F. Mu\u00f1oz et al 1995<\/em>).<\/p>\n\n\n\nThis text proposes a more comprehensive verification method than the one previously mentioned, based on the combination of two techniques: Seismic Refraction and Passive Seismic (ReMi). Furthermore, it provides the data obtained from their application in verifying the Dynamic Compaction treatment carried out during the construction of the Duba Green Combined Cycle Power Plant, executed by Orbis Terrarum in Saudi Arabia. In this project, the method was applied as a complement to the design and verification tests of the compaction system, which were conducted by Trevi ASC.<\/p>\n\n\n\n
The combined use of Seismic Refraction and Passive Seismic (ReMi) techniques provides more accurate data regarding the depth distribution of ground layers with varying seismic properties compared to using these methods independently. Furthermore, it enables the calculation of dynamic moduli for the different soil layers. Additionally, this approach offers fundamental advantages over other seismic methods with similar capabilities, such as cross-hole or down-hole testing; it not only eliminates the need for boreholes and complex installations but also significantly reduces testing time,<\/p>\n\n\n\n
It is worth noting that, although the effectiveness of seismic methods for verifying ground improvement treatments is well-established, it is by no means the most common practice, as...<\/p>\n\n\n\n
...with more traditional geotechnical procedures being those commonly employed, such as penetration tests (both dynamic and static) or pressuremeter tests.<\/p>\n\n\n\n
The proposed methodology involves conducting combined seismic refraction and passive seismic surveys both prior to the execution (during the geotechnical campaign phase) and following the compaction process. This approach allows for a direct comparison of results, enabling a clear determination of whether the ground treatment has been sufficient or requires further intervention.<\/p>\n\n\n\n
2. Dynamic Compaction.<\/h4>\n\n\n\n Dynamic Compaction is a ground improvement treatment patented by Louis Menard <\/em>in 1970, consisting of ground compaction by striking the surface with a mass suspended from a crane (or similar equipment) that is dropped freely onto the soil to be compacted. The primary objective of the treatment is to improve the bearing capacity of large areas of compressible ground by densifying it through the rearrangement of particles and the reduction of initial porosity.<\/p>\n\n\n\nThe primary effects of Dynamic Compaction are (J.C. Montejano et al<\/em>):<\/p>\n\n\n\n\n Improvement of the deformation modulus to values between 20 and 30 MPa, with the consequent reduction of relative and absolute settlements in both the short and long term.<\/li>\n\n\n\n Increase in bearing capacity, achieving allowable bearing pressures ranging from 0.2 to 0.3 MPa.<\/li>\n\n\n\n Homogenization of the mechanical behavior of non-homogeneous and unclassified soils. <\/li>\n\n\n\n Ground improvement to mitigate liquefaction and\/or collapse risk.<\/li>\n\n\n\n Induction of settlements ranging from 5% to 15% of the treatment depth, serving as a direct surface reflection of the reduction in the void ratio of the treated ground.<\/li>\n<\/ul>\n\n\n\nIt is important to emphasize that Dynamic Compaction is a treatment primarily intended for granular soils with low fines content, although the presence of isolated lenses or thin layers of cohesive material is permissible.<\/p>\n\n\n\n
Dynamic Compaction is a method that lacks a proven mathematical framework to determine, through formulas alone, the exact amount of treatment required for a given soil type. Consequently, the methodology relies on prior experience in similar ground conditions, the development of a test area (trial plot) to define treatment parameters\u2014such as the impact grid, tamper weight, and drop height\u2014and the post-treatment verification of the results achieved.<\/p>\n\n\n\n
From a design and treatment effectiveness control perspective, it is essential to monitor several key aspects, including:<\/p>\n\n\n\n
\nControl of induced settlements by measuring the crater depth (imprint) and ground deformation following the impact.<\/li>\n\n\n\n Monitoring of ground improvement parameters in terms of shear strength and deformability.<\/span><\/li>\n\n\n\nVibration control to prevent impacts on nearby structures or industrial processes.<\/li>\n<\/ul>\n\n\n\nBoth the first and the last of the three aforementioned aspects will be monitored for the treatment design. The second, however, will be implemented across all phases\u2014design, execution, and control\u2014as it serves as the foundation for setting the treatment objectives and determining its overall validity. The most commonly used testing methods for monitoring shear strength and deformability parameters in conjunction with this technique are as follows:<\/p>\n\n\n\n
\nDynamic penetration tests, including both DPSH (N20) and SPT (N30).<\/li>\n\n\n\n Pressuremeter Tests (PMT).<\/li>\n\n\n\n Static Cone Penetration Tests (CPT \/ CPTu).<\/li>\n<\/ul>\n\n\n\n3. Techniques employed.<\/h4>\n\n\n\n During the construction project of the Duba Green Combined Cycle Power Plant (Duba, Saudi Arabia), a ground improvement treatment using Dynamic Compaction was implemented, covering a total area of 213,894.344 m\u00b2 (divided into 8 sub-areas). The site consists of sedimentary layers, most notably a silty sand layer with occasional presence of gravel, with compactness ranging from very loose to medium dense, the improvement of which is the primary objective of the treatment. The main objectives of treating this area are to improve the ground stiffness and increase its density, which also results in a direct increase in bearing capacity and a reduction in liquefaction risk.<\/p>\n\n\n\nFig01. Geological profile of the treated ground.<\/em><\/p>\n\n\n\nThe treatment design, carried out by Trevi ASC, is based on previous geotechnical studies, supported by the Detailed Geotechnical and Geophysical studies developed by Orbis Terrarum and RGF, and finalized through on-site trial areas conducted for this purpose.<\/p>\n\n\n\n
The method employed by Trevi to verify performance consists primarily of conducting Pressuremeter Tests (PMT) both before and after the treatment, including intermediate tests to assess the progress of the works. The design of the verification campaign proposed by the ground improvement contractor depends on the type of structures intended to be founded on each area, proposing one PMT for every 3,500 m\u00b2.2<\/sup> treated in the most sensitive areas, or every 5,000 m\u00b2.2<\/sup> in areas where secondary structures will be located. Additionally, CPT (Cone Penetration Tests) will be performed at the same density to evaluate the liquefaction potential of the treated ground. The planned depth for both investigations is eight meters or refusal, occasionally reaching depths of up to twelve meters in specific cases.<\/p>\n\n\n\nFor the external audit of the treatment performance, Orbis Terrarum\u2019s Applied Geophysics and In-Situ Testing department proposes a verification method based on conducting geophysical profiles through a combination of seismic refraction and passive seismic (ReMi) techniques.<\/p>\n\n\n\n
Seismic refraction techniques provide depth distribution profiles of P-wave propagation velocity (VP<\/sub>), while passive seismic (ReMi) provides S-wave propagation velocity values (VS<\/sub>), from which it is possible to determine the stiffness and deformability of the ground, as well as the value of VS30<\/sub>, which is a fundamental parameter for evaluating ground behavior for seismic-resistant design.<\/p>\n\n\n\nThe ReMi (Refraction Microtremor) passive seismic technique (Louie, 2001) studies the shear wave propagation velocity<\/p>\n\n\n\n
(S) based on the spectral analysis of ambient noise (or microtremors), which propagates through the ground primarily in the form of Rayleigh waves. The applications of this technique in civil engineering are numerous, but those focused on seismic ground characterization through internationally recognized parameters such as Vs30 are particularly prominent.S30,<\/sub> or the detection of soft zones (or cavities), thanks to the capability of this technique to observe velocity inversions.<\/p>\n\n\n\nAt a pragmatic level, the combination of both techniques offers multiple advantages, such as a reduction in transport costs (both in economic terms and timeframes), as the equipment required to perform them is the same\u2014this being a lightweight kit whose components can be transported in conventional travel suitcases. The practical benefits do not end there, given that the layout required for both tests is identical, which approximately halves the time needed to conduct the tests and, consequently, reduces the total timeframe for field execution. Specifically, for the verification of the Dynamic Compaction treatment for the Duba Green project, a total of 64 combined Refraction-ReMi profiles have been completed to date (34 for pre-treatment characterization and 30 for verification), using the following layouts:<\/p>\n\n\n\n
\n24 geophones. 4-meter spacing between geophones.<\/li>\n\n\n\n 7 \"shots\", every 16 meters, starting 2 meters before the first geophone position.<\/span><\/li>\n\n\n\nTotal deployment length 96 m.<\/li>\n<\/ul>\n\n\n\nFigure 02. Views of one of the layouts performed<\/em><\/p>\n\n\n\nThe combined use of Seismic Refraction and Passive Seismic (ReMi) techniques provides more accurate data regarding the depth distribution of ground layers with varying seismic properties compared to using these methods independently. Furthermore, it enables the calculation of dynamic moduli for the different soil layers. Additionally, this approach offers fundamental advantages over other seismic methods with similar capabilities, such as cross-hole or down-hole testing; it not only eliminates the need for boreholes and complex installations but also significantly reduces testing time,<\/p>\n\n\n\n
At a technical level, the combination of both techniques offers the advantages listed below:<\/p>\n\n\n\n
\nHigher precision in profile interpretation: The combination of both techniques allows for a more accurate adjustment of the physical models that generate the recorded response. Furthermore, the ReMi technique enables the detection of velocity inversion layers\u2014that is, lower velocity at depth\u2014which is impossible using refraction alone.<\/li>\n\n\n\n Realistic calculation of dynamic moduli: Wave propagation velocities directly depend on the physical properties of the material through which they propagate (density and deformability). Therefore, by knowing the P-wave and S-wave propagation values and the ground density, it is possible to calculate its moduli in the low-strain range using the following formulas:<\/li>\n<\/ul>\n\n\n\nFurthermore, it is possible to determine dynamic design parameters such as the elastic spring coefficients (K) and the damping factor (D) to establish a visco-elastic model that represents the soil-structure interaction under dynamic loads.<\/p>\n\n\n\n
\nDetermining the improvement of ground behavior under seismic action: Given that one of the results of increasing ground compactness is an improvement in seismic response and a reduction in liquefaction potential, the presented method allows\u2014through parameters such as Vs30S30,<\/sub> to compare the improved ground with the previously existing soil in earthquake-resistant terms.<\/li>\n<\/ul>\n\n\n\n4. Comparison of Results.<\/h4>\n\n\n\n To validate the proposed verification procedure, the results obtained by the treatment contractor\u2019s methods (PMT and CPT) are compared with those obtained through seismic testing. Table 01 shows the average values obtained from the pre- and post-treatment PMT tests, considering a simplified three-layer ground model.<\/p>\n\n\n\nTable 01. Average values obtained from Pressuremeters.<\/em><\/p>\n\n\n\nObserving the table above, it can be concluded that the treatment is effective, especially within the first six meters, yielding results that homogenize the ground properties in the first twelve meters. However, these raw data are insufficient to determine if the ground achieves the properties required in the project design. To this end, Trevi ASC calculates the static and dynamic moduli of the ground through correlations and compares them against the client\u2019s technical specifications.<\/p>\n\n\n\n
The proposed method, serving as a means to audit the results provided by the treatment contractor, provides a more intensive analysis of the ground, performing 96 m long profiles for which P and S-wave transmission velocities are calculated for each identified geotechnical unit. The average values obtained per unit, as well as their improvement percentages, are shown below.<\/p>\n\n\n\nTable 02. Average values obtained from the Refraction-ReMi seismic tests.<\/em><\/p>\n\n\n\nComparing both methods, it is possible to affirm that there is an evident improvement in the ground properties within the first 10-12 meters, provided that the ground at these depths is susceptible to improvement\u2014meaning it is not rock or highly cemented material. Consequently, the treatment verification performed by Trevi ASC can be considered valid.<\/p>\n\n\n\nFigure 03. Pre- and post-treatment ReMi passive seismic profiles (SRP-02 and SRP-27 respectively).<\/em><\/p>\n\n\n\nIn addition to the treatment validation, the proposed method provides realistic dynamic moduli values, whereas PMT tests only allow for their calculation through SPT-based correlations, which significantly underestimate the actual values. Realistic knowledge of the dynamic moduli leads to an optimization of the calculation models, which can translate into a reduction in foundation construction costs and an increase in operational confidence.<\/p>\n\n\n\nTabla 03. comparativa de modulos dinamicos calculados a partir de correlaciones a partir de Vp y Vs.<\/p>\n\n\n\n
It is also possible to verify the overall improvement provided by the ground treatment regarding earthquake-resistant design. Using the Vs30 value as a referenceS30<\/sub>a value used by the IBC (International Building Code) as the baseline for ground characterization regarding seismic action, it can be stated that the ground has improved following the treatment, with this value increasing approximately 1.5 times compared to the pre-treatment values.<\/p>\n\n\n\n5. Conclusions<\/h4>\n\n\n\n Following the analysis of the field data obtained for the Dynamic Compaction treatment validation, it can be concluded that the treatment is valid as a means to increase ground stiffness and compactness.<\/p>\n\n\n\n
By comparing the results obtained through the proposed seismic method with those obtained from the more conventional pressuremeter-based (PMT) method, the following can be concluded:<\/p>\n\n\n\n
\nBoth methods conclude that an improvement in the mechanical properties of the ground occurs within the first 10 to 12 meters. Therefore, the proposed method can be considered valid for use as a verification method.<\/li>\n\n\n\n The proposed seismic method results in savings in machinery costs and a better ratio between the meters of ground investigated and the time spent, while also being a non-invasive method.<\/span><\/li>\n\n\n\nThe dynamic moduli calculated from wave velocities correspond to their actual physical formulation rather than any correlation; therefore, they can be considered more representative, avoiding the underestimation of these values that occurs when they are calculated through correlations.<\/span><\/li>\n\n\n\nThe seismic method does not provide static values, nor does it allow for the precise calculation of the improved ground\u2019s bearing capacity. Therefore, other types of investigations will be necessary to achieve this objective.<\/li>\n<\/ul>\n\n\n\nTherefore, a mixed treatment verification method is recommended, combining refraction and ReMi techniques with direct investigations at a lower point density, selecting structurally critical locations for the latter. It should be noted, however, that as a method for treatment validation by an entity independent of the contractor responsible for the execution, the proposed method is valid on its own, rendering further testing unnecessary.<\/p>\n\n\n\n
In light of the results obtained, it can also be confirmed that the proposed method is not only valid as a verification method for Dynamic Compaction treatment, but can also be employed as a control method for any treatment that affects the overall stiffness of the treated ground.<\/p>\n\n\n\n
6. References<\/h4>\n\n\n\n Louie, J.N. (2001): \u201cFaster, better: Shear-wave velocity to 100 meters depth from refraction microtremor arrays\u201d. Bulletin of the Seismological Society of America, <\/em>91<\/strong>, 2, 347\u2013364.<\/p>\n\n\n\nMu\u00f1oz, C. Cuellar, V. and Valerio, J. (1995): \u201cEvaluation of ground improvement in civil engineering through surface wave analysis.\u201d F\u00edsica de la Tierra 7<\/strong>, 259-280. Servicio de Publicaciones, Universidad Complutense<\/em>.<\/p>\n\n\n\nMontejano, J.C. P\u00e9rez Rodr\u00edguez, T. (2012) \u201cRecent applications of mechanical compaction\/replacement techniques in the field of industrial foundations\u201d. 9\u00ba Simposio Nacional de Ingenier\u00eda Geot\u00e9cnica. Cimentaciones y Excavaciones Profundas 111- 123.<\/em><\/p>\n\n\n\n<\/p>","protected":false},"excerpt":{"rendered":"
La necesidad de construir en terrenos poco apropiados es cada vez un problema m\u00e1s habitual en la ingenier\u00eda civil, debido fundamentalmente a […]<\/p>\n","protected":false},"author":3,"featured_media":2833,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-2823","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-publicaciones"],"_links":{"self":[{"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/posts\/2823","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/comments?post=2823"}],"version-history":[{"count":3,"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/posts\/2823\/revisions"}],"predecessor-version":[{"id":2838,"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/posts\/2823\/revisions\/2838"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/media\/2833"}],"wp:attachment":[{"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/media?parent=2823"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/categories?post=2823"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/orbisterrarum.es\/en\/wp-json\/wp\/v2\/tags?post=2823"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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