The distinct particle breakage characteristics of calcareous sand can induce extra settlement in calcareous sand foundations, posing a significant challenge to the safety of island and reef engineering. To explore the particle breakage, settlement characteristics and internal stress variations of calcareous sand foundations, the laboratory loading tests for calcareous sand foundations with different particle gradations were conducted. Particle Image Velocimetry (PIV) technology and tactile pressure sensor systems were also utilized. The study reveals that the tested calcareous sand foundations have differential settlements subjected to external loading, which has a strong relationship with the particle breakage. It is found that the nonuniform internal stresses between the sand particles can induce different degrees of the particle breakage, which in turn changes internal stresses and redistribution of particle positions in calcareous sands, and further causes the uneven settlement of the foundation. The degree of uneven settlement in calcareous sand foundations increases with an increase of external load and decreases with an increase of the coefficient of uniformity Cu for calcareous sands. During creep, the vertical and lateral stresses on the inter-particle contacts within the calcareous sand foundation exhibit an overall trend of decrease in weak forces and increase in strong forces. This continuous increase in strong forces results in a growth of creep deformation in calcareous sand foundation, while the degree of differential settlement in the foundation decreases with the progression of creep.

Taking a caisson foundation engineering of a railway across-river bridge as the case, the technical characteristics and key challenges of over-deep inclined caisson were described firstly. Subsequently, the main controlling factors of the uneven settlement were analyzed. In view of the difficulty in obtaining the parameters of disturbed grouting soil, as well as the large adjustment of subsequent construction loads, an uneven settlement method based on over-deep underwater lateral pressure test and high-pressure consolidation test was proposed. The proposed method was simulated by finite element method to analyze the variations of total settlement, differential settlement and inclined attitude of caisson foundation under different loading stages. The results showed that the difference in the thickness of the disturbed layer was the dominant factor of uneven settlement, finally controlling the inclination shape. Grouting reinforcement was conductive to improving the settlement of caisson foundation. The maximum total settlement, differential settlement and offset after reinforcement were reduced to 249.53 mm, 19.54 mm and 29.20 mm, respectively. The deformation mainly occurred in the loading stage before the platform construction, accounting for about 60 %. If it is considered to level the top surface, adjust the elevation and load center during the construction of platform, the incremental settlement, the north-south differential settlement and the offset of top surface corresponded to 94.26 mm, 10.31 mm and 17.52 mm, respectively. Finally, the reliability of above method was fully verified by comparing the measured data with calculated value. The results will provide certain ideas and methods for relevant engineering problems. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Uneven settlement phenomenon is very easy to occur in the sandy pulverized ground stratum, the underground pipe corridor longitudinal and transverse stiffness difference is obvious, so that it is easy to crack and deformation due to uneven settlement in this type of stratum. This paper carries out research on uneven settlement and cracking and deformation of Qihe tube corridor, analyzes the reasons leading to uneven settlement and the factors affecting the deformation and cracking of the tube corridor, and provides guidance for foundation treatment and tube corridor repair and mixing and reinforcement. It was found that the concrete structure of the corridor itself had exposed reinforcement, pockmarks and holes, and that cracks on the structure of the corridor sprouted and expanded from these defects. Defects and damages on the concrete structure of the pipeline corridor are contributing factors to the deformation and cracking of the members, and the uneven settlement of the foundation is the main initiating factor for the cracking and deformation. The analysis of the numerical simulation results of similar underground pipeline corridors is carried out, and it is found that the simulation results are consistent with the deformation characteristics of the Qihe pipeline corridor, which further supports the conclusions of this paper. The main stratigraphic factors contributing to the inhomogeneous settlement were found to be the water-rich and loose bodies in the lower part of the strata, as revealed by the physical means and the experimental verification boreholes. Localized hydraulic effects such as pumping further accelerate the uneven settlement of the foundation.