Physical Model Tests on Reinforced Loess Foundation Model Under Wetting and Loading
ObjectiveReinforcement method is utilized to treat the collapsible loess foundation in this study. The reinforced loess foundation is constructed by excavating a portion of the collapsible loess, laying geosynthetic reinforcement layers at specific spacing, and then backfilling and compacting the e...
Saved in:
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Editorial Department of Journal of Sichuan University (Engineering Science Edition)
2025-07-01
|
| Series: | 工程科学与技术 |
| Subjects: | |
| Online Access: | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202400249 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | ObjectiveReinforcement method is utilized to treat the collapsible loess foundation in this study. The reinforced loess foundation is constructed by excavating a portion of the collapsible loess, laying geosynthetic reinforcement layers at specific spacing, and then backfilling and compacting the excavated soil. This study evaluates the improvement effect of geogrid reinforcements on the differential settlement of the collapsible loess foundation.MethodsPhysical model tests were conducted on reinforced loess foundations under wetting and loading to examine the influence of the compaction degree of backfill and the stiffness, number, and spacing of reinforcement layers on the earth pressures and deformation of reinforced loess foundations. The width (<italic>B</italic>) of the strip footing above the foundation is 90 mm. The model foundation has a length of 900 mm (10.0<italic>B</italic>), a height of 550 mm, and a width of 400 mm. The length of the model reinforcement layer is 450 mm (5.0<italic>B</italic>). The uppermost reinforcement layer is 27 mm (0.3<italic>B</italic>) away from the surface of the foundation. Loess from Yan’an was selected for the foundation soil, and biaxial geogrids with different stiffnesses were used as model reinforcements. Linear variable differential transformers were installed above the foundation surface to measure the settlements of the foundation. Earth pressure sensors were installed below the reinforced zone. The load was applied gradually. When the load reached 120 kPa, the deformation was wetted gradually under this load. Finite element numerical simulations were conducted to model the physical tests and analyze the optimal parameters and arrangements of reinforcement layers for reinforced loess foundations.Results and DiscussionsThe results showed that, compared to the pure loess foundation, the inclusion of geogrids within the collapsible loess foundation significantly improves the stress diffusion effect of the foundation and thus reduces the internal earth pressures and surface settlements within the width of the footing. After reinforcement with geogrids, the failure mode of the composite foundation shifts from the punching shear failure of the pure loess foundation to overall shear failure. During the process of wetting and loading, longitudinal cracks develop from the foundation surface into the internal soil on both sides of the reinforced zone. When the foundation was damaged, the crack depth equaled the depth of the entire reinforced zone, and the maximum crack width reached 2.5 cm. The occurrence of these cracks resulted from the inability of the soil adjacent to the reinforced zone to deform in coordination with it due to the large difference in deformation modulus between the two parts. The internal earth pressures of the reinforced loess foundation decrease with the increase in compaction degree of the backfill, the stiffness, and the number of reinforcements, whereas they increase with greater reinforcement spacing. The increased compaction degree of the backfill enhances the deformation modulus and the friction between the reinforcements and soil, which improves the stress diffusion effect and thus reduces the earth pressures below the reinforced zone. The greater the reinforcement stiffness, the higher the load borne by the reinforcements and the smaller the load transferred to the soil below the reinforced zone. The maximum earth pressures below reinforced foundations with reinforcement stiffnesses of 252 and 526 kN/m decreased by 14% and 29%, respectively, compared to the pure foundation. As the number of reinforcement layers increases, the proportion of the load carried by the reinforcements also increases, resulting in reduced load transmission to the soil beneath the reinforcement zone. In addition, increasing the number of reinforcement layers enhances the friction between the reinforcement and soil, which increases the stress diffusion effect and thus decreases the earth pressure within the width of the footing. As the vertical spacing between reinforcement layers increases, the restraint of the reinforcements on backfill deformation decreases, leading to a weakened stress diffusion effect of the foundation. Therefore, the earth pressures below the reinforced zone increased and became more unevenly distributed. Increasing the number of reinforcement layers proved most effective in reducing soil pressure, achieving a maximum reduction of 50% compared to the pure loess foundation. The reinforced loess foundation primarily relied on the bearing capacity and stress diffusion effect of the reinforcement layers within a specific depth range below the surface to reduce settlement, indicating the presence of an effectively reinforced depth. Altering reinforcement parameters beyond this depth does not affect reducing the differential settlement of the foundation. The effectively reinforced depth was approximately 0.5 times the width of the footing (0.5<italic>B</italic>). The optimal length and stiffness of the reinforcement layers were 3.0<italic>B</italic> and 500～700 kN/m, respectively.ConclusionsReinforced loess foundation represents an economical and environmentally friendly method for treating collapsible loess foundations. This study confirms that placing geosynthetic reinforcements in loess can effectively reduce the uneven settlement of collapsible loess foundations and the earth pressure beneath the footing. The reinforced loess foundation is suitable for treating collapsible foundations in engineering projects such as roads and oil and gas drilling platforms in the northwest loess region. It can also be applied to reduce the load above underground structures, including comprehensive pipe galleries. However, the longitudinal cracks observed on both sides of the reinforced zone constitute a disadvantageous factor during the working process of the reinforced loess foundation. Future research can consider overlapping geotextiles at both ends of the geogrids to reduce the modulus difference between the reinforced zone and the pure soil, enhancing the coordinated deformation ability of the reinforced and unreinforced zones. Therefore, the formation of cracks can be eliminated. |
|---|---|
| ISSN: | 2096-3246 |