Types of Backfill Materials

建筑业使用不同类型的回填材料。新利客户常用的回填材料如下新利客户所述，其工程属性描述。

1。粗粒土壤

粗粒土壤include gravelly and sandy soils and range from clayey sands (SC.) through the well-graded gravels of gravel-sand mixtures (GW) with little or no fines. They will exhibit slight to no plasticity. All of the well graded soils falling in this category have fairly good compaction characteristics and when adequately compacted provide good backfill and foundation support.

（一种）One difficulty that might arise with soils in this category would be in obtaining good compaction of the poorly graded sands and gravels. These poorly graded materials may require saturation with downward drainage and compaction with greater compaction effort to achieve sufficiently high densities. Also, close control of water content is required where silt is present in substantial amounts. Coarse-grained materials compacted to a low relative density are susceptible upon saturation to liquefaction under dynamic loads.

（b）对于少量或没有罚款的沙子和砾石砂，可以在空气干燥或饱和条件下实现良好的压实。如果使用饱和度以帮助压实，则需要向下排出向下的排水以在向下的方向上保持渗漏力。

Consideration may be given to the economy of adding cement to stabilize moist clean sands that are particularly difficult to compact in narrow confined areas. However, the addition of cement may produce zones with greater rigidity than untreated adjacent backfill and form “hard spots” resulting in non uniform stresses and deformations in the structure.

（C）无粘性材料非常适合放置在邻新利客户近的结构中，包括围绕结构的狭窄区域，其中不允许和在不规则形状的结构下以及隧道，涵洞，公用事业和坦克中的不规则设备。清洁，粒度，较高的材料，最大尺寸为1英寸，95％通过4号筛新利客户子和5％或更少的通过的No.200筛，适用于这些区域。然而，存在产生渗水水可能积聚和饱和相邻的内聚土壤的区域存在危险，导致不希望的固结或肿胀。在这种情况下，需要提供粒状回填，密封表面的规定，以及远离结构的表面水。

2。细粒土壤低至中等可塑性

在有机粘土（CL）低至中等塑性（砾石，桑迪或粉质粘土和瘦粘土）和无机淤泥和非常细的砂岩（ML这种类别中包含低塑性（粉质或粘土细砂和粘土硅）。无机粘土相对渗透，可以用重压力设备相当容易地压实，以提供良好的稳定回填。

Soils in the CL group can be compacted in confined areas to a fairly high degree of compaction with proper water content and lift thickness control. The clayey sands of the SC group and clayey silts of the ML group can be compacted to fairly high densities, but close control of water content is essential and sometimes critical, particularly on the wet side of optimum water content. Some ML soils, if compacted on the dry side of optimum, may lose considerable strength upon saturation after compaction. Considerable settlement may occur.

因此，必须在使用这些土壤中以回填，特别是低于地下水位。而且，在动态加载时，饱和Ml土壤可能高易受液化的影响。如果这些土壤用作地震易发区域的回填，应进行实验室测试以确定其液化潜力。

3.Rock

The suitability of rock as backfill material is highly dependent upon the gradation and hardness of the rock particles. The quantity of hard rock excavated at most subsurface structure sites is relatively small, but select cohesionless materials may be difficult to find or may be expensive. Therefore, excavated hard rock may be specified for crusher processing and used as select cohesionless material.

4.Shale

Although shale is commonly referred to as rock, the tendency of some shales to breakdown under heavy compaction equipment and slake when exposed to air or water after placement warrants special consideration.

（一种）一些柔软的Shales在重型压实设备下分解，导致材料在压实前的压实后具有完全不同的性质。在这种类型的材料用于回填之前，应识别此事实。建立适当的压实标准可能要求承包商构建测试填充并改变含水量，提升厚度和覆盖数，并利用所提出的设备用于回填操作。这种类型的回填只能在不受限制的开放区域中使用，其中重型拖曳或自推进设备可以运行。

（b）一些页岩倾向于打破或熟化when exposed to air. Other shales that appear rocklike when excavated will soften or slake and deteriorate upon wetting after placement as rock fill. Alternate cycles of wetting and drying increases the slaking process. The extent of material breakdown determines the manner in which it is treated as a backfill material. If the material completely degrades into constituent particles or small chips and flakes, it must be treated as a soil-like material with property characteristics similar to ML, CL, or CH materials, depending upon the intact composition of the parent material. Complete degradation can be facilitated by alternately wetting, drying, and disking the material before compaction.

5.边缘材料新利客户

边缘材料是这些材料新利客户，由于它们的压实，固结或溶胀特性的差，通常不会被用作回填，如果可用的合适材料。被认为是边缘的材料包括高可塑性和膨胀粘土的细粒土壤。使用边缘材料的决定应基于经济和节能的考虑，包括获得合适的材新利客户料，无论是否来自遥远的借用区域或商业来源，可能会使用边际材料造成的痛苦修复成本，以及所涉及的额外费用处理，放置和充分压实边缘材料。

（一种）The fine-grained, highly plastic materials make poor backfill because of the difficulty in handling, exercising water-content control, and compacting. The water content of highly plastic fine grained soils is critical to proper compaction and is very difficult to control in the field by aeration or wetting. Furthermore, such soils are much more compressible than less-plastic and coarse grained soils; shear strength and thus earth pressures may fluctuate between wide limits with changes in water content; and in cold climates, frost action will occur in fine-grained soils that are not properly drained. The only soil type in this category that might be considered suitable as backfill is inorganic clay (CH). Use of CH soils should be avoided in confined areas if a high degree of compaction is needed to minimize backfill settlement or to provide a high compression modulus.

（b）The swelling (and shrinking) characteristics of expansive clay vary with the type of clay mineral present in the soil, the percentage of that clay mineral, and the change in water content. The active clay minerals include montmorillonite, mixed-layer combinations of montmorillonite and other clay minerals, and under some conditions chlorites and vermiculites.

Problems may occur from the rise of groundwater, seepage, leakage, or elimination of surface evaporation that may increase or decrease the water content of compacted soil and lead to the tendency to expand or shrink. If the swelling pressure developed is greater than the restraining pressure, heave will occur and may cause structural distress. Compaction on the wet side of optimum moisture content will produce lower magnitudes of swelling and swell pressure. Expansive clays that exhibit significant volume increases should not be used as backfill where the potential for structural damage might exist. Suitability should be based upon laboratory swell tests.

（C）Additives, such as hydrated lime, quicklime, and fly ash, can be mixed with some highly plastic clays to improve their engineering characteristics and permit the use of some materials that would otherwise be unacceptable. Hydrated lime can also be mixed with some expansive clays to reduce their swelling characteristics.

Laboratory tests should be performed to determine the amount of the additive that should be used and the characteristics of the backfill material as a result of using the additive. Because of the complexity of soil-additive systems and the almost complete empirical nature of the current state of the art, trial mixes must be verified in the field by test fills.

6.商业副产品

使用商业的副产品,如炉slag or fly ash as backfill material, may be advantageous where such products are locally available and where suitable natural materials cannot be found. Fly ash has been used as a lightweight backfill behind a 25-foot-high wall and as an additive to highly plastic clay. The suitability of these materials will depend upon the desirable characteristics of the backfill and the engineering characteristics of the products.