Coefficient of earth pressure at rest for normal,consolidated soils

In this study consecutive consolidated isotropically drained triaxial tests for the coefficient of earth pressure at rest(K0)were carried out to investigate its rules of evolution as well as its strength characteristics for normal,consolidated saturated silt under high pressure.The tests results indicate that: 1)for normal,consolidated saturated silt,K0 values increase as the consolidation stress increases at high pressure levels,while the nonlinear characteristics of K0 are inconspicuous compared to cohesive soils; 2)the Jaky and Roscoe equations,used to calculate K0,are only suitable for certain soils,but cannot represent these values for normal,consolidated saturated silt due to the variation in bilinear strength at high pressure; and 3)there are close relations between the nonlinear characteristics of K0 and the void ratio,measured in the tests.Both share the same functional form while under pressure.Based on our experimental results,we developed an empirical linear model to interpret the rules of nonlinear variation for the coefficient of earth pressure at rest.     

Coefficients of earth pressure at rest in thick and deep soils

The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest, K0, was investigated under high pressures. The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0. Moreover, K0 increases during the loading process becoming greater at high pressures. In the unloading process, however, K0 increases only at the initial stage but decreases thereafter. In addition, the incremental magnitude definition, K0=dσ3/dσ1, gives higher values than the total magnitude definition, K0=σ3/σ1, under loading. This is also true during initial stages of unloading. The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures. R is necessary to choose the appropriate Ko to avoid some accidents.     

原状黄土增湿过程中的静止土压力系数变化规律试验研究

目前得到的湿陷性黄土静止土压力系数K₀,无法反映应力和含水两个因素的影响。本文开展了原状黄土增湿过程中K₀变化规律的试验研究,得到了力水耦合作用下K₀的计算方法。首先引入“增湿水平”这一概念描述土体的含水状态;开展竖向压力作用下的侧限分级浸水试验,分别研究增湿水平、基质吸力、竖向应变与K₀的相关关系;开展黄土湿陷的离心模型试验,验证室内试验结论的有效性。试验结果表明：“增湿水平”物理意义明确,能够反映土体的含水率初始情况和增湿过程;原状黄土K₀随着增湿水平的增大而线性增加,增加速率取决于竖向压力的大小,竖向压力越大增加速率越慢;增湿过程中K₀随着吸力的减小而线性增加,竖向压力越大K₀增加的速率越慢,与增湿水平对K₀的影响规律相似;不同竖向压力下增湿过程中的竖向应变ε与静止土压力系数K₀试验点分布在一个较窄的范围内,可以采用同一双曲线描述,且不同压力作用与浸水作用的先后次序对ε-K₀曲线影响较小。基于上述新疆伊犁黄土试验规律,建立以增湿水平和竖向压力为自变量的K₀的表达式,以及以竖向应变为自变量的K₀的表达式。     

＂Nonlinear＂ characteristics of the static earth pressure coefficient in thick alluvium

Exact calculations of the static earth pressure from a thick alluvium require accurate K0 values. These calculations influence the sinking cost and the safety of the freezing method. The static earth pressure coefficient (K0) of thick and deep soil was analyzed using laboratory tests. The results show that the static earth pressure coefficient of thick and deep soils is nonlinear and different from that of superficial soils. The constant of superficial soils is usually invariant and the total stress or incremental stress definitions used in traditional geo-mechanics give the same value. The influence of load increments when calculating for superficial soil is ignored. The difference in values of K0 for thick alluvium defined by the total stress or the incremental stress methods is over 10%. The effects of the thick alluvium on K0 should be considered during the design of frozen shaft projects. Such things as the frozen shaft thickness and the excavated section height should be chosen to assure the rationality of the design and to avoid potential faults and accidents.     

悬臂式挡土墙地震主动土压力拟动力分析

地震作用下悬臂式挡土墙主动土压力的计算十分重要。为了分析悬臂式挡土墙在地震荷载作用下主动土压力分布情况,基于滑楔体平衡理论,考虑水平、竖向地震力随时间变化对地震主动土压力的影响,运用拟动力学方法,推导出地震主动土压力、第二临界破裂角的计算公式,并研究挡土墙后填土的内摩擦角和粘聚力、挡土墙与后填土之间的摩擦角和粘聚力、墙体倾角等参数对地震主动土压力系数和临界破裂角的影响。研究结果表明:第二临界破裂角随竖向地震力系数、挡土墙后方填土内摩擦角的增大而增大,随水平地震力系数、挡土墙与后方填土摩擦角的增大而减小;地震主动土压力随水平、竖向地震力系数的增大而增大,随挡土墙后方填土内摩擦角的增大而减小。     

测算物体导温系数及定压比热的方法研究

导温系数α及定压比热Cp是热工计算中的两个重要参数,其数值测算的精度如何直接影响到许多相关专业.本文运用导热反问题的方法对α及Cp进行了数值估算的研究,得出了具有较好实用价值的方法.     

深部土K_0试验方法及对减载力学特性的影响

为获得K0试验方法对土体K0固结-减载(保持轴压恒定卸除围压)变形和强度的影响,采用室内常见两种K0方法研究了深部土固结-减载应力-应变和强度特性,并分析了不同K0试验方法的误差.结果表明:采用不同K0试验方法进行固结的深部土减载路径中均呈现出脆性,但刚性压力室-柔性侧限方法下的脆性特征不明显,此种方法下进行的减载试验将低估深部土抵抗破坏的能力;刚性压力室-伺服控制试样某一高度处侧向变形为零的方法可有效控制试样平均径向变形,优于前者而对深部土更具有适用性.     

气流紧实中砂型内摩擦角ψ的变化

利用微型半导体应力传感器对气流作用下砂型内摩擦角的变化进行了研究，结果表明：在气流的作用下，与压实紧实相比，砂型内摩擦角减小，砂型紧实阻力减小，提高了紧实压力传递率，从而能够获得高紧实度的砂型。     

高压下声速温度系数的一种新算法

从声速的定义出发，由热力学基本关系给出了声速温度系数(偏微熵)的一种计算方法.以顽火辉石为例，计算结果显示，在40～140 GPa压力范围内，其纵波、体波的温度系数随压力的增大而减小，分别由40 GPa时的0.386、0.255(m/s)·K,降至80 GPa时的0.298、0.204 (m/s)·K，120 GPa时的0.244、0.175(m/s)·K，140 GPa时的0.197、0.162(m/s)·K.将这一规律内推到零压得到(dK/dT)₀=0.027 9 GPa·K^-1，与静高压下的实验数据吻合很好.     

喷射沉积超高强铝合金热变形摩擦行为研究

以喷射沉积Al-Zn-Mg-Cu-Zr-Sc-Ni铝合金为研究对象,分别在370和420℃研究4种不同润滑条件下圆坏压缩的摩擦行为,并与DEFORM-3D的数值模拟结果相对比.研究表明,采用纯铝+石墨+机油为润滑剂试样的摩擦系数最小,其值只有未加润滑剂时试样的1/4~1/5左右.在圆环最外边缘区域容易产生"单鼓形"或裂纹,边界模型中的摩擦系数大小是影响模拟结果的关键因素.     

考虑倾角影响的扩大头锚杆极限抗拔力

扩大头锚杆因其对土层的选择要求而常常具有一定的锚杆倾角,而目前工程实践中未充分考虑该倾角对锚杆抗拔力的影响.为此,在原有研究基础上,采用莫尔-库伦强度理论推导考虑倾角影响的扩大头锚杆极限端压力和抗拔力的表达式,从力学机制层面解释土体黏聚力、内摩擦角和扩大头埋深对极限端压力随锚杆倾角变化的影响.结果表明:极限端压力在静止...     

装配式盖板涵受力特性及构件搭接处强度分析

提出了装配式盖板涵洞的施工工法,通过数值模拟研究了预制盖板涵周围土压力的分布情况。对涵洞构件的内力进行了分析,利用所得到的内力值,对涵洞侧墙的稳定性以及其与基础搭接部位的强度进行了验算。结果表明：涵周土压力呈非线性分布,盖板上垂直土压力中间较小,两侧支撑处较大。侧墙水平土压力近似呈抛物线形分布,最大土压力位于距其底端1/2～2/3处。涵洞侧墙与基础底板搭接处强度要求可根据侧墙底端剪力或底板轴力进行确定。侧墙在基础中5 cm的嵌固深度可以为侧墙提供足够的水平抗力,拼装结构满足结构安全要求。