客观的

在不受干扰或后润的情况下测定土壤的CBR

Reference Standards

IS: 2720(Part 16)-1973- Methods of test for soils: Laboratory determination of CBR.

设备/设备

• Compression machine
• Proving ring, Dial gauge, Timer
• 采样管
• Split mould
• Vernier caliper, Balance

Preparation sample

The test may be performed

（a）未受干扰的土壤标本

（b）在remoulded土壤标本上

(a) On undisturbed specimen

未受干扰的样品通过装配到模具，钢切削刃为150mm内径，并尽可能将模具推入地面。当模具充满土壤时，应通过挖掘除去。然后修剪顶部和底部表面，以提供所需的样品长度。

（b）在remoulded标本上

The dry density for remoulding should be either the field density or if the subgrade is to be compacted, at the maximum dry density value obtained from the Proctor Compaction test. If it is proposed to carry out the CBR test on an unsoaked specimen, the moisture content for remoulding should be the same as the equilibrium moisture content which the soil is likely to reach subsequent to the construction of the road. If it is proposed to carry out the CBR test on a soaked specimen, the moisture content for remoulding should be at the optimum and soaked under water for 96 hours.

土壤Sample- 在筛选的重新样本中使用的材料是筛子的。可以通过将其通过19mm筛网的相等量的材料更换而是通过将其保留在4.75mm上的等量的筛分来制备较大材料的含量。如果土壤颗粒的尺寸主要大于19毫米，则该方法并不令人满意。样品可以静态或动态地压实。

I. Compaction by Static Method

计算所需水分含量的湿土的质量，以在占用模具中占据标准试样体积时所需的密度。一批土壤与水彻底混合，得到所需的含水量。将湿土质的正确质量置于模具中并通过压制置换盘获得的压实，滤纸放置在盘状和土壤之间。

II. Compaction by Dynamic Method

For dynamic compaction , a representative sample of soil weighing approximately 4.5 kg or more for fine grained soils and 5.5 kg or more for granular soil shall be taken and mixed thoroughly with water. If the soil is to be compacted to the maximum dry density at the optimum water content determined in accordance with light compaction or heavy compaction, the exact mass of soil required is to be taken and the necessary quantity of water added so that the water content of soil sample is equal to the determined optimum water content. The mould with extension collar attached is clamped to the base plate. The spacer disc is inserted over the base plate and a disc of coarse filter paper placed on the top of the spacer disc. The soil water mixture is compacted into the mould in accordance with the methods specified in light compaction test or heavy compaction test.

Procedure

1. 含有具有底板的样品的模具，但是暴露的顶面被放置在试验机的下板上。
2. Surcharge weights, sufficient to produce an intensity of loading equal to the weight of the base material and pavement is placed on the specimen.
3. 为了防止土壤的变速进入附加额度的孔，在置于渗透柱塞之前，将2.5kg环形重量放置在土壤表面之后，之后放置了附加重量的其余部分。
4. The plunger is to be seated under a load of 4 kg so that full contact is established between the surface of the specimen and the plunger.
5. The stress and strain gauges are then set to zero. Load is applied to the penetration plunger so that the penetration is approximately 1.25 mm per minute.
6. 载荷的读数在0.0，0.5,1.0,1.5,2.0,2.5,4.0,50,7.5,10.0和12.5 mm的渗透处。
7. The plunger is then raised and the mould detached from the loading equipment.

Calculation

Load-Penetration curve:

The load penetration curve is plotted taking penetration value on x-axis and Load values on Y-axis. Corresponding to the penetration value at which the CBR is desired, corrected load value is taken from the load-penetration curve and the CBR calculated as follows

California bearing ratio = (P_T/ P_S)x100

Where

P_T= Corrected unit (or total) test load corresponding to the chosen penetration curve, and

P_S= Unit(or total) standard load for the same depth of penetration as for P_S取自标准代码。

报告

通常计算CBR值以渗透为2.5mm和5mm。报告CBR值是正确的第一个小数位。

Safety & Precautions

• 筛选后，在刷子的帮助下清洁筛子
• While weighing put the sieve with soil sample on the balance in a concentric position.
• Check the electric connection of the sieve shaker before conducting the test.