This study investigates building settlements near excavations in soft clay. A simplified theoretical method is proposed to predict the additional settlements and axial forces of excavation-adjacent existing building floating piles in soft clay. The soil displacement is simplified as a line or broken line along the depth direction, depending on the distance from the excavation. A hyperbolic model is applied to calculate the skin friction and tip resistance induced by the vertical soil displacement. The parameters of the hyperbolic model are corrected to fit data from in-service piles. Based on the load-transfer curve method, the additional settlements and axial forces are determined. The measured data of 17 floating piles from two excavation cases in Hangzhou, China, show good agreement with the calculated values. The results show that the position of the neutral point of the loaded pile varies with the soil settlement. Because of the upper structure, the theoretical settlements for piles near the excavation are larger than those obtained from the measured values; for distant piles, this relationship is reversed. The proposed prediction methodology is expected to guide the design of practical excavations.
This article reports the field performance of deep excavations of two subway station cases, including the lateral wall deflection behavior and settlement trends of the surrounding soil and nearby buildings. The retaining structures employed in these cases were contiguous pile walls (CPW), soil-mixing walls, and diaphragm walls (DW), all of which were embedded in soft clay. The measured wall deflection profiles exhibited typical bulging behavior at the end of the excavation. The ratios of the measured maximum wall deflection to the excavation depth were found to be similar for all three types of retaining wall. Furthermore, the maximum and minimum corner effects on the wall deflection development were obtained for the DW and CPW, respectively. The measured ground surface settlement increased linearly with increased maximum lateral wall deflection, while the settlement magnitude became extraordinarily large because of the presence of sludgy soil. A concave pattern was proposed for the surface settlement profiles for all three types of retaining wall. The building settlement was quantified, with the value lying between those of the surface settlement and soil settlement at 10-m depth. The soil displacement field induced changes in the side and end resistance behaviors of the loaded piles, along with additional settlement of pile-foundation buildings. In addition, the pile-foundation building settlement was influenced by the corner effect. These research results will enhance our understanding of the deformation characteristics of the retaining structure and nearby buildings. Meanwhile, the findings will provide guidance for the optimal design of the retaining structure in soft soil.
By analyzing the extensive field data from a long and large excavation in soft clay, this study investigates the three-dimensional deformation behavior induced by excavation. Significant inhibition effects of corner on both wall deflections and ground settlements were observed and quantified. Thus, a modified function for estimating the distribution of deformation parallel to the excavation is proposed and evaluated. Further analyzing shows that the pipeline settlement can be well estimated by the modified function combining with settlements profile proposed by Hsieh and Ou, and the reduction coefficient is about 0.8; the calculated maximum distortion of the pipeline can provide reliable reference. In addition, it is found that the cement-soil partition walls can also considerably reduce the wall deflections and ground settlements even after the part that is above the excavation base were removed.
This study investigates the effect of shield tunnel grouting on excess pore pressure distributions around tunnel and ground consolidation settlement. First, it presents half-plane excess pore pressure around an unlined tunnel caused by grouting pressure based on the complex variable theory and the conformal mapping method. Second, the analytical solution for the soil consolidation is derived using the conformal transformation method and the consolidation theory of Terzaghi–Rendulic. The drainage conditions of the tunnel lining are idealized into three cases: fully drained, partially drained, and impermeable along the tunnel circumference. The impacts of the burial depth of the tunnel, the permeability coefficient of the tunnel lining and the surrounding soil, the Poisson’s ratio of the soil, the lateral Earth pressure coefficient of the soil, and the shear modulus are investigated.
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