The soakaway or percolation test is used to determine if a new or replacement soakaway can be installed. There are two very different types of soakaway – foul water soakaways and surface water soakaways. Foul water soakaways deal with small volumes over a long period surface water deal with large volumes over a short duration.
Geoinvestigate conducts Soakaway tests for surface water soakways in accordance with BRE 365 Soakaway Design. These tests are carried out in test pits dug to a depth of about 2m or 2.5m using a mini excavator with a 0.3m to 0.6m wide bucket.
Soil permeability is measured by filling the pit with water from a bowser and recording the length of time for 75% of the volume of water to drain away. Soil permeability can also be measured in Boreholes.
The test uses a thick-walled sample tube, with an outside diameter of 50.8 mm and an inside diameter of 35 mm, and a length of around 650 mm. This is driven into the ground at the bottom of a borehole by blows from a slide hammer with a mass of 63.5 kg (140 lb) falling through a distance of 760 mm (30 in). The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. The sum of the number of blows required for the second and third 6 inches of penetration is termed the “standard penetration resistance” or the “N-value”. In cases where 50 blows are insufficient to advance it through a 150 mm (6 in) interval the penetration after 50 blows is recorded. The blow count provides an indication of the density of the ground, and it is used in many empirical geotechnical engineering formulae.
The shear vane test is a method of measuring the undrained shear strength of a cohesive soil. The test is carried out with equipment consisting of a rod with vanes mounted to it that is inserted into the ground and rotated. A gauge on the top of the rod measures the torque required to cause failure of the soil and provides a conversion to shear strength. The equipment has been in use since at least 1948. The equipment has also been used since at least 1967 to assess the shear strength of packs of snow at risk of forming a slab avalanche.
The plate load test is a field test, which is performed to determine the ultimate bearing capacity of the soil and the probable settlement under a given load. This test is very popular for the selection and design of the shallow foundation.
For performing this test, the plate is placed at the desired depth, then the load is applied gradually and the settlement for each increment of the load is recorded. At one point a settlement occurs at a rapid rate, the total load up to that point is calculated and divided by the area of the plate to determine the ultimate bearing capacity of soil at that depth. The ultimate bearing capacity is then divided by a safety factor (typically 2.5~3) to determine the safe bearing capacity.
The cone penetration or cone penetrometer test (CPT) is a method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the 1950s at the Dutch Laboratory for Soil Mechanics in Delft to investigate soft soils. Based on this history it has also been called the “Dutch cone test”. Today, the CPT is one of the most used and accepted soil methods for soil investigation worldwide.
The test method consists of pushing an instrumented cone, with the tip facing down, into the ground at a controlled rate (controlled between 1.5 -2.5 cm/s accepted). The resolution of the CPT in delineating stratigraphic layers is related to the size of the cone tip, with typical cone tips having a cross-sectional area of either 10 or 15 cm², corresponding to diameters of 3.6 and 4.4 cm. A very early ultra-miniature 1 cm² subtraction penetrometer was developed and used on a US mobile ballistic missile launch system (MGM-134 Midgetman) soil/structure design program in 1984 at the Earth Technology Corporation of Long Beach, California.
Dynamic Penetration Testing (DPT), commonly referred to as Dynamic Probing, is a fast and relatively low cost Ground Investigation method. It involves driving a cylindrical sacrificial or fixed cone into the ground using a high frequency percussive hammer. The cone is attached to a 1m section steel rod with a nominal diameter of approximately 35mm and graduation markings set at 100mm intervals. Depending upon the chosen method, the drop height can be adjusted.
Blows per 100mm are recorded and after every 1m section, a further rod is added and the process is continued until the probe refuses to penetrate the ground or the test reaches the required depth.
The results from this method can be correlated directly to a standard penetration test ‘N’ value. The results are plotted on a graph, providing a visual interpretation of the strengths of the different soil strata encountered.
