Experimental And Theoretical Study On Behaviour Of Deep Excavations In Coastal Area

With the rapid development of economy of China, more and more coastal excavations are emerging in recent years. Behaviours of the excavations neighboring sea or river are probably affected by the water level fluctuation due to wave and tide, nevertheless, the study on the pore pressure response of the soil around the excavations to the wave has been rarely published. Meanwhile, marine saturated soft clay which has the engineering characteristics of very high compressibility and low strength, is widely distributed in coastal area, where the deformation and the stability of the excavations is very difficult to control.Firstly, this paper studies the pore pressure response of the soil around excavation by means of wave model test of coastal excavations. The monitoring data of a soft clay excavation in Hangzhou is analyzed in detail. Finally, considering the anisotropy of the shear strength of Hangzhou marine soft clay, the upper bound solution of stability against basal heave of excavation is presented. The following are the main work of this paper.1. Wave model test of coastal excavations is based on the excavation located in Lingding Ocean of the Hong Kong-Zhuhai-Macau Bridge project. The physical size of the testing model is determined by theory of similar scale. Then, detailed testing scheme is designed and the related preparatory work is completed.2. A series of model tests are carried out in the multifunctional wave-current flume of Zhejiang University to study the pore pressure response around excavation. The influences of various parameters on pore pressure around the excavation are investigated. These parameters include the wave height, the wave period, the depth of water, the depth into the soil of the retaining wall and the distance from the breakwater to the retaining wall.3. The monitoring data of a soft clay excavation in Hangzhou is analyzed thoroughly. In addition the soil pressure and the axial forces of the struts, the deformation characteristics of the excavation, as well as the maximum creep deformations and creep rates are investigated.4. The upper bound solutions of stability against basal heave of homogeneous and heterogeneity soft clay excavation are presented using the plastic limit theory, which is based on the modified formula of the anisotropic clay strength from the Hangzhou intact soft clay tests that were finished by hollow cylinder apparatus (HCA), and the assuming the Prandtl slip failure mode. Furthermore, the influence on stability against basal heave of excavation caused by the factors such as the anisotropy ratio of soil, the embedded depth of the retaining wall, the thickness of soft clay layer between the foundation base and the underlying hard stratum as well as the wall roughness is discussed. The influence of heterogeneous coefficient is discussed for heterogeneous soft clay excavation. Finally, the method proposed in this paper is verified by a case study in Hangzhou soft clay.