynamic Load Testing is an important part of the construction process, which ensures the foundation will be able to uphold the structure built on top of the foundation.Another test method is Static Load Testing, which is used to determine the bearing capacity of piles. Piles are the part of the foundation that transfers the load from the building to the soil. Static Load Testing is considered the fundamental form of load testing and has been influential in the porcess of load testing.

Dynamic Load Testing

Dynamic Load Testing involves using a piling hammer to hit the top of the pile causing resultant strains and accelerations. The strain and acceleration resulting from the hammer are measured and used to calculate the pile’s reaction to the applied load. The reaction to the applied load is an important measurement for piles, since this can be used to determine how well the foundation will hold up when it is supporting the designed load.

A benefit of Dynamic Load Testing is that it is a fast method with a lower cost than Static Load Testing. Dynamic Load Testing also has the advantage of being onsite and can provide a way to monitor the hammer performance directly on site.

Dynamic Load Testing History

A research project began in 1964 to develop new technologies of pile testing. The development began in Cleveland, Ohio and was funded by the Ohio Department of Transportation. The research produced an electronic device, which would be used to calculate the bearing capacity of a pile based on the fundamental stress wave theory. This new method was found to be a good alternative to static load testing and would be called Dynamic Load Testing. In order to get the technology for Dynamic Load Testing into the work force, Pile Dynamics Incorporated (PDI) was formed in 1972. PDI has been working on further developing Dynamic Load Testing as well as providing the equipment for Dynamic Load Testing. Another organization was made to provide Dynamic Load Testing services; this company was called GRL Engineers Inc. and was founded in 1976.

Dynamic Load Testing Procedure

One important aspect of the Dynamic Load Testing procedure is to allow enough time after the pile is driven for the soil to re-stabilize. This is an important step, which will allow for the results to be accurate. The first step of performing a Dynamic Load Test is to place the sensors near the pile head, the sensors will give the system the strain that is caused by they test load. The next step is to apply the test load to the pile using either a hammer or a drop weight. The load will create compression waves that the sensors will detect and send to the system being used. the system then will gather all the measurements needed and calculate the bearing capacity of the pile. The calculation of the bearing capacity completes the procedure of a Dynamic Load Test.

Static Load Testing

Static Load Testing is done my measuring the displacement of the pile after applying a load to the pile. Static Load Testing is used to ensure the stability of the soil that a pile is placed as well as the stability of the structure. This procedure precedes the Dynamic Load Testing, in that it was used before Dynamic Load Testing was founded. Static Load Testing can be performed using a load ranging from on 100,000 to 12,000,000 Newtons. The load is applied with a jack hitting a reaction beam. Using the measurements made of how the pile moved, the bearing capacity can be calculated for the pile. The test load is usually applied at an incremental rate that is specified for each static load test. The results of a static test load are normally given in the form of a graph showing the applied load versus the pile displacement.

Static Load Testing Procedure

Static Load Testing can be done during the engineer's survey of the construction site or during construction itself as a test. The procedure is started by applying a test load to the pile head using a hydraulic hammer. The impact of the hammer causes a displacement of the pile which is measured by deflectometers. Deflectometers are gauges that measure displacement to one hundredth of a millimeter. Each deflectometer is positioned on a glass reference plate that is cemented to the pile head. The measured deflection of the piles are then used to calculate the bearing capacity of the pile. The test load is increased in stages and the test is done in three cycles to produce accurate results. The first cycle will use a load that is equal to the working load of the pile, the second load applies a load twice the size of the working load, and the third cycle is done with a load that is two-and-a-half times the size of the working load.

Kentledge Static Load Tests and Load Tests with Anchor Piles

A Kentledge Static Load Test is done in cases where anchor piles cannot be used. The Kentledge test has a high cost associated with it, which is the reason for limiting the use of this form of Static Load Testing. A load twice the size of the design load is applied to a pile when using the Kentledge test, which will determine the accuracy of the pile design. A Kentldge test is performed by installing four gauges to an independent frame, the gauges will measure the displacement of the pile. The next step is to the load is applied to the pile as specified by the owner of the project. After the Kentledge test is completed, all data is recorded for further analysis. When the use of anchor piles is allowed, Static Load Testing with Anchor Piles is the form of test used. This will be a cost effective way to complete the load test. A Static Load Test with Anchor Piles is done by setting up two, three, four, six or eight anchors around the pile. Then the test load is applied to the pile and the displacement of the pile is measured.