Determination of Field Unit Weight of soil by Sand Cone Method

(Field Density test or Sand Replacement Method)

 

Testing objectives:
Determine the in-situ density of natural or compacted soils using sand replacement method.

Need and Scope:

The main application of this test is the cases like embankment and pavement construction, this is basically a QC test or quality control test where certain degree of compaction is required. 

This test is also used in stability analysis of embankments and slopes, for the calculation of pressure in underlying strata for settlement problems and also design of underground structures.

 

Notice: Since the water content of the soil is very likely to vary from time to time and hence the field total unit weight,  the dry unit weight of the soil is always used as a means of reporting the test results and eventually applying in real application.  The established relation between the two reads as follows:

 

gd = gt / (1+ w)

gd = Dry unit weight ( KN/ m3 )

gt = Total unit weight

w = Water content (%)

Apparatus Required:

 

Photos (Test Procedure, the table to be filled in comes right after photos):

Test Equipments

Step 1- . Weight of Proctor mold, W1

Step 2a- Pouring the sand into the compaction mold

Step2b- Making the surface leveled

Step2c- Compaction mold filled out with sand

Step 2d-Weight of proctor mold + Sand, W2

Step 5. Weight of plastic Gallon+Cone+Sand (before use)

Step 6a-Close the valve of the cone attached to the cone

Step 6b- turn the cone and gallon upside down

Step 6c- open the valve, sand flows from the gallon to the cone, after the flow stops close the valve and take the gallon+cone from the tray

Step 6d- CNTD...

Step 6e- Weight of plastic Gallon+Cone+Sand (after use)

Step 8a- Weight of plastic Gallon+Cone+Sand (before use)

Step 8b- Go to the field where the soil's unit weight is to be measured and place the metal tray and fasten the 4 screws.

Step 8c- Dig up a hole about 10 to 15 cm deep.

Step 8d- As you are digging the hole put the retrieved soil into the plastic bag in order that the soil does not lose moisture.

Step 8e- All of the soil is transferred into the bag

Step 8f- The soft soil at the bottom of the hole is poured into the bag as well.

Step 8g- All of the soil is transferred into the bag

step 8h-Having the valve closed turn the gallon+cone upside down and place the cone in the center hole of tray and open the valve so that sand flows

Step 8i- sand flows CNTD... Unlike this photo plastic bag should be kept closed

Step 8j- After flow of sand stops close the valve and pick the assembly up, the sand in the cone will be poured into the tray.

Step 8k- CNTD

Step 8L- The sand in the hole and the overflow sand will be left in the field, grab all parts and get back to the lab.

Step 9- Weight of plastic Gallon+Cone+Sand (after use)

Step 11- Weigh the evaporating dish

step 12- Weigh the evaporating dish + wet soil from the field

Step 13- Put the evaporating dish + wet soil in the oven and after 24hrs weigh it again

Relevant table:

Test Steps

Quantity

Obtaining the unit weight of the sand used
1. Weight of Proctor mold, W1 4.178 kg
2. Weight of proctor mold + Sand, W2 5.609 kg
3. Volume of the mold, V1 0.00095 m3
4. Dry unit weight, gd (sand) = (W2 - W1) / V1 1506 kg/m3

Calibration cone
5. Weight of plastic Gallon+Cone+Sand (before use), W3 5.466 kg
6. Weight of plastic Gallon+Cone+Sand (after use), W4 3.755 kg
7. Weight of the sand to fill the cone, Wc = W4- W3 1.711 kg

Results from field tests
8. Weight of plastic Gallon+Cone+Sand (before use), W5 7.387 kg
9. Weight of plastic Gallon+Cone+Sand (after use), W6 3.919 kg
10. Volume of hole, V2 = (W5-W6-Wc)/ gd (sand) 0.00117m3
11.Weight of evaporating dish, W7 0.507 kg
12. Weight of evaporating dish + wet soil from the field, W8 2.334 kg
13. Weight of evaporating dish + dry soil after 24hrs, W9 2.251 kg
14. Moist unit weight of the soil in the field, gt (in-situ soil) = (W8 - W7) / V2 1561  kg/m3
15. Water content in the field, w(%)= (W8 - W9) / (W9- W7)*100 4.76%
16. Dry unit weight in the field, gd (in-situ soil)= [gt (Row 14)] / [1+ w(%) / 100] 1490 kg/m3
17.

 

Conversion factors (Unit weight):

 

1000 kg/m3  = 9.81 KN/m3  = 62.4 lb/ft3