Impact of Dicranopteris linearis roots on the shear strength of different soil layers in collapsing wall of Benggang

Abstract

‘Benggang’ is a local term for a widespread type of severgully erosion with steep collapsing walls in granitic, low, hilly areas of southern China, and its development and expansion are closely related to the shear strength of the collapsing wall. Plant roots play an important role in improving soil shear strength. However, the shear strength of root‐soil complexes in different layers of collapsing walls remains obscure. We selected Dicranopteris linearis fern roots and adopted the direct shear method to evaluate the effect of root weight density (RWD) (0–1.25 g 100 cm−3) on the shear properties of the lateritic, sandy and detritus layers. The results showed that roots could enhance soil shear strength, and the maximum increase in the lateritic layer was 11.53%, higher than that in the sandy (5.84%) and detritus layers (3.17%). As the root content increased, the cohesion of the sandy and detritus layers increased and then decreased, and their maximum increase in cohesion and the fitting optimal RWD were lower than those of the lateritic layer. The internal friction angle was not affected by roots. When the root content was constant, the shear strength and cohesion of the lateritic layer were significantly higher than those of the sandy and detritus layers, while their internal friction angle was significantly lower than that of the latter two layers. The average increment of soil cohesion calculated by the Wu‐Waldron model (WWM) was 10.52 kPa, which was 0.30, 3.75 and 19.38 times the measured average values of the lateritic, sandy and detritus layers, respectively. The correction coefficient k′ was 0.02–1.18, and the truek'¯$$ \overline{k\hbox{'}} $$ in the lateritic layer was the highest (0.82), followed by that in the sandy and detritus layers. By combining the modified WWM with Coulomb's formula, new shear strength equations for root‐soil complexes of D. linearis were established. The predicted shear strength compared well with the measured shear strength (R2 > 0.90, NSE >0.90). Overall, the roots only had a significant reinforcement effect on the lateritic layer, and they could still not change the mechanical properties of the collapsing wall, which were more stable in the upper layers and weaker in the bottom. Therefore, other measures should be taken in the bottom layers to improve the stability of Benggangs. Highlights Effect of D. linearis roots on the shear strength of collapsing walls in Benggang was studied. Roots could improve collapsing‐wall soil shear strength, mainly reflected in the cohesion. The roots enhancement effect in lateritic layer was better than that of sandy and detritus layers. New shear strength equations of root‐soil complexes were established based on the Wu‐Waldron model.

Effect of Soil Moisture Content on the Shear Strength of Dicranopteris Linearis-Rooted Soil in Different Soil Layers of Collapsing Wall

“…Shuai et al [22] suggested that among the four herbs plants, the soil reinforcement effect of Pennisetum sinese and Odontosoria chinensis was higher than that of Dicranopteris linearis and Neyraudia reynaudiana. In the three layers of collapsing wall, the root system of Dicranopteris linearis significantly increased the shear resistance and compressive strength of the first layer but not in the other two [19,23]. In short, root density [19,24], species of plants [25] and soil properties and configurations [26] affect the effect of the root system on soil reinforcement.…”

“…In the three layers of collapsing wall, the root system of Dicranopteris linearis significantly increased the shear resistance and compressive strength of the first layer but not in the other two [19,23]. In short, root density [19,24], species of plants [25] and soil properties and configurations [26] affect the effect of the root system on soil reinforcement.…”

“…The composite material formed by roots and soil not only makes full use of the advantages of roots but also overcomes the weaknesses of soil [15]. Therefore, the shear strength and cohesion of soils with root materials are stronger than soils with no root materials [16][17][18][19][20]. In recent years, increasing attention has been given to the effect of root systems on Benggang soil reinforcement.…”

Deformation characteristics test and mechanism of arbor taproot soil complex in rainforests

“…In recent years, scholars have conducted several studies on the soil consolidation effect of plant roots. Indoor or field tests have confirmed the ability of plant roots in significantly improving the shear strength and ductility of soil [1][2][3][4][5][6][7][8][9] . These research results have shown that the natural attributes of roots considerably affected the soil consolidation effect, such as their species [10][11][12][13][14][15] , growth age [16][17][18][19] , and root morphology [20][21][22][23][24] .…”

Soil physics matters for the land–water–food–climate nexus and sustainability

“…Plant root-soil complexes are important features influencing soil characteristics such as soil structural stability and functions. Zhou et al (2022), employing a Dicranopteris linearis fern root-soil system and an adopted direct shear measurement methodology, illustrated that roots could improve the collapsing-wall soil shear strength typically in soil lateritic layer other than the sandy and detritus layers. They further established new shear strength equations for root-soil complexes of D. linearis based on the modified Wu-Waldron model and Coulomb's formula.…”