Field testing forms an integral part of any geotechnical investigation or construction site. STS with its experienced staff and standardized equipment provide multi-dimensional field testing facilities to our clients.
Standard Penetration Test
Standard penetration tests (SPT) are carried out at regular intervals of depth in soil layers to assess the in-situ compactness of various soil layers.
SPT is by far the most popular and economical method of obtaining subsurface information. A number of foundation design procedures make use of SPT results. The test is carried out by driving a split spoon sampler of specified dimensions a distance of 46 cm into the soil at the bottom of the borehole. A 63.5-kg hammer falling free from a height of 76 cm is used to drive the sampler. Number of blows required to drive it 30.5cm is recorded as ‘N’ value.
Plate Load Test
Plate load test is used to obtain the settlement and ultimate bearing capacity. Rigid Steel plate of 30cm, 25mm is used. Capacity is determined by hydraulic loading. Rate of loading is about 1/5 of expected bearing capacity. The maximum load is about 1.5 times the allowable bearing capacity. The dial gauge (measuring device) is used on the loading column. When the test is in an excavation on borehole a separate reference column on invent tap is used.
Field Density Test
Field density of natural ground is generally determined by sand replacement method. The basic principle of sand replacement method is to measure the in-situ volume of hole from which the material was excavated from the weight of sand with known density filling in the hole. The in- situ density of material is given by the weight of the excavated material divided by the in-situ volume.
Well Pumpout Test
Well pump out tests are conducted to estimate the hydraulic properties of an aquifer including safe yield, hydraulic conductivity, transmissivity, and storativity, radius of influence, etc.
The test is performed by extracting groundwater from a water well at specified discharge rate for specific duration (24 hours to 72 hours) and observing the draw down in main well and at least two observation wells.
Field Permeability Test
In-situ permeability tests in boreholes are carried out by inducing a pressure different from that in the ground. Pressure can be increased with the introduction of water in the boreholes, this method is called Falling Head or Inflow test. Similarly pressure can be decreased by pumping the water out from the boreholes, this method is called Rising Head or Outflow test. Permeability tests are of two types
• Constant Head test
• Variable Head test
In constant head test, the pressure is kept constant throughout the duration of the test while in variable head test, pressure may be allowed to vary.