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There is currently a lack of an available design approach to estimate the earth pressure in narrow backfills behind retaining walls rotated about the top (RT). The considerations of some significant factors, primarily load transfer mechanisms (soil arching effect and horizontal shear stress in soils), failure mechanisms (shape and number of slip surfaces) and soil cohesion are often neglected for brevity in routine design. Such simplifications may lead to significant deviations from reality. This paper first uses the finite element limit analysis (FELA) technique to identify the underlying failure mechanisms and load transfer mechanisms. The results observed in FELA models indicate that active rotation of walls about the top develops one curved slip surface, which can be approximated by the log-spiral function. Under the soil arching effect, the upper intermediate passive zone with major principal stress rotation trajectory and the lower active zone with minor one can be defined. The arched differential element method (ADEM) is then introduced to formulate the earth pressure calculation. The results from newly published tests, existing analytical approaches, and FELA are compared to validate the accuracy of the proposed approach in both purely-frictional and cohesive-frictional soils. Parametric studies are further conducted to thoroughly understand the earth pressure problems, considering the effects of sensitive design variables (e.g. aspect ratio, soil strength parameters, and wall-soil interface friction angle). The analytical approach presented here would be a great extension to the design guidelines for the retaining structures with narrow backfills.

Field test and numerical analysis were conducted to investigate the soil stress variation and lateral pile response to whole excavations from cone penetration tests (CPTs). The effects of excavation unloading on the performance of CPT cone resistances and p-y curves were examined. The p-y responses were related to the excavation-induced both stratigraphic variation and soil stress relief. Based on CPT profiles, the numerical calculations of the lateral pile responses before and after excavations were obtained and compared using a CPT-based p-y method. Finally, the suggestion on the design of laterally loaded piles considering excavation unloading was given.

Retaining walls are sometimes unavoidably constructed near existing stabilized structures to maintain stability of narrow retained c-ϕ soils. Although some analytical approaches have been presented to estimate active earth pressure on the wall undergoing rotation about the base (RB), the contributions of soil cohesion and horizontal shearing forces in c-ϕ soils are typically neglected for brevity. Hence it is always expected to be improved, and to seek a more economical design framework used in the retaining wall with narrow c-ϕ soils. This paper first uses finite element limit analysis (FELA) to study the developed failure mechanisms under RB mode, which provides a basis to establish a calculation model. An analytical framework using arched differential element method is further presented with overall considerations of soil cohesion, soil arching effect, shearing forces between adjacent elements and the studied failure mechanism. The calculation flowchart is mapped and executed under C++ environment. The results from centrifuge test, existing analytical approaches and FELA are compared for validation in both purely-frictional and cohesive-frictional soils. A parametric study considering the effects of sensitive variables (e.g. aspect ratio, soil strength parameters and wall-soil interface friction angle) on the design is carried out. For the use of proposed analytical framework in practice, two simplified design equations are provided to correlate standard Coulomb’s solutions.

P-y curve representing lateral soil-pile interaction mechanism is a well-adopted approach to analyze laterally loaded piles. To date, there is still a lack of clear understanding of the lateral pile performance under active and passive composite loadings based on the p-y method. This paper presents a series of p-y oriented modellings on the effect of loading sequences on soil-pile interactions due to a nearby excavation. The loading sequences were divided into firstly applying active loading on pile head and then passive loading caused by adjacent excavation (i.e. active–passive loading sequence) and firstly excavation-induced passive loading and then applying active loading on pile head (i.e. passive-active loading sequence). In this study, the rules of the p-y curve evolution due to different loading sequences were obtained, and the effect of loading sequences on the lateral soil-pile interaction due to excavations was analyzed. Finally, enlightenment based on the mechanism of soil-pile interaction was discussed to guide the design of pile foundations subjected to excavations.

Due to rapid population growth and infrastructure demand in China, more effective use of existing land is required. Infrastructure construction in coastal regions has driven rapid economic development. With increasing numbers of port facilities, cross-sea bridges and offshore engineering projects, large diameter and super-long cast-in-place piles are increasingly needed in these regions. The p-y curves of piles are key to evaluating their horizontal bearing characteristics, which is critical to the risk evaluation, design and construction of large infrastructural supports. In the present study, a p-y curve analysis method based on piezocone penetration test (CPTu) data is proposed, which uses the Matlock and hyperbolic p-y models. The relationship between CPTu cone tip parameters (qt, u2 and qe) and p-y curve parameters (pu and y50) is established. Moreover, the deformation and mechanical characteristics of large diameter and super-long cast-in-place piles in the Yangtze River floodplain are analysed thoroughly. The feasibility and reasonability of the proposed p-y curve method based on CPTu test data are verified through numerical simulation and horizontal load field tests. A hyperbolic p-y model based on CPTu test data is applicable to sandy soils, while a Matlock p-y curve model based on CPTu test data is applicable to cohesive soils.

The present study aims to develop a theoretical model to capture the shear behaviors of solidified soils at the framework of conservation of energy. The correlation of required energy with work done by external loads in the plane shear process was systematically studied. Some laboratory experiments were conducted to evaluate the mechanical properties of lignin solidified silt. The results revealed that the total energy required for shearing the solidified soil could be divided into four components (viz., conserved deformation energy, cementation breakage energy, rolling energy, and sliding energy). This total energy was equal to the work done by the applied loads without considering energy dissipation. Lignin solidified silt possessed higher strength and better ductility as compared to the compacted natural silt, which was mainly attributed to the presence of particle cementation. The stress-strain characteristics of this solidified silt changed from ‘harden’ to ‘soften’ and finally returned back to ‘harden’ with an increase in normal stress. The proposed theoretical model accurately described the shear behaviors of lignin solidified silt at a wide range of normal stress, resulting in a good agreement between the predicted curves and the measured ones. The prediction performance of ‘harden’ curves was slightly superior to that of ‘harden’ curves. Additional research is recommended to incorporate the issues of particle morphology and cementation breakage process into the proposed shear model.

Numerical investigations of the whole installation process of giant deep-buried circular open (GDCO) caissons in undrained clay were conducted using 3D large deformation finite-element (LDFE) method performed by the Coupled Eulerian-Lagrangian (CEL) approach. This study was focused on the installation mechanism and soil deformation characteristics of GDCO caissons. A kinematic and continuous numerical technique based on the CEL approach accounting for the synchronous coupling between the penetration and excavation was first introduced to simulate real installation process of GDCO caissons. An advanced user-defined hypoplastic (HP) constitutive model was applied to match the clay behaviors realistically. The measured values of penetration resistance and ground surface settlement were compiled from centrifuge tests available to validate the proposed numerical technique and show the superiorities of HP model. The plastic zone, deformed soil flow, stress distribution and penetration resistance developed in clay were effectively captured to investigate the installation mechanism. Furthermore, the soil deformation including ground surface settlement and radial displacement around the caisson were examined. The simplified semi-empirical equations were then proposed to predict the ground surface settlement pattern and maximum value.