Plate Bearing Tests

5 Special-Purpose Tests 4.5.1 Plate Bearing Tests 

The plate load test is well known and, like the standard penetration test, has been in use for a long time period, but neither of these two tests is used very often when the water depth is greater than about 30 m. A limited niunber of plate bearing tests (plate loading test [PLT]) have been carried out at three locations in the North Sea typically, a seabed jacking system has been used to load the plates. The main limitation of the PLT is that it only tests the upper 0.5-1.0 m, luiless it is of the screw-plate type (Kummeneje, 1955 Schmertmann, 1970). 

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Plate bearing tests are field tests that are also used to evaluate subgrades for pavements. 

Field test are carried out in the excavated pits or boreholes at the required depths. The results reflect the mass characteristics of the ground as well as overcome disturbance effects of samples retrieved for laboratory tests. Common field tests carried out to assess strength, compressibility and seepage parameters are as presented in Table 3.5 (Canadian Geotechnical Society 1987). Typical equipment for pressuremeter test and test setup for plate bearing test are shown in Figures 3.6 and 3.7 respectively. 

Plate bearing test and Screw plate test Sand and clay Deformation modulus Modulus of subgrade reaction Bearing capacity Strictly applicable only if the deposit is uniform size effects must be considered in other cases ASTM D 1994-72 BS 5930 (1999)-Cl 25.6... 

Direct measurements on settlement and bearing capacity may be carried out vide plate bearing tests or pressuremeter tests conducted in boreholes at the required depths. 

Similar to the above section, plate bearing tests or pressuremeter tests carried out in boreholes are applicable for the assessment of bearing capacity and settlement. For initial reference to assess engineering properties of engineered fill, empirical chart and table in NAVFAC (1971) manual publication reproduced in Figure 3.12 and Table 3.9 may be of assistance. 

The plate bearing test is used for the determination of soil bearing capacity with respect to the modulus of surface reaction (k value). The subgrade bearing capacity in terms of k value is used, mainly, in rigid pavement design methodologies. 

The test is carried out on compacted material with certain moisture, using a steel circular plate and a load application system. The steel plate can be of various diameters, but the plate normally used has a 762 mm diameter. For increasing plate s rigidity, two additional circular plates of smaller diameter (approximately 650 and 550 mm) are placed on top of it. Load application is usually carried out with hydraulic jack assembly, which is properly adjusted to a fixed reaction beam of a load vehicle. Plate bearing test arrangement is shown in Figure 1.9. 

Using the above relationships, the plate bearing test is used by some organisations, as well as for the estimation of CBR of soil layer, which contains a high percentage of coarse soils. 

Modulus of elasticity of the subgrade for static load could be calculated with the Boussinesq theory in conjunction with the plate bearing test. The relationship, which can be... 

In some countries, the satisfactory compaction is judged by running the plate bearing test twice, with two different numbers of passes. The surface stiffness modulus is determined in both cases (Ej and 2) from the k value obtained. If the 2/ i ratio is less than 2, the compaction is considered satisfactory. 

The in situ determination of the strength of the compacted unbound layer is carried out by the Dynamic Cone Penetrometer (DCP) or by the plate bearing test. The DCP test is gaining grounds because of its simplicity in use. It must be reminded that the penetration index, determined by DCP, or k value, determined by the plate bearing test, can be correlated to the CBR value (see Sections 1.6.3 and 1.7). 

The validity of the above equation is restricted to fine soil material with laboratory CBR values ranging from 2% to 12%. For coarser materials, the plate bearing test may also be appropriate. 

The Zone Load Test is also a direct method for checking the bearing capacity of the reclaimed land. The Zone Load Test is, in principle, a large-scale Plate Bearing Test and, hence, also a direct method to determine the bearing capacity of a shallow foundation placed on or in the fill mass. This test is executed with a rigid square or rectangular plate of dimensions that may be equal to those of the proposed foundations (practical maximum size approximately 3x3 m), which implies... 

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