## 3 Results
### Stress-Strain Behaviour at \(-33\) kPa Matrix Suction  
Figure 6 presents the stress-strain responses (average of three samples) of untreated, cement-treated, and guar gum-treated soils assessed at \(-33\) kPa matric suction following exposure to 1, 5, 10, and 15 wetting-drying (WD) cycles. The corresponding moisture contents are given in Appendix A. Unlike the untreated and guar gum-treated soils, the cement-treated samples consistently exhibited strain-softening behaviour, demonstrating pronounced strain-hardening characteristics across all WD cycles (Figure 6).  
Figure 3: Comparison of volume change in samples treated with cement (**left**) and guar gum (**right**) at \(-1500\) kPa of matric suction. The cement-treated specimen shows significant volume increase and cracking, whereas the guar gum-treated specimen exhibits minimal cracking and more stable volume.  
At \(-33\) kPa matric suction, all soil samples exhibited a reduction in undrained shear strength (\(S_{\text{u}}\)) compared to those tested at \(-1500\) kPa, primarily due to the increased pore water content diminishing matrix suction. The untreated soil demonstrated a progressive  
Figure 4: Deviator stress is plotted as a function of axial strain (average for three samples) measured at the matric suction of \(-1500\) kPa for (**a**) untreated soil, (**b**) cement-treated soil, and (**c**) guar gum-treated soil for 1, 5, 10, and 15 wetting–drying cycles.  
Figure 5: Variation in (**a**) undrained shear strength, (**b**) secant modulus of elasticity, and (**c**) modulus of toughness measured at \(-1500\) kPa matric suction for untreated soil and soil treated with cement and guar gum, subjected to 1, 5, 10, and 15 wetting–drying cycles.  
Figure 6: Deviator stress is plotted as a function of axial strain (average for three samples) measured at the matric suction of \(-33\) kPa for (**a**) untreated soil, (**b**) cement-treated soil, and (**c**) guar gum-treated soil for 1, 5, 10, and 15 wetting–drying cycles.  
decline in strength with increasing WD cycles, decreasing from 54 kPa after the first cycle to 33 kPa after 15 cycles--a reduction of approximately 39%. Cement-treated soil initially recorded the highest \(S_{\text{u}}\) (235 kPa), but this value declined steadily to 156 kPa after 15 cycles (34% reduction), indicating degradation of cementitious bonds due to moisture ingress. Nevertheless, it consistently outperformed the other treatments throughout the WD cycles. Guar gum-treated soil displayed an intermediate response, with \(S_{\text{u}}\) decreasing from 124 kPa to 92 kPa (26% reduction), suggesting relatively better resilience against moisture-induced weakening than the untreated soil, albeit inferior to cement treatment in terms of absolute strength (Figure 7a). The variation in the secant modulus of elasticity (\(E_{50}\)) with respect to WD cycles mirrored the trends observed in \(S_{\text{u}}\) (Figure 7b). Interestingly, the guar gum-treated soil exhibited the highest modulus of toughness (\(U_{\text{I}}\)), surpassing both cement-treated and untreated soils (Figure 7c), indicating its superior energy absorption capacity under cyclic moisture fluctuations.