深槽地基土加固方法对防渗墙的影响研究

以龙开口水电站坝基防渗墙工程为例,采用精细化有限元法,针对砂卵石层开挖施工工序,建立防渗墙墙后砂卵石地基在直接开挖、灌浆固结及设置旋喷桩加固三种加固方案下的有限元分析模型,研究不同加固方案下防渗墙变形、内力及应力的变化规律,分析不同开挖方案对防渗墙安全性的影响。分析结果表明:直接开挖方案和灌浆固结方案防渗墙最大变形为0.5~3.7 mm,最大正弯矩为300~1 000 kN·m,最大负弯矩为-2 100~-800 kN·m,最大剪力为800~1 300 kN;设置旋喷桩加固方案防渗墙最大变形为0.2~0.3 mm,最大正弯矩为100~150 kN·m,最大负弯矩为-300~-200 kN·m,最大剪力为300~400 kN。三种方案中直接开挖方案变形最大,最大变形不到防渗墙左侧宽13.6 m的万分之三;加固砂卵石层地基可显著降低防渗墙的变形、内力及应力,显著提高防渗墙的安全性。研究结果为龙开口水电站坝基深槽砂卵石层的开挖加固方案提供了理论基础,在保证防渗墙安全可靠的前提下优化了地基土加固方案的设计。

Study on impact from method for reinforcement of deep groove foundation soil on cutoff wall

By taking the project of the cutoff wall for the dam foundation of Longkaikou Hydropower Station as a study case，the finite element models under three reinforcement schemes，i.e. direct excavation，grouting consolidation and arrangement of rotary jet grouting pile for reinforcing the sandy gravel foundation behind the cutoff wall，are established with high precision finite element method for the construction procedure of the excavation of the sandy gravel layer therein，and then the changing laws of the deformation of cutoff wall，the internal force and stress under different reinforcement schemes are studied，while the impacts from different schemes on the safety of the cutoff wall are analyzed as well. The analysis result shows that the maximum deformation is to be 0.5~3.7 mm，the maximum positive bending moment is to be 300～1 000 kN·m，the maximum negative bending moment is to be -2 100～-800 kN·m and the maximum shearing force is to be 800～1 300 kN for both the direct excavation scheme and the grouting consolidation scheme，while the maximum deformation is to be 0.2～0.3 mm，the maximum positive bending moment is to be 100～150 kN·m，the maximum negative bending moment is to be -300～-200 kN·m and the maximum shearing force is to be 300～400 kN for the scheme of the arrangement of rotary jet grouting pile. In these three schemes，the deformation from the direct excavation scheme is the largest，which is 3/10 000 of the left width （13.6 m） of the cutoff wall，while consolidating the sandy gravel foundation can significantly lower the deformation，internal force and stress of the cutoff wall，thus obviously enhance the safety of the cutoff wall. The study result provides the theoretical basis for the consolidation scheme for the deep groove excavation of the sandy gravel layer of the dam foundation for Longkaikou Hydropower Station and optimizes the design of the foundation soil reinforcement scheme under the premise to ensure the safety and reliability of the cutoff wall.