Enhaced Geotechnical Exploration


MYV determines the stratigraphy and nature of subsurface materials at any project site, revealing subsurface conditions that could lead to construction difficulties or potential geotechnical problems. In this regard, MYV has exploration equipment ranging from simple tools to state-of-the art technology. In this field, our main services are as follows:

ENGINEERING GEOLOGY

In either complex geologies or complex problems, the engagement of an Engineering Geologist is key for properly understanding the spatial distribution and properties of geological materials, as well as geological phenomenon such as erosion, local failure planes, and the like. The Geologist plays a key role in the geotechnical exploration, thereby assuring a more precise understanding of the interaction among Geologic Environment – Engineering Issues – Project Development.

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BASIC EXPLORATION

SPT (STANDARD PENETRATION TEST)

In Costa Rica, SPT is the most used type of in situ test and its execution usually meets ASTM D1586. The use of this in situ test has advantages as well as disadvantages. Therefore, MYV has mainly used the SPT testing in residential projects and developments. Nevertheless, it was due to SPT disadvantages and shortcomings that MYV decided to introduce enhanced and mega enhanced in situ testing in Costa Rica.

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FVT (FIELD VANE TEST)

FVT test stands for Field Vane Test. Its execution meets ASTM D2573. In order to perform FVT tests as professional as possible, MYV decided to purchase the Vane Tester Geonor H-70 that was developed in Norway by Geonor (Commercial Branch of the NGI – Norwegian Geotechnical Institute). The Geonor H-70 allows for safe vane boring down to 10 meters by simple hammering, drilling or pressing. Its unique anti-friction slip coupling system always ascertains the real friction between rods and soil.

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TERRIER (ROTARY DRILLING)

The crawler mounted terrier, acquired by MYV in 2010, is a multi-purpose drilling rig capable of using techniques from drive sampling to down the hole hammer drilling. It can deploy SPT, dynamic probing and undisturbed sampling techniques for geotechnical investigation. The small portable drilling rig can also operate any rotary drilling technique from auger drilling to diamond core drilling.

MYV technicians are trained in the use of all potential maneuvers of the Terrier, from auger drilling, sludge sampling, tricone drilling, rotation drilling and drilling with compressed air hammer. The Terrier is a highly versatile equipment that complements the in situ equipments of MYV.

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UNDISTURBED SOIL SAMPLING

MYV owns specialized field equipment aimed for extraction of undisturbed soil samples, as required in strength and compressibility testing. The soil sampler is inserted into the ground by means of CPT static push. This sampler is designed by PAGANI (Campeonatore type) and it is rather similar than the MOISTAP sampler from AP VAN DEN BERG. Nominal diameter of the extracted soil sample is 3 inches (76 milimeters). In addition, MYV built its own soil sample ejector system to extract the sample from the tube, by means of compressed air, whose use reduces the disturbance while retrieving the sample. ASTM Standard for undisturbed soil sampling is ASTM D1587-08 (Standard Practice for Thin-Walled Tube Sampling of soils for geotechnical purposes).

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NON DESTRUCTIVE TESTING (NDT)

SASW (SPECTRAL ANALYSIS OF SURFACE WAVES)

Standards for the SASW method include ASTM D6758-02 for measuring stiffness and apparent modulus of soil and soil-aggregate in-place by an electro-mechanical method and ACI 228.2R for NDE applications. MYV owns two versions of the SASW equipment: SASW-S (for pavements and structures) and SASW-G (for geologic profiles). The method uses the dispersive characteristics of surface waves to determine the variation of the shear wave velocity (stiffness) of layered systems with depth.

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SASW-S (Version for pavements and structures)

SASW-S test method is applied primarily to assess material stiffness and condition, and layer thickness (for profiles no deeper than 3 meters) without the need of drilling or coring. SASW-S is a powerful tool to determine material properties at different depths. SASW-S method can be applied to: identification of damage on concrete elements due to either fire exposure or cracking, estimation of concrete strength (also applies for masonry and rock), determination of surface opening crack depths, determination of resilient modulus of pavement layers (surface layer, base and subgrade materials), condition assessment of concrete liners in tunnels, slabs, and other concrete members, condition assessment of rigid pavements and slabs-on-grade in general.

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SASW-G (Version for Geologic Profiles)

SASW-G method (version for geologic profiles) allows determining the variation of the shear wave velocity (Vs) of layered systems with depth, within the first 30 meters bgs (below ground surface). These Vs profiles can be used for: Earthquake Site Response, Liquefaction Analysis, Soil Compaction Control, Mapping subsurface stratigraphy, foundation design of vibratory machines, determination of the natural period (Tn) of soil profiles, determination of VS30 for a given project site (average shear wave velocity over the top 30 meters) and consequently, CSCR-2010 site classification for seismic design of structures (Site Types: S1, S2, S3, S4).

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OHMMAPPER

The OhmMapper is a capacitively-coupled resistivity meter that measures the electrical properties of rock and soil without galvanic electrodes used in traditional resistivity surveys. A simple coaxial-cable array is pulled along the ground either by a single person or attached to an all-terrain vehicle. Data collection is continuous so the near surface (top 8 – 10 meters) is finely sampled, providing high quality data even in areas with complex geology. Among important applications of the equipment, the most important are as follows: geologic mapping, detection of geologic faults, detection of fractured zones, detection of aquitards, image of clay layers, measurement of the integrity of levees, detection of voids under roads and building sites, measurement of depth to bedrock, and the like.

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PDA (Pile Driving Analysis) and DLT (Dynamic Load Testing)

MYV recently acquired a state-of-the-art pile testing system for PDA and DLT. The equipment allows continuous monitoring of strain and acceleration during pile driving (PDA) and single blow registration for Dynamic Load Testing (DLT) during restrike.

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DCP (Dynamic Cone Penetrometer)

MYV recently acquired a Dynamic Cone Penetrometer (DCP). The DCP measures the shear strength of soils with a CBR between 0,5 and 100. With it MYV can produce CBR value profiles in the field.

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MEDIDOR DE VIBRACIONES ACTIMON-X1

MYV acquired by mid-2013 the acceleration and tilt sensor Actimon-X1 of Roctest. The Actimon-X1 is a very versatile all-in-one sensor for monitoring many conditions by combining a 3-axis accelerometer (X, Y, Z), a 2-axis inclinometer (X, Y) and one temperature sensor into one small sensing equipment. The sensor is very useful for the analysis of vibrations in buildings and foundations, in a range of 0 to 200 Hz.

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PRESIÓMETRO PENCEL

In early 2013 MYV acquired a new pressuremeter model called Pencel, produced by the Canadian company Roctest. The Pencel pressuremeter is a mono-cellular pressuremeter system used to run in situ loading test in soils. The conception and design of the Pencel is based upon accumulated experience gained by Roctest from the utilization of other pressuremeters, such as the TEXAM, which MYV also has. The Pencel pressuremeter provides an efficient and proven method for acquiring foundation design parameters for footings, piles, pavements, laterally loaded pylons.

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PERMEABILITY TESTING IN SITU

PERMEABILITY TESTING IN SITU

The Lefranc test, applicable to soils, allows obtaining the permeability coefficient of granular permeable or semi permeable soils, located below the water table, and of highly fractured rocks. There are two methods for performing the test: at constant level and at variable level. MYV has the equipment to perform the test by both methods.

The Lugeon test applicable to rock masses is performed inside drillings and allows to semi quantitatively calculate the permeability coefficient of the rock mass, for any lithology and level fracturing. Its application is very useful in assessing the overall permeability of a rock mass.

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LUGEON / LEFRANC

MCPT (MECHANICAL CONE PENETRATION TEST)

In Cone Penetration Testing (CPT), a cone on the end of a series of rods is pushed into the ground at a constant rate and continuous or intermittent measurements are made of the resistance to penetration of the cone (qc). Simultaneously, 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 (fs, friction sleeve).

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CPTU (PIEZOCONE)

MYV owns an electric cone (ASTM D5778) type ICONE developed by AP VAN DEN BERG, Dutch company worldwide leader in the industry of equipment for in situ geotechnical exploration. MYV was in interaction with APV in order to produce equipment customized to fit MYV needs. The ICONE uses a DAQ (Data Acquisition System) to digitally capture data coming from the several sensors (cone resistance qc, sleeve friction fs, pore pressure u2, Ix Inclination, Iy Inclination). Data are recorded every 1 – 5 cm of depth, along the whole length of the CPT sounding, at a rate of 2 cm /second. Real time of the data is achieved through the screen of a laptop computer. The piezocone is a unique tool for stratigraphy, identification of soil types, and determination of geotechnical parameters for foundation design (both shallow and deep foundations).

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DMT (Marchetti Dilatometer).

A dilatometer test (DMT, ASTM D6635 and Eurocode 7 – Part2) consists of pushing a flat blade located at the end of a series of rods. Once at the testing depth, a circular steel membrane located on one side of the blade is expanded horizontally into the soil. Typically, Nitrogen gas is used to inflate the circular membrane. The pressure is recorded at specific moments during the test:

  • the A-pressure, required to just begin to move the membrane against the soil (“lift-off”)
  • the B-pressure, required to move the center of the membrane 1.1 mm against the soil.
  • A third reading C (“closing pressure”) can be taken by slowly deflating the membrane soon after B is reached.

Once the membrane deflated completely, the blade is then advanced to the next test depth.
The main engineering application of the DMT is for settlement calculation of shallow foundations on either Sand or Clay deposits, as well as the estimation of strength parameters for both cohesive and granular soils. Other applications are as follows: compaction control, detection of slip surface in landslides, assessment of liquefaction potential, calculation of P-Y curves for laterally loaded piles and calculation of axial capacity of driven piles as well as drilled shafts, and analysis of geotechnical problems using the soil parameters for which the instrument provides estimates.
During the past years, MYV has become highly specialized in the use of the DMT because of two (2) main factors: A) A number of big and small projects for which the geotechnical exploration was carried out by means of our DMT and B) A continuous and kind assistance on the side of Prof. Silvano Marchetti (inventor of the DMT) with whom MYV has a close working relationship with since our visit to Studio Marchetti located at Rome, Italy for a 3-days training course (year 2006).

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PRESSUREMETER PMT TEXAM

The TEXAM is a pressuremeter used to run in-situ loading tests at various depths on a routine basis. It has been developed to offer an easier-to-operate type of pressuremeter. Cyclic and creep testing can be performed with this type of pressuremeter. It is a reliable instrument for the evaluation of most ground engineering problems. The well-proven method, developed by Louis Menard, is used to interpret the test results for calculation of:

  • Bearing capacity of shallow and deep foundations
  • Settlement of all types of foundations
  • Deformation of laterally loaded piles and sheet piles
  • Resistance of anchors

In early February 2011 MYV held its first practice on the use of the Texam pressuremeter. MYV plans to use the pressuremeter in those geologies that are not penetrable with the Marchetti Dilatometer or Piezocone. MYV is pleased to offer this equipment to the engineering community. Its main advantage is that it allows obtaining complete stress-strain curves in soil and is very useful for calibrating geotechnical finite element models (FEM).

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MEGA ENHANCED IN SITU TESTING

SDMT (Seismic Dilatometer).

SDMT (Seismic Dilatometer) is the combination of the standard Flat Dilatometer (DMT) with a seismic module. Such module is a probe outfitted with two receivers, spaced 0.5 m, for measuring the shear wave velocity Vs. From Vs one can determine the small strain shear modulus Go. SDMT provides profiles of Vs in a quick and precise way (repeatability of Vs 1-2 %). SDMT provides, besides Vs, all the information obtained by the traditional DMT.
According to Prof. Dr. Paul Mayne from GeorgiaTech, SDMT is one of the most advanced in situ tests there is worldwide in characterizing mechanical properties of soils (static and dynamic properties).
We MYV have performed several SDMT soundings with a Campanella pendulum hammer as a wave-generating system. Nevertheless, last year MYV imported an AUTOSEIS from Vancouver, Canada (ConeTec), which is an automatic seismic source designed by the GeorgiaTech. The Autoseis source can increase both consistency and productivity of both SDMT soundings (Seismic Dilatomer) and SCPTu soundings (Seismic Piezocone).

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GEOSTATISTICAL MAPS / 3D MODELS OF THE GROUND SUBSURFACE

MYV has been involved in a continuous cycle of research process – practical applications on the use of geostatistic techniques (spatial distribution of geomechanical properties) and RBD techniques (Reliability Based Design). In this manner, MYV has gained insight on the use of these techniques as tools to create maps of the spatial distribution of ground properties such like: strata thickness, undrained strength, constrained modulus M, and the like. This is a highly practical approach, specially used to generate synthetic data at those locations of the project where no exploration soundings are available

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Soil resistivity apparatus

This soil resistivity equipment, acquired by MYV on 2012, utilizes the four electrode method developed by the National Bureau of Standards known as the Wenner 4-pin Method (ASTM G57). Measurement of soil resistivity is used for the control of corrosion of buried structures, both for the estimation of expected corrosion rates and for the design of cathodic protection systems.

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Soil pH meter equipment

On 2012 MYV acquired soil pH meter equipment. The information on pH of soil is used as an aid in evaluating the corrosivity of a soil environment (ASTM G51). The main use of the test is to supplement soil resistivity measurements and thereby identify conditions under which the corrosion of metals in soil may be accentuated.

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