Table 6 Variation of different characteristic parameters of expansive trench slope with depth.
Depth range (m) | Dry weight γd (g/cm3) | Unconfined compressive strength qu (kPa) | Three-way expansion force \({\text{P}}_{{{\text{oz}}}}\), \({\text{P}}_{{{\text{ox}}}}\), \({\text{P}}_{{{\text{oy}}}}\) (kPa) | Unlimited expansion VH (%) |
|---|---|---|---|---|
0–0.5 | The surface soil is highly loose with minimal dry bulk weight, which gradually increases with depth | Strength is strongly influenced by the plant root system, ranging from large to small, with depth | In the surface layer, due to the minimum dry weight, the three-way expansion force increases gradually with depth after reaching the minimum,\({\text{P}}_{{{\text{oz}}}} > {\text{P}}_{{{\text{ox}}}} ,{\text{P}}_{{{\text{oy}}}}\); \({\text{P}}_{{{\text{ox}}}} \approx {\text{P}}_{{{\text{oy}}}}\) | The surface layer exhibits the swelling characteristics of a remodelled soil, i.e., a large amount of swelling, ranging from large to small with depth, and a high water content after swelling |
0.5–1.0 | The dry mass continues to increase, reaching 1.0 m, essentially 99% of the deep dry mass | The strength increases after the minimum value occurs, and the specimen’s damage is bulging, cracking, or cracking | Continued slow increase | Expansion continues to decrease, reaching 1.0 m, essentially the minimum expansion |
1.0–2.0 | Slight increase in dry weight, reaching 2.0 m, essentially the same as the deeper layers | Strength continues to increase; specimen destruction has more apparent damage to the surface | Continuing to increase slowly. But the rise is even smaller | Swelling increases slightly with depth, which is associated with a slight increase in dry bulk weight |
> 2.0 | Dry weight remains constant | A slight increase or decrease in strength is related to the proportion of damage along the cleavage plane, but overall strength remains constant | Expansion force remains essentially unchanged | The expansion amount stays the same, and the water content after expansion slightly increases by 2–3% compared with the natural water content |
