二级公路毕业设计外文文献

外文资料及翻译

Effects of Design Features on Rigid Pavement Performance

The performance of rigid pavements is affected by a variety of design features, including slab thickness, base type, joint spacing, reinforcement, joint orientation, load trans fer, dowel bar coatings, longitudinal joint design, joint sealant, tied concrete shoulders ,and subdrainage . A study was made by ERES Consultants, Inc. under FHWA contract on the effects of these features on rigid pavement performance . Ninety-five pavemen tsections located in four major climatic regions were thoroughly evaluated . The following conclusions, which provide some revealing insights into pavement performance, are abstracted from the report (Smith et al., 1990a).

Slab Thickness The effect of slab thickness on pavement performance was significant.It was found that increasing slab thickness reduced transverse and longitudinal cracking in all cases. This effect was much more pronounced for thinner slabs than fo rthicker slabs . It was not possible to compare the performance of the thinner slabs and the thicker slabs directly, because the thick slabs were all constructed directly on th esubgrade and the thinner slabs were all constructed on a base course .

Increasing the thickness of slab did not appear to reduce joint spalling or join tfaulting . Thick slabs placed directly on the subgrade, especially in wet climates an dexposed to heavy traffic, faulted as much as thin slabs constructed on a base course .

Base Type Base types, including base/slab interface friction, base stiffness, base erodibility, and base permeability, seemed to have a great effect on the performance of jointed concrete pavements . The major performance indicators, which were affected by variations in base type, were transverse and longitudinal cracking, joint spalling, and faulting .

The worst performing base type, consisted of the cement-treated or soil cement bases, which tended to exhibit excessive pumping, faulting, and cracking. This is most likely due to the impervious nature of the base, which traps moisture and yet can brea- k down and contribute to the movement of fines beneath the slab .

The use of lean concrete bases generally produced poor performance . Large curl -ing and warping stresses have been associated with slabs constructed over lean concrete bases. These stresses result in considerable transverse and longitudinal cracking of the slab . The poor performance of these bases can also be attributed to a bathtub design, in which moisture is trapped within the pavement cross section .

Dense-graded asphalt-treated base courses ranged in performance from very poor to good. The fact that these types of bases were often constructed as a bathtub design contributed to their poor performance . This improper design often resulted in severe cracking, faulting, and pumping.

The construction of thicker slabs directly on the subgrade with no base resulted In a pavement that performed marginally. These pavements were especially susceptible to faulting, even under low traffic levels.

Pavements constructed over aggregate bases had varied performance, but were generally in the fair to very good category. In general, the more open-graded the aggregate,the better the performance . An advantage of aggregate bases is that they contribute the least to the high curling and warping stresses in the slab . Even though aggregate bases are not open-graded, they are more permeable and have a lower friction factor than stabilized bases .

The best bases in terms of pavement performance were the permeable bases . Typical base courses have permeabilities ranging from 0 to less than 1 ft/day (0 .3 m/day) ; good permeable bases have permeabilities up to 1000 ft/day (305 m/day) . Specific areas of concern were the high corner deflections and the low load transfer exhibited by the permeable bases . These can affect their long-term performance, so the use of dowel bars might be required . An unexpected benefit of using permeable bases was the reduction in "D" cracking on pavements susceptible to this type of distress .

Slab Length For JPCP, the length of slabs investigated ranged from 7 .75 to 30 ft(2.4to9.1m). It was found that reducing the slab length decreased both the magnitude of the joint faulting and the amount of transverse cracking. On pavements with random joint spacings, slabs with joint spacings greater than 18 ft (5.5 m) experienced more transverse cracking than did the shorter slabs .

For JRCP, the length of slabs investigated ranged from 21 to 78 ft (6 .4 to 23 .9 m) .Generally, shorter joint spacings performed better, as measured by the deteriorated transverse cracks, joint faulting, and joint spalling . However, several JRCP with long joint spacings performed quite well . In particular, the long jointed pavements in New Jersey, which were constructed with expansion joints, displayed excellent performance .

An examination of the stiffness of foundation was made through the use of the radius of relative stiffness, f . Generally speaking, when the ratio L/E, where L is the length of slab, was greater than 5, transverse cracking occurred more frequently . This

factor was further examined for different base types . It was found that stiffer base courses required shorter joint spacings to reduce or eliminate transverse cracking .

Reinforcement The amount of steel reinforcement appeared to have an effect in controlling the amount of deteriorated transverse cracking . Pavement sections with less than 0.1% reinforcing steel often displayed significant deteriorated transverse cracking.A minimum of 0 .1% reinforcing steel is therefore recommended, with larger amounts required for more severe climate and longer slabs.

Joint Orientation Conventional wisdom has it that skewed joints prevent the application of two wheel loads to the joint at the same time and thus can reduce load-associated distresses . The results from the limited sample size in this study were ambiguous, but all of the nondoweled sections with skewed joints had a lower PSR than similar designs with perpendicular joints . The available data provide no definite conclusions on the effectiveness of skewing transverse joints for nondoweled slabs . Skewed joints are not believed to provide any benefit to doweled slabs.

Load Transfer Dowel bars were found to be effective in reducing the amount of joint faulting when compared with nondoweled sections of comparable designs. The diameter of dowels had an effect on performance, because larger diameter bars provided better load transfer and control of faulting under heavy traffic than did smaller dowels.It appeared that a minimum dowel diameter of 1 .25 in . (32 mm) was necessary to provide good performance .

Nondoweled JPCP slabs generally developed significant faulting, regardless of pavement design or climate . This effect was somewhat mitigated by the use of permeable bases. However, the sections in this group had a much lower number of accumulated ESAL, so no definite conclusions can be drawn yet .

Dowel Bar Coatings Corrosion-resistant coatings are needed to protect dowels from the adverse effects of moisture and deicing chemicals .While most of the sections in this study did not contain corrosion-resistant dowel bars, those that did generally exhibited enhanced performance. Very little deteriorated transverse cracking was identified on these sections. In fact, one section in New Jersey with stainless steel-clad dowel bars was performing satisfactorily after 36 years of service .

Longitudinal Joint Design The longitudinal joint design was found to be a critical design element.Both inadequate forming techniques and insufficient depths of joint can contribute to the development of longitudinal cracking . There was evidence of the ad vantage of sawing the joints over the use of inserts . The depth of longitudinal joints is generally recommended to be one-third of the actual, not

designed, slab thickness, but might have to be greater when stabilized bases are used .

Joint Sealant Joint sealing appeared to have a beneficial effect on performance . This was particularly true in harsh climates with excessive amounts of moisture . Preformed compression sealants were shown to perform well for more than 15 years under heavy traffic.Except where "D" cracking occurred, pavement sections containing preformed sealants generally exhibited little joint spalling and were in good overall conditions.Rubberized asphalt joint sealants showed good performance for 5 to 7 years.

Tied Concrete Shoulders It is generally believed that tied concrete shoulders can reduce edge stresses and corner deflections by providing more lateral supports to the mainline pavement, thus improving pavement performance . Surprisingly, this study showed that, although tied concrete shoulders performed better than asphalt shoulders,many of the tied shoulders were not designed properly and actually contributed to poor performance of the mainline pavement . The tiebars were spaced too far apart ,sometimes at a spacing of 40 in.(1016 mm), and were not strategically located near slab corners to provide adequate support . In some cases, tied concrete shoulders were constructed over a stabilized dense-graded base in a bathtub design, resulting in the poor performance of mainline pavement.

Subdrainage The provision of positive subdrainage, either in the form of longitudinal edge drains or the combination of a drainage layer and edge drains, generally reduced the amount of faulting and spalling related to "D" cracking . With few exceptions, the load-associated distresses, especially faulting and transverse cracking, decreased as the drainage characteristics improved . The overall pavement performance can be improved by using an open-graded base or restricting the percentage of fines . A filter layer must be placed below the permeable base, and regular maintenance of the outlets must be provided .

译文

结构特点对刚性路面性能的影响

刚性路面的性能受种种结构特点的影响，如板厚、基层类型、接缝间距、钢筋用量、接风方向、荷载传递、传力杆涂层、纵缝设计、接缝填封料、有拉杆混凝土道肩和地下排水等。ERES咨询公司于联邦公路局（FHWA）签订合同，研究这些结构特点对刚性路面的影响。对四个主要气候区内95个路面段作了详细的评定。从研究报告（Smith等，1990a）摘录了以下结论，以便对路面性能有一透彻的理解。

一、板厚

板厚对路面性能的影响很大。发现在所有的实例中，增加板厚，是纵向和横向开裂减小。这种影响对对薄的路面板，比厚板更为明显。不可能直接将薄板的想能与厚板进行比较，因为板厚都直接铺筑在土基上，而薄板都铺筑在基层上。

增加板厚并不能减少接缝剥落及接缝错台。厚板直接铺在土基上，尤其是气候潮湿交通繁重的情况下，产生的错台同铺筑在基层上的薄板同样也很多。

二、基层类型

基层类型，包括基层与板的界面摩擦力、基层刚度、基层抗冲刷能力和基层透水性，看来对有接缝混凝土路面性能有很大影响。受各种基层类型影响的主要性能指标是横向额纵向开裂、接缝剥落和错台。

性能最差的基层类型是水泥稳定或水泥土基层，最容易于楚翔很对唧泥、错台和开裂。这很可能是因为基层不透水，它吸收水分，易于断裂，使得板下的细颗粒发生移动。

应用贫混凝土基层，一般工作性能都很差。很大的翘曲应力是与贫混凝土基层上铺筑路面板有关系的。由于这些应力，使得面板产生很多横向和纵向的裂缝。这些基层的性能差，还可能是由于路面横截面按盆状设计，造成水分集中。

密级配沥青稳定基层的性能从很差到好都有。性能低劣的原因是这些基层类型经常采用盆状设计，这种错误设计结果将产生严重的开裂、错台和唧泥。

厚的面板直接铺筑在不舍基层的土基上，路面勉强合格。这些路面特别容易错台，即使交通量不大也是如此。

铺筑在集料基层上的路面具有不同性能，但是一般属于良好到很好等级。通常，集料开集配空隙越多。性能越好。集料基层的优点是由于基层引起的面板翘曲高应力是最小的。即使集料基层不是开集配的，也比稳定基层具有较好的透水性和较低的摩擦系数。

在路面性能方面最好的基层是透水基层。常用基层的渗透率在0至0.3m/d(1ft/d)，而好的透水基层渗透率达305m/d(1000ft/d)。需要特别考虑的

问题是透水基层板角部位挠度大，且传荷能力低。由于这将影响其长远性能，要应用传力杆是必不可少的。应用透水基层有一种意想不到的好处，它能够是容易产生“D”裂缝的路面，裂缝数量减少。

三、板长

调查的JPCP路面板长度在2.4--9.1m（7.75--30ft）之间，发现板长减小，接缝错台的大小和横向开裂的数量两者都减少。在接缝间距不规则的路面上，接缝间距大于18ft（5.5m）的板，横向开裂多余较短的板。

对于调查的JRCP路面板长度在6.4—23.9m（21--78ft）之间。一般地，从调查损坏的横向裂缝、接缝错台和接缝剥落来看，接缝间距有短的一些的路面性能好些。然而，有些接缝间距长的JRCP，性能也很好。尤其是新泽西州的长接缝路面，筑有膨胀缝，呈现出极好的性能。

通过相对刚度半径l调查了地基的刚度。一般来说，当L/l比值（L为板长）大于5，横向开裂较多。这一因素对不同基层类型作了进一步研究。发现基层刚度愈大，所需的接缝间距愈短。这样便能减少或消除横向开裂。

四、钢筋用量

看来钢筋用量对控制横向开裂损坏时有影响的。钢筋用量小雨0.1%的路面段经常呈现明显的横向开裂损坏。因此建议最小钢筋用量为0.1%，对于气候恶劣以及采用较长的路面板时，需要较多的钢筋用量。

五、接缝方向

一般看法认为斜接缝避免了两个车轮同时通过接缝，因此可降低与荷载有关的损坏。从有限尺寸板的研究结果却相反，所有不舍传力杆的斜向接缝，他的PSR 值小于同样设计的垂直接缝。现有的数据无法对无传力杆板斜向横缝的有效性作出肯定的结论。不能认为斜接缝比有传力杆的板有任何优点。

六、荷载传递

若与设计相仿的不舍传力杆路段作比较，传力杆对减少接缝错台是有效的。传力杆的直径对路面性能有一定的影响，因为在重型车辆的作用下，直径大的传力杆比直径小的传力杆更能底荷载和控制错台。看来，为了保证路面有良好的性能，传力杆的最小直径应为32mm（1.25mm）。

通常，不设传力杆的JPCP板有明显的错台，这与路面设计和气候无关。若采用透水基层，这种影响有所缓和。不过，这种路段的累计当量单轴荷载（ESAL）很低，因此还不能作出肯定的结论。

七、传力杆涂层

为了防止传力杆受水分和除冰化学物质的有害影响，必需采用防锈涂层。在此项研究的大部分路段，都没有防锈传力杆。事实上，在新泽西州一个用不锈钢包裹过传力杆的路段，使用了36年后，路面性能仍然良好。

八、纵缝设计

经研究发现，纵缝设计是最关键的设计部位。接缝施工不恰当或深度不够，均可造成纵向开裂。锯缝法比欧诺个嵌条有明显欧典。纵缝深度，不设计的一般建议取路面厚度的三分之一，若采用稳定基层，还可以更深一些。

九、接缝填封料

看来接缝填封料对路面性能是有利的。这在水分过量的不利气候地区，更是如此。欧诺个预压成型的填缝料，在重型车辆作用下使用15年以后，仍然能很好地工作。除了有“D”裂缝产生的位置之外，有预压成型填缝料的路面段一般只有很小的接缝剥落，总的情况是良好的。橡胶沥青接缝填封料使用5—7年后性能仍然良好。

十、设拉杆的混凝土路肩

通常认为设拉杆的混凝土路肩为主车道路面提供了侧向支承，可以减小板边应力和板角挠度，从而改善了路面的性能。可是意想不到，在此项研究中，一方面发现设拉杆的混凝土路肩的性能优于沥青路肩，然而，许多设拉杆的路肩设计不当，实际上使主车道路面的性能变坏。拉杆相隔间距太远，有时达到1016mm （40in），又不能有针对性地放在靠近板角的至，以提供适当的支承。有时候，设拉杆的混凝土路肩铺筑在密级配稳定基层上，按盆状设计，结果是主车道路面性能变坏。

十一、地下排水

提供良好的地下排水，无论是纵向边沟排水，还是综合应用排水层和边沟排水，一般都可以减小与“D”裂缝有关的错台剥落。除少数情况之外，随着排水状况的改善，与荷载的有关的损坏，尤其是错台和横向开裂都减少了。应用开集配基层，或者限制细颗粒的百分数，都可以改善整个路面的性能。在透水基层西面必须设置过滤层，必须对出水口做定期维护。