Settlement Analysis on Building near Retaining Pile of Deep Foundation Pit

The building settlement near a foundation pit project in Yanzhou is calculated by using calculation method related to settlement of the soil near a foundation pit, Comparing and analyzing calculated settlement values with measured settlement ,the reason for the gap between theoretically calculated values and measured settlement values is pointed out, On the foundation of careful research and analysis of the measured building settlement values ,the factors influencing the settlement of building near the foundation pit are summarized. Finally, according to practical measured values and influ- encing factors, how the settlement of building near the foundation pit is influenced was carefully analyzed. A conclusion that has practical role in Engineering is presented,which can serve reasonably for instructing foundation pit retaining design.     

复合土钉支护转角有利影响范围

基坑复合土钉墙转角处有明显的空间效应，受力变形较小，对支护结构有利，但不清楚转角定量的有利影响范围，目前设计中仍按照与基坑中部一样保守设计，为在此范围内降低土钉用量，避免保守设计，对水泥土搅拌桩复合土钉支护结构建立了全尺寸整体三维有限元模型，这种模型包含基坑的转角，能考虑基坑的空间效应，通过建立接触面单元，能考虑土体和搅拌桩、土体和土钉的相互作用，量化分析了基坑转角对支护结构受力和变形的有利影响范围，计算结果表明，基坑转角对开挖面水平位移、地表沉降、坑底隆起、土钉轴力的有利影响范围分别约为1.3、1、1、1.2倍的开挖深度。经与实际工程现场实测值对比，验证了该模型分析结果的可靠性，同时分析结果优于平面二维和局部三维有限元模型，结论为复合土钉支护结构的优化设计和安全施工提供了理论依据和研究方法。     

基坑开挖及降水对坑外地表沉降的影响

考虑降水、支护结构变形以及基坑隆起3个因素引起的基坑周围土体的沉降,根据降水引起土体沉降的机理,运用修正的分层总和法单独计算出由降水引起的周围土体沉降。通过研究基坑开挖引起坑外土体沉降的规律,推导出由基坑开挖引起的坑外土体沉降理论公式。把降水引起的沉降及基坑开挖引起的沉降进行叠加,加入修正系数,最终以简化的理论公式合理地计算出基坑周围土体沉降。具体工程验证表明,推导的理论解析解与实测数据十分接近,能有效预估基坑周围土体沉降,为施工方案编制提供可靠的理论依据,最大限度减少基坑施工对周围环境的影响。     

Earth Pressure on Retaining Structure of Round Deep Foundation Pit in Sand-cobble Soils

In recent years, the round deep foundation pits engineering gradually appears in Chengdu Plain whose strata are mainly sand-cobble soils. However, there are no proper calculation methods of earth pressure in retaining structure like this and distribution mode of the pressure is unknown. With the use of elastoplastic numerical simulation method involved in interaction between retaining piles and soil, the distribution law of earth pressure of the round deep foundation pit retaining structure is determined. The result shows that distribution of earth pressure on a pile is triangular and the maximum lies in the location of pit bottom, but the average value of the pressure is less than Rankine active earth pressure. Model tests have also been carried out so as to verify the distribution mode. As for the test model, the values obtained by the numerical simulation method are approximately similar to the experimental results in the distribution law as a whole, which to some degree suggests the rationality of the numerical simulation results.     

Fisher discriminant analysis model for selecting the retaining structure type of deep foundation pit

Aiming at the problem of traditional evaluation methods of deep foundation pit for selecting the retaining structure type, based on the statistical theory and following the principle of security, economic and reasonable, a Fisher discriminant analysis(FDA) model for selecting the retaining structure type for deep foundation pit is established. 10 selected indicators which influence selection of deep excavation program are taken into account as discriminant factors, and the supporting schemes for deep foundation pit are classified into 5 groups, viz. gravity of the cement-soil type, soil nailing wall, pile anchors, pile supports and underground continuous wall. After training and testing 64 sets of measured data, the discriminant functions of FDA are solved, the re-substitution method is introduced to verify the stability of FDA model and the ratio of mis-discrimination is 14.1%. Another 10 groups of measured data are tested as forecast samples by the proposed model, and the correct rate is equal to 100%. Therefore, the feasibility of the proposed model is validated. Moreover, the proposed model is adopted for the New World Center Project in China, and the prediction results are in line with the artificial neural network(ANN) and the actual situation. The result shows that the deep foundation pit supporting structure lectotype decision of FDA model has excellent discriminant performance and the resubstitution error rate is low. It is easy and efficient to make discriminant analysis using this model and it provides efficient method to select deep excavation retaining structure and a practical new approach to choose the structural type of deep foundation pit optimization.     

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。     

对称式基坑渗流涌水量的计算方法

随着地铁、越江隧道等地下工程的日益增多，涌现出了大量的对称式基坑。基于共形映射理论，推导了对称式基坑涌水量计算表达式，并对其计算参数进行分析。研究表明，对称式基坑的单宽涌水量与渗透系数、基坑内外水头差成正比，与（相对）隔水层层顶到坑底的距离和基坑两侧止水帷幕间距的比值、止水帷幕嵌固深度和（相对）隔水层层顶到坑底距离的比值、基坑内外水头差和（相对）隔水层层顶到坑底距离的比值成反相关。     

Calculation of Influence on Longitudinal Deformation of Adjacent Tunnels Due to Excavation

Unloading of excavation of foundation pit has influence on adjacent tunnels, therefore it is important to predict the deformation of metro tunnels to ensure the operation of tunnel. The displacement effect due to the surrounding wall soil unloading of adjacent excavation was not considered by the theoretical analysis method, and the analysis procedure of FEM was usually too complicated to get a satisfied result, so the horizontal and vertical additional stress were calculated by the Mindlin solutions. Furthermore, the tunnel structure was considered as the beam with infinite length. The additional stress was imposed on the Winkler model and the governing equation was built up on the adjacent tunnel structure. Finally, displacements and internal forces of existing tunnels were obtained. Compared with the numerical simulation and an engineering case, the results of the presented formula are in good agreement. It can provide certain theoretical and calculation basis for metro tunnels influenced by adjacent excavation.     

Design Problems of Internal Bracing and Composite Soil Nailing Wall in Foundation Pits under Binary Geological Conditions

Combined with the design practice in foundation excavation engineering,the problems for combined supporting from inner supports and composite soil nailing wall under binary geological conditions,including soil layers and rock stratum with weak intercalation in range of excavation depth,are analyzed.These problems mainly include the following: calculation model of earthen pressure,the local bearing capacity of foundations below steel pipe piles,stiffness coordination at the junction of rigid and flexible supports,internal bracing stability influencd by restrained condition of upright post,etc.Problems of concern for design of similar foundation pit supports are pointed out,and measures for solving these problems are proposed.All these can provide references for similar projects.     

Factors Influencing Deformation of Underground Diaphragm Wall in Deep Excavation Based on Centrifugal Model Test

To know well the impact on the deformation of underground diaphragm wall caused by soil excavation, centrifugal model tests reflecting Shanghai soft soil creep effects were designed, and finite element was used to calculate the deformation of underground diaphragm wall caused by different excavation timeline, sequence and width based on the top down construction method in the deep and large foundation pit of Shanghai Expo axis underground complex project. Centrifuge model tests and monitoring data indicate that the results of numerical calculation are approximately close to the horizontal displacement of the underground diaphragm wall measured in site, which reflects the deformation behavior of excavation. The results show that remained berm and middle plate have good control over the deformation of underground diaphragm wall. Most part of underground diaphragm wall deformation caused by soil creep occurs after the remained berm is excavated. So in order to decrease the deformation of underground diaphragm wall, it would be useful to conduct plate structures as soon as the remained berm is excavated. The excavation width of remained berm in the north part is less than that in the south part. It will be advisable to finally excavate the remained berm where there are protected objects nearby.     

Finite Difference "m-k" Method of Calculation of Anchor-stabilizing Piles

Based on the principle of the foundation coefficient " m-k " method,the ginite difference method is presented to analyze the internal forces of a whole prestressed anchor stabilizing pile. The calculation and figure treatments are programmed. An example shows that the high precise solution can be obtained if the segments are small enough, though more computing time may be consumed. Obviously,the calculation precision is better than that of traditional method. The results of figure treatments by the program can optimize the construction design of stabilizing piles. Three kinds of support condition are taken into account.The foundation coefficient "m-k " method applies to the situation that above the slide-surface is soil layer or efflorescence layer,while below the slide-surface is terrane.     

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.     

Q235钢在不同湿度红壤中的腐蚀形貌研究

采用10%、20%和30%的土壤湿度,土壤中埋藏2个月的Q235钢腐蚀试验显示,在酸性红壤中,土壤的湿度差异是影响红壤中Q235钢腐蚀性的主要因子。在实验条件下,不同湿度对土壤中Q235钢的腐蚀速度影响较大。在湿度为30%左右的土壤中试样的腐蚀速度最大。同时土壤湿度对Q235钢的腐蚀形貌有较大影响,随湿度增加腐蚀从局部腐蚀向均匀腐蚀转化。     

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.     

Analysis on Deformation Characteristics of CFG Piles-Gravel Cushion Composite Foundation of the Deep Embedded Secret Passage

In order to investigate the issue in the field of the application of CFG pile application of CFG pile composite foundation technology in deep embedded secret passage of such special structure ground treatment, the settlement deformation of CFG pile composite foundation according to deep are studied and detailed analysis are given in the field test and indoor model test of the gravel cushion with different thickness. Moreover it points out that the cushion compressive deformation must be taken into account, and that the settlement deformation calculation cannot simply consider the amendments of composite foundation. The amendments of cushion deformation must be considered. The effect of the different thickness of cushion on pile-soil stress ratio, total settlement of composite foundation, cushion compression and axial stress of pile body were analysed by using ABAQUS finite element method. Through the analysis of the field test, indoor model test and the numerical simulation of CFG piles-gravel cushion composite foundation of the deep embedded secret passage, a settlement deformation monitoring method has been described and the selection principle of the cushion has determined so as to provide the cushion design basis in the process of composite foundation design.     

Image-Based Soil Deformation Measurement in Geotechnical Model Test

Deformation measurement and analysis play an important role in geotechnical model tests. Using the concept of quadrilateral isoperimetric element, the strain filed was achieved from the calculation method based on displacement modes, and the verification results show that this measurement technique has a reliable precision. The soil deformation in model test of square shallow foundation was measured by using this technique, and the results show that the measurement system based on digital image correlation method can realize the whole process quantitative measurement of soil displacement field and shear strain filed. This deformation measurement technique provides a tool for the qualitative and quantitative analysis of soil micromechanics characteristics.     

承压水基坑突涌的水力劈裂

突涌是基坑工程施工过程中常遇的主要灾害之一。现有的承压水基坑突涌稳定分析方法均不能反应突涌破坏机理。从水力劈裂的机理入手,建议承压水基坑突涌问题应考虑应力-渗流场耦合作用。在Biot固结理论基础上,建立了基坑突涌分析水力劈裂耦合模型,考虑了土体物理力学性质的动态演化。试图通过分析工作面推进过程中基底土体应力场和渗流场的变化,来判断突涌发生的可能性。研究结果表明：突涌始于基底隔水层所发生的张拉破坏,基底周边是发生突涌的危险位置;渗透弱面(初始张拉裂缝)的水压楔劈效应所导致的水力劈裂为基坑突涌提供了通道;高水压力的存在是突涌发生的前提条件,高水力梯度的产生是基坑突涌的根源。     

Optimum Design of Individual Foundation and Its Application

On the basis of analysing the defaults occuring in normal design,a new method of optimum design for individual foundation is put forward in this paper.This method can solve some problems successfully such as the strengh and deformation can be considered at the same time,which cannot be done in the current specification.The optimal mathematical models of individual foundation design and the bottom surface dimension design under eccentric load are derived.The optimal solution is decided by method of optimization and the method selected is penalty function and complex method, and the programs of optimum algorithm have been compiled and design and drawing of individual foundation have been completed. The final result suggests that a fair-sized economic efficiency can be obtained by using optimum method for foundation design.     

Reinforcement Treatment on the Uneven Subsidence of Foundation

There are several methods to cope with the common problem of the uneven subsidence of foundation. The reason for uneven settlement of foundation of the frame structure was analyzed in this paper. Considering the limitation of the construction site and the principle of consolidation, a feasible reinforcement measure was taken. Meanwhile, a practical construction pattern was chosen upon the comparison of the reinforcement technology analysis and the construction method. The observation of the settlement result after consolidation of the structure shows that the result of this reinforcement treatment pattern is effective.     

Numerical simulation analysis on small clear spacing crossing viaduct pile foundation of shielded subway tunnels

Aimed at the problem of the in partial section of the Nanjing Metro Line 3, the three-dimensional pattern of tunnel, segment and pile foundation was established after appropriate simplification. The simulation results showed that, the Overpass pile foundation of Shield Tunneling to Adjacent Metro Shield Tunnel will have effect on the force and deformation of the earth's surface and pile foundation, the maximum deformation value of the earth's surface is larger than that of the pile foundation top, stress concentration appeared in right working slope lower side segment of tunnel. Through the comparison with field monitoring results, the field dates is consistent with the Numerical Simulation Results, the execution parameters are advised to be well controlled in the further construction, in the same time strengthing the track monitoring, tracking grouting reinforcement should be carried when necessary. The research results could provide reference for the smooth going of the project.