Long-term cyclic loading from wind, waves, and currents alters the mechanical properties of marine soils, threatening the stability of offshore engineering structures; therefore, investigating the dynamic response of coastal silty clay under cyclic loading is crucial for the safety of marine structures. In this study, coastal silty clay was subjected to more than 300 dynamic triaxial tests to systematically examine the effects of different drainage conditions, confining pressure levels, cycle numbers, loading frequency, bias consolidation ratio (K), cyclic stress ratio (CSR), and soil density on its dynamic response. The evolution laws of cumulative plastic strain, pore water pressure, dynamic elastic modulus (Ed), and residual strength were comprehensively analyzed under multiple loading conditions. The results revealed notable differences in soil dynamic response under drained and undrained conditions. The cumulative plastic strain followed a ‘stable growth’ mode when CSR was below a critical value, transitioning to ‘destructive growth’ when it exceeded this value. Notably, the critical CSR of soil exhibiting a post-consolidation strength of less than 60 kPa was 0.6–0.8, whereas that of soil exhibiting an initial strength of more than 60 kPa exceeded 0.8 after bias consolidation. Under undrained conditions, the residual strength of soil decreased to 24

Photovoltaic power generation, as an emerging method of energy utilization, has demonstrated unique advantages in resource development. Offshore photovoltaic systems, characterized by their high-power generation capacity, low land occupation, and ease of integration with other industries, have become a highly regarded energy choice. These systems frequently make use of fixed pile foundations, and the crucial aspect of their design lies in the horizontal bearing capacity of these foundations. This study investigates the horizontal load-bearing properties of steel pipe piles used in offshore photovoltaic systems by conducting field tests with single-pile horizontal static loads and performing numerical analysis. The analysis findings indicate a notable increase in the horizontal movement of the pile structure as the load is progressively augmented. The site is topped with a heavy deposit of muddy soil. During the unloading stage, the rebound deformation is incomplete, resulting in significant residual deformation of the pile body after unloading. The simulation results from the numerical analysis closely match the measured values, confirming the accuracy of the mode. Furthermore, the impact of factors such as pile diameter and rock penetration depth on the horizontal bearing capacity of the test piles is analyzed. Under the same horizontal load, increasing the pile diameter and rock penetration depth can effectively reduce the displacement of the single-pile foundation. However, when the rock penetration depth exceeds four times the pile diameter, the resistance of the deep rock mass cannot be fully utilized, and the increase in the horizontal bearing capacity of the pile body slows down. The study's conclusions furnish a comprehensive reference point for evaluating the horizontal load-bearing capabilities of offshore photovoltaic pile foundations, enabling further advancements in design strategies and optimization.

The overconsolidation ratio considerably affects the physical and mechanical properties of soil as well as the interaction between structures and soil. Scale and consolidation time limitations render the preparation of overconsolidated soil for small-scale model tests difficult. Therefore, studying structure-soil interactions, especially the vertical bearing capacity of pile foundations in overconsolidated soil becomes challenging. Given the importance of reliable overconsolidated soil in physical model tests for studying soil-structure interactions, this study, based on the fundamental of the overconsolidation ratio, established a reliable method for preparing overconsolidated soil by altering centrifuge acceleration. Piezocone penetration tests were conducted to validate the accuracy of this method. Furthermore, vertical bearing capacity of pile foundations was evaluated in various overconsolidated soils. The vertical ultimate bearing capacity of pile foundations, cone penetration resistance, pore water pressure, and sleeve friction resistance were obtained in soils with various overconsolidation ratios. Based on the results of both tests, a formula was developed to calculate the vertical ultimate bearing capacity of pile foundations, taking into account the overconsolidation ratio of soil. This proposed method for evaluating vertical bearing capacity of pile foundations in overconsolidated soil can also be applied to study interactions between other marine structures and soil. The results of the study can provide technical support for designing the foundations of offshore oil and gas facilities, wind power, and other structures.

In order to improve the evaluation ability of bearing capacity of offshore large-diameter monopile, the initial high strain detection and repeated high strain detection with an interval of 10-84 days were carried out on 6 large-diameter monopiles with a diameter of 7.2m-7.4m in the offshore wind field dominated by cohesive soil layer. The results show that the time-dependent increase of tip resistance, pile side resistance and total resistance of large-diameter monopiles in the same offshore wind farm has great discreteness, and the axial force increment of pile has a consistent change trend. This paper puts forward the prediction interval of 95% guarantee rate of bearing capacity increment of offshore large-diameter single pile based on depth, which provides a basis for the design of large-diameter monopile.

为探讨桩端阻力和桩侧摩阻力对静压桩贯入机制的影响以及贯入过程中的荷载传递规律,通过在桩身埋设光纤光栅(FBG)传感器,对足尺闭口PHC管桩静力压入层状土地基的沉桩过程进行监测.试验结果表明:光纤光栅传感器的稳定性好、抗干扰性强,对桩身应力的监测效果较好;压桩力的变化规律基本反映了土层的分布情况,桩端土层的软硬程度制约着压桩力的变化;桩端由黏土层进入到粉土层时,压桩力平均增加2.5倍,桩侧摩阻力平均增加1.7倍且占沉桩阻力的44.99％;桩端阻力受桩端土性的影响较大,粉土层的桩端阻力约为黏土层的2倍且占沉桩阻力的59.84％;桩端由硬土层进入软土层时,需考虑沉桩速度和桩身表面切向力对桩侧摩阻力的影响;在沉桩过程中,随着贯入深度的增加,同一标高处桩侧水平应力逐渐释放,桩侧摩阻力不断减小且其退化现象明显.

为研究静压管桩贯入过程中桩土界面总径向土压力的变化规律,选取山东东营某工地进行现场足尺试验,得到贯入过程中桩侧总径向土压力随贯入深度的变化规律;然后,结合土的极限平衡理论,考虑贯入过程中粉土中孔隙水的消散和桩土界面循环剪切引起的桩土界面土压力的退化,建立沿深度方向桩土界面总径向土压力的极限平衡理论修正公式,探讨贯入过程中桩土界面总径向土压力的分布特征.研究结果表明:桩土界面总径向土压力与土层性质密切相关;在同一贯入深度不同桩身位置处(H/D)桩土界面总径向土压力存在退化现象,并且粉土中的退化幅度比粉质黏土中的退化幅度大,退化幅度最大相差14.22％;在饱和粉土中采用极限平衡理论计算桩土界面总径向土压力时,应考虑孔隙水的消散特性,超孔压消散系数为0.7～0.8;不同土层桩土界面总径向土压力退化幅度与H/D有关,两者呈幂函数关系,粉土和粉质黏土中剪切退化系数分别为0.19和0.12;采用极限平衡理论计算沉桩过程中不同桩身位置处(H/D)桩土界面总径向土压力时,需考虑桩长效应即剪切退化效应;所提出的考虑孔隙水消散和剪切退化修正的极限平衡理论公式,理论计算结果与实测结果吻合较好.

饱和黏性土地基中桩土界面的受力特性会对静压桩沉桩效应及长期承载力的发挥产生重要影响.通过黏性土地基中桩身表面嵌入式安装硅压阻式传感器的静压桩模型试验,分别对开口和闭口静压桩沉桩和加载过程的桩土界面超静孔隙水压力和有效径向应力进行研究.结果 表明:在沉桩过程中,桩土界面超静孔隙水压力及有效径向应力随入土深度逐渐增加,沉桩结束时增量幅值随着h/D(h为传感器距桩端距离,D为桩径)增大而减小,同一h/D位置处闭口桩的增量幅值大于开口桩的;同一入土深度处,桩身不同h/D位置处桩土界面有效径向应力存在退化现象,且随着h/D和入土深度的增加退化越明显.在加载过程中,h/D=1和h/D=5位置处桩土界面超静孔隙水压力相比沉桩结束时减小,且随着h/D增大,减小幅度也增大;同一h/D位置处,桩土界面有效径向应力增量幅值随着桩顶施加荷载值增加而增大.沉桩过程和加载过程桩土界面超静孔隙水压力和有效径向应力均随着h/D的增加而减小,不同h/D位置处桩土间的有效径向应力变化是沉桩和加载过程桩土界面受力机理不同的重要原因.

Prestressed high-strength concrete (PHC) pipe pile with static press-in method is widely used in recent years. The earth pressure at the pile-soil interface caused by the process of pile jacking has an important influence on the jacked pile construction and even the bearing characteristics. Based on a construction project in Dongying, the change law of earth pressure at pile-soil interface caused by the penetration of PHC pipe pile is analyzed by monitoring the earth pressure at pile-soil interface during pile jacking, and the evolution characteristics of earth pressure at pile-soil interface in viscous soil foundation are revealed. The results show that the earth pressure at the pile-soil interface at different positions (h/B) caused by the penetration of PHC pipe pile gradually increases with time. In the process of pile jacking, the influence of pile jacking on the earth pressure at the pile-soil interface on the pile body and part that exceeds the relative distance of effective pile end (h/B) is weak. In the process of pile jacking, the earth pressure at the pile-soil interface is greatly affected by the relative height of the pile end (h/B), so it is necessary to consider the effect of the pile length to calculate the earth pressure at the pile-soil interface. The phenomenon of "lateral pressure degradation" exists with the increase of h/B in the earth pressure at the pile-soil interface. The research results have certain engineering guiding significance for construction and bearing capacity determination of jacked pile in viscous soil foundation.

为研究开挖卸荷过程中淤泥质土体侧移对既有嵌岩桩基影响,在淤泥质土体开挖前预设多个测斜点,长时间监测开挖卸荷过程中与开挖面不同距离下各深度的变形数据,根据淤泥土体位移变化规律结合郎肯土压力理论建立计算模型,利用该模型进行桩基嵌岩深度范围的确定及桩身优化设计.研究结果表明:(1)基坑开挖卸荷时在开挖面下2 m处土体位移达到最大,最大影响深度约为4 m;(2)基坑开挖卸荷2天内土体变化较明显,2 d后土体位移趋于稳定;(3)淤泥质土层嵌岩桩嵌固端具体深度并不是定值,应根据桩顶土体侧移力及桩身的长度反推确定.

通过在桩身表面安装微型硅压阻式压力传感器测得桩土界面孔压增量和径向应力,研究静压桩桩土界面的受力特性.针对双壁开口和闭口模型管桩,采用桩身开孔嵌入套筒式安装方法,通过全方面监测静压沉桩、超孔压消散及加载阶段受力特性,进行了开口和闭口静压桩贯入及加载全过程的受力特性室内模型对比试验.试验结果表明:同一入土深度处,开口和闭口静压桩桩土界面总径向应力均随着h/L(h为传感器距离桩端的高度;L为桩长)的增加而越小;不同桩端形式下超孔压消散期在不同h/L位置处沉桩阶段与沉桩结束后的有效径向应力之比均在0.6±0.1;桩土界面总径向应力的变化值在桩端位移达到1.0 mm左右时发生突变,加载结束后,同一深度处桩土界面总径向应力变化值随着h/L的增加而减小.该研究结果对于静压桩施工和设计具有工程参考价值.

To extensively study the applicability of Fiber Bragg grating (FBGs) sensing technology in the penetration test of jacked piles, a large-scale model test system is used to conduct the penetration test of jacked piles. This paper uses a fiber grating strain sensor for data testing, while using a spoke type pressure sensor and a fiber grating pressure sensor as control groups. By installing a full -section dynamic spoke pressure sensor and a fiber grating pressure sensor at the end and top of the pile, respectively, the difference between the penetration processes of the jacked piles based on the two sensing technologies is compared and analyzed. Simultaneously, the pile body strain data is collected based on the FBG sensing technology, and the penetration characteristics of the side frictional resistance, the axial force, and the unit side frictional resistance of the pile arc studied. Results show that the FBG sensing technology has superior performance in the penetration test of static pressure piles, can accurately reflect the penetration characteristics of jacked piles, and can clearly reflect the pile jacking-in process with the increase of pile driving length. Furthermore, it is found that the driving pressure, the end resistance, the axial force, and the unit side frictional resistance of the pile body have the characteristics of a steady-state penetration. Therefore, this study presents a great reference for the model test and the engineering design of static pressure piles.

In order to explore the variation law of soil particle displacement and pile force around piles during penetration process, the DEM (Discrete Element Method) model is used to test the penetration of pile foundation in layered soft soil foundation. The variation law of pile penetration force, radial pressure at pile-soil interface, friction resistance at pile side, displacement field and force field between particles during penetration process is analyzed. Research shows: (1) The penetration force increases with the increase of penetration depth and pile diameter. The increase of pile diameter is beneficial to overcome the influence of unfavorable strata. (2) At the same penetration depth, with the continuous penetration of the pile body, the radial pressure gradually decreases, showing a significant degradation phenomenon. The reason for the degradation of lateral friction is essentially the degradation of the radial pressure. (3) The distribution of contact force chain in different soil layers is similar, but the range of action is different. The contact force in silt layer is obviously larger than that in silty clay layer. The compressive stress of the soil at the end of the pile transfers radially with tensile stress. With the increase of pile diameter, the compressive stress and tensile stress in soil layer are gradually increasing, and the influence range of compressive stress and tensile stress is also gradually increasing. (4) The displacement of the soil below the pile tip is triangular, and the soil at the pile tip is squeezed around under the action of the pile tip. The influence range of particle displacement in each soil layer is different, and the influence range of particle displacement in silt layer is obviously smaller than that in silty clay layer.

In order to have a better understanding of the real contact area of granular materials, the white light interference method is applied to explore the real surface morphology of clay soils under high stress. Analysis of the surface profile indicates that there exists a support point height z0 with the highest distribution frequency. A concept of a real contact region (from z0 to z0 + d90; d90 represents the particle size corresponding to 90% of the volume fraction) is proposed by combining a surface profile with the particle size distribution of clay soil. It was found that under the compressive stress of 106 MPa–529 MPa, the actual contact area ratio of clay soil varies between 0.375 and 0.431. This demonstrates an increasing trend with the rise of stress. On the contrary, the apparent porosity decreases with an increasing stress, varying between 0.554 and 0.525. In addition, as the compressive stress increases, the cumulative frequency of apparent profile height (from z0 − d90 to z0 + d90) has a concentrated tendency with a limited value of 0.9.

Prestressed high-strength concrete (PHC) pipe pile with the static press-in method has been widely used in recent years. The generation and dissipation of excess pore water pressure at the pile–soil interface during pile jacking have an important influence on the pile’s mechanical characteristics and bearing capacity. In addition, this can cause uncontrolled concrete damage. Monitoring the change in excess pore water pressure at the pile–soil interface during pile jacking is a plan that many researchers hope to implement. In this paper, field tests of two full-footjacked piles were carried out in a viscous soil foundation, the laws of generation and dissipation of excess pore water pressure at the pile–soil interface during pile jacking were monitored in real time, and the laws of variation in excess pore water pressure at the pile–soil interface with the burial depth and time were analyzed. As can be seen from the test results, the excess pore water pressure at the pile–soil interface increased to the peak and then began to decline, but the excess pore water pressure after the decline was still relatively large. Test pile S1 decreased from 201.4 to 86.3 kPa, while test pile S2 decreased from 374.1 to 114.3 kPa after pile jacking. The excess pore water pressure at the pile–soil interface rose first at the initial stage of consolidation and dissipated only after the hydraulic gradient between the pile–soil interface and the soil surrounding the pile disappeared. The dissipation degree of excess pore water pressure reached about 75–85%. The excess pore water pressure at the pile–soil interface increased with the increase in buried depth and finally tended to stabilize.

When the open-ended pile penetrates the soil layer, the resistance generated by the soil plug cannot be ignored. A pile with a full-size pressure sensor installed at pile tip can detect resistance more accurately than a microsensor when the pile penetrates into the soil. In this paper, the pile installed full-size pressure sensor was used for penetration test and the relationship between formation parameters and pile tip force is obtained. Using the solution of the Kelvin problem in infinite space and the plane stress distribution function, the analytical solution of the bearing capacity of the soil plug is derived under the condition that the displacements of the bottom of the pile and the soil plug are consistent. The results show that the ultimate stress of the soil plug is closely related to the pile diameter and pipe thickness. The bearing capacity of the soil plug is closely related to the properties of the soil layer. The analytical solution of the bearing capacity of the soil plug has a linear relationship with the formation parameters SPT and CPT. The analytical solution of the ultimate bearing capacity of the soil plug has been verified by field test data and has a good match with the geometric dimensions of the pile tip and the formation parameters.

为了揭示黏性土受压时的真实接触面积及细观物理参数的变化规律,利用白光干涉技术测量黏性土在高压应力作用下的真实表面轮廓,对不同压应力作用下表面轮廓点云数据进行分析,并通过Logistic函数推导极限压缩状态下的极限值.结果表明:压缩后的黏性土真实表面轮廓呈偏态分布,存在黏性土颗粒的支撑中心及颗粒压缩接触域;在106～529 MPa的压应力作用下,黏性土实际接触面积占截面面积的比例为0.375～0.431,表观孔隙率为52.5％ ～55.4％,随着压应力增大,孔隙范围有集中趋势且存在极限值;在支撑中心上、下1倍粒径范围内,表面轮廓分布存在极限渐进值.

为了更进一步研究黏性土地基上静压桩贯入及承载特性,通过在桩身安装光纤光栅(FBG)以及在桩顶安装温度自补偿传感器,对双壁开口模型管桩的沉桩和单桩承载特性进行研究.结果表明:压桩力、桩端阻力、桩侧摩阻力随着贯入深度的增加而增大,且桩端阻力为沉桩过程的主要阻力,沉桩结束时占比为66.7％.相比于外管,内管桩侧摩阻力和桩身轴力均较小.荷载-位移曲线为陡降型,最大沉降为47.72 mm,极限荷载为6.3 kN,是沉桩终压力的2.48倍.试桩内管桩身轴力在土塞高度范围内以及外管桩身轴力在桩长范围内随着桩身埋深逐渐减小.内管桩侧摩阻力仅在土塞高度的范围内随着深度逐渐增加;外管桩侧摩阻力在荷载小于7.0 kN时,随着深度呈先增大后减小的趋势,当桩顶荷载达到7.0 kN时,随着深度逐渐增大.在各级荷载作用下桩端阻力占桩顶荷载的比例为53.6％～65.1％,表现出了较好的端承桩性状.研究结果对双壁开口管桩内外管贯入及承载特性的研究具有重要的意义.

In order to explore the relationship between the critical bearing capacity and settlement of closed pile tip pierced into the soil, based on the Boussinesq solution and the Kelvin solution, the analytical solution between the critical bearing capacity and the critical settlement of the closed pile tip is derived by combining the stress distribution function. The analytical solution of critical bearing capacity and settlement of pile tip is verified by field test of static pressure pile penetrating into layered soil with a full-section pressure sensor installed at pile tip. The results show that during the penetration process, the bearing capacity increase stage of the pile tip is divided into linear steepening section and nonlinear slow increasing section. The soil in the linear steep increase section behaves as an elastic state. The bearing capacity of the pile tip before the punctured soil layer is linear with the settlement, and the final value of the linear steep increase section is the elastic limit value and the critical bearing capacity of the piercing pile tip. When the residual pile tip force is not considered, the critical settlement of the pile tip is between 0.095-0.119d; when considering the residual pile tip force, the critical settlement is between 0.091-0.105d. In particular, when the Poisson's ratio is 0.5, the analytical solution of the semi-infinite space is equivalent to the analytical solution of the infinite space.

Based on an analysis of the development of economic decision support systems, agents are applied to construct intelligent economic decision support systems. This paper proposes a task-oriented agent design concept and designs multiple types of agents to complete the decision-making tasks with the task as the core. The structure of multi-agent based systems is provided, and the concrete realization structure of different types of agents in the system is also provided. Additionally, this study discusses the operational mechanism of the whole system and the cooperation between multiple agents in the system. Finally, these functions are implemented through a combination of VC++ 6.0, multi-threading technology and the expert system tool CLIPS. The economic decision support system combines complex system theory, decision theory, information collection, knowledge discovery technology, economic decision making and simulation technology. It can aid users in making decisions by using communication and cooperation between multiple agents.

To monitor the pile-sinking process of high-strength prestressed concrete (PHC) pipe piles more accurately and study the variation laws of pile-pushing force, pile axial force, pile end resistance, and pile side friction resistance with penetration depth, in this study, a low-temperature sensitive fiber Bragg grating (FBG) sensor was arranged on the pile body and a soil pressure sensor was installed at the pile end. The penetration characteristics of two closed (P1, P2) and one open (P3) full-length PHC pipe piles were tested in the field. The test results showed that the pile driving force increased with increase of penetration depth of the pile body, and the pile-pushing force of P3 was less than the pile-pushing force of P1 or P2, about 33.9%-79.7% of P1 or P2. The axial force of the pile body decreased gradually with increase of penetration depth. The axial force of the pile body of P3 was less than the axial force of the pile body of P1 or P2, and the end of the pile had a value of about 59.16%-67.75% of P1 or P2. The pile end resistance was closely related to the soil layer distribution and the characteristics of the soil layer. When the pile end resistance was harder, the soil layer changes had a greater impact on P1 and P2. As the penetration depth increased, the degradation of the lateral frictional resistance of the pile was more obvious. The test results have great significance for the application of PHC pipe piles in road engineering.