Cone Penetration Test

In the Cone Penetration Test (CPT), a cone on the end of a series of rods is pushed into the ground at a constant rate of 2 cm/sec. and contionuos or intermittent measurements are made of the recistance to penetration of the cone. Measurements are also made of either the combined resistance to penetration of the cone and outer surface of a sleeve or the resistance of a surface sleeve. Pore pressure measuring is also becoming a standard within CPT.

Geotech products: CPT Systems

Seismic profiling

A seismic piezocone is pushed progressively into the ground. Each metre or so it is stopped. A hammer is used at the surface, to produce seismic waves. For shallow saturated soil the compressional (P) wave velocity is normally primarily a function of the bulk modulus of the pore water, and is not sensitive to changes in the stiffness of the soil skeleton. Shear waves are usually used, and are typically generated by placing a wooden sleeper under the wheel of the penetrometer truck and striking it horizontally with a large hammer.

Geotech products: Seismic CPT 

Dynamic Sounding Test

Dynamic sounding is the in situ measurement of the penetration resistance from driving a cone vertically into the ground. A hammer of a given mass at a constant height of fall is used to drive the cone, while the number of strikes for penetration a predetermined depth is counted.
The results from dynamic sounding are used mainly to derive the strength and compressibility of primarily cohesion less soils.

Selection of dynamic methods

Geotech products: Dynamic Sounding Apparatus  

Rotary/Percussion Sounding

Rotary/Percussion sounding can be performed in different ways and was in the early years a method to determine the level between soil and rock.
These methods was developed in Scandinavia and the most advance method today is Norwegian total sounding also called Soil/Rock total sounding in Sweden. By recording parameters like depth, penetration time, feed force, rotation speed, hammer pressure and penetration speed you will be able to obtain the stratigraphy in almost all soils including rock and determine where to go further with test like CPT and vane tests.

Soil/rock total sounding:
The sounding starts with a pre drilling hole of 0,5 meter then static penetration with a rotation speed of 25 rpm and a penetration speed of 20 mm/s is taken place. When it’s no longer possible to obtain the penetration speed percussion is started with first the flushing and then the hammer. When the boulder, obstacle or firm soil is penetrated the drill bit is moved up and downed together with flushing to prevent that no friction will occur to the drill rod. Then the static penetration with rotation is resumed.

Geotech products: Rotary/Percussion

Weight Sounding Test 

The weight sounding test was developed in Sweden in about 1915 and became a national standard in 1917. The method is normally used for preliminary investigations in differing soils. The test result could also be used for design and inspection investigations in most common soils but are primarily applied in very soft to stiff cohesive soils and very loose to dense cohesion less soil. In very dense sand and gravel and tills pre-drilling could be necessary. The results are generally used to evaluate the thickness and extent of different soil layers but also for the assessment of the design parameters for spread foundations and piles.

The method is included in the European standardisation, ENV 1997-7,3

Geotech products: Weight Sounding

Diamond Coring

Diamond drilling provides a 'drill core' of the rock penetrated by the hole. This drill core provides a continuous sample of the rock penetrated, and the geologist can examine that core as he would a surface rock exposure for rock type, alteration, mineralization and structural features such as bedding and fractures.

The hole is drilled using a hollow drill bit whose annular face is set, or impregnated, with small diamonds. The bit is attached to a string of hollow drill rods which are rotated by a gasoline or diesel powered engine. Drilling fluids, usually just water, are forced down the inner side of the drill rods, out around the drill bit face and returned up the hole between the drill rods and the drill hole wall carrying the drill cuttings (sludge) which have been produced by the face of the drill bit. The drill core consists of the column of rock remaining in the center of the bit as it cuts a circular hole. This drill core, as the hole progresses, stands within the bit and within the following core tube. When the core tube is full, the shock breaks off the core near the bottom of the hole. The core is prevented from slipping out of the core tube by retaining springs. In the old style 'standard' drilling method, the drillers would have to pull the whole string of rods, rod by rod, to recover the core tube and empty out the drill core. With modern 'wire line' systems, a retrieving device is dropped down the hole, within the drill rods, using a wireline cable. This device snaps unto the core tube, unlocks it from the core barrel, and pulls the core tube up to surface to be emptied into the core box.

Geotech products: Diamond core drilling

Column Penetration Test (KPS)

A common method for quality control of lime/cement columns is the Column Penetration Test (KPS).
The test is carried out by pushing a winged probe through the centre of the column with a speed of 20mm/s and the shear strength of the column is evaluated based on the force required to push the probe through the column.

The width of the wings is slightly less than the column diameter (normally 100mm). The idea is to obtain a mean value of the shear strength for the larger part of the cross section.

Geotech products: Lime/Cement probes

Vane Shear Test

The Vane Shear test is used to estimate the undrained shear strength of a soil, and is particularly appropriate for assessing very soft and sensitive clays, which can not be tested accurately in a laboratory as it is difficult to obtain an undisturbed sample. 

A rod with a four blade vane is pushed into the ground and rotated generally at a slow rate of 6o to 12o per minute. Every 15 - 30 seconds the torque force is measured, once maximum torque has been reached, the vane is rotated rapidly for ten revolutions to induce shear failure. After shearing, the slow rotation rate is resumed to determine the remoulded shear strength. The shear strength is proportional to the torque/blade diameter3. 

The test can be done at the base of a drill hole or trial pit, or at ground level. If the test is being conducted at the bottom of a drill hole it is important that the test area has not been disturbed by boring, generally the test is conducted five borehole diameters below the borehole base.

Geotech products: Electrical Vane Instrument

Pore Water Pressure

The piezometer, also known as pore pressure meter, is used to measure pore water pressure in soil. It provides significant quantitative data on the magnitude and distribution of pore pressure and its variations with time. It also helps in evaluating the pattern of seepage, zones of potential piping and the effectiveness of seepage control measures undertaken. The use of a piezometer helps in monitoring the behaviour after construction and indicates potentially dangerous conditions that may adversely affect the stability of the structure, its foundation and appurtenant. It also provides basic data for design improvement that will promote safer and more economical design and construction.

Geotech products:  Electric Piezometer

Standpipe Piezometer Test

The simplest form of pore pressure measuring device is the observation well or standpipe. This consists of an open-ended tube which is perforated near the base, and is inserted in a borehole.

Measurements of water level in the standpipe are made by lowering an electrical ‘dipmeter’ down the open standpipe. The dipmeter normally consists of a coaxial or twin cable connected at the surface to a battery and some device to detect closure of the electrical circuit. This may consist either of a milliammeter or an oscillator, giving either a visual or a audible signal when the water level is met. The base of the coaxial cable, which is lowered down the standpipe, is covered with a metal probe so designed that the electrical circuit will not be closed by stray water clinging to either the cable or the inside of the standpipe.

Geotech products: Open Standpipe piezometer