软土地区公路地基沉降的分析预测

交通运输的客观要求,时常需要在软土地区修筑公路,而路基沉降的预测是一个亟待解决的关键问题。文章概述了一些工程上常用的预测方法,指出了一些不足之处。在此基础上,建议在推算地基沉降时,应当选取荷载稳定后的沉降资料采用曲线拟合法进行预测,而且需要根据施工进程的不同,分段进行。     

Non-linear description of ground settlement over twin tunnels in soil

Tunneling inevitably leads to ground settlement. The ground settlement trough over a single tunnel is well described by the generally accepted Peck’s formula. A new model of settlement trough is proposed by extending Peck’s formula to the case of horizontally aligned twin tunnels, which is a widely used tunnel configuration in urban metro projects. The feasibility of the new model is demonstrated through exploration of a large amount of ground settlement data accumulated from a metro tunnel project in China. Two numerical methods are implemented in the data exploration process to solve the problem of non-linear curve-fitting and estimation of model parameters. The Levenberg–Marquardt method is shown to be more suitable than the Nelder–Mead method. Based on the new model of settlement trough, a new method for calculating ground loss over twin tunnels is also proposed. The concluded empirical value of the ratio of ground loss is considered to provide an excellent reference for similar urban railway projects in the future.     

Use of artificial neural networks to predict 3-D elastic settlement of foundations on soils with inclined bedrock

The application of the theory of elasticity for the calculation of foundation settlements has yielded equations that are well-established and consolidated in geotechnical standards and/or that are recommended for use. These equations are corrected by an influence factor in order to increase their precision and to encompass the existing complex geotechnical casuistry. The study presented herein utilizes neural networks to improve the determination of the influence factor (I_α), which considers the effect of a finite elastic half-space limited by the inclined bedrock under a foundation. The results obtained through the utilization of artificial neural networks (ANNs) demonstrate a notable improvement in the predicted values for the influence factor in comparison with those of existing analytical equations.     

On numerical simulation of tunnel installation

The design of tunnels requires a proper estimate of surface settlements and lining forces. In engineering practice different design methods tend to be used, varying from simple empirical and analytical formulations to advanced finite element analyses. This paper begins with a review of empirical and analytical analyses for settlements and lining forces placing emphasis on the sequences of excavation and installation of support. Such installation procedures range from open face to closed face tunnelling and they tend to have a significant effect on deformations and lining forces. Hereafter the focus is on two-dimensional FE-analyses; again both for open face and for closed face tunnelling. Results for different installation procedures will be presented on the basis of two case studies. It is shown that installation procedures are most important to be considered in order to arrive at proper predictions for tunnelling settlements, horizontal deformations and lining forces. For the installation of closed face shield tunnelling a novel simulation method is presented, named the grout pressure method. It is shown that the grout pressure method yields the best predictions for both ground movements and structural forces.     

Tunnel spoil classification and applicability of lime addition in weak formations for muck reuse

Tunnel construction planning requires careful consideration of the spoil management part, as this involves environmental, economic and legal requirements. In this paper a methodological approach that considers the interaction between technical and geological factors in determining the features of the resulting muck is proposed. This gives indications about the required treatments as well as laboratory and field characterisation tests to be performed to assess muck recovery alternatives. While this reuse is an opportunity for excavations in good quality homogeneous grounds (e.g. granitic mass), it is critical for complex formation. This approach has been validated, at present, for three different geo-materials resulting from a tunnel excavation carried out with a large diameter Earth Pressure Balance Shield (EPB) through a complex geological succession. Physical parameters and technological features of the three materials have been assessed, according to their valorisation potential, for defining re-utilisation patterns. The methodology proved to be effective and the laboratory tests carried out on the three materials allowed the suitability and treatment effectiveness for each muck recovery strategy to be defined.     

浅谈建筑施工对邻近房屋的影响及处理

通过工程实例,探讨了在建高层地下工程施工及采用锚杆静压桩处理地基对邻近房屋的影响,并对受影响房屋提出了处理的方法,为受影响房屋的鉴定和加固提供依据,为安全可靠地施工提供依据。     

今日深基坑工程

随着我国城市建筑和市政工程的高速发展,近１０余年来深基坑工程数量急剧增长,并积累了极其丰富的经验。本文着重介绍国内基坑工程设计、施工主要方面的现状和形成的一些主要观念,以及在基坑工程中为防患于未然应重视的问题。     

Winkler springs for axial response of suction bucket foundations in cohesionless soil

Jacket structures mounted on suction buckets carry potential as cost-efficient foundations for next-generation 10 MW+ offshore wind turbines located in transitional water depths. Given this foundation method, resistance to overturning moment relies mainly on the axial response of the buckets. In practice, suction bucket foundations can be modelled as “Beams on Non-Linear Winkler Foundation” where soil is idealised as non-linear springs. This paper describes the derivation process of static load-transfer or t–z curves for suction buckets installed in cohesionless soil. The mathematical formulation of the curves is based on regression analysis of data obtained from 100 axisymmetric numerical models in a medium characterised by the Hardening Soil model for representing the stress–strain relationships for Frederikshavn sand, which is a typical offshore sand. Various bucket dimensions, soil properties and drainage conditions were simulated considering tension and compression, in order to describe frictional behaviour at the skirt–soil interface. The non-linear springs' properties are therefore linked to foundation diameter, friction angle and vertical overburden pressure. By superimposing the effects of all springs, load–displacement curves are generated and compared with results from available experimental and numerical studies on suction buckets, revealing reasonable agreement. It is shown that the existing t–z formulations for piles are inapplicable to large-diameter suction buckets.     

深圳机场停机坪桩网结构软基处理沉降监测分析

深圳机场普遍分布有深厚的海积淤泥层,该土层具有承载力低,压缩性大等特点,机场扩建停机坪软基处理成功运用了桩网复合地基处理技术。本文详细介绍了桩网复合地基的施工和沉降监测情况,并根据观测成果分析这一方法的可行性,为同类工程积累经验。     

考虑承台底土作用的群桩沉降计算方法研究

目前群桩沉降计算方法主要有:等代墩基法,Mindlin-geddes法,等效作用分层总和法等等,通过考虑承台底土分担一定荷载对沉降的影响,对群桩沉降计算方法进行进一步的分析与修正,为工程中群桩沉降计算提供指导。在实际工程中,运用补偿原理,考虑桩土共同分担荷载,实现抽桩后沉降仍然控制在允许范围内,从而实现安全经济的目标。     

压力注浆法在莱钢办公楼加固工程中的应用

由于地基沉降,某办公楼出现大面积沉降。通过方案比较,决定采用压力注浆法对地基进行加固,对由于沉降而破坏的部位进行加固修复,并取得显著效果。     

袁林照壁裂缝成因分析及掏土迫降法治理

通过实地测量与计算分析 ,确定安阳袁世凯陵墓照壁裂缝是由于地基的不均匀沉降引起的 ,根据差异沉降计算所得裂缝宽度与实测宽度吻合。采用掏土迫降及注浆抬升等综合方法对裂缝进行治理。施工完成后的变形监测结果表明治理效果良好     

大型油罐软弱地基充水预压加固试验沉降监测

结合很多工程项目的实践经验,对大型油罐软弱地基充水预压加固试验的沉降监测作专题简述。分析了软弱地基、大型油罐给沉降监测带来的特定条件;阐述了其所表现的主要特点;介绍了所采取的有针对性的有关措施。并提出所采用的精度指标确定方法。