土压平衡泥水输送法在顶管施工中的应用

分析了顶管施工中常用的刃口式推进、泥水推进和土压式推进三种施工技术的优缺点,介绍了土压平衡泥水输送施工方法。实践证明,在土压平衡顶管施工中采用水力运输系统可节省空斗车入井和斗车装满挖掘土后出井所需的时间,能达到连续顶进作业,提高施工效率的目的。

采用填土反压法治理公路滑坡病害

填土反压法是滑坡灾害治理工程的主要措施之一。由于其施工简便、见效较快和稳定滑坡作用可靠等特点 ,在滑坡治理工程生产实践中具有明显的优势。介绍福建省福三线郭畲滑波的病害特点。通过调整公路线路纵坡 ,采用填土反压方法作为主体工程措施 ,达到整治滑坡病害的目的 。

土压平衡矩形顶管施工引起的地表沉降探究

顶管施工引起周围土体移动会对路面结构层造成破坏。采用大断面矩形土压平衡顶管顶进工法所引起的地表沉降一直是岩土工程领域技术工作者所关注的热点与难点之一。通过内蒙古科技大学地下过街通道工程,分析了路基变形的实测数据,Peck公式对矩形顶管地表变形预测的适用性,数值模拟不同覆土深度下的顶管施工对地表的变形影响。研究表明:顶进时轴线上的纵向测点变形总趋势是先隆起,后沉降,并趋于稳定状态;横断面上位于轴线10 m左右范围内为主要影响区域,在此范围内沉降槽体积约占总体积的90%;当地层损失率Vl取0.4%,沉降槽宽度参数K取0.4时,实测值与Peck公式法的预测结果曲线拟合较好;当覆土深度增加,地表沉降值逐渐减小,且沉降范围逐渐增大。研究成果为大断面土压平衡矩形顶管与类似工程的施工提供了理论参考及应用借鉴。

板式地锚的抗拔稳定校核方法比较

板式地锚主要有土重法和土压法两种抗拔稳定校核方法,在同样的输入参数下,土重法计算结果偏大,土压法计算结果偏小,该文分析了两种校核方法的使用条件和异同,通过安全系数取值,将两种校核方法结合起来,以便于工程施工及应用。

基于砂箱模型试验的加筋土挡墙合理布筋方式探讨

针对加筋土挡墙中拉筋水平和垂直间距、筋带宽度和拉筋长度的合理布设问题,根据拉筋所受土压力相等的等土压应力面积法,提出了拉筋水平等间距、垂向沿埋深逐层加密的布置方式及相应的计算式;采用砂箱模型试验,以墙体处于极限稳定状态下的最少用筋面积为条件,探讨了加筋土挡墙的合理布筋方式。试验分析表明:采用与土压力沿深度逐渐增大相适应的拉筋"上疏下密"布置形式可实现筋带均衡受力,在"窄筋密布"的条件下具有更好的稳定性且用筋量更少;与墙后填土潜在破裂楔体呈上宽下窄形状相适应的筋带"上长下短"布置方式稳定性优于"上下等长"布置;采用"窄筋长布"的方式较"宽筋短布"能增加筋带有效锚固面积,提高挡墙稳定性。

超短工期大面积填土工程勘察及地基处理技术

2022年5月中旬,北京市确定建立某紧急隔离点,从开工到交付使用的整体工期仅为20天,且使用期限为10年(介于临时性建筑与永久建筑使用年限之间)。通过对北京市某隔离点集装箱式房场地范围填土地基勘察及处理方法的总结,对大面积填土工程地基勘探点的布置原则、钻进、取样、试验方法、验槽及填土地基的处理措施积累了经验,对类似应急工程具有重要参考价值。

CALCULATION METHOD FOR EARTH PRESSURE CONSIDERING DISPLACEMENT

The calculation of earth pressure is a difficult problem in the pit foundation design. Aiming at the problem, the earth pressure calculation formulas considering the displacement are proposed. A method for determining the limit displacement is given and it is convenient for use. The result indicates that the earth pressure calculated by the formulas is between the earth pressure at rest and the Rankine earth pressure, the formulas can reflect the change rules of active and passive earth pressures along with the displacement. Moreover, the calculation result using the formulas is approximate to the monitoring result. It confirms the validity of the formula deduction and the rationality of the calculation results. As for the passive earth pressure, the calculation method is theoretically feasible.

某市政排水顶管工程施工技术

结合成功的工程实例，介绍了顶管施工技术中的土压平衡式顶管方式施工要点，包括顶推力计算、导轨及工具管安装、触变泥浆减阻技术、施工测量、常见问题及处理措施，最后提出质量保证措施要求。

长距离顶管技术在蓟运河穿越管涵中的应用

蓟运河穿越管涵工程采用了土压平衡法顶管施工工艺,顶管距离为437m,顶管管径为D02 000,管道埋深约为17m。通过保持土仓压力与顶管掘进机前方土压力的平衡,减小了对河底的扰动,使顶管平稳顺利地通过蓟运河。通过优化触变泥浆减阻工艺,可使顶管顶力增长缓慢,压力表峰值小于中继间启动压力,减少了中继间的启动,缩短了施工工期,降低了成本,总共节约施工成本约80万元。

提高渠系水有效利用系数

提高渠系水有效利用系数是节约用水、扩大水田灌溉面积的重要举措。简单介绍了影响提高渠系水有效利用系数的几个因素,并针对这些影响因素提出了治理措施。

Nonlinear analysis of consolidation with variable compressibility and permeability

Terzaghi gave a theory of soil consolidation based on the effective stress principle, which was derived on several ideal assumptions to get a simplified theory. To avoid the limitations involved in Terzaghi’s theory, many efforts are being made by scholars to solve the problems in practical engineering situations. This paper presents a generalized theory for one dimensional consolidation of saturated soft clay with variable compressibility and permeability. The semi-analytical solution presented here takes into account the well known empirical e-logk and e-logp′(σ′) relations under instantaneous loading. Study of the consolida- tion behaviors showed that the ratio of Cc and Ck (the slope of e-logp and e-logk respectively) govern the ratio of consolidation. A simulative laboratory investigation with GDS advanced consolidation system was made to analyze the clay consolidation process and compare the results with the semi-analytical solution.

A Generalized Limit Equilibrium Method for the Solution of Active Earth Pressure on a Retaining Wall

In this paper, a generalized limit equilibrium method of solving the active earth pressure problem behind a retaining wall is proposed.Differing from other limit equilibrium methods, an arbitrary slip surface shape without any assumptions of pre-defined shapes is needed in the current framework, which is verified to find the most probable failure slip surface. Based on the current computational framework, numerical comparisons with experiment, discrete element method and other methods are carried out. In addition, the influences of the inclination of the wall, the soil cohesion, the angle of the internal friction of the soil, the slope inclination of the backfill soil on the critical pressure coefficient of the soil, the point of application of the resultant earth pressure and the shape of the slip surface are also carefully investigated. The results demonstrate that limit equilibrium solution from predefined slip plane assumption, including Coulomb solution, is a special case of current computational framework. It is well illustrated that the current method is feasible to evaluate the characteristics of earth pressure problem.

Active earth pressure acting on retaining wall considering anisotropic seepage effect

This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of cohesionless and fully saturated sand with anisotropic permeability along the vertical and horizontal directions. The extremely unfavourable seepage flow on the back of the retaining wall due to heavy rainfall or other causes will dramatically increase the active earth pressure acting on the retaining walls, increasing the probability of instability. In this paper, an analytical solution to the Laplace differential governing equation is presented for seepage problems considering anisotropic permeability based on Fourier series expansion method. A good correlation is observed between this and the seepage forces along a planar surface generated via finite element analysis. The active earth pressure is calculated using Coulomb's earth pressure theory based on the calculated pore water pressures. The obtained solutions can be degenerated into Coulomb's formula when no seepage exists in the backfill. A parametric study on the influence of the degree of anisotropy in seepage flow on the distribution of active earth pressure behind the wall is conducted by varying ratios of permeability coefficients in the vertical and horizontal directions,showing that anisotropic seepage flow has a prominent impact on active earth pressure distribution. Other factors such as effective internal friction angle of soils and soil/wall friction conditions are also considered.

Influence of Dry Density on Soil-Water Retention Curve of Unsaturated Soils and Its Mechanism Based on Mercury Intrusion Porosimetry

The soil-water retention curve(SWRC)can be used to evaluate the ability of unsaturated soils to attract water at various water contents and suctions. In this study, drying SWRCs for a kind of sandy soil were obtained in the laboratory by using self-modified SWRC apparatus. In addition, the porosity and the pore size distribution of the samples were investigated by a mercury porosimetry test in order to analyze the effect of dry density. Results showed that the soil-water retention of the soil specimens was strongly dependent on the dry density. Under zero suction, soil specimens with a higher dry density exhibited lower initial volumetric water content. The higher the dry density of soil, the more slowly the volumetric water content decreased with the increase of suction. There was a general and consistent trend for a soil specimen to possess a larger air-entry value and residual suction, while smaller slope of SWRC when it had a higher density. This was probably attributed to the presence of smaller interconnected pores in the soil specimen with a higher dry density. The proportion of large diameter pores decreased in comparison to pores with small diameters in the soil tested. The measured total pore volume of the soil specimen, which had a larger dry density, was lower than that of the relatively loose specimens.

Computation of one—dimensional consolidation of double layered ground using differential quadrature method

The authors give the solution to the problem of one-dimensional conso l idation of double-layered ground with the use of the differential quadrature me t hod. Case studies showed that the computational results for pore-water pressure in soil layer agreed with those of analytical solution; and that in the computat ional results for the interface of soil layer also agreed with those of the anal ytical solution except for the small discrepancies during shortly after the star t of computation. The advantages of the solution presented in this paper are tha t compared with the analytical solution, it avoids the cumbersome work in solvin g the transcendental equation for eigenvalues, and in the case of the Laplace transform s olution, it can resolve the precision problem in the numerical solution of long time inverse Laplace transform. Because of the matrix form of the solution in th is paper, it is convenient for formulating computational program for engineering practice. The formulas for calculating double-layered ground consolidation may be easily extended to the case of multi-layered soils.

Discrete element simulation of mechanical characteristic of conditioned sands in earth pressure balance shield tunneling

The discrete element method (DEM) was used to simulate the flow characteristic and strength characteristic of the conditioned sands in the earth pressure balance (EPB) tunneling. In the laboratory the conditioned sands were reproduced and the slump test and the direct shear test of the conditioned sands were implemented. A DEM equivalent model that can simulate the macro mechanical characteristic of the conditioned sands was proposed,and the corresponding numerical models of the slump test and the shear test were established. By selecting proper DEM model parameters,the errors of the slump values between the simulation results and the test results are in the range of 10.3%-14.3%,and the error of the curves between the shear displacement and the shear stress calculated with the DEM simulation is 4.68%-16.5% compared with that of the laboratory direct shear test. This illustrates that the proposed DEM equivalent model can approximately simulate the mechanical characteristics of the conditioned sands,which provides the basis for further simulation of the interaction between the conditioned soil and the chamber pressure system of the EPB machine.

Application of Compactness Detection to Complicated Concrete-Filled Steel Tube by Ultrasonic Method

An example of using ultrasonic method to detect the compactness of complicated concrete-filled steel tube in certain high-rise building was discussed in this study.Because of the particularity of the complicated concrete-filled steel tubular column,the plane detection method and embedded sounding pipe method were adopted in the process of effectively detecting the column.According to the results of the plane detection method and embedded sounding pipe method,the cementing status of steel tube and concrete can be concluded,which cannot be judged by the hammering method in the rectangular steel tube-reinforced concrete.

Three-dimensional consolidation deformation analysis of porous layered soft soils considering asymmetric effects

Long-term settlements for underground structures, such as tunnels and pipelines, are generally observed after the completion of construction in soft clay. The soil consolidation characteristic has great influences on the long-term deformation for underground structures. A three-dimensional consolidation analysis method under the asymmetric loads is developed for porous layered soil based on Biot's classical theory. Time-displacement effects can be fully considered in this work and the analytical solutions are obtained by the state space approach in the Cartesian coordinate. The Laplace and double Fourier integral transform are applied to the state variables in order to reduce the partial differential equations into algebraic differential equations and easily obtain the state space solution. Starting from the governing equations of saturated porous soil, the basic relationship of state space variables is established between the ground surface and the arbitrary depth in the integral transform domain. Based on the continuity conditions and boundary conditions of the multi-layered pore soil model, the multi-layered pore half-space solutions are obtained by means of the transfer matrix method and the inverse integral transforms. The accuracy of proposed method is demonstrated with existing classical solutions. The results indicate that the porous homogenous soils as well as the porous non-homogenous layered soils can be considered in this proposed method. When the consolidation time factor is 0.01, the value of immediate consolidation settlement coefficient calculated by the weighted homogenous solution is 27.4% bigger than the one calculated by the non-homogeneity solution. When the consolidation time factor is 0.05, the value of excess pore water pressure for the weighted homogenous solution is 27.2% bigger than the one for the non-homogeneity solution. It is shown that the material non-homogeneity has a great influence on the long-term settlements and the dissipation process of excess pore water pressure.

Seismic Deformation and Seismic Resistance Analysis of Shapai Roller Compacted Concrete Arch Dam Based on Field Monitoring and Dynamic Finite Element Method

Shapai Roller Compacted Concrete(RCC) Arch Dam is the highest RCC arch dam of the 20th century in the world with a maximum height of 132m,and it is the only concrete arch dam near the epicentre of Wenchuan earthquake on May 12th,2008.The seismic damage to the dam and the resistance of the dam has drawn great attention.This paper analyzed the response and resistance of the dam to the seismic wave using numerical simulations with comparison to the monitored data.The field investigation after the earthquake and analysis of insitu data record showed that there was only little variation in the opening size at the dam and foundation interface,transverse joints and inducing joints before and after the earthquake.The overall stability of the dam abutment resistance body was quite good except a little relaxation was observed.The results of the dynamic finite element method(FEM) showed that the sizes of the openings obtained from the numerical modeling are comparable with the monitored values,and the change of the opening size is in millimeter range.This study revealed that Shapai arch dam exhibited high seismic resistance and overload capacity in the Wenchuan earthquake event.The comparison of the monitored and simulated results showed that the numerical method applied in this paper well simulated the seismic response of the dam.The method could be useful in the future application on the safety evaluation of RCC dams.