Subsurface Technologies - Service Overview

subsurface technoloiges - service overview

Our self-contained unit is enclosed in an all weather van for year-round operation. It is mounted on an FL70, two-wheel drive, with four independent outriggers for leveling. A 200-gallon on board water tank is located in rear bumper. The total weight of the equipment is approximately 26,000 lbs. and may be loaded to approximately 30,000 lbs. The probe is located as near the center of gravity as possible to take advantage of the existing reaction force.

Typical probe depths normally range from 25 to 180 feet with some probes extending to 230 feet plus. Probe depths are often limited by the inherent of the cone itself, or the imposed load restriction due to repeated heavy stressing of rods. We feel that the Dutch Cone Penetrometer we are currently using strikes a good balance between the down pressure and overall cone and rod capacity.

The Seismic Cone Penetration test (SCPT) consists of measuring the travel times of body waves propagating between a wave source and the ground surface and an array of geophones in an in-situ seismic cone penetrometer. These body waves comprise shear waves (S-waves) and compressional or primary pressure waves (P-waves). Performing this measurement during CPT soundings is much quicker and less expensive that standard crosshole tests or downhole tests.

The seismic cone penetration test (SCPT) combines the seismic downhole method and the logging capabilities of the cone penetration test (CPT) to provide rapid, reliable and economic means of determining soil stratigraphy, relative density, strength, shear and compressional wave velocities. From interval shear wave velocity and the mass density of a soil layer, the dynamic shear modulus of the soil over a specific interval may be calculated.

One capability of a typical CPT probe that is often overlooked is the ability to perform dissipation tests – pore pressure versus time. This test involves recording the dissipation of pore pressure as it approaches static equilibrium. Dissipation tests can be performed at any depth by pausing the advancements of the probe. Dissipation test data determines the groundwater table.

The CPT probe has the capability to acquire pore pressure data versus time. At anytime during a CPT test, the push can be paused to record pore pressure dissipation as at approaches static equilibrium, thus allowing real time decisions regarding the depth(s) of the test(s), compressibility and permeability within the surface strata. No time is required to initiate a test. The time required for a test – from seconds to hours – is fully dependent on the soil.

Cone Penetrometer Testing employs a technique that pushes, instead of drills, an instrumented probe into the soil to obtain soil properties.

Major components of a CPT system

Instrumental probe
Data acquisition system
Push vehicle

The CPT Probe Measures

Tip stress
Sleeve friction stress
Pore water pressure
Inclination
Seismic

General CPT Advantages

For most applications, CPT is faster and more cost effective than conventional drilling and sampling. CPT sensors allow detection in situ, which eliminates errors due to poor or improper sampling techniques.

A complete, real time profile is created from ground surface to depth of penetration, thereby identifying important layers that may be missed in an interval sampling approach.

CPT is a minimally invasive approach to site characterization that minimizes potential cross contamination in environmentally sensitive areas. Drilling waste is virtually eliminated. This brings significant savings in the cost of hazardous waste disposal.

There is a significant reduction of exposure to potentially hazardous material, which means increased worker safety.

Engineering Analysis Parameters

The engineering analysis parameters that can be determined using a typical CPT probe include:
Soil stratigraphy
Soil behavior type
Relative density (Dr)
Overconsolidation ratio (O.C.R.)
Blow count (n)
Friction angle (o)
Undrained shear strength (Su)
Groundwater table location (with dissipation tests)
Compressibility (c) (with dissipation tests)
Permeability (k) (with dissipation tests)

CPT Truck

Want to learn more about the equipment used for these cpt tests. Just follow the link below to see photos, specs, descriptions & other info.

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