| description:
|
<DIV STYLE="text-align:Left;"><DIV><P><SPAN>These layers evaluate the geotechnical behavior and associated hazards and risks of dune sands using clustering analysis based on the coefficient of uniformity (Cu), coefficient of curvature (Cc), and fines content (%) of samples collected from the dunes in the Mecca Province.</SPAN></P><P><SPAN>These grain-size parameters collectively control soil fabric, pore structure, permeability, and interparticle bonding, which in turn govern key engineering behaviors such as collapsibility, compressibility, and bearing capacity (Terzaghi et al., 1996; Das, 2016). We used an unsupervised K-Means algorithm to partition our dataset into K distinct, non-overlapping clusters. Two clusters were identified, each representing a distinct geotechnical material class.</SPAN></P><P><SPAN>These clusters reflect end-member behaviors of dune sands in arid and semi-arid environments and provide a framework for evaluating geotechnical hazards.</SPAN></P><P><SPAN>Cluster 1 is characterized by Cu values ranging from 1.37 to 5.07 (mean ≈ 2.05), Cc values from 0.64 to 1.64 (mean ≈ 1.15), and very low fines content ranging from 0.1 to 5.1% (mean ≈ 1.52%) (Figs.8.5-7). These properties indicate predominantly clean to slightly silty sands with a relatively narrow grain-size distribution. Under the Unified Soil Classification System (USCS), this cluster corresponds mainly to poorly graded sands (SP) with local transitions to sand with minor fines (SP–SM). The soil fabric is open and granular, with limited interparticle bonding and high permeability (Holtz et al., 2011; Das, 2016).</SPAN></P><P><SPAN>Cluster 2 is defined by high Cu values ranging from 3.05 to 6.45 (mean ≈ 4.39), Cc values from 1.26 to 2.37 (mean ≈ 1.90), and high fines content ranging from 6 to 10.5% (mean ≈ 7.3%). Figures (8.5-7). These parameters indicate heterogeneous, poorly graded sands with significant silt and clay-sized particles. Geotechnically, this cluster corresponds to silty sands (SM) under the USCS. The soil fabric is metastable, where fines form fragile clay–silt bridges between sand grains under dry conditions, creating an apparent strength that masks inherent instability (Jennings & Knight, 1975).</SPAN></P><P><SPAN /></P></DIV></DIV> |