Sedimentary stylolite networks and connectivity in limestone: Large-scale field observations and implications for structure evolution

Stylolites are rough surfaces, formed by localized rock dissolution, and prevalent in carbonates and other sedimentary rocks. Their impact on porosity and permeability, and capacity to accommodate compactive strain, are well documented. This paper presents a meso-scale field study on sedimentary stylolites in carbonates, characterizing large-scale distributions of stylolites, including measurements conducted on longer than kilometer-long stylolites. Our field study suggests that on large scales connections between stylolites become important. Since connectivity, and also lack of connectivity, are expected to play a significant role in strain accommodation and hydraulic rock properties, we suggest that large-scale analysis may require a new characterization scheme for “stylolite populations”, based on their connectivity. We therefore divide sedimentary stylolite populations into three end-member types, which are correlated with the three possibilities for percolation of such systems: isolated stylolites (with zero percolation/connectivity), long-parallel stylolites (with 2-dimensional percolation/connectivity), and interconnected stylolite networks (with 3-dimensional percolation/connectivity). New statistical parameters and measures are devised and used to quantitatively characterize the different population types. Schematic mechanistic models are then offered to explain the evolution of the three end-member connectivity-classes. In addition we discuss the effect on fluid flow of the different population types.     

Assessment of soil–pile–structure interaction influencing seismic response of mid-rise buildings sitting on floating pile foundations

The role of the seismic soil–pile–structure interaction (SSPSI) is usually considered beneficial to the structural system under seismic loading since it lengthens the lateral fundamental period and leads to higher damping of the system in comparison with the fixed-base assumption. Lessons learned from recent earthquakes show that fixed-base assumption could be misleading, and neglecting the influence of SSPSI could lead to unsafe design particularly for structures founded on soft soils. In this study, in order to better understand the SSPSI phenomena, a series of shaking table tests have been conducted for three different cases, namely: (i) fixed-base structure representing the situation excluding the soil–structure interaction; (ii) structure supported by shallow foundation on soft soil; and (iii) structure supported by floating (frictional) pile foundation in soft soil. A laminar soil container has been designed and constructed to simulate the free field soil response by minimising boundary effects during shaking table tests. In addition, a fully nonlinear three dimensional numerical model employing FLAC3D has been adopted to perform time-history analysis on the mentioned three cases. The numerical model adopts hysteretic damping algorithm representing the variation of the shear modulus and damping ratio of the soil with the cyclic shear strain capturing the energy absorbing characteristics of the soil. Results are presented in terms of the structural response parameters most significant for the damage such as foundation rocking, base shear, floor deformation, and inter-storey drifts. Comparison of the numerical predictions and the experimental data shows a good agreement confirming the reliability of the numerical model. Both experimental and numerical results indicate that soil–structure interaction amplifies the lateral deflections and inter-storey drifts of the structures supported by floating pile foundations in comparison to the fixed base structures. However, the floating pile foundations contribute to the reduction in the lateral displacements in comparison to the shallow foundation case, due to the reduced rocking components.     

Slip line theory applied to a retaining wall–unsaturated soil interaction problem

An extension of slip line theory to unsaturated soils is presented and applied to the problem of a rigid retaining wall rotating about its toe into unsaturated soils. Suction is introduced using the effective stress concept. Soil–wall interface friction is defined carefully. The influence of suction on limiting passive earth pressures is analysed for two soils under steady state evaporation and infiltration. Suction increases the limiting passive stress at the soil–wall interface, with a dependence on the steady state flow type. The displacement of the retained soil is studied assuming the wall undergoes a rotation increment. The results show a clear difference in the displacement for evaporation and infiltration.     

Semi-analytical solution to one-dimensional consolidation for viscoelastic unsaturated soils

This paper presents a semi-analytical solution to one-dimensional consolidation of viscoelastic unsaturated soils with a finite thickness under oedometric conditions and subjected to a sudden loading. The solution is obtained by using Lee’s correspondence principle based on the semi-analytical solution to one-dimensional consolidation of elastic unsaturated soils. The boundary contains the top surface permeable to water and air and the bottom impermeable to water and air. A typical example is given to show the evolution of excess pore-air and pore-water pressures as well as the total degree of consolidation of the soil layer with time for different ratios of air–water permeability coefficient, elastic modulus and viscoelastic coefficient. The one-dimensional consolidation behavior of viscoelastic unsaturated soil is discussed according to the semi-analytical solution. These results contribute to a better understanding of the consolidation behavior of viscoelastic unsaturated soils.     

Analytical solutions for nonlinear consolidation of soft soil around a shield tunnel with idealized sealing linings

This paper presents the analytical solutions for nonlinear consolidation of soft soil around a shield tunnel with idealized sealing linings. By introducing the empirical relation between permeability and compressibility, along with the conformal transformation, the governing equations of nonlinear consolidation are established, and the corresponding analytical solutions are derived. Then, the Terzaghi consolidation solutions are derived from the degenerate governing equation of nonlinear consolidation. Through the predictions of different consolidation theories in both completely permeable and impermeable lining conditions, the influences of a tunnel acting as a drain and impacting the dissipation of pore pressure, degree of consolidation, long-term ground settlements and ground settlement rates are investigated. During the early stages of consolidation, the case studies reveal that the predictions made by this study strongly agree with the field data when a completely permeable lining is applied. This study confirms that a tunnel acting as a drain can accelerate the consolidation of soil and enlarge soil deformation due to consolidation. During long term consolidation, a notable nonlinearity of the soil consolidation is exhibited by a small and gradually decreasing settlement rate, showing agreement with the tendency of field data from the impermeable conditions.     

Assessment of the dynamic behaviour of saturated soil subjected to cyclic loading from offshore monopile wind turbine foundations

The fatigue life of offshore wind turbines strongly depends on the dynamic behaviour of the structures including the underlying soil. To diminish dynamic amplification and avoid resonance, the eigenfrequency related to the lowest eigenmode of the wind turbine should not coalesce with excitation frequencies related to strong wind, wave and ice loading. Typically, lateral response of monopile foundations is analysed using a beam on a nonlinear Winkler foundation model with soil–pile interaction recommended by the design regulations. However, as it will be shown in this paper, the guideline approaches consequently underestimate the eigenfrequency compared to full-scale measurements. This discrepancy leads the authors to investigate the influence of pore water pressure by utilising a numerical approach and consider the soil medium as a two-phase system consisting of a solid skeleton and a single pore fluid. In the paper, free vibration tests are analysed to evaluate the eigenfrequencies of offshore monopile wind turbine foundations. Since the stiffness of foundation and subsoil strongly affects the modal parameters, the stiffness of saturated soil due to pore water flow generated by cyclic motion of monopiles is investigated using the concept of a Kelvin model. It is found that the permeability of the subsoil has strong influence on the stiffness of the wind turbine that may to some extent explain deviations between experimental and computational eigenfrequencies.     

CORS系统在GPSC级控制网测量中的应用

简要介绍了CORS系统的发展情况,分析了GPS C级控制网测量的精度,就GPS网的布设、基线解算、GPS网平差及检核进行有益的探讨,旨在发挥CORS的优势,解决GPS控制网测量中控制点缺乏的问题,提高CORS的应用水平。     

松嫩平原耕层土壤固碳潜力估算

提高土壤碳收集能力对减缓全球温室效应具有重要意义。利用松嫩平原南部第二次土壤普查及多目标区域地球化学调查获取的两期表层土壤有机碳数据,根据近20年来各土壤类型不同土地利用方式土壤有机碳量变化趋势,估算了松嫩平原南部各土壤类型、各用地方式下土壤碳源、汇潜力。由估算得出,如果目前的土地利用方式、气候条件、耕作方式、种植技术不变,松嫩平原耕地土壤0~20 cm土层的固碳潜力为-1.229Tg碳,各土壤类型的林地土壤固碳潜力绝大多数为正值,说明林业用地为碳汇区,固碳潜力合计为3.169Tg碳,而天然牧草地绝大多数的固碳潜力为负值,固碳潜力合计为-2.235Tg碳,为碳源区,本次研究估算得出,松嫩平原总体的固碳潜力为-0.917Tg碳。     

桩基优化设计经济效益分析

分析岩土工程勘察报告中所揭示的地基土层特性,根据所掌握的大量桩基工程检测试验数据、沉降观测实测数据,对桩周（端）地基土的受荷性能以及基桩工作性状进行研究,通过静载荷试验的实际桩基承载能力,分析推导出优化地基土桩基设计参数。据此优化带来了一定的经济效益。     

基于试验的模拟月壤表层取样理论修正及其应用

月球探测对于我国各方面综合实力的提升均具有巨大的推动作用。当前我国各研发机构对月球采样的研发重点集中于采样机具的设计制造上,对采样机具和月壤之间相互作用却研究较少。与地球土壤相比,月壤的形成环境与条件完全不同,从而造就了其较为特殊的物理力学性质。在利用与真实月壤类似的模拟月壤进行的薄壁圆筒贯入试验中,发现存在月壤滞留和月壤附壁现象,从而分析得出在采样机具表面与月壤相互作用的理论分析中,除了传统的摩擦力理论外,还可通过最大抗剪强度进行分析。通过对试验现象和数据对比摩擦力理论和最大抗剪强度理论发现,最大抗剪强度理论更加符合实际情况。故将最大抗剪强度理论引入已有的月球螺旋钻进采样的理论模型中,通过计算得出基于最大抗剪强度理论计算的螺旋临界转速低于基于摩擦力理论计算的临界转速,在一定程度上能够降低采样机具的能耗。