These tests have shown that the difference between horizontal and vertical cone resistance is greatest for medium dense sands, but show little dependancy on the gradation of the sand. The ratio of horizontal over vertical sleeve friction on the other hand shows little variation for different densities, but is strongly dependant on the coarseness of the sand.
The interpretation is not so easily converted however. In tion. The interpretation of the obtained measurements vertical CPT this is the stress that acts in the plane is subsequently made using analytical and empirical perpendicalur to the penetration direction, and in this models, as well as experience, which all implicitely or plane can be considered a radially uniform stress com- explicitely use the assumption that the penetration dir- ponent.
In the case of HCPT the stress state perpen- ection is vertical. Those measures are taken because the deflection those in vertical CPT.
The calibration chamber tests the tunnel. The horizontal cone cognised that this could complement the information resistance was on average 1. Initiatives have also been medium densified sands, whereas the ratio was closer unfurled to execute horizontal CPTs through retain- to one for very loose or dense sands.
The horizontal ing walls of building pits to investigate the soil con- friction ratio on the other hand was clearly lower than ditions below adjacent buildings, or through existing the vertical friction ratio, but showed little dependancy railway embankments and land fills, without disturb- on the density of the sand. A similar image can be derived from the field meas- Now the equipment used to perform a vertical CPT urements by van Deen et al. The hori- zontal cone resistance measured was greater than the vertical, even up to three times greater in clay.
And again the horizontal friction ratio was on average lower than the vertical. And although on one hand these res- ztop ults strengthen the results from the calibration chamber tests, they also indicate that there may be an influence of the soil type.
See for example the overview of soil classification charts presented by Lunne et al. It is also very likely that HCPT measurements show a similar dependancy on the gradation of sand, but this dependancy is not necessarily exactly equal. In order to investigate this behaviour a number of tests has been executed in the large rigid wall cal- Figure 1. These tests have been limited to sand samples, as the preparation of large, homogeneous, cohesive samples in a calibration chamber is difficult and time- method is that the preparation of the sample is so consuming.
Three different sands have been used, labour-extensive; a new sample can be prepared each which have been prepared at various densities. Within day, requiring only one man-hour actual work during each sample two vertical and one horizontal CPT has this period. The disadvantages are that the samples been made and the measurements at the depth of the are somewhat less homogeneous over the height of the HCPTh have been compared.
This The DUT calibration chamber is a 2m diameter rigid last problem can be circumvented completely, as the wall calibration chamber, as sketched in figure 1. At chamber allows the testing of fully saturated samples the bottom of the tank a system of filter drains connec- as well, but this option has not been used in this test ted to a pumping system is embedded in the sand.
This series. A couple of vibrators affixed to the sides of the is a rigid wall calibration chamber, meaning that the tank can be used to vibrate the entire tank and thereby lateral boundaries are stiff and disallow any deforma- densify the sand. To prepare a sample the sand is first tion of the sample. This in contrast to the often used fluidised and, when fully liquified, the water is allowed flexible wall chambers, where a pressurised membrane to drain.
The vibrators are then used for a period of 0 is used at the lateral boundaries to keep a constant lat- to 8 minutes, dependant on the relative densify of the eral pressure. As is common the lower boundary is the sand that is required.
After that the remaining water stiff chamber floor, whereas at the top an overburden is allowed to drain and the density of the sample is load could be applied. The sample is large enough determined by measuring the top level of the sand. The result of this combination of boundaries is ferences between the DUT calibration chamber and that the DUT chamber falls somewhere between BC2 most other chambers.
Sieve curves for all sands Figure 3. Sieve curves for sand 2 at different depths; influ- ence of segregation Table 1. Minimal and maximal densities Sand emin emax 1 0. Introduction to Soil Mechanics Laboratory Testing. Peck, Gholamreza Mesri - Purushothama Raj. Pesquisar no documento.
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