Knowledge of the subsurface soil and geologic conditions extant on a particular site is imperative to the proper design and construction of any structure supported on the earth.  DHLA utilizes two basic methodologies for subsurface exploration.  Open pits or trenches excavated either by hand or mechanized earth-moving equipment are used where it is important to expose a broader and shallower area of the earth materials or structures for observation and mapping, such as for exploration of geologic fault line traces or investigation of damaged foundation elements.  Boreholes are utilized where it is more important to observe and sample a deeper column of the earth materials, where groundwater would interfere with an open excavation or the nature of the earth materials mandates sampling procedures appropriate only to boreholes.

DHLA contracts with only experienced and professional geotechnical labor support and drilling companies to obtain the highest quality subsurface information logs and samples.  Our engineering technicians and geologists are highly experienced with logging and sampling all types of subsurface drilling, including boreholes drilled using limited access or truck-mounted rotary wash, hollow-stem flight auger and bucket-auger drilling rigs.  As with all other aspects of our business, during all exploration operations our personnel comply strictly with all rules and regulations governing safety as set forth in Article 6, Sections 1539-1547 of the State of California, Construction Safety Orders (CAL/OSHA).

DHLA uses a number of different techniques for in-situ testing and obtaining the highest quality soil and rock samples for laboratory testing. 

The sampling methods employed are all in compliance with American Society for Testing and Materials (ASTM) standards, when applicable, and include the following:

  • Open drive sampler with liners (California DRIVE Sampler)
  • Open Thin-Wall sampler (“Shelby Tubes”)
  • Piston sampler (Osterburg sampler) – for extremely soft or delicate soils
  • Sand Replacement Density Method (sand cone)
  • Standard penetration test (spt)
  • Cone Penetrometer (CPT), when subsurface conditions allow
  • Core Barrels:
  • Large-Diameter double-tube core barrel (pitcher sampler) for soil sampling
  • Small-Diameter double-tube core barrel – for soft rock sampling
  • Small-Diameter single-tube core barrel – for hard rock coring
  • Wireline core barrel – for soft & hard rock coring

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