How Different Soil Types Affects Trenchless Construction


The dirt beneath your feet isn’t just soil. It comes in 12 different types and six basic taxonomic categories based on tactile reactions, and it’s frequently mixed in with various rocks. The issue is that in an ideal world, the soil would be present in discrete, horizontal strata, with each layer containing a different soil type.

Drillers, drilling engineers, and designers, on the other hand, deal with mixed soils and rock in each project. The design path, machinery, bit and bottom hole assembly, and mud selection are all influenced by these variances in soil and rock.

Soil and Drilling

The USDA and the SSSA recognize 15 types of soil, namely:

  • Organic and wet
  • Sandy and acidic
  • Frozen
  • Volcanic ash
  • Shrink and swell
  • Very weathered
  • Weathered
  • Very dry
  • Moderately weathered
  • Deep, fertile
  • Newly Formed, or young
  • Slightly developed

Soil also has six general properties, most of which are tactile:

  • clay
  • loamy
  • silty
  • sandy
  • chalk
  • peaty

Each of the six is quite simple to drill through if that’s all there is to it. But, nothing is ever that simple when it comes to hdd projects.

Soil is often made up of a loose mixture of gravel and dirt. A fly cutter bit, maybe with mud jet capabilities or high-pressure water, may be the best choice for this loose mixture.

The high-pressure features may not be necessary in compacted alluvial soils, but a milled tooth bore opener bit or a fly cutter with bi-directional reaming capabilities is the best solution.

Types of Rock

●      Sedimentary Rock

The compressive strength of sedimentary rock is 7,000 PSI (Pounds Per Square Inch) or less. Sandstone and shale are the two most well-known rocks in the category, which began as muck on the seabeds of ancient times. Because it’s a soft rock, a milled tooth profile hole opener is usually the best choice.

●      Igneous Rock

It is a type of metamorphic rock that has come to the surface as a result of millions of years of weathering or as a remnant of the last Ice Age. Igneous rock, which includes basalt, granite, marble, and rhyolite, is formed by volcanic fire or high temperatures caused by high pressure.

●      Consolidated Crystalline Rock

Harder granites, basalt, and taconite are examples of consolidated crystalline rock systems. They have the same origin as weaker igneous rocks, but their compressive strengths range from 7,000 to 18,000 PSI due to the higher pressures they were subjected to during their formation. A carbide conical tooth bit or tungsten is needed to bore through these extremely tough rock formations.

The Trenchless Game Plan

Geotechnical data derived from boreholes, earth cores, or shovel-dug holes in Earth is prone to omissions. In their coring and potholing, these investigations may even miss a vertical wall of granite, the ultimate relics of a once-massive subsurface pluton.

As a result, the ideal trenchless strategy for  hdd projects frequently relies on the most basic concept. There’s no need to start with the bit that will cause the most damage to the hardest rock or soil you’ll encounter.


Soil conditions have everything to do with safety, which is why it’s important for workers in dangerous jobs like construction to know about them. For instance, clay soil absorbs the shock of a heavy object better than hard dry dirt does so when you’re building on top of this type of ground your tool won’t bounce back up and hit you or someone else nearby as easily. Also if there are any cracks around where you’ll be working they can fill those holes with water because wet soils make good stabilizers.

Also, when operating in the immediate area of an open hole, Make sure your team has a sufficient barrier around the hole to prevent them from falling in, or utilize a safety harness with the tether linked to an appropriate anchoring point. You may need to increase the distance between them and the drilling site.