Thermal performance of cast-in-place piles with artificial ground freezing in permafrost regions

During the construction of cast-in-place piles in warm permafrost,the heat carried by concrete and the cement hydration reaction can cause strong thermal disturbance to the surrounding permafrost.Since the bearing capacity of the pile is quite small before the full freeze-back,the quick refreezing of the native soils surrounding the cast-in-place pile has become the focus of the infrastructure construction in permafrost.To solve this problem,this paper innovatively puts forward the application of the artificial ground freezing(AGF)method at the end of the curing period of cast-in-place piles in permafrost.A field test on the AGF was conducted at the Beiluhe Observation and Research Station of Frozen Soil Engineering and Environment(34°51.2'N,92°56.4'E)in the Qinghai Tibet Plateau(QTP),and then a 3-D numerical model was established to investigate the thermal performance of piles using AGF under different engineering conditions.Additionally,the long-term thermal performance of piles after the completion of AGF under different conditions was estimated.Field experiment results demonstrate that AGF is an effective method to reduce the refreezing time of the soil surrounding the piles constructed in permafrost terrain,with the ability to reduce the pile-soil interface temperatures to below the natural ground temperature within 3 days.Numerical results further prove that AGF still has a good cooling effect even under unfavorable engineering conditions such as high pouring temperature,large pile diameter,and large pile length.Consequently,the application of this method is meaningful to save the subsequent latency time and solve the problem of thermal disturbance in pile construction in permafrost.The research results are highly relevant for the spread of AGF technology and the rapid building of pile foundations in permafrost.

Field observation of the thermal disturbance and freezeback processes of cast-in-place pile foundations in warm permafrost regions

The bearing capacity of pile foundations is affected by the temperature of the frozen soil around pile foundations.The construction process and the hydration heat of cast-in-place(CIP)pile foundations affect the thermal stability of permafrost.In this paper,temperature data from inside multiple CIP piles,borehole observations of ground thermal status adjacent to the foundations and local weather stations were monitored in warm permafrost regions to study the thermal influence process of CIP pile foundations.The following conclusions are drawn from the field observation data.(1)The early temperature change process of different CIP piles is different,and the differences gradually diminish over time.(2)The initial concrete temperature is linearly related with the air temperature,net radiation and wind speed within 1 h before the completion of concrete pouring;the contributions of the air temperature,net radiation,and wind speed to the initial concrete temperature are 51.9%,20.3%and 27.9%,respectively.(3)The outer boundary of the thermal disturbance annulus is approximately 2 m away from the pile center.It took more than 224 days for the soil around the CIP piles to return to the natural permafrost temperature at the study site.

Quality Control Measures of Bored Pile in Bridge Construction

In order to improve the quality of bored piles in bridge construction and ensure the overall quality of the bridge,we analyzed a series of problems in the construction process of bored piles,then propose corresponding quality control measures,in hopes of improving quality control of bored piles in bridge construction in our country.

A case study on behaviors of composite soil nailed wall with bored piles in a deep excavation

深挖掘的一个完全的盒子被探索。根据实际工作条件， 3D 非线性的有限元素过程被用来模仿合成土壤支持的深挖掘有在软土壤的无聊的堆积的钉的墙。修改凸轮泥土模特儿在数字模拟作为土壤的组成的关系被雇用。从数字分析的结果与领域数据被适合很好，它显示使用的研究途径是可靠的。基于数据和钉的合成土壤的四个不同模式支持的深挖掘的数字结果围的地，重要角落效果深在 3D 被成立挖掘。如果无聊的堆积或土壤锚在钉的合成土壤被认为墙，他们对减少的变丑和在深挖掘附近的无聊的堆积，混合堆积的水泥，土壤锚，土壤钉和土壤的内部力量有益。而且，效果由于无聊的堆积比从土壤锚推出的那些更重要。上面提及的所有证明合成土壤与无聊的堆积钉了墙在深挖掘是可行的。

Regressive approach for predicting bearing capacity of bored piles from cone penetration test data

In this study, the least square support vector machine(LSSVM) algorithm was applied to predicting the bearing capacity of bored piles embedded in sand and mixed soils. Pile geometry and cone penetration test(CPT) results were used as input variables for prediction of pile bearing capacity. The data used were collected from the existing literature and consisted of 50 case records. The application of LSSVM was carried out by dividing the data into three sets: a training set for learning the problem and obtaining a relationship between input variables and pile bearing capacity, and testing and validation sets for evaluation of the predictive and generalization ability of the obtained relationship. The predictions of pile bearing capacity by LSSVM were evaluated by comparing with experimental data and with those by traditional CPT-based methods and the gene expression programming(GEP) model. It was found that the LSSVM performs well with coefficient of determination, mean, and standard deviation equivalent to 0.99,1.03, and 0.08, respectively, for the testing set, and 1, 1.04, and 0.11, respectively, for the validation set. The low values of the calculated mean squared error and mean absolute error indicated that the LSSVM was accurate in predicting the pile bearing capacity. The results of comparison also showed that the proposed algorithm predicted the pile bearing capacity more accurately than the traditional methods including the GEP model.

Comparative Examinations of Single Bored Piles Using International Codes

This paper presents some aspects of the load-settlement behavior for large diameter bored piles using four different international codes, namely: ECP 202 [1], DIN 4014 [2], AASHTO [3] and French Code [4]. Ultimate capacities for 38 pile load tests founded in realistic multi-layered soils in Delta and Port Saidareas atEgyptare evaluated using modified Chin (1970) method and compared to ultimate load predictions obtained by the aforementioned codes. Many statistical analyses were conducted on the total pile loads and individual contributions of tip and skin resistances. Based on code predictions of ultimate pile loads, an empirical modified load-settlement model is proposed. This model will simplify to a great extent the analysis of piled-raft systems as it can effortlessly predict pile settlement due to the load on pile itself. Comparisons showed that the pile load test is an irreplaceable process for determining the ultimate capacity of piles.

Dynamic estimation and reliability control of quality assurance for bored piles

A systematic method was proposed to estimate the occurrence probability of defective piles(OPDP) from a site according to quality assurance inspection. The OPDP was firstly suggested as the criterion to weight the performance of a pile foundation. Its prior distribution and updating distribution were deduced to follow Beta distributions. To calibrate the OPDP, a dynamic estimation model was established according to the relationships between prior mean and variance and updating mean and variance. Finally, a reliability-control method dealing with uncertainties arising from quality assurance inspection was formalized to judge whether all the bored piles from a site can be accepted. It is exemplified that the OPDP can be substantially improved when more definite prior information and sampling formation become available. For the example studied herein, the Bayesian estimator of updating variance for OPDP is reduced from 0.0037 to 0.0014 for the first inspection, from 0.0014 to 0.0009 for the second inspection, and with less uncertainty by incorporating experience information.

Physical modeling of behaviors of cast-in-place concrete piled raft compared to free-standing pile group in sand

Similar to free-standing pile groups, piled raft foundations are conventionally designed in which the piles carry the total load of structure and the raft bearing capacity is not taken into account. Numerous studies indicated that this method is too conservative. Only when the pile cap is elevated from the ground level,the raft bearing contribution can be neglected. In a piled raft foundation, pileesoileraft interaction is complicated. Although several numerical studies have been carried out to analyze the behaviors of piled raft foundations, very few experimental studies are reported in the literature. The available laboratory studies mainly focused on steel piles. The present study aims to compare the behaviors of piled raft foundations with free-standing pile groups in sand, using laboratory physical models. Cast-in-place concrete piles and concrete raft are used for the tests. The tests are conducted on single pile, single pile in pile group, unpiled raft, free-standing pile group and piled raft foundation. We examine the effects of the number of piles, the pile installation method and the interaction between different components of foundation. The results indicate that the ultimate bearing capacity of the piled raft foundation is considerably higher than that of the free-standing pile group with the same number of piles. With installation of the single pile in the group, the pile bearing capacity and stiffness increase. Installation of the piles beneath the raft decreases the bearing capacity of the raft. When the raft bearing capacity is not included in the design process, the allowable bearing capacity of the piled raft is underestimated by more than 200%. This deviation intensifies with increasing spacing of the piles.

Field study of plastic tube cast-in-place concrete pile

The compositions, technical principles and construction equipments of a new piling method used for ground improvement plastic tube cast-in-place concrete pile were introduced. The results from static load tests on single piles with different forms of pile shoes and on their composite foundations were analyzed. The distribution patterns of axial force, shaft friction and toe resistance were studied based on the measurements taken from buried strain gauges. From the point of engineering application, the pile has merits in convenient quality control, high bearing capacity and reliable quality, showing higher reasonability, advancement and suitability than other ground improvement methods. The pile can be adopted properly to take place of ordinary ground improvement method, achieving greater economical and social benefits.

Evaluation of the Ultimate Capacity of Friction Piles

The precise prediction of maximum load carrying capacity of bored piles is a complex problem because the load is a function of a large number of factors. These factors include method of boring, method of concreting, quality of concrete, expertise of the construction staff, the ground conditions and the pile geometry. To ascertain the field performance and estimate load carrying capacities of piles, in-situ pile load tests are conducted. Due to practical and time constraints, it is not possible to load the pile up-to failure. In this study, field pile load test data is analyzed to estimate the ultimate load for friction piles. The analysis is based on three pile load test results. The tests are conducted at the site of The Cultural and Recreational Complex project in Port Said, Egypt. Three pile load tests are performed on bored piles of 900 mm diameter and 50 m length. Geotechnical investigations at the site are carried out to a maximum depth of 60 m. Ultimate capacities of piles are determined according to different methods including Egyptian Code of practice (2005), Tan-gent-tangent, Hansen (1963), Chin (1970), Ahmed and Pise (1997) and Decourt (1999). It was concluded that approxi- mately 8% of the ultimate load is resisted by bearing at the base of the pile, and that up to 92% of the load is resisted by friction along the shaft. Based on a comparison of pile capacity predictions using different method, recommendations are made. A new method is proposed to calculate the ultimate capacity of the pile from pile load test data. The ultimate capacity of the bored piles predicted using the proposed method appears to be reliable and compares well to different available methods.

静钻根植桩竖向承载性能现场试验研究

通过一组现场试验对同一场地内静钻根植桩的抗压和抗拔承载性能进行研究,试桩均加载至极限状态。通过抗压和抗拔静载试验对静钻根植桩的抗压和抗拔承载性能进行对比分析。试验结果表明:静钻根植桩的抗压承载性能相比传统钻孔灌注桩有显著提高,本次试验场地各土层中静钻根植桩的桩侧摩阻力是规范建议的钻孔灌注桩极限侧摩阻力的1.49~3.21倍;静钻根植桩抗拔承载性能也明显优于钻孔灌注桩,抗拔试桩的极限承载力是根据规范计算的钻孔灌注桩极限抗拔承载力的1.52~1.55倍;静钻根植桩抗拔状态下桩侧摩阻力明显小于抗压状态下的桩侧摩擦力,即静钻根植桩也存在侧阻抗拔系数。

静钻根植桩施工环境效应现场试验研究

静钻根植桩采用先钻孔注浆后植桩的施工技术,可以解决传统预制桩施工过程引起的挤土效应问题。然而,静钻根植桩施工过程中钻孔和注浆过程会对周围土体产生一定扰动,目前没有相关研究。文章通过一组现场试验对静钻根植桩施工过程中的钻孔、注浆搅拌和植桩阶段对周围土体的扰动规律进行研究。静钻根植桩施工前在钻孔周围土体中埋设土压力传感器,孔隙水压力传感器和测斜管,分别测试静钻根植桩施工过程中周围土体中水平土压力,超静孔隙水压力和深层土体水平位移的变化规律。研究结果表明:静钻根植桩施工过程会对周围土体造成一定扰动,而施工完成后周围土体中的水平土压力、超静孔隙水压力和深层土体水平位移迅速恢复;当水平距离达到4D(D为钻孔直径)时,静钻根植桩施工过程基本不会对土体产生影响;试验结果可以为静钻根植桩在地铁周围等施工位移控制敏感区域的应用提供理论依据。

钻孔灌注桩技术在房建工程施工中的应用

为深入探究钻孔灌注桩技术在房建工程施工中的应用,结合某房屋建筑工程对钻孔灌注桩技术的实际应用进行深入探究,经过研究表明钻孔灌注桩技术在房屋建筑工程中应用能够显著提升房建工程施工质量和效率,保证了工程施工阶段的安全性与规范性,对建筑工程具有显著的积极作用。

市政路桥工程的钻孔灌注桩施工技术分析

对市政路桥工程的钻孔灌注桩施工工艺进行分析,探讨市政路桥工程的钻孔灌注桩施工应注意的问题,如护筒下沉、钻孔倾斜、坍孔缩孔、断桩,结合工程案例对市政路桥施工中钻孔灌注桩施工技术的应用进行详细介绍。

岩溶强发育及超厚回填土地层钻孔灌注桩施工技术

针对复杂地层中钻孔灌注桩常见的施工问题,以某工程项目为例,基于岩溶强发育及超厚回填土地层钻孔灌注桩施工技术,对超厚回填土地层、岩溶强发育地层以及上覆超厚回填土与下伏岩溶强发育叠加地层3种不同工况进行了应用分析,结果表明:该技术有效解决了复杂地层中成孔难、易扩缩径、灌注难等诸多工程难题,相较于传统工艺,可大大节省施工材料、降低施工成本,为项目缩短工期15天,累计节约旋挖钻机30台班,将灌注桩充盈系数从1.5降至1.05~1.1,为项目桩基施工节约综合成本35%以上。根据低应变检测结果可知,灌注桩均为Ⅰ,Ⅱ类桩,其中Ⅰ类桩占所测桩数的96.5%,Ⅱ类桩仅占所测桩数的3.5%,充分证明了该技术的可靠性。

钻孔灌注桩孔壁稳定性影响因素的研究进展

孔壁稳定性是制约钻孔灌注桩成桩质量的关键因素。将影响孔壁稳定性的因素分为桩孔设计参数、施工工艺和土体性质。在桩孔设计参数中,孔径和孔深是影响孔壁稳定的关键因素。施工工艺中,泥浆相对密度、护筒深度和成孔时间是影响孔壁稳定的关键因素。土体性质中,土体类别和土体物理力学性质是影响孔壁稳定的关键因素。针对各关键因素提出相应的管控措施。在桩孔设计参数方面,选取合适钻具,精确控制孔径和孔深。在施工工艺方面,基于孔壁稳定和经济性选择合适的泥浆相对密度和护筒深度,合理安排施工组织,缩短成孔和灌注间隔时间,严格把控钻进速度和钻具压力。在土体性质方面,重点关注软弱地层和砂土层,采用地基处理、加深护筒和增加泥浆相对密度等措施保证孔壁稳定性,为钻孔灌注桩的设计和施工提供参考。

某市市域铁路基坑支护设计案例分析

开展基坑支护既要考虑支挡岩土体,又要形成有效的止水帷幕。某地下基坑支护工程采用钻孔灌注排桩+两道钢筋砼内支撑,在被动区采用三轴水泥搅拌桩加固土体的支护体系,对该基坑计算参数和施工要点进行分析,为类似基坑工程提供参考,进一步提高基坑发展水平。

房屋建筑工程钻孔灌注桩施工技术应用研究

介绍了钻孔灌注桩施工技术的基本机理、步骤,以及其应用领域与效果,从施工准备、钻孔工艺、混凝土灌注、成桩质量控制等方面详细分析了钻孔灌注桩施工技术的要点,从而提高钻孔灌注桩的施工技术水平,保证建筑工程的施工质量。

桥梁项目中钻孔灌注桩施工技术应用

首先分析了钻孔灌注桩施工技术特点,其次结合实际工程案例,从施工准备、场地整平放样、制备泥浆、埋设护筒、钻孔等多方面分析桥梁项目中钻孔灌注桩施工技术,并同时提出该技术应用的质量控制措施,以期能够有效提高桥梁项目的整体质量。

不良地质中粗砂层钻孔灌注桩施工质量的控制研究

结合城市人行天桥工程项目实例,着重分析不良地质中粗砂层钻孔灌注桩施工质量的控制,主要包括双层钢护筒设计、特殊桩位钢护筒加长、钢护筒埋深、钢护筒拔出等质量控制措施。根据现场实际地质情况,编制合理的施工方案,结合EPC项目特点,确保施工费用有效控制,施工质量管控到位以及合同按期履约。