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.     

Shear Capacity Calculation Analysis of Reinforced Concrete Beams Based on Truss-arch Model

According to the theory of truss-arch model, the shear mechanism of reinforced concrete beam was analyzed, and formula of shear bearing capacity was proposed. In this formula, softening effect of concrete and the arch function were taken into account, and the coefficients in the formula were amended with experimental data. When the performance difference between the structural material and the original material is huge, the code formula of shear bearing capacity calculation is inapplicable. After the computation, the ratio of the results calculated by truss-arch model theory formula and the results calculated by the current code formula was close to 1, and the standard deviation coefficient and coefficient of variation were smaller than those of standard formula results, and the results calculated by truss-arch model formula were in good agreement with the experimental results. The collected experimental data was calculated with the shear capacity formula in ACI318-08, and the calculation results showed that United States building code was more conservative than the standard of China. The results indicate that the shear bearing capacity formula based on truss-arch model can be used for computation of shear bearing capacity of reinforced concrete beams.     

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.     

深层开挖条件下自平衡试桩法上段桩承载力损失简化计算方法

针对在深层开挖条件下进行自平衡法试桩时,通过采取有效措施消除开挖段的侧摩阻力影响后,由于深层覆土开挖卸荷导致工程桩桩周土体围压减小,从而导致荷载箱上段桩抗拔承载力降低这一问题,通过借鉴目前在抗拔桩方面已有的相关分析方法、负摩阻力、基底附加应力以及相关土力学基础理论,提出了基于Mindlin解的简化分析方法以及负摩阻力-附加应力法两种简化分析方法,并以北京某地铁车站中间柱下桩为例,分别估算深层开挖土体卸荷引起的上段桩承载力的损失值。两种方法所得出的估算值存在较大差异,对其原因进行了初步分析。两种简化分析方法的合理性及准确性还有待于进一步完善和实践验证。     

成孔机构与土壤相互作用的力学模型及应用

为实现油菜移栽机成孔机构形成满足农艺要求的栽植孔,并为设计新型移栽机提供理论依据,针对不同类型土壤具有不同物理机械力学特性等问题,进行成孔机构与土壤相互作用力学试验研究。分析土壤极限抗剪承载力Qu与土壤摩擦阻力Qf的计算公式,建立成孔机构与土壤相互作用的力学模型,完成不同类型土壤的物理机械力学特性指标的测定,结合成孔机构相关结构参数,求解圆柱形孔刺垂直刺入土壤75cm处所受抗剪阻力Ff1与垂直弹出土壤时所受摩擦阻力Ff2,得出圆柱形孔刺在不同类型土壤中,其抗剪阻力Ff1最大值1139.7N,摩擦阻力Ff2最大值达到107.6N。该研究为设计栽植孔成型机构提供了试验依据,为进一步研究不同类型土壤与成孔机构的阻力提供了理论依据。     

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.     

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.     

红层泥岩桩岩接触面本构模型试验及数值模拟

桩-岩（土）接触面力学特性的研究是桩基承载机理研究的基础。通过红层泥岩桩岩接触面大型直剪试验，研究了红层泥岩桩岩接触面的力学特性，结果表明：接触面剪应力先随剪切位移增大而增大，在达到峰值后，剪应力随着剪切位移增大而降低，并最终趋于稳定值，应力应变曲线呈现出应变软化的特征。根据剪切试验结果，推导出桩岩接触面应变软化本构方程。利用fish语言对FLAC^3D中自带的理想弹塑性接触单元进行二次开发，并应用开发的模型对桩岩接触面直剪试验进行了数值模拟，分析剪应力与剪切位移之间的关系，证明了该本构能够较好地模拟接触面间的应变软化特性。     

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.     

八地脚螺栓刚性塔座板的承载力

随着中国电网技术的发展，杆塔负荷越来越大，八地脚螺栓塔座板应用越趋普遍。但现有计算理论与实际情况不符，为了使八地脚螺栓塔座板的计算方法合理、可靠，通过试验对八地脚螺栓刚性塔座板承载力进行了研究，同时借助有限元对构件进行了参数化分析。结合经典力学理论、试验及有限元数据，提出了全新的计算方法，引入了等效计算宽度和有效力臂的概念，充分考虑了底板刚度，屈曲后强度和垫板对承载力的影响，对工程设计具有指导意义。     

Calculation of the Ultimate Bearing Capacity of Foundation under Triaxial Compressive Loading

It is of important significance to study the ultimate bearing capacity of foundation in three-dimensional stress. In this paper, a formula is established for ultimate bearing capacity of foundation taking three-dimensional stress into account. According to the numerical results, the ultimate bearing capacity of foundation with consideration of three-dimensional stress is improved, which is of important significance for engineering.     

Experimental Analysis on Mechanical Properties of Corroded Stud Shear Connectors

Four series stud push-out specimens were conducted to study static mechanical behavior when stud shear connectors of composite beams were corroded. Firstly, the studs were manually rapidly corroded by electrochemical methods, and then a static load test was performed on them. Test results show that when corrosion occurs at stud rod especially close to combined surface, the ultimate bearing capacity reduces most by 18%, slip under the same load increases, and slip relative to the ultimate load reduces most by 12%. When corrosion occurs at the large end of stud, it has little effect on ultimate bearing capacity of push-out specimens, but deformation performance of stud shear connectors is affected seriously.     

Experimental Analysis on Shear Strengthening Capacity of Secondary Dapped end Beams

Because section steel can only be extended to the edge of the support, when a simple support RC beam is reinforced by bonded section steel, a notch comes into being at the end of the beam which is called a secondary dapped end beam, making the stress state of the beam more complex. Through experimental analysis on 21 dapped end beam specimens shear reinforced by steel plate bonded, the deformation process, performing characteristics and failure mechanism of the specimens were investigated. The result shows that two steel bonded forms, including horizontal steel plate and oblique steel plate with angle 45° bonded, delay the appearance of cracks significantly and improve the maximum bearing capacity by 102% and 93%. Due to the impact of stress concentration at the notch, the main modes of damage include concrete tensile or shear failure with the result of bonding failure of a steel plate. By changing the width of steel plates and analyzing different reinforcement effects, formula of bearing capacity of shear reinforcement was proposed based on the method of truss analogue, which provides a reference for engineering application.     

Study on the Terzaghi Ultimate Bearing Capacity of Foundation Based on the Unified Strength Theory

The ultimate bearing capacity of foundation based on Mohr-Coulomb strength criterion did not analyze effect of intermediate principal stress on yield and failure of soil so that the disparity between results obtained using Mohr-Coulomb strength criterion and those from experimental data are produced .In the paper , The ultimate bearing capacity of foundation based on unified strength theory is established and a unified solutions are obtained. The corresponding solutions of different materials can be got from it .The unified solution can not only be used to fit the properties of the materials with different tension-pressure strength but also those with equal tension-pressure strength, Results show that ones make full use of the properties of the materials so as to reduce supports,which is of important significance for 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。     

基础尺寸对碎石土地基扩底基础上拔承载力影响的现场试验研究

影响基础上拔承载能力的因素包括地基土物理力学参数及基础尺寸参数,而确定混凝土方量最小、基础上拔承载力最大的基础参数配比是基础优化设计的关键。以戈壁滩碎石土地基中的原状土扩底基础为研究对象,采用正交设计方法,以立柱直径、深宽比、扩展角为影响因素,以基础上拔承载力为分析指标,设计出9组尺寸的足尺基础。通过现场试验,获得了各试验基础的荷载位移曲线和上拔承载力值,提出了采用渐变率的概念表征荷载位移曲线的非线性变化特征,通过分析发现基础荷载位移曲线渐变率与承载能力呈负相关。结合正交试验分析结果,得出立柱直径、深宽比、扩展角3个因素中对碎石土地基原状土扩底基础抗拔承载能力的影响程度由大到小依次为深宽比、立柱直径、扩展角,表明在戈壁滩碎石土地基基础的工程设计中增加深宽比能提高基础抗拔承载能力。     

Behavior Analysis of Laterally Loaded Single Pile under Large Deflection

Based on the simplified elastoplastic constitutive model of soil, the calculation method for the laterally loaded single pile with large deflection was submitted. The coefficient of subgrade reaction was presumed to increase linearly with depth, which simulates the soil resistance close to ground well. The relevant program was then developed using FORTRAN language. The examples show that (1)the displacement and bending moment increase nonlinearly when the lateral load and the moment load increase. (2)The pile displacement decreases with depth. (3)The pile displacement at the point which is over ten times pile diameter from ground is so small that can be neglected. (4)The pile head condition is the key factor, which influences the distributions of pile responses along depth. (5)By improving the mechanical properties of soil around pile, the maximum lateral displacement and bending moment can be decreased efficiently. The calculation results are in good agreement with the field test results and are better than those obtained using the pre existing solutions, which shows the presented solutions are reliable.     

m法下的双曲线型p-y曲线

工程中基桩大多处于复杂的成层地基中，鲜有位于单一土层中，从宏观角度出发，引入初始地基比例系数，提出了基于m法的双曲线型p-y曲线。某现场7根试桩地基土非线性显著，实测和理论计算的地面处桩身水平位移水平荷载关系曲线均呈良好的二次抛物线关系，且理论与实测曲线吻合良好，验证了本文p-y曲线模型。地基土非线性对桩身最大弯矩、桩侧地基土压力影响显著，不容忽略。工程实际中采用m法计算基桩最大弯矩值偏小，建议乘以1.05~1.25的系数，以计入地基土非线性影响。     

Stratification and Bearing Capacity Prediction Method Based on BP Neural Network for Foundation in Huaibei Plain

According to the features of stratification and obvious inhomogeneity in geological soil in Huaibei plain, BP neural network prediction method for stratification and bearing capacity calculation of multiple cross-bedded foundation was proposed. By comparing the results of drill sampling, static cone penetration tests and screw plate tests, plate loading tests, penetration resistance ps value was found as an evaluation index for stratification and bearing capacity prediction of cross-bedded foundation. Moreover, gradient descent algorithm and conjugate gradient algorithm BP neural network models were obtained, and the calculation results of the two algorithms were comparatively analyzed. The results show that penetration resistance value can be taken as an evaluation index for stratification and bearing capacity prediction of cross-bedded foundation in Huaibei plain. Gradient descent algorithm and conjugate gradient algorithm BP neural network models have good results for soil identification and bearing capacity determination, which can meet the accuracy requirements of actual engineering. However, the computational efficiency of gradient descent algorithm is significantly lower than that of conjugate gradient algorithm.     

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.