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Spring 2008 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• Longitudinal cracks occur above. and roughly parallel to. the edges of the lonpwall mining panel <br />above the `.;ate road pillars (Figure 1). Lon(itlldinal cracks conlnlonly remain open, particularly <br />in areas above klate roads with it ri2id-pilli_ur conl'iguration. The cracks may he open or closed in <br />areas ahove irate roads with it co?nlhination ri(,id-pillar/yield-pillar con fio ,Lira( ion, <br />Z? 17 <br />('utllpreSSloll features (hul1es and Warils) also occur ahove the longwall nlining panels in arells <br />where the ground surface undergoes compression in the suhsidence process. The compression <br />I'catul'cs, which 0CCUr (ow,rrd the center of the training panel in zones of m:rXlllll1111 Co111111'csslt111. <br />are usually ?rlore d1l'ficult to recognize. They often are masked, or ithsorhed, by soil and <br />c011u\iuill. or are hidden in the hrush Zind grass. Thee also nliry he indistineuishahle 11'0111 nattural <br />hun111S and 111111IMIS 111 the soul Lind Colluvium. <br /> <br /> <br />• <br />• <br />. i ? ? _. .`)- !?. _,?w' 1 NUJ ?? ? ll -•i.' ? <br />Q, _vk <br />Figure 1. Examples of subsidence cracks located at Apache Rocks in hard sandstone jIeft) and claystone (right) <br />above the head gate entry pillars of mined Longwall Panel 14. <br />2.2 Construction Cracks <br />Cracks caused by construction activities are common on the hanks of newly constructed roads <br />and drill pads (Figure 2). These cracks arc often Caused by the hulldozer durinty construction <br />activities. They are most noticeable where fractured and weathered hedrock is encountered <br />during exCavation. l-lo%VCVer, this type of cracking also occurs in soil and Colltlviunl where roots <br />of hrush and trees are pulled out of the road cut by the bulldozCr. In Contrast to suhsidenCe <br />Cracks, COnstrLlCtloll cracks OCCllr Ill it rather continuous zone where wrtthercd ,old/or l'racturcd <br />831-032.790 Wright Water Engineers, Inc. Page 5 <br />August 2008