**7.2 Determination of strains**

Generally, when determining the observed strains from overcoring, a stable value is preferential before overcoring starts and after overcoring stops. The difference among these values is understood to correspond to the strain relief involved in the overcoring process [12]. Generally, each HI-Cell plot shows a peak strain followed by a flat portion that decreases toward the end of the over-core (**Table 13**). The final strains for the site overcore were obtained by averaging the readings in the flat portion of the curve. The recommended overcoring speed of the


#### **Table 13.**

*Change in strain from overcoring HI-Cell.*

*Hydraulic Fracturing in Porous and Fractured Rocks DOI: http://dx.doi.org/10.5772/intechopen.106552*

**Figure 31.** *Overcoring, strains for the KTK 8 incline site.*

chuck is 120 rpm to minimize core breakage. **Figure 31** shows overcoring strains as a function of distance for each HI-Cell [14].
