J&S has experienced staff and equipment to conduct the following geophysical testing:

  • Ground Penetrating Radar (GPR)
  • Electrical Resistivity(ER) Surveys
  • Seismic Refraction
  • Downhole/Crosshole Seismic Survey

Ground Penetrating Radar (GPR)

GPR is a technique typically used for non destructive detection of subsurface features such as underground voids, utilities, rebars and other objects of interest in soil and concrete structures. GPR method is performed by displacing an electromagnetic antenna through the surface of the test area while a periodic pulse is transmitted and received in form of echoes. This electromagnetic wave pulses are transmitted at the antennas center frequencies ranging from 100 and 1500 Mhz. Pulses propagate through the test medium directly under the antenna. Some energy becomes reflected back whenever a change in electric impedance is encountered, such as at a rebar, utility or void. The received echoes are amplified and filtered with specialized GPR software. A distance wheel odometer records scan distance along test path, allowing for the determination of relative location of features from start point. The resulting raw data is obtained in the form of echo amplitude versus time. The material’s dielectric constant is used to define velocity which is then used to convert echo time data to echo depth. GPR has the limitation of not being effective in detection of features on clayey subgrade.


This method consists of mapping resistivity changes in the earth which is commonly useful for detection of voids, discontinuities or variations on the ground. . Resistivity is a fundamental parameter of the material that describes how easily the material can transmit electrical current. High values of resistivity imply that the material is very resistant to the flow of electricity, and low values of resistivity imply that the material transmits electrical current very easily. J&S typically uses either the Dipole-Dipole or the Wenner Method.

Dipole-Dipole is useful for detection of discontinuities or voids along a survey line. The dipole-dipole method commonly requires placement of 56 electrode/stainless steel stake on the ground at equally spaced intervals in the order of 1 to 2 meters.

The four point Wenner method is performed by placement of four (4) stakes in the ground at equally spaced intervals to make single measurements of the electrical resistivity values at certain depth. Electrode spacing is varied to obtain values for different depths. This method is commonly used for determination of soil electrical resistivity for grounding (earthing) of cell phone towers, wind turbines, electrical substations among other electrical transmission facilities.

surveyscan ER Survey Scan depicting a profile with void zones in limestone

Seismic Refraction (SR) Survey:

Seismic refraction is mostly used to determine depth to bedrock, rock rippability, fault zones and variations in the subsurface conditions. SR surveys are performed by placement of a string of geophones over the ground. A seismic wave is generated and the arrival times are recorded for each seismograph. The data is fed into processing software for the calculation of p wave velocity profiles along the survey line. These profiles are useful for interpreting condition variation between boreholes. ER surveys can be correlated to the published rock rippability charts for different bulldozer sizes. ER survey can also serve as a guide to evaluate if explosives will be required to achieve excavations in rock.

Jaca Sierra GP 08

Seismic refraction survey colored profile showing the p wave velocity gradient being correlated to rock weathering horizons

Figure8: Seismic Refraction Survey used for detecting transition of zones with different geology

Borehole Seismic Surveys: Downhole Seismic (DHS) or Crosshole Seismic (CHS):

The DHS test is performed by drilling a borehole to the required tests depth to sample soils and install a PVC casing. The test consists of lowering two (2), three component (triaxial) geophone receivers to each measurement depth and impacting the ground adjacent to the borehole in the vertical and horizontal directions. The arrival times of the shear and compression waves are determined for each measurement depth. The change in arrival times from depth point to depth point will give the local shear and compression wave velocities (Pseudo Interval Velocities). DHS field procedures and computations are made in accordance to ASTM D 7400. J&S has also capabilities of conducting this test with the Cone Penetration Test (CPT) equipment which is equipped with seismic sensor.

A CHS test is a variation of the DHS where two (2) casings are installed and the geophone (receiver) is placed in one of the casings and the seismic source in the other adjacent casing. CHS test measurements of seismic wave velocities are made by recording the corresponding horizontal travelling wave arrival times between source and receiver at different depths.

J&S has completed many of these tests within the past 10 years, mostly with the objective of establishing the average shear wave velocities for seismic site response. These tests can be used to obtain a more accurate determination of the IBC 2009 seismic site classification. It is also used for site specific seismic studies or probabilistic seismic hazard analysis. DHS or CHS data can be used to obtain the required soil dynamic properties for the seismic response modeling and/or seismic soil structure interaction modeling.Jaca Sierra GP 09

Seismic wave time arrival record

Geotechnical Engineering Consulting

Our staff combines local and international experience that work hard on providing our clients practical solutions to the projects geotechnical conditions. Our engineers are used to challenges and our goal is to assist our clients on finding reasonable recommendations for the respective projects geotechnical conditions. J&S invests in the latest engineering software, tools and testing equipment. J&S has advanced field testing equipment such as Seismic piezo Cone Penetration Tester (SCPT), borehole and surface seismic geophysical testing which provides our engineers with the tools. In addition, our modern soil mechanics laboratory is equipped with state of the art, automated consolidation, triaxial and permeability testing apparatus, among other soil testing equipment.

A list of some of our consulting specialties is provided below:

  • Complete Site Geotechnical Evaluation and Engineering Reports
  • Earthwork Recommendations
  • Earth Retaining Structure evaluation
  • Excavation Support System Consulting and Design
  • Soil and Rock Slope Stability Evaluation
  • Landslide Repair & Mitigation
  • Foundation Analysis and Recommendations
  • Seismic Site Specific Evaluations
  • Liquefaction Potential Analysis
  • Settlements Estimates and Mitigation
  • Expansive Soils
  • Seepage Analysis on Dams, Levees and Excavations
  • Dewatering Systems and Design (Design-Build)
  • Erosion Control and Bridge Scour
  • Deep Foundations/ Driven or Drilled (ACIP, CFA or Displacement) Piles
  • Pile Driving Criteria/Pile Load Test Evaluation
  • Drilled Shaft Testing and Evaluation
  • Micropiles
  • Ground Improvement
  • Stone Columns and Aggregate Piers Ground Improvement
  • Pressure Grouting, Compaction Grouting and Permeation Grouting
  • Karst Terrain and Sinkhole Activity Consulting
  • Geotechnical Engineering Forensics and Expert Witness Services
  • Geological Studies and Engineering Geology
  • Geo-Structural Analysis and Design
  • Deep Foundations Soil Structure Interaction Modelling
  • Port Facilities and Marine Structures
  • Concrete Repair, Basement Waterproofing

Geotechnical Drilling Capabilities

Currently our firm has six (6) drilling crews on active duty for geotechnical and environmental drilling. Our drillers are well experienced and have capabilities of hollow stem auger drilling, wireline rock coring, air hammer drilling and tricone bit mud rotary drilling, NW/HW casing advancer system, among other techniques.

Drilling Rigs

  • CME 55 (5 rigs)
  • CME 45 (1 rig)
  • Mobile Drill B61 HDX truck mounted
  • Ingersoll-Rand T4 (2 rigs) (Air Drilling Rigs)-Deep Wells
  • Geoprobe Model 7720- Track Mounted DPT
  • Geoprobe Model 5400

Drilling and Subsurface Soil/Rock Sampling

  • Deep Hollow Stem Auger Borings with soil sampling (Auger Sizes-ID: 2.25, 3.25, 4.25, 6.25 & 8.25 inches).
  • Diamond bit wireline rock coring (NQ, HQ & PQ size)
  • Rotary Wash Boring with Casing
  • HW and NW Casing Advancer System
  • Deep Mud Rotary Drilling
  • Air drilling with down the hole hammer for deep boreholes in rock.
  • Soil/Rock anchor drilling and installation
montserrat Geotechnical Drilling in Montserrat Island, W.I.
access rigGeotechnical Investigation with limited access rig

Field Testing Services:

In-Situ Geotechnical Investigation Tests

  • Standard Penetration Testing (SPT)
  • Cone Penetration Testing (CPT)-Seismic and Piezocone Capabilities
  • Pressuremeter
  • Borehole Packer Testing
dat record

The following is a list of some of the projects where Jaca & Sierra has completed Geotechnical Investigations and engineering consulting services

  • Veterans Affairs Multistory Parking, San Juan, PR
  • Walmart at Bayamon Towne Center, Bayamon, PR
  • SPM Project, Nustar Facilities, St. Eustatius, Dutch Caribbean
  • Home Depot, St. Croix, USVI
  • American University Expansion at St. Maarten, N.A.
  • Ross University School of Veterinary Medicine Expansion, St. Kitts, W.I.
  • Pipers Pond New Capital Buildings Project, Montserrat, W.I.
  • Virgin Gorda Clinic, BVI
  • Walmart/Sams Combo Site, Barceloneta, PR
  • Bristol Myers Squibb Expansion, Humacao, PR
  • San Francisco Hospital, New Emergency Building, San Juan, PR
  • Leachate Tanks over Municipal Solid Waste Deposits, Ponce, PR
  • San Fermin Solar Farm, Loiza, PR
  • Home Depot, Humacao, PR

Marine Geotechnical Investigation

Jaca & Sierra has vast experience in performing marine geotechnical investigation at different locations within the Caribbean. Jaca & Sierra can either deploy its own sectional spud barge or sub-contract regional barges to perform investigations. We can complete deep borings with undisturbed Shelby or Piston Tube sampling and perform HQ or PQ wireline diamond bit rock coring. Marine geotechnical investigation have been completed for new wharfs, piers, bridges, marina and offshore industrial facilities. Jaca & Sierra has completed marine geotechnical investigations for the following projects:

  • Tortola Cruise Ship Pier, Tortola, BVI
  • North Sound Yacht Club, Virgin Gorda, BVI
  • Deep Bay Marina, Oil Nut Bay, Virgin Gorda, BVI
  • Cargo Ferry Pier at Spanish Town, Virgin Gorda, BVI
  • New Marina and Restaurant at Jost Van Dyke, BVI
  • WICO Cruise Ship Pier, St. Thomas, USVI
  • Schooner Channel Dredging, St. Croix, USVI
  • Crown Bay Pier Extension, St. Thomas, USVI
  • Veterans Drive Expansion, St. Thomas, USVI
  • Yacht Haven Marina, St. Thomas, USVI


  • Bridge Foundation Engineering
  • Deep Foundations
  • Dynamic Compaction
  • Excavation Support Design
  • Landslide Investigation
  • Marine Geotechnical Investigation
  • Pile Loading Tests
  • Slope Stabilization
  • Vibro Compaction
  • Marine Geotechnical Testing
  • Excavation Support Design
  • Rock Coring
  • Driven Piles
  • Geotechnical Drilling
  • Green MSE Walls
  • CFA Pile