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(1)最近几年来世界各国(苏联、美国、瑞典、挪威等)其中也包括中国高价的沥青混凝土路面由于道路基层强度不够而大量损坏。基层通常用碎石、大石块、砾石、泥结碎石和各种粘结料(沥青、柏油、水泥、石灰)改善的土壤建造。目前美国、西欧各国和苏联只有在偶而情况下才采用“大石块”基层。现在道路基层的材料主要是碎石、砾石、泥结碎石和稳定土壤。 (2)使用沥青混凝土路面的实践证明,只有在用碎石基层时这种路面的使用期限才能达到18—30年。采用其他柔性类基层时路面会出现大量损坏的现象,因为按混合料最佳级配原则来计设它们并不是适合的。最佳级配原则只有在由砾石、泥结碎石和其他相似材料构成过渡式路面时才是合理的。但是把它应用来建造沥青混凝土路面下的基层是不正确的。沥青混凝土路面的临界挠度比砾石、泥结碎石或稳定土壤等路面小1/2 或3/4。因此对沥青混凝土路面下道路基层材料的要求应该比用于建造过渡式路面时来得高。 (3)莫斯科建筑工程学院城市建设与经营教研组和全苏道路科学研究院进行的研究证明:砾石、泥结碎石和其他相似基层在潮湿时对自己强度的改变敏感性很高,这是因为基层包含细土粒(颗粒小于0.5公厘)之故,即使其数量不大于15％也是如此。 (4)野外和实验室试验曾经确定,例如砾石材料的含水量由4％增加到6％(按重量计),则其形变模量将由600公斤/平方公分降低到180,但是在设计沥青混凝土路面时,设计师总采用砾石材料的最大形变模量数值为800,甚至有时E=1000公斤/平方公分,却不管在混合料内细土的含量常常超过20％(按重量计)的事实,并且砾石和其他当地材料一样,其质量是非常不匀一的。我们的试验查明,只有筛过的砾石颗粒大小从60—15公厘时,其形变模量为E=800公斤/平方公分。但是,同样的砾石如果不过筛,又包含小于0.05公厘的颗粒为3％和小于2公厘的颗粒为17—20％,而细土粒在饱和状态下的塑性指数达4的话,则其变形模量仅350—500公斤/平方公分左右,甚至更低。 (5)1948—1956年对苏联各种自然条件下沥青混凝土路面损坏地段进行研究指出,大多数砾石、碎石(采用抗压强度小于500公斤/平方公分的石料)和泥结碎石基层在秋季特别是春季处于极潮湿的情况下,其形变模量不是设计值800—1000公斤/平方公分,而是E≤500公斤/平方公分。 (6)采用强度弱的石料建造沥青混凝土路面下的基层,特别在加强原有次高级路面时,显然是不利的。抗压强度小于500公斤/平方公分的软石料,只有预先用沥青或柏油处理后才能用来建造沥青混凝土路面的基层。 (7)在沥青或柏油处治的土壤基层上铺筑沥青混凝土路面,同样不是有效的。用水泥或石灰加固的当地土壤所建造的基层,此采用沥青或柏油处治的土壤时来得较为坚固。 (8)基层为混凝土甚至其中掺用碎砖的混凝土,则沥青混凝土路面的工作情况很好。 (9)分析提高沥青混凝土路面使用期限方面所积累的经验可得出下列各点结论: A.有适当垫层的混凝土基层应该认为是最完善的一种基层; B.沥青混凝土路面可以敷设在形变模量为E=1000公斤/平方公分(单层式时)和E=800公斤/平方公分(双层式时)的材料所组成的柔性的基层上; B.只有抗压强度超过R=800～1000公斤/平方公尺的石料所造成的基层方能满足上述要求,这种基层可按碎石路、弹石路和大石塊形式敷设。石料强度很小,但不小于R≥400公斤/平方公分时,这种材料只准用于冰冻深度小于0.3—0.4公尺地区的干燥地段上; Γ.沥青混凝土路面不宜铺筑在沥青或柏油处治土壤基层上; π.砾石或泥结碎石材料只应该用于干燥地段的道路基层中,假如其中包含小于5公厘的颗粒不超过20％,小于0.5公厘不大于10％,小于0.074公厘不超过3％,并且在使用石灰岩时材料的强度(根据苏联规定的石料分类)应该是2—3级。在潮湿地方也可使用泥结碎石或不低于2—3级石灰岩或砾石,但其中包含小于5公厘的颗粒要在10％以下,要完全没有小于0.5公厘的颗粒,即实质上使用冲洗过的砾石。如泥结碎石或砾石材料的质量较坏,只有先用各种粘结料改善后才能使用,或者按表1的标准用于道路基层下层。 (10)第(9)项中所规定的建造沥青混凝土路面基层的砾石和泥结碎石材料的标准,和瑞典、美国的道路建筑实践是相结合的。只有这一种质量的砾石,不论其含水量如何(最大含水量可达到按重量计的4—5％),能在10次重复加荷的情况下不呈现“弹簧”状态。 (11)在北京、上海、南京、杭州和中国其他城市内,黑色路面的总厚度多为25—40公分,在这些路面上观察到无数裂缝和损坏,这些显然与道路的基层上层中包含细土粒过多有关。中国设计和建筑路面的专家们,必须参考世界各国用砾石或泥结碎石为基层设计沥青混凝土路面的经验,再根据自己当地的特点来制订砾石或泥结碎石材料的适当的技术规范。
(1) In recent years, many countries in the world (the Soviet Union, the United States, Sweden, Norway, etc.), including China’s high-priced asphalt concrete pavement, have been greatly damaged due to inadequate road infrastructure. The grass-roots level is usually built of rubble, boulders, gravel, masonry and soil modified with various binders (bitumen, tar, cement, lime). At present, the United States, Western European countries and the Soviet Union only use the “big boulders” grassroots only if they do so on an occasional basis. At present, the material of the grassroots roads are mainly gravel, gravel, mudstone and stable soil. (2) The practice of using asphalt concrete pavement proved that the period of use of such pavement can reach 18-30 years only when using gravel base. The use of other flexible grassroots pavement will be a lot of damage to the phenomenon, because the principle of best mix grading them are not suitable. The best grading principle is only reasonable when transitional pavements are made of gravel, clay bonded stones and other similar materials. However, it is not correct to apply it to build grassroots under asphalt pavement. The asphalt concrete pavement has a critical deflection of 1/2 or 3/4 smaller than that of gravel, clay-bonded or stabilized soils. Therefore, the requirements of road base material under asphalt pavement should be higher than when used to construct transitional pavement. (3) Research conducted by the Urban Construction and Management Research Team and Moscow Institute of Road Research, Moscow Institute of Architectural Engineering proved that gravel, clay-bonded gravel and other similar substrates are highly sensitive to changes in their strength when wet, because The grassroots contain fine soil particles (particles less than 0.5 mm), even though their number is not more than 15%. (4) Field and laboratory tests have determined that, for example, when the moisture content of gravel material is increased from 4% to 6% by weight, the modulus of deformation will be reduced from 600 kg / cm 2 to 180% When paving, the maximum gross modulus of deformation of the designer for the gravel material is 800, sometimes even E = 1000 kg / cm², despite the fact that the content of fine soil in the mix often exceeds 20% by weight, And gravel and other local materials, the quality is very uneven. Our tests revealed that the modulus of deformation of a screened gravel particle is E = 800 kg / cm² only when it is 60-15 mm in size. However, if the same gravel is 17 to 20% less than 3% for particles less than 0.05 mm and less than 2 mm for particles of less than 0.05 mm and the plastic index of fine particles in saturated state is 4, then Deformation modulus of only 350-500 kg / cm ^ 2, or even lower. (5) From 1948 to 1956, the study on asphalt pavement damaged lots under various natural conditions in the Soviet Union pointed out that most of gravel, gravel (using stone with compressive strength less than 500 kg / cm ^ 2) In autumn, especially in the spring when it is extremely damp, the deformation modulus is not designed to be 800-1000 kg / cm 2, but E ≤ 500 kg / cm 2. (6) It is clearly unfavorable to construct grassroots under asphalt pavement using weak stone materials, especially when strengthening the original sub-high pavements. Compressive strength of less than 500 kg / cm of soft rock, asphalt or asphalt can only be used beforehand for the construction of asphalt concrete pavement base. (7) It is equally inefficient to lay asphalt concrete pavement on asphalt or asphalt-treated soil base. The grass-roots built with cement or lime-fortified native soils are more robust when used with asphalt or tar soil. (8) The asphalt concrete pavement works well for the concrete or even concrete with broken brick. (9) The accumulated experience gained in analyzing the service life of asphalt pavements can be concluded as follows: A. The concrete foundation with proper cushion should be regarded as the most perfect one. B. Asphalt concrete pavement can be laid on The flexural modulus of deformation for the E = 1000 kg / cm² (single-layer) and E = 800 kg / cm² (double-layer) materials; B. Only when the compressive strength exceeds R = Grass-roots levels from 800 to 1,000 kg / m 2 of stones can meet the above requirements and can be laid in the form of gravel roads, boulders and boulders. Stone strength is small, but not less than R ≥ 400 kg / cm ^ 2, this material is only for frozen depth less than 0.3-0.4 meters area of dry areas; Γ. Asphalt Pavement should not be paved asphalt or asphalt The gravel or clay-bonded stone material should only be used in the road base of dry lots, provided that it contains no more than 20% of particles less than 5 mm, less than 10% less than 0.5 mm, less than 0.074 The thickness of the material does not exceed 3% in mm, and the strength of the material (according to the stone classification prescribed by the Soviet Union) when using limestone should be 2-3. In wet places can also use clay aggregates or not less than 2-3 limestone or gravel, but less than 5% of which contains less than 10% of particles to completely no less than 0.5 mm particles, that is, essentially Use rinsed gravel. Mudstone or gravel materials, such as clay, are of lesser quality and can only be used if they have been modified with a variety of binders or used as per Table 1 below. (10) The standards for gravel and clay-bonded stone materials for the construction of asphalt pavement base course stipulated in (9) are combined with road construction practices in Sweden and the United States. Only this quality of gravel, irrespective of its water content (maximum water content of 4-5% by weight), does not assume a “spring” condition with 10 repetitions. (11) In Beijing, Shanghai, Nanjing, Hangzhou, and other cities in China, the total thickness of black pavements is mostly 25-40 cm. Numerous cracks and damages are observed on these pavements. Obviously, the upper grassroots level roads contain fine Soil is too much about. Chinese experts in the design and construction of pavements must make reference to the experience of other countries in the world in designing asphalt concrete pavements using gravel or clay bonded gravel as the grassroots level and then formulate appropriate technical specifications for gravel or clay bonded materials according to their local characteristics.