含裂缝砾石土的反滤准则

砾石土为高土石坝普遍采用的防渗材料。由于分层施工填筑或心墙拱效应,高土石坝的防渗心墙常会出现裂缝,对于含裂缝砾石土的反滤设计准则的研究成果缺乏。开展了不同含砾量的含裂缝砾石土在不同级配、不同密度的反滤料保护情况下的反滤试验研究。总结了现有的适用于砾石土的反滤设计准则并与试验结果进行对比分析。分析表明现有反滤准则都不能完全适用于含裂缝砾石土的反滤设计。基于试验和对比分析结果,同时考虑含裂缝砾石土及反滤料联合抗渗机理,提出了适用于含裂缝砾石土的反滤准则。用反滤试验结果进行验证表明本文提出的反滤准则适用于不同含砾量的含裂缝砾石土的反滤设计。     

土工合成材料在防治路面反射裂缝中的应用

概述了土工合成材料防治路面裂缝的效果,分析了土工合成材料防治路面反射裂缝的机理和影响因素,并介绍了土工合成材料沥青罩面的设计方法。     

土工合成材料在防治路面反射裂缝中的应用

概述了土工合成材料在防治路面反射裂缝中的效果 ,分析了土工合成材料防治路面反射裂缝的机理和影响因素 ,并介绍了土工合成材料沥青罩面的设计方法。     

吐鲁番市某教学楼裂缝调查及原因分析

分析了吐鲁番市某教学楼裂缝的原因,根据该教学楼的裂缝形态及当地气候特点,确定该裂缝为温度裂缝,进行温度观测,应用王铁梦的简化计算方法计算温度应力,对墙体裂缝作定性分析,进而提出对裂缝的处理方法。     

非饱和土力学实用化之路探索

非饱和土力学的研究水平目前还停留在学院式阶段,主要原因在于吸力量测的困难。为了促进非饱和土力学的实用化,在分析吸力的3种作用机制的基础上提出了几种吸力的替代方案,如饱和度、折减吸力和广义吸力。此外,孔隙气压力的计算也是一件麻烦事,为此提出了简化计算方法。最后探讨了非饱和土中表面裂缝的形成对边坡稳定和变形的影响。     

上部土钉、下部桩锚结构的复合型围护结构计算方法的探讨

本文讨论了上部土钉、下部桩锚结构的复合围护结构两种简化计算方法的可行性。采用数值分析软件ZS0IL．PC 2007,通过对某特定的土层建模分析,认为简化方法中应考虑上部土钉支护开挖卸载过程中释放的应力对下部结构的影响。结合数值分析结果,提出了新的简化计算方法,使其在受力上更加接近实际。     

土石坝的裂缝和压实质量

本文讨论了土石坝由变形而产生裂缝的类型和成因。根据对国内外已建坝的裂缝调查资料和变形观测资料的分析,总结出一些规律。用非线性弹性增量理论解释了变形和应力的关系并说明验算裂缝的方法。从而确认防止裂缝的关键是减小变形并使变形协调。提高土石坝的压实质量是达到上述要求的主要措施。最后,就压实标准和压实方法提出建议。     

土心墙堆石坝坝顶裂缝扩展有限元模拟

基于ABAQUS计算平台,采用扩展有限元方法对某土心墙堆石坝坝顶裂缝的发生及扩展情况进行了模拟,针对含初始裂缝的简化平面有限元计算模型,得到了以下结论:坝顶裂缝的产生原因主要是上下游的不协调变形,上游坝壳的湿化变形会加剧此不协调变形;坝顶裂缝多出现在心墙下游侧,其扩展的方向为朝下游侧且与水平面呈45°左右夹角,初始裂缝的长度对裂缝扩展方向影响较小;开发编制了求裂纹扩展长度及开度的插件,以靠近心墙中心的初始裂缝为例,在库水压力及湿化作用下,裂缝扩展的平均长度为2.5 m,裂缝平均张开距离为0.18 m;初始裂缝越靠近心墙中部,裂缝扩展长度及开度越大。设计及施工中在加强接触部位碾压质量的同时应注重坝顶心墙中部的压实质量以减小坝顶裂缝发生的危害。     

砂性土地质条件下泡沫轻质土路基病害处理分析

以实际工程为例,结合工程的具体情况对砂性土地质条件下轻质泡沫土路基出现裂缝的原因进行了分析。经过分析证明,泡沫土路基出现病害主要是因水诱发导致泡沫土产生裂缝及起拱病害,针对这一情况,重新对破坏的路基及台阶进行浇筑。     

某湖底隧道主体结构的裂缝分析

基于非线性有限元分析,对某湖底隧道主体结构关键区段在土水压力、不均匀沉降、温差等因素作用下的裂缝分布规律进行了研究,指出各区段在土水压力作用下均为带裂缝工作,裂缝分布在顶板跨中底面、外侧墙顶部外侧以及顶板正中顶面等位置,较小的不均匀沉降对各区段的裂缝分布影响不大,温度应力对裂缝分布的影响较大,降温会导致底板出现新的微裂缝。其结果可供类似隧道的设计、施工和管养参考。     

土石坝心墙水力劈裂的非饱和土固结方法研究

针对土石坝心墙土在初次蓄水前为饱和度高于80%的非饱和土,提出了研究心墙水力劈裂问题的非饱和土固结简化计算的有效应力分析方法。该方法不仅可反映孔隙中气体对水压上升的影响,还可合理分析心墙土的渗透性、初始饱和度和蓄水速度等心墙水力劈裂的影响因素。以糯扎渡堆石坝为例,研究发现:填筑竣工时,尽管心墙中部水压很高,但心墙仍处于非饱和状态;初次蓄水时,上游水压力不能及时渗入心墙内部,形成了心墙内外的水压力突变,可导致心墙水力劈裂的发生。同时研究发现:提高心墙的渗透系数、提高心墙填筑土的初始饱和度、在初次蓄水时,放慢蓄水速度等均可防止心墙水力劈裂的发生。因此非饱和土固结简化计算的有效应力方法分析水力劈裂问题是合理的,它可为实际心墙土石坝预防水力劈裂问题提供科学依据,并可进一步提高土石坝设计水平。     

盾构隧道同步注浆引起的地表变形分析

壁后注浆是盾构隧道施工的关键环节,对控制地表变形影响显著。为建立同步注浆引起的地表变形计算理论,在分析同步注浆对隧道周围土体的作用机理的基础上,将同步注浆对地层的压力效应概化为半无限弹性体中的柱形孔扩张问题,采用镜像法导出了同步注浆引起地表变形的计算式。通过一具体实例,分析了影响同步注浆引起地表变形的因素,结果表明：同步注浆引起的地表变形值受注浆压力、隧道埋深、隧道开挖半径、初始水土压力、土体弹性模量、泊松比等因素影响。     

胶结黏土中正断层扩展的变形和孔压变化研究

 基岩断层错动而引起的上覆土体变形会对地表以及地下结构物造成破坏。上覆土体的胶结特性和隐伏断层的存在,使得断层错动的变形机制更为复杂。采用滤纸技术模拟隐伏断层,通过2组离心机试验研究胶结土体中正断层裂缝的扩展机制及伴随的孔压变化规律。对土体的变形分析和孔隙水压力的监测加深了对地裂缝的认识。研究发现,正断层错动引起胶结黏土的变形机制为受弯变形。隐伏断层使得土体受弯区变小、土体破坏程度加剧。胶结黏土受弯形成的地裂缝分为张拉裂缝和剪切裂缝,这些地裂缝的发展为超孔压的消散提供了优势路径。     

Resilient behavior of compacted subgrade soils under the repeated triaxial test

Subgrade soils are very important materials to support highways. Resilient modulus (M_r) has been used for characterizing stress-strain behavior of subgrades subjected to repeated traffic loadings. Recently the repeated triaxial test procedure has been upgraded through AASHTO T 307. Since the testing procedure is still complex, the testing has not been widely implemented in practice. In order to evaluate resilient behavior of compacted subgrades soils, the repeated triaxial test and the unconfined compressive test as well as some fundamental property tests were conducted. In this study, the applicability of a simplified procedure with a confining pressure of 13.8 kPa and deviator stresses of 13.8, 27.6, 41.4, 55.2, 69 and 103.4 kPa was investigated on the typical sandy–silty–clay and silty–clay subgrade soils encountered in Indiana. The results obtained from the simplified procedure are comparable with those obtained from AASHTO T 307 which calls for 15 combinations of stresses. This shows the simplified procedure to be feasible and effective for design purpose. Some soils compacted wet of optimum moisture content showed an excessive permanent deformation. This phenomenon was investigated by the comparison of the unconfined compressive test and the repeated triaxial test results. For soils exhibiting excessive permanent deformation, use of deformed length is desirable for more accurate calculation of M_r. Usually the soils compacted dry of optimum shows the largest M_r for sandy–silty–clay soils due to capillary suction, but it is not necessarily true for silty–clay soils. A predictive model to estimate regression coefficients k₁, k₂, and k₃ using 11 soil variables obtained from the soil property tests and the standard Proctor compaction tests was developed. The predicted regression coefficients compare well with measured ones.     

挡土墙后粘性填土的土压力计算

本文根据库伦原理,推导出了一个比较简单的计算粘性土土压力的公式。对无粘性土也适用。     

The use of recycled tire chips to minimize dynamic earth pressure during compaction of backfill

The backfill areas of concrete culverts constructed in roads have been subjected to differential settlement due to poorly compacted soils. Dynamic compaction rollers cannot be fully utilized to compact the backfill soils near the culverts because the high earth pressure induced by dynamic loading frequently results in cracks in the culvert walls. In this study, two cushion materials, recycled tire chips and expanded polystyrene (EPS) boards are applied on the culvert walls in backfill areas to reduce the dynamic earth pressure induced by the compaction loading as well as to improve the characteristics of compacted soils. A numerical analysis is carried out to study the effects of the cushion materials on the stress variation with soil depth in the backfill areas. The numerical analysis shows that a cushion material with low elastic modulus and high damping ratio can effectively reduce the dynamic earth pressure. Field tests are also performed to study the performance of the two cushion materials. It is found from the field tests that the both cushion materials reduce the dynamic earth pressure acting on the culvert wall. However, the recycled tire chips are more efficient in reducing the dynamic earth pressure because of its relatively high damping ratio and low stiffness values compared to the EPS.     

Pullout tests conducted on clay reinforced with geogrid encapsulated in thin layers of sand

The interaction between reinforcement and backfill materials is a significant factor for analysis and design of reinforced earth structures which is simplified as pullout or direct shear resistance. This paper presents the results of pullout tests aimed at studying the interaction of clays reinforced with geogrids embedded in thin layers of sand. Pullout tests were conducted after modification of the large direct shear apparatus. Samples were prepared at optimum moisture content and maximum dry densities obtained from standard Proctor compaction tests. Tests were conducted on clay-geogrid, sand-geogrid and clay-sand-geogrid samples. A unidirectional geogrid with sand layer thicknesses of 6, 10 and 14 mm were used. Results revealed that encapsulating geogrids in thin layers of sand under pullout conditions enhances pullout resistance of reinforced clay. For the clay-sand-geogrid samples an optimum sand layer thickness of 10 mm was determined, resulting in maximum pullout resistance which increased with increasing confining pressure. The optimum sand layer thickness was the same for all the normal pressures investigated. For sandy soils the passive earth pressure offered the most pullout resistance, whereas for clayey soils, it was replaced by frictional resistance. It is anticipated that provision of thin sand layers will provide horizontal drainage preventing pore pressure built up in clay backfills on saturation.     

冲击荷载作用下花岗岩残积土的动力损伤与破坏机理

为调查冲击荷载作用下花岗岩残积土的力学行为,开展了不同冲击频率(3～15 Hz)和振幅(100～400 kPa)影响的循环冲击试验,分析冲击荷载引起的超静孔隙水压力和变形的发展规律。结果表明:振幅和频率的影响均存在临界值,振幅与频率超过临界值时,土体损伤强烈会引起强度迅速衰减。低频与超高频冲击下更易产生较高孔压,从而导致有效应力降低进而引起强度下降。根据冲击应力与应变的滞回曲线的形态特征提出了花岗岩残积土冲击动力损伤的3个定量评价参数,并据此提出了3种冲击破坏类型与辨识方法,指出冲击能量耗散引起的结构损伤及塑形变形累积是花岗岩残积土产生冲击破坏的根本原因,其影响程度取决于土的原始结构强度与微观裂隙发育程度,也与冲击模式和应力水平导致的裂隙扩展规律和塑性累积变形大小有关。工程实践中应查明土体在冲击荷载下的临界振幅与临界频率,尽可能避免采用高振幅与低频率及超高频率荷载冲击土体。研究有助于了解冲击荷载的作用规律和土体力学响应,为中国花岗岩风化地层的施工与设计提供科学理论指导。     

土体干缩裂隙发育方向及演化特征的层间摩擦效应研究

自然界中的土体通常成层分布,在干旱条件下,表层土体的干缩开裂过程极易受层间接触条件的制约。为了探究土层间摩擦效应对土体干缩裂隙发育方向及其演化特征的影响,开展了一系列室内干燥试验。试验共配置了3组初始饱和的泥浆样,在30℃的室温条件下干燥失水,通过在试样底部铺设不同粗糙度的砂纸来模拟不同土层间的摩擦效应。试验过程中对试样表面及侧面进行定时拍照,从不同角度记录了裂隙发育全过程,通过分析,获得了一些新发现:(1)干缩裂隙不仅能从土体表面向下发育,而且还可能率先从土体底部向上发育,这不同于以往的习惯性认识;(2)初始裂隙的发育位置受土质条件及基底摩擦条件的共同制约,对于非均质性比较严重或者表面存在明显"杂点"的土体而言,裂隙往往首先从表面"杂点"处产生并向下发育,而对均质性较好的土体而言,在基底摩擦效应的影响下裂隙可以率先从土体底部生成并逐渐向上发育,且土体底部的裂隙发育程度甚至会高于表面的裂隙发育程度;(3)底部生成的裂隙以斜向上发育居多,这可能与裂隙发育过程中受到的剪切应力作用有关;(4)干燥过程中,土体呈向心收缩,存在明显的收缩核现象;(5)基底摩擦效应能改变土体干缩开裂过程中内部应力场的演化,从而对土体的横向和纵向收缩应变及剖面含水率的空间分布产生影响,如基底摩擦越大,土体横向收缩应变越小,而纵向收缩应变越大。