Assessing subgrade strength using an instrumented dynamic cone penetrometer

The liquefaction of gravelly soils during earthquakes remains a challenging hazard to evaluate because larger soil particles can interfere with traditional in situ tests such as the standard penetration test (SPT) and cone penetration test (CPT). This study investigates six sites affected by the 2020 Mw 6.4 Petrinja, Croatia earthquake, where gravelly liquefaction ejecta was observed. Subsurface investigations included boreholes to define the soil profile, shear wave velocity (Vs) profiling using the multichannel analysis of surface waves (MASW) and horizontal to vertical spectral ratio (HVSR), and large-diameter (74-mm) dynamic cone penetration tests (DPT). At several sites, DPT blow counts increased through silty clay surface layers, whereas CPT tip resistance from companion testing remained constant. The increase in DPT resistance was thus attributed to side friction along the drill rods, and two subsequent DPT soundings were conducted to isolate this effect: (1) a cased DPT (cDPT), where the overlying material was removed and the hole was cased to the target gravelly layer; and (2) an instrumented DPT (iDPT), used to measure the hammer energy transferred to the cone. Corrected DPT blow counts (N120′) and normalized shear wave velocities (Vs1) from critical gravelly layers were evaluated using recent probabilistic DPT- and Vs-based liquefaction triggering models. These methods correctly predicted liquefaction manifestation at each of the sites. Results support the continued development of energy-corrected DPT and Vs-based approaches for liquefaction assessment in gravelly soils and provide valuable case history data to continue refining probabilistic triggering relationships.

In road construction, there is a need to assess the adequacy of the subgrade to behave satisfactorily beneath a pavement. The adequacy usually representated as California Bearing Ratio (CBR) value. In-situ penetration tests have been widely used in geotechnical and foundation engineering for site investigation in support of analysis and design. The CBR in-place is typical in-situ penetration test. While the Dynamic Cone Penetration Test (DCPT), relatively cost cheaper than CBR in-place test, could give the CBR value through formulas stated by researchers. This paper presented the comparison of CBR values found from CBR in-place test and DCP test along 22,4 km of road construction at WKS road, Merlung Region of Jambi Province. The result shown the same trend of CBR value of both methods. However, difference between two test method will result in different of segment CBR as use for pavement design. Based on minimum criterion, the minimum result should be use in design. Key words: daya dukung subgrade, CBR In-Place, DCP Test

India has one of the largest road networks in the world, aggregating to about 56 lakh km at present. At sites with inadequate CBR, problems of excessive rutting are very common. In order to overcome this ground improvement techniques such as inclusion of coir geotextile is a good option. Coir geotextiles are manufactured with coir fibers, extracted from the husk of coconut, and are more durable than other natural fibers due to high lignin content. Construction of pavements strengthened with coir geotextiles makes it cost-effective and eco-friendly. In this paper, the results of the performance study conducted on five coir geotextile reinforced and unreinforced roads in different parts of Kerala, after three to 6 years of construction are reported. Coir geotextile had been placed in between subgrade and sub base. The performance was evaluated by conducting Benkelman Beam Deflection (BBD), Field CBR and Dynamic Cone Penetration (DCP) test on reinforced and unreinforced roads. A reduction in characteristic deflection thereby decrease in bituminous Macadam overlay, decrease in DCP Index and improvement in in-situ CBR values ranging from 22% to 178% were obtained for roads on all types of soil. A correlation was also developed between field CBR and field DCPI.

Analyses of GPR signals for characterization of ground conditions in urban areas

This study aims to compare the Dynamic Cone Penetrometer (DCP) value with the laboratory California Bearing Ratio (CBR) value on soil classified as SC according to USCS and A-2-6 according to AASHTO. Soil samples were taken from the area of the Balai Besar Pelaksanaan Jalan Nasional (BBPJN) South Sumatra at a depth of ±60 cm in three test points. The laboratory tests included natural moisture content, specific gravity, Atterberg limits, sieve analysis, and standard Proctor compaction. The compaction test results showed an optimum moisture content of 18.06% and a maximum dry density of 1.70 g/cm³. The CBR values were obtained from laboratory testing, while the DCP values were measured through dynamic cone penetration on the same samples. Correlation analysis using four methods (PUPR, ASTM, Kleyn, and Zumrawi) indicated varying results. The PUPR method produced the most consistent estimates compared to laboratory data, while ASTM D6951-03 achieved the highest coefficient of determination (R^2 = 0.9743). The Kleyn method remained applicable though less accurate, whereas the Zumrawi method showed significant deviations and was unsuitable for the soil conditions in this study. These findings confirm that the DCP test can serve as a rapid and efficient alternative for estimating CBR values of subgrade soils with similar characteristics.

The recurrence of building collapses and resulting casualties is overwhelming in Lagos State as the state records the highest cases in recent times. This work used geophysical (Ground magnetic (GM) and Electrical resistivity imaging (ERI)) and geotechnical (Dynamic cone penetration test (DCPT)) methods in delineating the subsurface conditions for its competence in foundation structures. Ten profiles of 200 m ground magnetic data were collected at 2 m spacing likewise for Wenner arrays on each profile. DCPT data were collected at points 0 m, 50 m, 100 m,150 m, and 200m to the depth of 3 m on each of the profiles occupied by GM and ERI. The data obtained were processed and interpreted using RES2DINV software for ERI, Excel package for both Magnetic and DCPT. The ground magnetic results gives the minimum relative magnetic intensity as -1689.78 nT representing possible fault/fractured zone and maximum value of 2943 nTindicating area of competence for foundation structure. ERI results gives a resistivity value ranging from 2 Ωm – 7602 Ωm depicting four zones of incompetent/sub-competent clay/sandy clay, moderately competent clayey sand, competent sand and highly competent lateritic sand. DCPT results is in the average range 11.20% to 39.87% representing Clay materials fairly competent for foundation structures, sand and well graded gravel that is competent for construction purposes. To prevent building collapsed in the study area, areas of incompetent materials should be excavated, refill and compact with lateritic sand before foundation is put in place.

Dynamic Cone Penetration Test (CPTu) profile offshore sediments by impact penetration. To exploit their results in full, the measured data are converted to obtain a quasi-static equivalent profile. Dynamic CPTu conversion requires calibrated correction models. Calibration is currently done by using paired (i.e., very close) quasi-static and dynamic tests. It is shown here that paired test data, which may be inconvenient to acquire offshore, are not strictly necessary to convert dynamic CPTu data. A new probabilistic methodology is proposed to call upon quasi-static results from a much wider area in the conversion procedure. Those results feed the prior distribution of a converted profile, within a Bayesian updating scheme where strain-rate coefficient and correction model error are also described by updated stochastic variables. The updating scheme is solved numerically using the Transitional Markov Chain Monte Carlo sampling algorithm. To avoid undue influence of local profile heterogeneity, the statistic treatment of the quasi-static CPTu data takes place in the frequency domain, using a discrete cosine transform. The new procedure is applied to a CPTu campaign offshore Nice (France): dynamic tests are converted with equal precision using quasi-static data acquired at distances orders of magnitude larger than what was previously employed.

For any major civil engineering construction, traditional geotechnical investigations like, standard penetration test (SPT), dynamic cone penetration test (DCPT) and static cone penetration test (SCPT) are carried out to assess the suitability of a site. These tests provide point information depthwise. However, non-invasive geoelectrical site investigations can provide subsurface resisistivity information in 1-D, 2-D and 3-D scales. Here, through a case study, an effort is made to relate the 2-D resistivity/IP sections to field geotechnical results and extend the scope of geoelectric sections to geotechnical site characterization. The available geotechnical test results like SPT, DCPT and SCPT for a multi-storeyed building in Indo-Gangetic Alluvial Plains are correlated with 2-D resistivity sections gained from two multielectrode resistivity-imaging experiments. The good correlation between SPT and IP sections allowed us to predict synthetic SPT from an interpreted IP section. The actual and synthetic SPT (normalized) match well in phase but differ in amplitude, which means that IP and SPT relationship is non-linear. In future, we hope that by a proper non-linear transformation the limitations of point mode geotechnical tests can be overcome.

The study for determination of dynamic cone penetration index (DCPI) of borrow pit materials for construction of low-volume roads was conducted in the Dodoma region in Tanzania. Samples for tests were collected from five borrow pits, which are Nkulabi, Zuzu, Mahomanyika, Dinda, and Ntyuka. Results of plasticity indices were 14%, 11%, 10%, 16%, and 13% for Nkulabi, Zuzu, Mahomanyika, Dinda, and Ntyuka borrow pits, respectively. Results of grading coefficients and shrinkage products were 33.7 and 148.1 units for Nkulabi, 19.9 and 295.9 units for Zuzu, 32.3 and 56.0 units for Mahomanyika, 25.4 and 391.3 units for Dinda, and 32.8 and 111.2 units for Zuzu borrow pits, respectively. Results of dynamic cone penetration indices were 5.8 mm/blow, 5.2 mm/blow, 4.7 mm/blow, 6.0 mm/blow, and 4.5 mm/blow for Nkulabi, Zuzu, Mahomanyika, Dinda, and Ntyuka borrow pits, respectively. Specifications require DCPI values for the tested material not to exceed 5.69 mm/blow in order to be suitable for use as gravel-wearing course material. Therefore, these results indicate that materials from Zuzu, Mahomanyika, and Ntyuka borrow pits have satisfied the requirement and hence qualify to be used as gravel-wearing course material. However, materials from Dinda and Nkulabi borrow pits have DCPI values above the limiting value of 5.69 mm/blow, and therefore they did not meet strength requirements as gravel-wearing course material. Based on grading coefficient, shrinkage product, and strength parameters, which are used for the selection of suitable materials, only Zuzu borrow pit materials qualified for the construction of the gravel wearing course. Therefore, engineering properties of materials from Dinda, Mahomanyika, Nkulabi, and Ntyuka need to be improved through the blending process.

Dynamic cone penetration test (DCPT) is a fast, economical and easy to conduct. It is widely used to assess the strength of natural and compacted soils. The device is introduced in the 1950s. However, it was newly introduced in Iraq. This study aims to evaluate the potentials of DCP in geotechnical explorations in the gypseous soil since it covers a large area of the country and to obtain correlations with the California bearing ratios (CBR) and investigating the effect of gypsum on the CBR-DCP relationship. Field and Laboratory tests were conducted on soil sample retrieved from six sites with different gypsum contents (28-41) %. Laboratory tests include performing CBR and DCP tests in a cylindrical mold. A statistical analysis of the results shows that gypsum content is an affecting factor on DCP and good CBR-DCP correlations on gypsum content were obtained.

The stiffness of the base layer is an important parameter for designing the pavement thickness needed to support traffic loads. It is normally related to the California bearing ratio (CBR). The spectral analysis of surface waves (SASW) method is introduced here as an in situ non-destructive seismic technique to obtain the CBR and dynamic cone penetrometer (DCP) values. They are found from measurement of wave velocity and correlation with the dynamic properties of the pavement system. In this study, the relationship between the shear wave velocity and dynamic stiffness of the SASW was found to correlate well with the DCP and CBR values. The empirical correlation of CBR to dynamic stiffness in terms of elastic modulus was found to be similar to a previously suggested correlation. Preliminary analysis also indicates that the empirical model could be used to predict the modulus of pavement base layer.

Remove-and-replace with suitable material has been the primary solution used for improving subgrades in Michigan, USA, when weak subgrades are encountered in road construction. Considering the large extent of silty and clayey soils found in southeastern Michigan, where much of the population and the roads are located within the state, the earthwork associated with this solution is massive and expensive. The use of cement kiln dust (CKD) or lime kiln dust (LKD) as a subgrade stabilizer can be a cost-effective solution if there is sufficient evidence to prove that such stabilization is suitable for the soils and the climate in southeastern Michigan. This became the subject of a field and laboratory investigation carried out in Michigan and sponsored by the Michigan Department of Transportation. The findings from the laboratory portion of this research (which were published in a separate manuscript) proved CKD’s suitability for long-term stabilization and LKD’s capacity for being a stabilizer for short-term modifications of clayey soils found in southeastern Michigan. This study covers the field testing portion of this investigation. Two CKD-stabilized and another two LKD-stabilized subgrades, which were already in use for 4–6 years, were tested for strength, using dynamic cone penetration (DCP) tests. The California bearing ratios estimated from the DCP tests showed that the CKD-stabilized and LKD-stabilized subgrades could offer strength gains as high as 200–515% and 149–257% compared to in situ soils, respectively, even after 4–6 years in use.

<p>Dynamic Cone Penetration test (CPTu) is a cost and time efficient way of collecting in situ geotechnical parameters (i.e. cone tip resistance, sleeve friction and total pore pressure) of near-surface marine sediments for submarine slope stability analysis. Conventional-established correlation for geotechnical parameters estimation from CPTu are built on static CPTu data, requiring correction of dynamic CPTu sounding records mainly due to strain-rate effects (i.e. increasing of soil resistance due to the increase of applied strain-rate). Empirical correlations have been proposed to overcome this issue, nevertheless, their application requires the quantification of correlation’s coefficients for which no general regression has been derived yet, arising strong uncertainty in data conversion and consequently geotechnical parameter prediction. Moreover, dynamic CPTu parameters are also uncertain due to their inherent variability and instrument precision. In this framework, this study proposes a multivariable Bayesian back-analysis for probabilistic conversion of dynamic CPTu parameters into static CPTu profile. Inherent variability of soil properties, instrument measurements error and uncertainty introduced by correlations used are modeled as random variables and updated within a Bayesian framework. Equivalent samples are randomly generated from established proposal distributions and integrated with parameter’s prior knowledge through a hybrid Markov-chain MonteCarlo procedure. The proposed approach is tested for 20 dynamic CPTu tests, characterized by different impact velocities, performed at Trondheim Fjord. The method applied aims to provide an improvement of strain rate correction with respect traditional data conversion. Preliminary results well match with ones computed from back-calculation employing both static and dynamic CPTu profiles. Results should be further validated for mechanical soil delineation and geotechnical parameters prediction from CPTu.</p>

국내외에서 널리 사용 중인 표준관입시험(Standard Penetration Test, SPT)은 작업의 용이성, 다양한 지반정수와 강도정수를 결정방법 등의 장점을 지니고 있다. 이러한 SPT 수행시에 발생하는 해머 에너지는 N치의 산정 및 보정에 매우 중요한 영향인자가 된다. SPT시험시 해머 타격에 의하여 롯드로 응력파가 전달되는 현상이 말뚝 항타 시에 발생하는 현상과 동일하다하여 SPT에 PDA장비를 적용하여 관입에너지를 측정하는 방법이 개발되어 사용 중에 있다. 본 연구에서는 SPT 롯드를 말뚝으로 가정하여 SPT 에너지 효율 측정롯드를 SPT시험과 동적콘관입시험에 적용하여 얻어진 힘과 속도의 파형을 매칭기법(CAPWAP, CAse Pile Wave Analysis Program) 분석을 수행하여 매입말뚝에 대한 극한선단지지력을 예측하는 기법을 제안하였다. 또한, SPT 에너지 효율 측정롯드에서 예측된 선단지지력과 실물 말뚝정재하시험을 통하여 산정된 선단지지력을 비교분석하였다. 연구결과를 토대로 SPT나 동적콘관입시험을 통하여 매입말뚝의 지지력을 간편하게 예측할 수 있는 경험식을 제시하였다. The standard penetration test (SPT) has been widely used because of its usability, economy, and many correlations with soil properties among other factors. In SPT, hammer energy is an important factor to evaluate and calibrate N values. To measure hammer energy, an instrumented SPT rod was developed considering that stress waves transferring on rods during SPT driving are the same as stress waves transferring on piles due to pile driving. Using this idea, an instrumented SPT rod with a pile driving analyzer was applied as a pile capacity prediction tool in this study. In order to evaluate this method, SPT and dynamic cone tests with the instrumented SPT rod were conducted and also 2 pile load tests were performed on pre-bored steel pipe piles at the same test site. End bearings were predicted by CAPWAP analysis on force and velocity waves from dynamic cone penetration tests and SPT. Comparing these predicted end bearings with static pile load tests, a new prediction method of the end bearing capacity using the instrumented SPT rod was proposed.

Saturation effects on calcareous desert sands: Ismael, N F; Al-Khalidi, O; Mollah, M A Trans Res RecN1089, 1986, P39–48