《Table 1 Penetration pressure as a function of penetration energy, i.e.hammer weight and drop height

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《Modified Rammsonde tests in layered compacted snow》

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Mellor（1975）stated that the Rammsonde penetration resistance R has the dimensions of force，but it actually represents the driving energy per unit penetration for a fixed cross-sectional area A of the penetrometer point；therefore，R/A can be interpreted as the specific energy required for penetration.During penetration，the energy is expended in breaking bonds，displacing material laterally，and compacting in an annular zone around the penetrometer hole（Mellor，1975）.It is thus easy to understand that when the snow density changes，or the number and size of bonds between the grains changes，the energy required to penetrate to a certain depth is different.However，the energy that Mellor（1975）refers to is actually different from the penetration energy that we discussed earlier.R/A can be regarded as the real energy transfer from the shaft to the snow，while the penetration energy mentioned before is the total energy，which includes energy losses.The greater the penetration energy，the more real energy is transmitted to the snow.But more energy is not always better，and vice versa.For low-density snow，excessive penetration energy may cause the penetrometer to move straight to a large depth，even down to the bottom of the layer after one or a few impacts.This distorts the results，which then cannot reflect the true resistance or hardness.For snow of high density，a penetration energy too small will cost more time and effort because penetration to the same depth will require more impacts.In this case，the main value of this test would be impaired because the advantage of the cone penetration testing lies in its simplicity of performance and evaluation.It is therefore necessary to choose an appropriate penetration energy or a uniform drop weight and distance when measuring hardness or resistance under different conditions.Niedringhaus（1965）and Waterhouse（1966）also noticed the influence of penetration energy on snow hardness measurements.After further study，Waterhouse（1966）proposed a new hardness formula which takes into account the influence of different hammer weights.But the correction Waterhouse（1966）offered is complex，it has not been used in practice and is not applied in this study.In technical reports of CRREL，the impact of penetration energy was not considered，which merits further study.