Influence of groundwater level changes on the seismic response of geosynthetic-reinforced soil retaining walls

Geosynthetic-reinforced soil retaining walls(GSRWs)have been widely used in civil engineering projects.However,as the climate changes,extreme weather conditions and natural hazards are likely to become more frequent or intense,posing a huge threat to the stability of GSRWs.In this paper,the effect of groundwater level fluctuations on the seismic response of GSRWs is investigated.First,a dynamic numerical model was established and validated through centrifugal shaking-table test results.Using the established numerical model,the seismic response of GSRWs under four different groundwater level conditions was then investigated,i.e.,an earthquake occurring at a low groundwater level(Case LW),an earthquake occurring when the groundwater level rises(Case RW),an earthquake occurring at a high groundwater level(Case HW),and an earthquake occurring when the groundwater level drops(Case DW).The results show that the GSRW in Case DW has the worst seismic stability because of the drag forces generated by the water flowing to the outside of the GSRW.For Case RW,deformation of the GSRW under earthquake forces was prevented by the drag forces generated by the water flowing to the inside of the GSRW and the water pressure acting on the outside of the facing,giving the GSRW the best seismic stability in this case.Compared with Case LW,the seismic stability of a GSRW in Case HW is worse,because the high groundwater level will generate excess pore-water pressure during an earthquake.On this basis,we provide engineering design suggestions to be considered by practitioners.

Active earth pressure acting on retaining wall considering anisotropic seepage effect

This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of cohesionless and fully saturated sand with anisotropic permeability along the vertical and horizontal directions. The extremely unfavourable seepage flow on the back of the retaining wall due to heavy rainfall or other causes will dramatically increase the active earth pressure acting on the retaining walls, increasing the probability of instability. In this paper, an analytical solution to the Laplace differential governing equation is presented for seepage problems considering anisotropic permeability based on Fourier series expansion method. A good correlation is observed between this and the seepage forces along a planar surface generated via finite element analysis. The active earth pressure is calculated using Coulomb's earth pressure theory based on the calculated pore water pressures. The obtained solutions can be degenerated into Coulomb's formula when no seepage exists in the backfill. A parametric study on the influence of the degree of anisotropy in seepage flow on the distribution of active earth pressure behind the wall is conducted by varying ratios of permeability coefficients in the vertical and horizontal directions,showing that anisotropic seepage flow has a prominent impact on active earth pressure distribution. Other factors such as effective internal friction angle of soils and soil/wall friction conditions are also considered.

Discussion of Fenlong Cultivation Supporting Food and Environment Safety and Broadening Survival and Development Space

A new high-efficiency farming method of global significance, Fenlong tech- nique capable of making soil fertile, increasing yield and improving ecological envi- ronment was introduced; and the Fenlong technique could deeply plough and scarify soil with a depth up to 30-50 cm, which is deeper than the depth of tractor tillage, solving the problem of difficulties in deeply ploughing and scarifying soil and keeping soil loose for muttiple seasons. The application to 20 crops in 18 provinces proved that yield could be increased by 10%-30% without increase in chemical fertilizer, quality could be improved by more than 5%, and water storage could be increased by 100%; yield could be increased for multiple seasons sustainably, and the yield of dry-land crops increased by 32.57%-38.2% from the second year to the fourth year; the net benefits of rice increased by 21.82% averagely from the first season to the sixth season; and the usage amount of chemical fertilizer decreased by 0.35-4.29 kg per 100 kg produced grain compared with conventional tillage, with an decrease amplitude of 10.81%-30.99%. It was discussed that the Fenlong technique could maximize friendly permanently-sustainable unitization of ＂natural resources＂ including soil nutrients, water, oxygen and light energy, and has good development potential in multiple fields. It was put forward that if it is popularized in 0.67x108 hm2, pro- ductivity of farmland could be newly increased by 0.1-0.13×10^8 hm2, 5.0 ×10^6 t of chemical fertilizer could be saved, the＇ storage of agricultural water could be in- creased by 3.0×10^10 m3, and increased food could feed 2,0-3.0×10^8 people.