View larger version (28K):
[in a new window]
|
Fig. 4 Dynamics in CO2 emission rate before and after controlled shear and compressive soil deformations
. All treatments resulted in enhanced CO2 emission of the soil upon deformation (see Table 1). The time refers to the hours before (negative values) or following (positive values) the soil deformations performed within the respirometer. (a) Compression alone with normal loads of 430 kPa, or (b) 79 kPa (6 and 4, respectively, in Fig. 2). Combined shear and compressive stresses of samples with different (precompression) stress histories: (c) samples precompressed with 430 kPa were sheared with the same load during shearing (Stress ratio 1, Point B in Fig. 2) or (d) reduced load (Stress ratio 0.05, Point D in Fig. 2); (e) samples precompressed with 79 kPa were sheared with the same load during shearing (Stress ratio 1, Point A in Fig. 2) or (f) reduced load (Stress ratio 0.05, Point C in Fig. 2). (g) The effect of the mechanical disturbance as summarized in Table 1 was assessed relative to untreated soil samples
|
with successive increase in normal load up to 430 kPa, followed by a successive decrease. The arrows indicate the pathways followed. The numbers (1–6) along the line are the treatments (for normal load) that were selected to asses the effect upon biological activity. The dashed line represents the critical state line that separates conditions that lead to consolidation from those that lead to volume expansion upon shearing (see text for further details). Letters (A–D) in the graph refer to four conditions that were selected to asses the effect of shearing upon biological activity, as defined in the text and summarized in 
