如何在现场进行土壤的板载试验？

Objective

To perform plate load test to obtain a load-settlement curve of a soil at a particular depth so as to estimate the ultimate bearing capacity a foundation.

Apparatus

1. Test plate of square size (300 mm or 450 mm or 600 mm or 750 mm)
2. Hydraulic jack (50 T capacity)
3. Hydraulic pump (50 T capacity)
4. Pressure gauge (to read 50 T load with a sensitivity of 0.5 T)
5. 证明环或载荷电池（50 T容量）
6. 4没有表盘仪（灵敏度为0.01 mm，行程为50 mm）
7. 装载列
8. Dial gauge supporting channels
9. Dial gauge stands
10. 表盘仪的磁性底座
11. 装载平台设备（梁，板，砂袋等）或桁架锚杆杆
12. Plumbob
13. Sprit level
14. 三脚架（竖立平台或桁架框架）
15. Pulley block (to lift the girders or truss frame)

程序

1. 挖掘测试坑。测试凹坑尺寸应为测试板尺寸的5倍（b_P.) and depth equal to the depth of foundation.
2. The loading platform should be erected over the test pit such that, the vertical line drawn through the center of gravity of the load passes through the centroid of the base of the test pit. This can be achieved by positioning the reaction girder (truss) with the help of the plum bob and spirit level. The load over the platform should be at least 50% more than the anticipated load to be transferred on the plate. This will ensure the safety of the platform for any small shift of the CG of the loading platform from the vertical axis of the pit.
3. 位置测试板集中t的底部he pit. Ensure that the ground surface below the test plate is perfectly horizontal and level so that no stress concentration takes place below the plate during loading. If the ground surface is slightly uneven a thin layer of sand is spread underneath the test plate.
4. 将液压插孔定位在板上，使得当液压建立起来时，插孔推动加载平台。如果要求在测试板和插孔之间放置装载列，以确保插孔到达装载平台。
5. 在角落处对角地（优选在测试板的所有拐角处的4个拨号仪上，以记录其沉降。应在稳定的基础上仔细支撑表盘仪，这些底座不会与板沉淀。这可以通过在磁性碱基的帮助下置于地面水平的两个横梁上来实现。板的沉降通过拨号仪支架传递到表盘仪表。
6. The dial gauges should be positioned such that the plunger of the dial gauges is at its beginning of rebound (i.e. the plunger is initially pushed up) so that it will get released as the plate settles and the reading changes and the difference in reading provided the settlement of the plate.(See fig-1 for plate load setup)
7. 通过将液压泵入千斤顶，将负载施加在板上。千斤顶柱塞的向上运动试图推动装载平台。由于千斤顶内建立的压力（例如1或2 T）远小于平台上的负荷，因此插孔中的压力将通过将装载平台（例如30至40t）作为刚性来推动测试板支持。这是一个类似于两个支持之间的系统的扩展的情况。由于扩展较弱的支持（地面）产量。
8. Apply a seating load of 0.7 T/m²在开始实际加载之前释放。
9. 注意表盘仪的初始读数。
10. 载荷以方便的增量通过液压千斤顶施加。负载增量可以是预期安全承载能力的五分之一或最终承载能力或任何其他较小负载的十分之一。从装配到液压泵的压力表或从千斤顶和反应平台之间固定的证明环读取施加的载荷。
11. 从拨号仪读数观察板的沉降。对于在1,4,10,20,40和60分钟之后，应当在每小时以每小时间隔，每小时变得小于约0.02mm，每小时沉降，因此应观察到沉降。新利18体育官网登录输入表格形式的读数。（见图2）
12. 在完成负载下的结算读数记录后，应用下一个负载增量，并在新负载下指出拨号仪读数。
13. The loading increments and the recording of the settlements under each load are continued until the maximum load is reached. The maximum load that is to be applied corresponds to 1.5 times the estimated ultimate load or to 3 times the proposed allowable bearing pressure.

观察和计算

The load intensity and settlement observation of the plate load test are plotted. The figure shown below (Fig-3) shows a set of typical load settlement curves. The ultimate bearing capacity is taken as the load at which the plate starts sinking at a rapid rate, i.e. when the curve drops down to a vertical line. From figure 3 it can be observed that in dense sand or stiff clays the failure is not pronounced. In such cases a plot of load and settlement, both being taken in logarithmic scales, gives two straight lines. The intersection of these lines is taken as the ultimate bearing capacity of soil (see fig.4).

Also read the post on涉及板载测试的不确定性。

Also Read:How to Calculate Bearing Capacity of Soil From Plate Load Test