Cyclic Thermo-Mechanical Analysis of Wellbore in Underground Compressed Air Energy Storage Cavern

The compressed air energy storage (CAES) method is a viable method of storing surplus energy underground when there is a mismatch between energy generation and demand. Wellbores embedded in rock are an integral part of energy storage structures, and are used for injecting and extracting the compressed air. During injection and production cycles, the storage reservoir and wellbore are subjected to cyclic change in external pressure and temperature, which may cause failure of the wellbore. In this paper, cyclic thermo-mechanical analysis of a horizontal wellbore in an underground CAES cavern is performed using finite element analysis. The rock behavior is simulated using the Mohr-Coulomb constitutive law. The reduction in the yield strength of rock with increase in the number of loading cycles is taken into account in the analysis. Parametric sensitivity studies are carried out to study the effects of dilation and friction angles of rock, the ratio of in situ horizontal and vertical stresses, loading frequency, and the magnitude of the temperature cycles in the cavern on the wellbore performance for different types of rock. The thermo-mechanical cyclic behavior leads to plastic strains that are greater than those obtained by performing mechanical analysis only. Significantly large deformation is generated in rock for large dilation angle and high loading frequencies.     

Axial Performance of Helical Tapered Piles in Sand

The axial capacity of novel spun-cast ductile iron (SCDI) tapered pile fitted with a lower helical plate is investigated. Seven instrumented piles, five SCDI tapered and two steel straight shafts, were installed in sand soil using mechanical torque. The piles were tested under axial compressive loading and their ultimate capacities were determined. To assess the cyclic loading effect on the piles performance, two load sequences were adopted: four piles were subjected to monotonic loading, and three were subjected to initial cyclic loading followed by monotonic loading. The installation torque was monitored and the resulting capacity-to-torque ratio was compared to the literature reported values. Tapered helical piles displayed a stiffer response and yielded higher capacities compared to the straight ones. Strain gauges were used to evaluate the piles load transfer mechanism, and demonstrated increased shaft resistance due to the pile taper. The taper helped compact the sand within the zone adjacent to the pile, originally disturbed by the helix penetration, hence increased the soil strength and stiffness. These effects were prominent for larger ratio of shaft/helix diameter. Finally, 3D finite element analyses were conducted to evaluate the axial performance of the system and demonstrated its enhanced frictional resistance. The experimental and numerical results confirmed the superior performance of the proposed system in sands.     

能源地下连续墙的热力学行为模型试验研究

鉴于目前国内外针对能源地下连续墙的热力学行为的研究较少,开展了能源地下连续墙的室内模型试验研究。为了 研究不同换热工况以及约束条件对墙体以及墙土接触面热力学行为的影响,设计了三组对照试验。通过对试验过程中读取 的温度、应力、应变数据进行分析,探索了地下连续墙在换热过程中的温度场、墙体内的垂向应变以及接触面法向应力的 变化规律。对比研究了不同工况下墙内轴向应变以及墙土接触面法向应力数据的差异性,揭示了温升变化和约束变化对这 些参数的影响机制以及重要程度。     

能源地下连续墙的热力学行为模型试验研究

鉴于目前国内外针对能源地下连续墙的热力学行为的研究较少，开展了能源地下连续墙的室内模型试验研究。为了 研究不同换热工况以及约束条件对墙体以及墙土接触面热力学行为的影响，设计了三组对照试验。通过对试验过程中读取 的温度、应力、应变数据进行分析，探索了地下连续墙在换热过程中的温度场、墙体内的垂向应变以及接触面法向应力的 变化规律。对比研究了不同工况下墙内轴向应变以及墙土接触面法向应力数据的差异性，揭示了温升变化和约束变化对这 些参数的影响机制以及重要程度。     

钙质砂动强度试验研究

钙质砂是一种ＣａＣＯ３含量超过５０％以上的特殊岩土介质,具有独特的力学和工程性状。利用动三轴试验,研究钙质砂在循环荷载作用下动应变,动孔压,动强度及液化特性。     

Effect of Compressive Load on Oblique Pull-out Capacity of Model Piles in Sand

Model tests on steel piles embedded in sand were carried out in the laboratory to study the effects of compressive load (i.e. 0, 25, 50, 75, and 100% of their ultimate capacity in compression) on oblique pull-out capacity of piles. The model piles were of 20 mm × 20 mm cross section, which had an embedded length of 400 and 600 mm. The pull was applied at an inclination of 0°, 30°, 60° and 90° with vertical axis of the piles. The experimental results indicate that the net oblique pull-out capacity of piles decreases with increase in % of compressive load and the decrease depends on the magnitude of the compressive load. Semi-empirical methods, based on experimental results, have been suggested to determine the oblique pull-out resistance of piles subjected to static compressive loads. A comparison of predicted values of the ultimate oblique resistance by proposed methods of analysis with experimental values, and also with those reported by others, showed reasonably good agreement.     

Discrete-Element Computation of Averaged Tensorial Fields in Sand Piles Consisting of Polygonal Particles

This work is a contribution to the understanding of the mechanical properties of non-cohesive granular materials in the presence of friction and a continuation of our previous work (Roul et al. 2010) on numerical investigation of the macroscopic mechanical properties of sand piles. Besides previous numerical results obtained for sand piles that were poured from a localized source (“point source”), we here consider sand piles that were built by adopting a “line source” or “raining procedure”. Simulations were carried out in two-dimensional systems with soft convex polygonal particles, using the discrete element method (DEM). First, we focus on computing the macroscopic continuum quantities of the resulting symmetric sand piles. We then show how the construction history of the sand piles affects their mechanical properties including strain, fabric, volume fraction, and stress distributions; we also show how the latter are affected by the shape of the particles. Finally, stress tensors are studied for asymmetric sand piles, where the particles are dropped from either a point source or a line source. We find that the behaviour of stress distribution at the bottom of an asymmetric sand pile is qualitatively the same as that obtained from an analytical solution by Didwania and co-workers (Proc R Soc Lond A 456:2569–2588, 2000).     

Multi-surface Cyclic Plasticity Sand Model with Lode Angle Effect

A Drucker-Prager J ₂ multi-surface-plasticity sand model is modified to employ the Lade-Duncan failure criterion as the yield function. This function includes the first and third stress invariants to account for the dependence of cyclic shear stress–strain behavior on confining pressure and the Lode angle. Related modifications to the flow rule and hardening rule are described. Dependence of dilatancy on confinement is also included. Salient features of the model performance are presented under general three-dimensional (3D) loading conditions, where the yield function provides a more accurate representation of nonlinear shear response. Dynamic response analyses of a mildly inclined infinite slope are performed to illustrate the influence of excitation direction on the accumulation of liquefaction-induced lateral ground deformation.     

钻孔灌注桩桩顶混凝土下沉冒水泛砂原因分析

近几年来,在温州地区钻孔灌注桩的施工与验收过程中,桩顶混凝土常出现3种现象：下沉、冒水、泛砂,严重影响到基桩的工程质量。从环境因素、材料因素、工艺因素出发,结合钻孔灌注桩的施工经验,分别对上述3种现象的形成原因进行分析研究,并作出相关解释,同时对3种现象之间的关联也作出了相应的说明。     

高含砂地层钻孔灌注桩施工常见事故处理及预防

温州某花苑工程场地高含砂量地层的基桩设计桩数多，施工工程量大，由于自始至终对施工中存在的泥浆质量问题未能统一认识，致使这个问题一直伴随着基桩施工的全过程，对工程施工造成了很多本来可以避免的事故和损失，值得在类似工程的施工中吸取有益的启示。     

Nonlinear Response of Single Piles in Sand Subjected to Lateral Loads using k hmax Approach

This paper presents results of analysis of full-scale pile load test data of 14 piles embedded in either loose or medium dense sands. The analysis was performed using two methods, p–y curve approach and a more recently developed k_hmax approach. Comparison of the results obtained using both the methods is also presented. A step-by-step analysis procedure is presented for predicting lateral load deflection response of single piles in sand using the k_hmax approach. The results presented show that the k_hmax approach has promise over the p–y curve approach because of its simplicity and the fact that it provides upper- and lower-bound curves, which are valuable guides to making engineering decisions. For loose sands, a new range of k_hmax values is recommended to better predict the lateral load–deflection response of single piles.     

Monotonic and Cyclic Behavior of Chiang Mai Sand Under Simple Shear Mode

Record of damages and casualties caused by earthquakes in Thailand reveals that Chiang Mai, the second largest province of Thailand, has faced the great threat among other provinces. Triaxial tests, standard penetration tests, and multichannel analysis of surface wave have been recently performed to understand the dynamic response of Chiang Mai ground. However, the cyclic simple shear test, which could convincingly represent the real seismic ground shaking under repeated horizontal shear force, has not been conducted yet. Therefore, this paper aims to characterize the behaviors of Chiang Mai sand under monotonic and cyclic loadings using a direct simple shear apparatus. Sand specimens taken from the Ping River were prepared by dry deposition technique. The mobilized friction angle at the critical state measured by the direct simple shear test is equal to 37.3° which is 9 % less than that measured by direct shear box test. This paper also provides the appropriate dynamic properties of Chiang Mai sand with the shear strain level <2 % for any practical purpose. Test results showed that the normalized shear modulus agrees well with other investigators while the damping ratio is noticeably smaller than the lower-bound range for sand reported in the past studies.     

饱水砂层深基坑中悬臂式双排桩支护及地下水处理方法

结合实例,对常用基坑支护及止水方法进行了比选,介绍了在饱水砂层深基坑中采用的悬臂式双排桩支护及高压旋喷止水帷幕技术。通过理论计算和监测数据分析了双排桩的支护效果,并探讨了高压喷射注浆止水技术在基坑支护中的应用。     

用标贯击数确定抗液化振动挤密砂桩的间距

在考虑了抗液化振动挤密砂桩的侧向和竖向加密的同时,又考虑了砂桩的充盈系数对加固作用的影响,从而提出了一种基于抗震规范的液化判别方法,根据标准贯入击数确定抗液化振动挤密砂桩间距的经验关系。     

单桩负摩阻力传递机理分析

本文基于桩的荷载传递概念,提出了计算单桩负摩阻力的力学模型,该模型不仅适用于端承桩,也适用于端承-摩擦桩或摩擦桩,同时该模型也便于考虑多层土中桩的负摩阻力的性状。两个实例的计算结果表明,本文提出的模型比较符合实测结果。     

砂土高压蠕变微观机理分析

砂土层在地面沉降过程中呈现一定的蠕变特性。文章采用一维压缩试验对4 MPa 下砂土的变形特征进行了研究,并 采用改进的试验装置对砂土的微观结构进行了提取。通过对8 组不同级配砂土样的蠕变特性和微观结构分析,得到如下结 论：粒径单一的砂土在蠕变过程中更容易出现突变,砂粒受力后更容易发生破碎,产生滑移错动;砂土蠕变的蠕变量与砂 粒级配密切相关,砂土的粒径越单一且粒径越大时,砂土的蠕变量也越大;采用表征砂土颗粒形状复杂程度的形状系数, 从微观上定量分析了砂土在蠕变过程中发生破碎的情况和蠕变量大小,且形状系数越小,表明该种砂土形状越复杂,在蠕 变过程中砂土的破碎性越高,蠕变量越大。     

Reliability Analysis of Quick Sand Condition

First order reliability method (FORM) is generally used for reliability analysis in geotechnical engineering. This article adopts generalized regression neural network (GRNN) based FORM, Gaussian process regression (GPR) based FORM and multivariate adaptive regression spline (MARS) based FORM for reliability analysis of quick sand condition. GRNN is related to the radial basis function (RBF) network. GPR is developed based on probabilistic framework. MARS is a nonparametric regression technique. A comparative study has been carried out between the developed models. The performance of GPR based FORM and MARS based FORM match well with the FORM. This article gives the alternative methods for reliability analysis of quick sand condition.     

Influence of Relative Pile-Soil Stiffness and Load Eccentricity on Single Pile Response in Sand Under Lateral Cyclic Loading

The environment prevalent in ocean necessitates the piles supporting offshore structures to be designed against lateral cyclic loading initiated by wave action, which induces deterioration in the strength and stiffness of the pile-soil system introducing progressive reduction in the bearing capacity associated with increased settlement of the pile foundation. A thorough and detailed review of literature indicates that significant works have already been carried out in the relevant field of investigation. It is a well established phenomenon that the variation of relative pile-soil stiffness (K _rs ) and load eccentricity (e/D) significantly affect the response of piles subjected to lateral static load. However, the influence of lateral cyclic load on axial response of single pile in sand, more specifically the effect of K _rs and e/D on the cyclic behavior, is yet to be investigated. The present work has aimed to bridge up this gap. To carry out numerical analysis (boundary element method), the conventional elastic approach has been used as a guideline with relevant modifications. The model developed has been validated by comparing with available experimental (laboratory model and field tests) results, which indicate the accuracy of the solutions formulated. Thereafter, the methodology is applied successfully to selected parametric studies for understanding the magnitude and pattern of degradation of axial pile capacity induced due to lateral cyclic loading, as well as the influence of K _rs and e/D on such degradation.     

嵌岩灌注桩竖向荷载测试与分析

嵌岩灌注桩是当前较常用的基础形式之一,但其理论分析、试验和测试研究远不能适应工程应用的需要.通过南京地区软岩嵌岩桩某试桩工程所作的单桩竖向抗压静载荷试验、基岩静载荷试验和桩周摩阻力及端承力试验,分析了嵌岩桩的荷载传递性状.