Plate Load Testing Specialists
For designing shallow foundations, testing crane pads or piling mats it is necessary to know the bearing capacity of soil at the desired depth.
The plate load test is performed on-site to determine the ultimate bearing capacity of soil at the desired depth.
Data from the plate load test is helpful to confirm the design assumptions made from soil tests or can be used as a design parameter.
The Process
The Plate Load Test consists in transmitting to the soil to be tested and the subsequent increasing load increments. Simultaneously detecting the settlement and therefore allowing us to directly determine the form of deformation or compressibility of the soil. The load transmission takes place via the application of a force by means of a hydraulic system of thrust, of a circular plate.
The subsidence induced by the ground plate is simultaneously detected by digital data acquisition systems. These are integral with a frame of reference outside the area of influence of the applied load.
Of fundamental importance, in any case, is the use of the proper contrast medium whose mass is a function of the expected load.
Plate Load Tests are generally conducted with metal plates of standard diameter D=300/450/600 millimetres. These could be carried out from ground level. As well as inside the wells whose depth is limited only by the size of the jack and related extensions.
Specification for the Plate Load Test
The plate load test shall be carried out at locations as shown in the drawings or as directed by the Engineer using approved equipment. The test should be carried out in accordance to BS 1377-9 .
Plate Load Test Equipment
Engineers will submit the equipment details for approval before the test is started. This includes certificates, agency approved calibration charts and the plate load test setup.
For bearing plates, three circular steel bearing plates, not less than 25mm in thickness and varying in diameter from 300mm to 1000mm. This includes the minimum and maximum diameter specified. Or square steel bearing plates of equivalent area. In rock, plates larger than 1000mm diameter may be used, depending on the jointing frequency. As an alternative, three small concrete footings of the size mentioned or larger can be cast in-situ. Such footing must have a depth of not less than two thirds of their width.
Process Specifications
The Hydraulic or Mechanical Jack Assembly should have sufficient capacity. Being able to to provide and maintain the maximum estimated load. But not less than 50 tons in any case.
The applied load shall be measured using calibrated electronic load cell. The force measuring devices should be capable of recording the load. With an error not exceeding ± 2 percent of the load increment used. Or 1% of maximum load whichever is lesser.
Precise levelling optical survey (to accuracy of 0.01mm) with respect to fixed datum to be carried out. This measures the plate settlement and movements of the reference beam for correction of dial gauges readings.
The reference beam and measuring devices should be protected from the direct rays of the sun and wind. By means of tarpaulins or other forms of shelter, to minimize errors of measurement which can easily arise from these causes.
Miscellaneous Apparatus required, including loading columns, steel shims, and other construction tools and equipment required for preparation of the test pits and loading apparatus.
Plate Test Procedure
The plate load test shall be carried out in accordance to BS5930 or BS1377 pt9 1990 with the following additional requirement:
The Plate Load Test pit should be at least 4 times as wide as the plate and to the foundation depth to be placed.
The test shall be carried out at the same level of the proposed foundation level or as directed by the Engineer. While the same conditions to which the proposed foundation will be subjected should be prepared if possible.
Guaranteeing Solid Results
To ensure even transference of the test load on to the test surface, the steel plate should be levelled and have full contact with the ground. Sand filling or cement mortar or plaster of paris could level small uneven ground surface.
If the plate bearing test is carried out below the groundwater level, it is essential to lower the groundwater level by a system of wells. Or by other measures outside and below the test position.
The preparation of the test surface may cause an unavoidable change in the ground stress which may result in irreversible changes to the subsoil properties. It is essential that the exposure time of the test surface and the delay between setting up and testing should be minimized. The time lag shall be reported with the test result.
Test Report
In addition to the continuous listing of all time, load, and settlement data for each test, the report shall include at least the followings:
- General information such as date, weather conditions, temperature, location of test, test surface soil description and others.
- Measured data. All data shall be checked for mis recording or miscalculation.
- Notes or abnormal phenomenon during the test shall be described.
- Load settlement relationship shall be plotted and presented in the report.
- Evaluation of the yielding load, elastic modulus, subgrade reaction and allowable bearing pressure.