Mechanical properties of root-bearing soils under freeze-thaw cycles
Plants are the engineers of the nature,they can effectively improve the strength of the soil and can en-hance the stability of shallow soil slopes and minimizing surface erosion.for their mechanical reinforcement to soil.Therefore,they are widely used in slope protection.However,in the seasonal frozen soil regions of the central and western areas,the repeated freeze-thaw cycles of vegetation slopes lead to changes in soil mechanics under the dual effects of plant root reinforcement and freeze-thaw damage,introducing uncertainties in slope sta-bility.Therefore,to explore the combined impact of freeze-thaw cycles and root distribution on soil,triaxial consolidation undrained(CU)tests were conducted under confining pressure from 25 kPa to 400 kPa,consider-ing different freeze-thaw cycles(0,1,5 cycles)and root distribution(vertical uniform distribution:one root in each of the three layers;horizontal uniform distribution:three roots in the middle layer).The materials were prepared with sands and sorbus pohuashanensis roots from Hailuogou in Minya Konka.To investigated the strength variations of root-containing soil under freeze-thaw cycles,stress-strain curves and pore pressure-strain curves were plotted respectively.Then the analysis of the stress-strain characteristics of the samples under differ-ent conditions was performed,and the total stress strength parameters and effective stress strength parameters were obtained from the shear strength envelopes.The results revealed that:(1)with the increase of freeze-thaw cycles,the peak strength of both the one-root-per-layer and three-roots-in-the-middle-layer samples gradually de-creased,along with reduced cohesion and internal friction.Under low confining pressure(25 kPa),the weaken-ing effect of freeze-thaw cycles on root-containing soil strength was more pronounced.However,under high confining pressure,the strengthening effect of plant roots on soil strength remained significant.(2)Under differ-ent freeze-thaw cycles,roots can still enhance the soil's strength to a certain extent,and the arrangement of one root in each of the three layers showed the most significant enhancement effect.The roots contact with soil,which leads to irregular occlusions and"self-locking",which has a positive effect on the enhancement of shear strength.(3)Under the same freeze-thaw cycle and confining pressure,samples with vertically distributed roots exhibited higher strength and cohesion,because the contact area was larger of roots placed in three layers along the height of the sample than the other distribution of samples.The distribution pattern of roots mainly influ-enced the soil's cohesion,with minimal impact on the internal friction angle.These findings can provide a theo-retical basis for ecological slope protection in cold regions.
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