Foundation pile test by self-balanced method of rock-socketed piles and friction piles in multilayer soil geological structure

结合检测工况对测试数据的影响,对自平衡“精确转换法”进行改进,提出摩擦桩位移协调转换法和嵌岩桩的荷载协调转换法,实际应用结果说明两种转换方法合理。所得测试结果表明湄公河大桥桩基承载力符合设计要求;分析湄公河大桥试桩的侧摩阻力和端承力分布,嵌岩桩和摩擦桩纵向承载均以侧阻力为主。     

Plastic upper bound theory reliability analysis of coal gangue hills

We established the plasticity limit analysis reliability limit state equation and the reliability calculating formula for gangue hills using the JC method. This work was based on the plasticity mechanics limit analysis upper bound theory and traditional slice methods. A reliability index of gangue hill stability was derived using this equation. It was found that the safety coefficient of gangue hills derived by the limit state equation risks failure if the variability of cohesion and internal friction angle are not considered. When the variability of the strength parameters rises, the reliability theory more consistently projects practicality than the limit state equation for gangue hill stability assessment.     

Field Comparative Experimental Study on Bearing Capacity of Both Bored Pile with Branches and Plates and Column Bored Pile at the Same Site

Compared with column bored pile,the bored pile with branches and plates is a new type of piles with higher bearing capacity and lower settlement.Field comparative tests related to ultimate bearing capacity of both the bored piles with branches and plates and column bored piles at the same site in Huzhou city of province Zhejiang in China were studied through self-balanced method under static pressure.The results testify that,compared with column bored pile under the same geological conditions,the bored pile with branches and plates can obtain better economic benefit such as: increasing ultimate compressive bearing capacity and ultimate extraction bearing capacity used per cubic meter concrete over 75.3%and 118.9%respectively,while dropping consumption of reinforced concrete upwards of 41.9%and 44.1% respectively,reducing settlement and pile length under the same loading.The tests will present an objective reference to the new type of piles in both theoretic study and application to analogous engineering.     

水平荷载作用下斜坡刚性桩非线性分析

在综合分析现有水平荷载作用下桩基分析方法的基础上,建立了考虑桩侧土体受力状态的斜坡刚性桩力学模型;根据极限平衡原理,建立横向荷载作用下斜坡刚性桩弯矩和应力平衡方程;引入考虑斜坡影响的p-y曲线方法,提出了综合考虑桩侧土体极限承载力与水平抗力系数沿深度呈线性增加的侧向极限承载力与土体抗力承载力系数计算方法,同时,将该方法应用于计算实例,通过与已有有限元和理论计算方法对比分析,计算结果验证了本文方法的合理性与可行性;并利用该方法,分析了斜坡坡角、桩土接触面系数以及地基水平抗力系数对斜坡刚性桩承载特性的影响因素。分析表明:斜坡的坡角、桩土接触面系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响明显,而桩侧土的抗力系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响不明显。     

Increase of Wave Velocity in Precast Pile along with Time and Its Analysis

Low strain dynamic testing on actual pile was conducted to investigate if the wave velocity is varied in the installed pre-cast pile.It was found that the wave velocity of the pile is raised along with time.The analysis has been carried out through with one dimension and three dimension stress wave propagation theories.Among various factors influencing the rise of wave velocity,the factor of the side soil contribution is the chief one.The soil around the pile works jointly with the pile,as if to enlarge the section size of the pile.Both the increase of wave velocity and the bearing capacity of pile are consistent.So the time effect of wave velocity can be used to study the time effect of bearing capacity of the pile and to determine the bearing capacity of piles.     

五星形桩与圆桩水平承载性能对比模型试验研究

五星形桩是一种横截面异形桩,是在圆桩的基础上向内切割5个圆弧,形成截面类似五星形的异形桩。按其截面性质分为周长最大化五星形桩F₁、周长面积比最大化五星形桩F₂两种桩型,为掌握五星形桩的水平承载性能进行了与圆桩的对比模型试验研究。试验用土为干砂,砂雨法土样制作,模型桩为预制钢筋混凝土桩,相似比为1∶8。模型试验桩包括：五星形桩F₁、五星形桩F₂、与五星形桩F₂截面周长相同的圆桩C₁、与五星形桩F₂截面面积相同的圆桩C₂。由于五星形桩水平承载性能具有方向性,试验采用理论计算中水平承载力最大的方向施加水平荷载,试验结果表明：F₁、C₁和F₂的水平极限承载力相当,但F₂的截面面积最小,仅为C₁的0.44倍;与C₂相比,F₂的水平极限承载力是其1.63倍,可见,合理截面形式的五星形桩可以提供更大的水平承载能力;五星形桩与圆桩弯矩分布规律基本一致,都在4倍直径左右（五星形桩为外接圆直径）达到最大,但五星形桩截面面积小,抗弯刚度不足,容易折断,总体水平承载性能不及截面周长相同的圆形桩,但优于截面面积相同的圆形桩。     

Discussion on Vertical Bearing Capacity of Rock-socketed Pile

Through analyzing the calculation of vertical bearing capacity of rock-socketed pile given in technical code for building pile foundations, some unreasonable issues in the code were found. At the same time, based on the contacting ways between the pile and the rock and the behaviors of force transfer acted step by step, the unreasonable issues have been proved and the issues to be improved were pointed out in this paper.     

土体抗剪强度指标变异水平对边坡稳定安全系数取值的影响

针对传统的边坡稳定极限平衡方法不能考虑土体抗剪强度指标变异性影响的问题,基于极限状态的概率分析原理,采用Monte-Carlo法对均质路堤边坡的稳定性开展了可靠度计算,讨论了稳定安全系数一定的条件下边坡失效概率随土体抗剪强度指标变异水平的变化规律,分析了安全系数与边坡可靠指标的对应关系及其随土体抗剪强度指标变异水平的变化特征。研究表明：边坡可靠度受土体抗剪强度指标变异性影响显著,呈现出随土体抗剪强度指标变异水平提高而急剧减小的趋势;为保证边坡具有相同的可靠性,安全系数的取值应与土体抗剪强度指标的变异性相适应,据此提出了基于可靠指标和土体抗剪强度指标变异水平的安全系数取值原则及其对应的三参数函数关系式。     

An Approach for Estimating the Final Ultimate-bearing Capacity of Driven Pile In Soft Clay

The prefabricated pile,driven in soft clay,can squeeze the soil laterally in a certain scope around the pile,and the void ratio is reduced significantly;consequently,the shear bearing capacity is raised.But the soil parameter,which is used to estimate the capacity of pile,is reduced according to the soil state before the pile was driven.Then,a certain difference appears when the pile is working.The calculation result usually is partial to conservative.This paper analyzes the squeezing mechanism of the pile using the theory of cylindrical cavities expansion.And a formula,which is used to estimate the increment of shear bearing capacity of soil around the pile when excess pore water pressure from pile driving distributes completely,is presented based on the unique relation between the shear bearing capacity and the density of the soil.This formula can be used to estimate the final ultimate-bearing capacity of the pile.The calculated results by the proposed formula are in good agreement with those of the site measurement.     

Influence of Pile Driving on Soil Resistance in Clay

With the increase of platform size, pipe piles with super large diameter and deep penetration are increasingly used in practice. In order to make accurate prediction of pile drivability, it is essential to evaluate the change of the soil properties under pile driving exactly, and it is the premise to predict the pile bearing capacity after pile driving. In order to learn more about the change of clay properties during pile driving, analysis on the pile driving record of 36 piles in Bohai area is conducted. According to the analysis, the soil resistance in the clay layers decreases as the depth increases, and it is very different from that in the sand layer. The FEM method is used to discuss the mechanism of this decrease. The back analysis is carried out to get more information. The results show that the clay properties are affected by the dynamic effect. The undrained shear strength of clay approximately decreases with the increase of thickness of the layer linearly. At the same time, a prediction is conducted based on results, and the result is closer to the pile driving record than that calculated by method normally used today.     

Plastic slip stability analysis of gangue granular media

This paper studies the landslide mechanism by the analysis of accumulation form, topography and geomorphology, self structure and natural river system of Weijiagou coal gangue hill. The limit state function is established based on plasticity mechanics limit analysis upper bound theorem and Bishop slices method, combining reliability theory. The safety coefficient and reliability index of Weijiagou coal gangue slope is calculated. The plasticity limit analysis upper bound theorem can consider the interior stress strain relation of soil, so the formula derivation process is stricter. It is the consideration of the variability of gangue parameters that making the evaluation result more reasonable.     

Analysis of bearing capability of CFG pile composite foundation

The CFG pile is used to consolidate the foundation in one passenger dedicated line. The field experiments including low strain dynamic testing, bearing capability of single pile and the composite foundation are done, and the bearing capability of composite foundation is calculated, too. The results show that the first and second class piles account for 93.9% and 6.1% respectively, and the bearing capability eigenvalues of single pile and composite foundation are larger than the designed values. The 3D FEM model is established to simulate the stresses of CFG pile top and inter-pile soil changing with load level, and the stress ratio between CFG pile and inter-pile soil is analyzed, too. The following results are got from the calculation results of FEM: 1) the stresses of CFG pile top and inter-pile soil increase with load level, but the increasing rate of the former is larger than the latter; 2) the stress ratio between CFG pile and inter-pile soil increases quickly when the load level is low, and it tends to convergent gradually with load increasing.     

Dynamic Response Analysis of High-rise Pile Cap-soil-structure under the Wave and Earthquake Action

Finite element software was used to simulate the internal force and deformation of high-rise pile cap-soil-structure under the wave and earthquake action. Meanwhile, wave force was calculated by using Morison equation, and the mechanical behavior of structure was simulated by inputing horizontal El-Centro wave. Then, the initial state and the state of the largest positive and negative acceleration were selected to study the structure according to the time history curve, and the displacement, bending moment, shear and axial force changes of pile foundation under wave and earthquake action were discussed, which was compared and analyzed with the structural response under the action of earthquakes solely. The result shows that the moment of front row of piles is biggest, and the force of pile bolck is the most dangerous; the axial force of the corner piles is the largest, and one of the center piles is the smallest under the action of wave and earthquake. When the wave forces and seismic forces are in the same direction, the displacement, moment, and shear force of pile bolck will be increased, on the contrary, the displacement, moment, and shear force of pile bolck will be decreased.     

Analysis of Wave Loads on the Grouping PileFoundation with Slab Merged in Water

In order to get the wave loads on pile groups with slab merged in water, an engineering approach was proposed. Three coefficients in terms of slab effect were discussed and a time -domain analysis of wave forces acting on piles was conducted. Wave diffraction from a slab was obtained by the potential theory and eigenfunction expansion method, while wave loads on piles were evaluated by Morison formula. The wave force on pile obtained by the proposed method and the numerical simulation are in good agreement, which shows a good reliability of the proposed method. The result shows that, owing to the size of slabs, there exist some differences in the changing rule of slab effect varying with the submerged depth. The resultant force decreases with the rise of incident wave number, and the changing trend of its acting point appears an inflection point at some wave number. The minimum force acting on piles lies in the meeting-wave side of the slab, while the maximum one arises at the back side or in the scope of 30 degrees between the axis of slab, which is perpendicular to the incident wave, and the back side. The presence of slab causes the deflexion and phase difference of inline force. Meanwhile, the grouping piles coefficient can be taken as 0.7.     

Diffusion Behavior of Chloride Ions in Concrete Pipe Piles

Concrete pipe piles, whose internal surface is usually closed and external one is exposed to chloride environment, are widely used in marine environment. Based on Fick second law and the boundary condition of pipe pile, the analytical solution to chloride diffusion equation was deduced with the method of separation of variables. The solution comprises two parts: a stationary solution consisting of Bessel functions, and a transient solution. This is different from the traditional analytical solution that is based on semi-infinite boundary condition. Applying this result to a typical PHC pipe pile, the diffusion of chloride concentration was analyzed. Furthermore, the effects of the ratio of outer radius and inner radius, diffusion coefficient and protective concrete cover thickness on diffusion of chloride concentration were also discussed. When the ratio of outer radius and inner radius equals 1.5, the decay rate of secondary segment of transient solution is 4 times larger than that of the primary part. This example provides a computational basis for the corrosion of steel bar and some reference for durability design of pipe piles as well.     

An Elastic Theory Approach and Parametric Analysis of Pile Group in Layered Soils

Based on the technique proposed by Muki & Sternberg, a rigorous analytical method for calculating the interaction factor between two piles with different lengths, diameters and properties is presented. The pile group in layered soils is calculated by using the principle of superposition. The validity of the presented method has been verified through comparing with those from other existing solutions. A parametric analysis is made to study the pile group settlement and the loads shared by the individual pile. The proposed interaction factors of pile-pile can consider the strengthening effect of intervening piles. The proposed method can be used to analyze the large pile group.     

Bearing Capacity Behavior of Roll Forming Filling Screw Pile

Bearing capacity behavior of roll forming filling screw pile (screw pile for short) is investigated through numerical calculation and static load test. The influence of pile-type parameters, such as width of thread tooth and thread pitch, on the ultimate bearing capacity of crew pile is studied; furthermore, the bearing capacity behavior of screw pile and that of pile with the same diameter are compared and analyzed through static load test. The results show that the ultimate bearing capacity of screw pile is a bit higher than that of pile with the same outside diameter; width of thread tooth has a distinct effect on ultimate bearing capacity which increases with the increment of width of thread tooth. When the screw pile is tested under light load, the resistance on pile side is distributed along screw pile, and tip resistance is small, but the resistance rises considerably with load increasing. Besides, the design formula of bearing capacity of screw pile is proposed.     

Parameter Analysis of Effects of Axial Load on the Lateral Response of Piles

Based on the small deformation assumption, the equations of the laterally loaded piles influenced by the axial load were established. The effect of axial load on the lateral response of piles was studied with parameter analysis. The analysis shows that internal force and deformation of laterally loaded pile under axial loading is actually closely linked with the values of axial and lateral loads. In general, the high level axial load should be focused on. It is more significant that the effect of axial load on the internal force and lateral deflection of the upper part of flexible piles, while there is little effect on deep of long-thin pile foundation. The effect of axial load on the lateral response of pile is the largest as coefficient form of subgrade reaction increases linearly, while the effect is minimal as coefficient form of subgrade reaction is a constant. Except in case of buckling, the changes of axial load along the pile direction have little influence on the magnitudes of deflection and moment. The assumption that the axial load is constant with depth can meet the requirements of engineering.     

Analysis of Load-bearing Characteristics of Concrete Pile Composite Foundation

Some conclusions were drawn from two groups of in-site tests on concrete pile composite foundations. In the tests, it was found that the pressure under the rigid loading slab is different, in which the pressure under the center of the slab is the less and under the edge of the slab is the biggest. The pile-soil stress ratio is not a constant; it increases with the adding of the load. Most of the pile-soil ratio vary from 9 to 13 in these tests and the load that the piles share can be more than seventy percent of the whole load. It was proved that the bearing capacity of the concrete pile composite foundation is high with a little settlement, so it will be used more and more in the future.     

Analysis of salt rock underground deposit failure probability in operation period based on response surface method

For the safety of salt rock underground deposit, uncertainties and their influences are considered, and failure probability during operation period is analyzed. Based on finite element model, equation of limit state surface is transformed into explicit equation by response surface method. Combined with Monte Carlo method, computation efficiency is improved. The deposit could be simulated as a series-parallel system. The element with highest failure probability is determined first, then failure mode and system reliability are computed. Taking Jintan underground gas deposit as an example, the analysis indicates that as storage pressure increases, failure probability of middle part of deposit decreases firstly, then increases gradually when storage pressure accumulates to a certain extent. The failure probabilities of upper part and underside of deposit increase as storage pressure increases. During operation period, controlled failure mode is shear failure of upper part and underside of deposit under high storage pressure. In conclusion, the storage pressure during operation period should be controlled strictly.