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Article CPT Parameters of in Lublin Area

Krzysztof Nepelski * and Agnieszka Lal *

Department of Geotechnical , Faculty of and Architecture, Lublin University of Technology, 20-618 Lublin, * Correspondence: [email protected] (K.N.); [email protected] (A.L.)

Abstract: Loess were created by the transporting particles with later or in parallel occurred protogenetic, syngenetic and epigenetic processes. As a result, various genetic processes affected strength and deformability characteristics. The aim of the study is to estimate the main CPT parameters of loess subsoil in Lublin area according to divided facies. The subsoil in the area of the Nał˛eczowskiPlateau, where Lublin is located, consists mainly of loess from aeolian and aeolian–diluvial facies, and in the deeper parts—from aeolian–alluvial facies. Most of the results obtained for the aeolian facies at the level of qc in the range from 4.5 to 8.0 MPa indicate that these soils are a good load-bearing substrate for building . Cone resistances mostly at the level of 1.5–4.0 MPa for the diluvial and alluvial facies confirm that these facies constitute less favorable conditions. The reduced resistance results mainly from the increased content in ground pores. It is especially the soils of the diluvial facies that provide unfavorable foundation conditions, as they occur near the surface. Genetic processes are a very important element that should be taken into account in engineering research.

Keywords: loess; facies; genesis; CPT/CPTU

 

Citation: Nepelski, K.; Lal, A. CPT 1. Introduction Parameters of Loess Subsoil in Lublin Loess soils are found in many regions of the world and constitute the subject of Area. Appl. Sci. 2021, 11, 6020. research by geotechnicians, (often in terms of ), paleopedologists https://doi.org/10.3390/app11136020 and scientists from other fields [1–3]. These soils are aeolian deposits, formed as a result of the accumulation of particles of the soil moved by the wind. In macroscopic Academic Editor: Giuseppe Lacidogna evaluation, loess is a relatively homogeneous, macroporous , most often of a light yellow or beige color [4]. Polish loess soils are mostly composed of coarse (10–50 µm). Received: 12 May 2021 The and find fractions range from 5 to 25%. They contain an average of 60–70% Accepted: 15 June 2021 of and , and dolomite in varying proportions. Loess Published: 28 June 2021 soils are partially aggregated, with a index ranging on average between 45% and 55% [5,6]. Publisher’s Note: MDPI stays neutral The research approach to the study of loess deposits varies depending on the type with regard to jurisdictional claims in of expected results. Many studies refer to particular features of soils without a detailed published maps and institutional affil- analysis of their genesis [7]. As a rule, loess soils were created by the wind transporting iations. particles. However, very often other genetic processes, such as runoff, slide or accumulation through the action of water, occurred in parallel or later. Therefore, loess soils should be divided into facies taking into consideration their genesis, which has long been emphasized in the most important publications on loess [1,2,5,8–11]. According to the authors of the Copyright: © 2021 by the authors. present publication, the clearest classification of loess is that proposed by Maruszczak [2]. Licensee MDPI, Basel, Switzerland. Apart from the genetic-facies classification, Maruszczak also divides loess according to This article is an open access article the , distribution and . The three types of classifications he uses are distributed under the terms and listed in Table1, while Figure1 shows an ideogram illustrating the and division conditions of the Creative of loess deposits. When describing the genetic and facies variations, the protogenetic role Attribution (CC BY) license (https:// of the wind is emphasized, therefore the name of each facies includes the word aeolian. creativecommons.org/licenses/by/ 4.0/). However, it should be emphasized that genetic divisions should not be considered as rigid,

Appl. Sci. 2021, 11, 6020. https://doi.org/10.3390/app11136020 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 14

Appl. Sci. 2021, 11, 6020 aeolian. However, it should be emphasized that genetic divisions should not be consid-2 of 14 ered as rigid, but only as indicating the leading factor. Genetic processes often occur in parallel and are not always clearly identifiable. For example, diluvia are combined with colluvia,but only alluvia as indicating with diluvia the leading or alluvia factor. with Genetic limnic processes processes. often As occur a result in parallel of additional and are processesnot always shaping clearly the identifiable. subsoil, the For influence example, of diluviathe protogenetic are combined factor with of the colluvia, wind on alluvia soil propertieswith diluvia decreases, or alluvia and with in the limnic genetic processes. context As these a result deposits of additional are often processes referred to shaping as lo- ess-likethe subsoil, [2]. the influence of the protogenetic factor of the wind on soil properties decreases, and in the genetic context these deposits are often referred to as loess-like [2]. Table 1. Division of loess according to Maruszczak [2]. Table 1. Division of loess according to Maruszczak [2]. Granular Type Facies Type Landform Type ofGranular the Loess Type ofFacies the Loess Type Landformof the Loess Type of the Loess - aeolianof the Loess of the Loess - - aeolianaeolian–diluvial - clayey loess - interfluve loess - - aeolian–diluvialaeolian– - - clayeysilty loess loess - - interfluveslope loess loess - silty loess - - aeolian–solifluctionaeolian–colluvial - slope loess - sandy loess - aeolian–colluvial - valley loess - sandy loess - valley loess - - aeolian–limnicaeolian–limnic - - aeolian–alluvialaeolian–alluvial

Figure 1. Figure 1.Ideogram Ideogram of of the the facial–genetic facial–genetic division division of of loess loess [2 ].[2]. The variety of loess soils results from protogenetic, syngenetic and epigenetic pro- The variety of loess soils results from protogenetic, syngenetic and epigenetic pro- cesses, which, depending on the dominance of a given process, shaped their features and cesses, which, depending on the dominance of a given process, shaped their features and translated, among other things, into strength and deformability characteristics. Genetic translated, among other things, into strength and deformability characteristics. Genetic processes are a very important element that should be taken into account in engineering processes are a very important element that should be taken into account in engineering research. The subsoil in the area of the Nał˛eczowskiPlateau, where Lublin is located, research.consists mainlyThe subsoil of loess in the from area aeolian of the andNałę aeolian–diluvialczowski , facies, where and Lublin in the is located, deeper parts,con- sistsfrom mainly aeolian–alluvial of loess from facies. aeolian and aeolian–diluvial facies, and in the deeper parts, from aeolian–alluvialAeolian (subaerial), facies. so-called typical loesses, sedimented in dry periods and areas, are the dominantAeolian (subaerial), facies. In Poland,so-called their typical formation loesses, is sedimented dated to the in period dry periods of the Weichselian and areas, areglaciation, the dominant but older facies. loess In soils Poland, are alsotheir found, formation which is alsodated occur to the in theperiod area of the Lublin. Weich- The seliansubaerial glaciation, loess covers but older usually loess have soils 90% are ofalso the found, silt fraction, which also and theiroccur characteristic in the area of color Lu- is yellow-grey, light or beige. They are located mainly on the uplands and partly on the slopes of valleys. They usually reach a thickness of up to 20 m, but locally they can reach even 30 m. The strength and deformability characteristics of this facies are the most Appl. Sci. 2021, 11, 6020 3 of 14

favorable among all loess materials. However, the phenomenon of collapse may still occur within this facies [2,5,6,12]. The second facies representing the Lublin subsoil is aeolian–diluvial loess soils, which are characterized by less favorable geotechnical parameters. This is mainly due to the action of postgenetic factors, especially in the form of rainwater, rinsing and washing the aeolian sediment into the lower parts of the slopes. On large plains without a clear slope of the , diluvia are evenly distributed in the subsurface layers of the subsoil. On hilltops, they form enclosed depressions, which during periods of long rainfall show the ability to retain water, while losing the features of a load-bearing soil. Within this facies, the content of the clay fraction is increased, which makes these loess soils more clayey. This facies also occurs in deeper parts, sometimes separating the typical younger aeolian loess from the older ones. In the upper part of older diluvia, which used to be the , traces of can also be encountered, they are the so-called [2,5,6,12]. Another facies found in Lublin is the aeolian–alluvial valley loess. This facies was formed as a result of the of wind-transported silt in water conditions and the redeposition of older aeolian and diluvia. It is located mainly in river valleys, old denudation and valleys. It is characterized by brick-yellow, yellow-grey or grey color. It contains numerous beds in it and it is sometimes lithologically heterogeneous. In terms of particle size distribution, it should be classified as clayey silt and silty clay, with a significantly higher content of clay particles compared to aeolian loess (up to 20%) [2,5,6,12]. Loess soils cover over 50% of Lublin’s area and determine the geotechnical condi- tions of the left-bank basin of the Bystrzyca River. In the Lublin region, they cocreate a foundation soil with usually favorable geotechnical parameters; however, an analysis of local conditions is necessary. Currently, one of the most popular field studies is CPT static sounding, which due to its specificity provides rich quasicontinuous data at depth. It makes it possible to examine the soil profile to considerable depths, to derive many geotechnical parameters of the soil from the measured values, and at the same time it remains a relatively economical and quick test [13,14]. CPT sounding is currently the most universal and there are numerous correlations both for deriving soil parameters from the data recorded during the test and for recognizing the type of soil [14–20]. In Poland, Robertson’s SBT (soil behavior type) [21] chart is widely used for the interpretation of , modified and adapted to Polish conditions by Młynarek et al. [22]. The results presented in the article add new data to the documented knowledge. The results of field studies and guidelines for conducting them on the loess of the Lublin region have been described in publications [23–27], and the data from soundings are the basis for determining soil parameters [17,28–31] and engineering calculations [12,32,33]. In the light of the above, linking the numerical results of CPT static sounding to the genesis of loess will bring significant benefits to geotechnicians and engineering geologists in terms of data interpretation.

2. Materials and Methods The basis for the characterization of Lublin loess soils was the results of in-situ tests— CPT and CPTU static soundings carried out in the years 2015–2020 by GeoNep company. As part of the analysis of static soundings, the geotechnical documentation prepared for 152 locations was reviewed (Figure2), from among which data were collected from a total of 1136 CPT and CPTU soundings with a total length of approximately 8385 m, including loess and loess-like deposits. Appl. Sci. 2021, 11, 6020 4 of 14 Appl. Sci. 2021, 11, x FOR PEER REVIEW 4 of 14

Figure 2. LocationLocation of of test points used to plot the subsoil cross-section.

StaticStatic soundings soundings were were performed performed with with a a pe penetrometernetrometer Pagani Pagani T63-200 T63-200 with with a a maxi- maxi- mummum ofof 200200 kN, kN, which which was was used used to pressto press the the measuring measuring cone cone at a speedat a speed of 2 cm/s. of 2 cm/s.In the In tests, the tests, mainly mainly a piezocone a piezocone with with an electronic an electronic measurement measurement system system (CPT/CPTU (CPT/CPTU test) test)was was used, used, with with automatic automatic data data recording recording every every 1 cm.1 cm. In In some some tests, tests, aa mechanicalmechanical cone (CPTM(CPTM test) test) was was used used in in which readings were taken manually at 20 cm intervals. In the casecase of of both both types types of of tests, tests, the the reco recordedrded values values were were the the cone cone resistance resistance qc andqc and the thefriction fric- ontion the on the friction sleeve sleeve fs. Thefs cones. The conesused for used the for tests the had tests standard had standard geometry, geometry, which whichcorre- spondedcorresponded to the to the surface base surface of 10 ofcm 102, the cm 2friction, the friction sleeve sleeve surface—150 surface—150 cm2 and cm 2theand cone the tipcone angle tip angle of 60 of degrees. 60 degrees. All Alltest testparameters parameters were were compliant compliant with with the the standards standards of of ISO ISO 22476-122476-1 [34] [34] and and ISO 22476-12 [35]. [35]. The The analyz analyzeded results results relate relate to 2287.2 m of soundings withwith a a mechanical cone cone and and 6097.6 m of soundings with the use of an electric cone, of whichwhich 1997.25 m of testing were CPTU soundings during which u2 waswas additionally measured. TheThe type type of of cone cone (electrical (electrical or or mechanical) mechanical) used used in inCPT CPT testing testing affects affects the thevalue value of the of qthec andqc andfs resultsfs results recorded. recorded. This Thisstatement statement is conf isirmed confirmed by the by results the results of many of many studies studies and described,and described, e.g., in e.g., [36]. in Based [36]. Based on the on comparative the comparative analysis analysis [37], it [was37], found it was that found for thattypical for aeoliantypical aeolianloess soils, loess the soils, qc values the qc obtainedvalues obtained from the from mechan the mechanicalical cone test cone constitute test constitute about 93%about of 93%the q ofc value the q obtainedc value obtained when measured when measured with an electric with an cone. electric On cone.the other On hand, the other the fhand,s values the obtainedfs values from obtained the mechanical from the mechanical cone soundings cone soundings are more arethan more twice than as twicehigh as thosehigh asindicated those indicated by electric by cone electric readings. cone readings. While the While difference the difference in the q inc readings the qc readings can be consideredcan be considered small, the small, difference the difference in fs is significant. in fs is significant. Taking into Taking account into accountthat the thatfriction the R f ratiofriction Rf, ratiowhich fis, whichused to is identify used to the identify type theof soil, type is of determined soil, is determined on the basis on theof fs basis, the type of s, the type of cone used should be taken into account when interpreting the results. The R of cone used should be taken into account when interpreting the results. The Rf coefficientf forcoefficient aeolian forloess aeolian determined loess determined with a mechanical with amechanical cone is 2.22 cone times is greater 2.22 times than greater that deter- than minedthat determined from the electric from the cone electric test [37]. cone test [37]. The value of pore water pressure u recorded in CPTU tests for aeolian and diluvial The value of pore water pressure u2 recorded in CPTU tests for aeolian and diluvial loessloess was was close close to to zero zero or or slightly slightly negative, negative, so so there there was was little little suction, suction, which which is typical is typical for for unsaturated soils. The increase in pore pressure u2 was significant only in the case of unsaturated soils. The increase in pore pressure u2 was significant only in the case of allu- alluvial loess. It is also a guideline when identifying facies from CPT soundings. Taking vial loess. It is also a guideline when identifying facies from CPT soundings. Taking into into account the obtained relatively high values of cone resistance qc and the values of u2 account the obtained relatively high values of cone resistance qc and the values of u2 close close to zero, for loess soils it can be assumed as a simplification that qc = qt. Only in the to zero, for loess soils it can be assumed as a simplification that qc = qt. Only in the rare case Appl. Sci. 2021, 11, x FOR PEER REVIEW 5 of 14 Appl. Sci. 2021, 11, 6020 5 of 14

of alluvial and older diluvial loess facies, when values of cone resistance qc are very low, e.g.,rare 0.7 case MPa, of alluvial and values and olderof u2 are diluvial relatively loess high, facies, the when difference values between of cone resistance qc and qt valuesqc are becomesvery low, noticeable, e.g., 0.7 MPa, but and still values remains of u 2insignificant.are relatively It high, is very the infrequent difference betweenthat SBTq cchartand analysisqt values identifies becomes noticeable,alluvial and but older still diluvial remains loess insignificant. with very It low is very qc and infrequent high u2 thatas more SBT sandychart analysissoil. identifies alluvial and older diluvial loess with very low qc and high u2 as moreHaving sandy soil.a large amount of data and referring to the division of loess according to Maruszczak,Having athe large authors amount of the of datapresent and pub referringlication to developed the division an of own loess representative according to cross-sectionMaruszczak, showing the authors the geologic of the presental structure publication of Lublin developed on the western an own side representative of Bystrzyca. Identificationcross-section showingof subsoil the laye geologicalrs was based structure on data of Lublinfrom selected on the westerngeotechnical side ofdocumenta- Bystrzyca. tionIdentification in terms of subsoilthe values layers recorded was based during on data static from soundings selected geotechnicaltests and soil documentation identification fromin terms . of the values The obtained recorded duringcross-section static soundingsrepresenting tests schematically and soil identification the geological from structureboreholes. of The Lublin obtained is presented cross-section in Figure representing 3. schematically the geological structure of Lublin is presented in Figure3.

Figure 3. The geological structure of Lublin—aLublin—a representative cross-section.

Among the the studied studied loess loess deposits, deposits, the the most most ch characteristicaracteristic facies facies of ofthe the region region can can be distinguished,be distinguished, i.e., i.e.,aeolian aeolian (older (older and andyounger), younger), aeolian–diluvial aeolian–diluvial (older (older and andyounger) younger) and aeolian–alluvialand aeolian–alluvial facies. facies. The results The results of in-situ of in-situ research research in the form in the of form CPT ofsoundings CPT soundings carried outcarried in the out western in the western part of partLublin of Lublinwere analyzed were analyzed for each for facies. each facies.In the further In the further part of part the study,of the study,the two-part the two-part names names of facies, of facies, for forthe thesake sake of ofsimplicity, simplicity, are are written written without without the “aeolian” part, which is intended to emphasizeemphasize the overriding impact of the wind in the process of loess genesis. Correct interpretation interpretation of of the the results results of of static static soundings soundings is isonly only possible possible when when the there- sultsresults of ofborehole are are taken taken into into consideration. consideration. In In order order to to identify identify the the type type of of soil, test boreholes were also drilled in the the immediate immediate vicinity vicinity of of the the selected selected soundings. soundings. Tradition- Tradition- ally used classification classification diagrams, e.g., by Robertson [21,38] [21,38] or Schmertman [[39],39], ascribe soil behavior type (SBT) to a given soil, which is why there are sometimessometimes discrepanciesdiscrepancies between the type of soil interpreted and identified identified from the borehole. The The proper proper litho- litho- logicallogical classification classification can only only be be performed performed macroscopically, macroscopically, and the results of the examination reflect reflect the engineering features of the identifiedidentified geotechnicalgeotechnical layers.layers. The profiles profiles obtained from static soundings were divided into smaller layers distin- guished due to the averaged values of cone resistance qc. Ultimately, 6855 layers with a guished due to the averaged values of cone resistance qc. Ultimately, 6855 layers with a thickness in range from 0.10 to 15.5 m were obtained that were considered to be uniform thickness in range from 0.10 to 15.5 m were obtained that were considered to be uniform in terms of parameters. Each time, weighted averages were used for statistical analysis; Appl. Sci. 2021, 11, x FOR PEER REVIEW 6 of 14

Appl. Sci. 2021, 11, 6020 6 of 14

in terms of parameters. Each time, weighted averages were used for statistical analysis; these refer to the thickness of the identified layers. A sample representative loess profile these refer to the thickness of the identified layers. A sample representative loess profile is is shown in Figure 4. shown in Figure4.

FigureFigure 4. 4. RepresentativeRepresentative CPTU CPTU profile profile from the Lublin.

TheThe analysis allowedallowed thethe authors authors to to determine determine the the typical typical values values of the of registeredthe registered cone resistance qc and friction on the friction sleeve fs for particular facies. In the considerations, cone resistance qc and friction on the friction sleeve fs for particular facies. In the consider- the friction on the friction sleeve was replaced by the Rf parameter (Equation (1)), which in ations, the friction on the friction sleeve was replaced by the Rf parameter (Equation (1)), practice is more often used to classify the type of soil based on the results of the CPT test. which in practice is more often used to classify the type of soil based on the results of the CPT test. qc R f = ·100% (1) fs 𝑞 𝑅 = ∙ 100% (1) In the paper, the authors focused on two𝑓 main measurements from the cone penetra- tionIn test the without paper, drawingthe authors a correlation focused on with two othermain measurements interpreted parameters from the likecone soil penetra- stress history or OCR. tion test without drawing a correlation with other interpreted parameters like soil stress history3. Results or OCR.

3. ResultsEach of the CPT soundings was interpreted only in terms of loess soils. The older subsoil, below the loess deposits, was excluded from the analysis. The identified layers wereEach assigned of the to CPT the appropriate soundings facies:was interpreted aeolian, older only aeolian, in terms diluvial, of loess older soils. diluvial The older and subsoil,alluvial. below In terms the ofloess grain deposits, size distribution, was excluded these from were the mainly analysis. The and identified sandy silts layers and, wereto a lesserassigned extent, to the clayey appropriate silt and facies: silty clay, aeolian, and older also very aeolian, locally diluvial, silty sand. older Thediluvial data and are alluvial.presented In interms intervals of grain of 0.5 size MPa. distribution, these were mainly silts and sandy silts and, to a lesser extent, clayey silt and silty clay, and also very locally silty sand. The data are pre- sented3.1. Diluvial in intervals Facies of 0.5 MPa. The data for the diluvial facies comprised 8.6% of the results. Loess diluvia are dark 3.1.beige Diluvial and brown Facies clayey silts and silts. The distribution of qc values obtained from static testsThe is shown data for in the Figure diluvial5a. The facies results comprised in the form 8.6% ofof theqc-R results.f were plottedLoess diluvia on Robertson’s are dark beigeclassification and brown chart clayey (Figure silts5b). and silts. The distribution of qc values obtained from static tests Withinis shown the in diluvial Figure facies,5a. The cone results resistances in the form fluctuated of qc- inRf thewere range plotted from on 0.3 Robertson’s to 7.0 MPa, classificationwith 81% of thechart results (Figure being 5b). values in the range from 0.3 to 4.0 MPa with a median of 2.6 MPa. The average cone resistance qc for this facies was 2.88 MPa with a standard deviation σ = 1.29 MPa. The average friction ratio was Rf = 3.77% with a standard deviation of 1.65%. Appl. Sci. 2021, 11, x FOR PEER REVIEW 7 of 14

Within the diluvial facies, cone resistances fluctuated in the range from 0.3 to 7.0 MPa, with 81% of the results being values in the range from 0.3 to 4.0 MPa with a median Appl. Sci. 2021, 11, 6020 of 2.6 MPa. The average cone resistance qc for this facies was 2.88 MPa with a standard7 of 14 deviation σ = 1.29 MPa. The average friction ratio was Rf = 3.77% with a standard deviation of 1.65%.

(a) (b)

FigureFigure 5. SummarySummary of of results results for for the the diluvial diluvial facies facies (a) distribution (a) distribution of qc ofvaluesqc values (b) sounding (b) sounding pa- parametersrameters plotted plotted against against Robertson’s Robertson’s chart chart (1—sensi (1—sensitivetive fine fine grained; grained; 2—organic 2—organic material; material; 3—clay; 4—silty clay to clay; 5—clayey silt to silty clay; 6—sandy silt to clayey silt; 7—silty sand to sandy 4—silty clay to clay; 5—clayey silt to silty clay; 6—sandy silt to clayey silt; 7—silty sand to sandy silt; silt; 8—sand to silty sand; 9—sand; 10—gravely sand to sand; 11—very silty fine grained; 12— 8—sand to silty sand; 9—sand; 10—gravely sand to sand; 11—very silty fine grained; 12—sand to sand to clayey sand; Dr— ratio; OCR—overconsolidation ratio; Sf—sensitivity factor; e— clayeyvoid ratio). sand; Dr—density ratio; OCR—overconsolidation ratio; Sf—sensitivity factor; e—). 3.2. Older Diluvial Facies 3.2. Older Diluvial Facies Older diluvial facies constitutes the smallest sample. The soils with the total length Older diluvial facies constitutes the smallest sample. The soils with the total length of the tested profiles of 31.9 m were assigned to it, which in relation to the total length of of the tested profiles of 31.9 m were assigned to it, which in relation to the total length of the tests was only 0.4%. Older diluvia appeared in the form of interbeddings in the deeper the tests was only 0.4%. Older diluvia appeared in the form of interbeddings in the deeper parts of the subsoil, separating younger aeolian loess deposits from the older ones. parts of the subsoil, separating younger aeolian loess deposits from the older ones. Cone resistances qc fluctuated in the range from 0.3 to 5.4 MPa, with 73% of the results beingCone values resistances in the range qc fluctuated from 0.3 to in 4.0 the MPa range with from a median0.3 to 5.4 of MPa, 3.0 MPa. with The73% average of the results cone being values in the range from 0.3 to 4.0 MPa with a median of 3.0 MPa. The average cone resistance qc for this facies was 3.11 MPa with a standard deviation σ = 1.13 MPa. The resistance qc for this facies was 3.11 MPa with a standard deviation σ = 1.13 MPa. The average friction ratio was Rf = 4.09% with a standard deviation of σ = 1.20%. Due to a relativelyaverage friction small sample, ratio was these Rf data = 4.09% should with be treateda standard as illustrative deviation in of statistical σ = 1.20%. terms. Due After to a collectingrelatively moresmall data,sample, changes these indata the should distribution be treated can be as expected, illustrative which in statistical was suggested, terms. Appl. Sci. 2021, 11, x FOR PEER REVIEW interAfter alia,collecting by the more lack data, of results changes for thein the older distribution diluvial faciescan be in expected, the8 qof 14range which from was 4.0 sug- to c c 4.5gested, MPa. interThe alia, above by data the lack are compiledof results infor a the diagram older showingdiluvial facies the distribution in the q range of q cfromvalues 4.0 (Figureto 4.5 MPa.6a) and The on above Robertson’s data are chartcompiled (Figure in a6 b)diagram showing the distribution of qc values (Figure 6a) and on Robertson’s chart (Figure 6b)

(a) (b)

Figure 6. Summary of results for the older diluvial facies: (a) distribution of qc values and (b) sound- Figure 6. Summary of results for the older diluvial facies: (a) distribution of qc values and (b) sounding parameters plotted ing parameters plotted against Robertson’s chart. against Robertson’s chart (1—sensitive fine grained; 2—organic material; 3—clay; 4—silty clay to clay; 5—clayey silt to silty clay; 6—sandy3.3. Alluvial silt to clayey Facies silt; 7—silty sand to sandy silt; 8—sand to silty sand; 9—sand; 10—gravely sand to sand; 11—very silty fine grained; 12—sand to clayey sand; D —density ratio; OCR—overconsolidation ratio; Sf—sensitivity factor; A total of 6.3% of the analyzedr loess formations belong to the alluvial facies. This e—void ratio). facies most often occurs in the deeper layers of the subsoil, in particular in areas of up- . On the slopes and in dry valleys, alluvia are much shallower and are covered with only a small layer of typical loess soils. Alluvia had a significantly higher content of clay fraction and were classified as silty clay and clayey silt. For the most part, they were plas- ticized, and in CPTU soundings there was an increase in pore pressure u2. Cone resistances qc fluctuated in the range from 0.3 to 10 MPa, with 72% of the results being values in the range from 0.3 to 4.0 MPa with a median of 2.7 MPa. The average cone resistance qc for this facies was 2.98 MPa with a standard deviation σ = 1.27 MPa. The average friction ratio was Rf = 4.68% with a standard deviation of σ = 1.62%. The data for alluvia were compiled in the diagram showing the distribution of qc values (Figure 7a) and on Robertson’s chart (Figure 7b).

(a) (b)

Figure 7. Summary of results for the alluvial facies: (a) distribution of qc values and (b) sounding parameters plotted against Robertson’s chart.

3.4. Aeolian Facies—Typical Loess The most numerous sample among the analyzed deposits is the typical loess of the aeolian facies. The total length of the tests within this facies was 6796.9 m, which was 81.0% of the total test run. The results discussed for this facies were therefore most repre- Appl. Sci. 2021, 11, x FOR PEER REVIEW 8 of 14

(a) (b)

Appl. Sci. 2021, 11, 6020Figure 6. Summary of results for the older diluvial facies: (a) distribution of qc values and (b) sound- 8 of 14 ing parameters plotted against Robertson’s chart.

3.3. Alluvial Facies A total of3.3. 6.3% Alluvial of the Facies analyzed loess formations belong to the alluvial facies. This facies most often occursA total in ofthe 6.3% deeper of the layers analyzed of the loess subsoil, formations in particular belong in toareas the of alluvial up- facies. This lands. On the slopesfacies mostand in often dry occursvalleys, in alluvia the deeper are much layers shallower of the subsoil, and inare particular covered with in areas of uplands. only a small layerOn theof typical slopes andloess in soils. dry valleys,Alluvia alluviahad a significantly are much shallower higher content and are of covered clay with only a fraction and weresmall classified layer of as typical silty clay loess and soils. clayey Alluvia silt.had For athe significantly most part, higherthey were content plas- of clay fraction ticized, and in andCPTU were soundings classified there as silty wasclay an increase and clayey in pore silt. pressure For the most u2. part, they were plasticized, Cone resistancesand in CPTUqc fluctuated soundings in the there range was from an increase0.3 to 10 inMPa, pore with pressure 72% ofu 2the. results being values in the Conerange resistancesfrom 0.3 toq 4.0c fluctuated MPa with in a themedian range of from 2.7 MPa. 0.3 to The 10 MPa, average with cone 72% of the results being values in the range from 0.3 to 4.0 MPa with a median of 2.7 MPa. The average cone resistance qc for this facies was 2.98 MPa with a standard deviation σ = 1.27 MPa. The resistance q for this facies was 2.98 MPa with a standard deviation σ = 1.27 MPa. The average friction ratio was cRf = 4.68% with a standard deviation of σ = 1.62%. The data for average friction ratio was R = 4.68% with a standard deviation of σ = 1.62%. The data for alluvia were compiled in the diagram showingf the distribution of qc values (Figure 7a) and on Robertson’salluvia chart were (Figure compiled 7b). in the diagram showing the distribution of qc values (Figure7a) and on Robertson’s chart (Figure7b).

(a) (b)

Figure 7. SummaryFigure 7. ofSummary results for of theresults alluvial for the facies: alluvial (a) distributionfacies: (a) distribution of qc values of andqc values (b) sounding and (b) sounding parameters plotted against Robertson’sparameters chart plotted (1—sensitive against Robertson’s fine grained; chart. 2—organic material; 3—clay; 4—silty clay to clay; 5—clayey silt to silty clay; 6—sandy silt to clayey silt; 7—silty sand to sandy silt; 8—sand to silty sand; 9—sand; 10—gravely sand to sand; 3.4. Aeolian Facies—Typical Loess 11—very silty fine grained; 12—sand to clayey sand; Dr—density ratio; OCR—overconsolidation ratio; Sf—sensitivity factor; e—void ratio). The most numerous sample among the analyzed deposits is the typical loess of the aeolian facies. The total length of the tests within this facies was 6796.9 m, which was 81.0% of the total3.4. test Aeolian run. Facies—TypicalThe results discus Loesssed for this facies were therefore most repre- The most numerous sample among the analyzed deposits is the typical loess of the aeolian facies. The total length of the tests within this facies was 6796.9 m, which was 81.0% of the total test run. The results discussed for this facies were therefore most representative. The influence of the cone used is also important. While in the light of the performed analyses [37] the difference in cone resistance qc was approximately 7%, the Rf values were more than twice as high when using a mechanical cone. Therefore, for the aeolian facies, the results taking into account Rf were additionally separated according to the type of cone. Cone resistances qc fluctuated in the wide range from 0.9 to 23.6 MPa; however, 67% of the results were values in the range from 4.5 to 8.0 MPa with a median of 6.5 MPa. The average cone resistance qc for this facies was 6.68 MPa with a standard deviation σ = 2.15 MPa, with the average qc = 6.48 MPa for the electric cone (CPT/CPTU) and a standard deviation σ = 2.20 MPa and qc = 7.23 MPa for the mechanical cone (CPTM) and a standard deviation σ = 1.81 MPa. The average friction ratio was Rf = 2.44% with a standard deviation of σ = 0.65% for the electric cone (CPT/CPTU) and Rf = 4.48% with a standard deviation of σ = 1.12% for the mechanical cone (CPTM). The data for the aeolian facies were compiled in a diagram showing the distribution of qc values (Figure8a) and on Robertson’s chart (Figure8b). Appl. Sci. 2021, 11, x FOR PEER REVIEW 9 of 14

sentative. The influence of the cone used is also important. While in the light of the per- formed analyses [37] the difference in cone resistance qc was approximately 7%, the Rf values were more than twice as high when using a mechanical cone. Therefore, for the aeolian facies, the results taking into account Rf were additionally separated according to the type of cone. Cone resistances qc fluctuated in the wide range from 0.9 to 23.6 MPa; however, 67% of the results were values in the range from 4.5 to 8.0 MPa with a median of 6.5 MPa. The average cone resistance qc for this facies was 6.68 MPa with a standard deviation σ = 2.15 MPa, with the average qc = 6.48 MPa for the electric cone (CPT/CPTU) and a standard de- viation σ = 2.20 MPa and qc = 7.23 MPa for the mechanical cone (CPTM) and a standard deviation σ = 1.81 MPa. The average friction ratio was Rf = 2.44% with a standard deviation of σ = 0.65% for the electric cone (CPT/CPTU) and Rf = 4.48% with a standard deviation of σ = 1.12% for the mechanical cone (CPTM). The data for the aeolian facies were compiled Appl. Sci. 2021, 11, 6020 9 of 14 in a diagram showing the distribution of qc values (Figure 8a) and on Robertson’s chart (Figure 8b).

(a) (b)

Figure 8. Summary of results for the aeolian facies: (a) distribution of qc values and (b) sounding Figure 8. Summary of results for the aeolian facies: (a) distribution of qc values and (b) sounding parameters plotted against Robertson’sparameters chart plotted (1—sensitive against Robertson’s fine grained; chart. 2—organic material; 3—clay; 4—silty clay to clay; 5—clayey silt to silty clay; 6—sandy silt to clayey silt; 7—silty sand to sandy silt; 8—sand to silty sand; 9—sand; 10—gravely sand to sand; 3.5. Older Aeolian Facies 11—very silty fine grained; 12—sand to clayey sand; Dr—density ratio; OCR—overconsolidation ratio; Sf—sensitivity factor; e—void ratio). The total length of the tests within the older aeolian facies was 228.4 m, which was about 2.7% of the examined deposits. Cone resistance qc varied in a very wide range from 3.5. Older Aeolian Facies 1.6 to 21.8 MPa. About 69% of the results were in the range from 6.0 to 11.5 MPa with a median of 8.7 MPa.The The total average length cone of theresistance tests within qc for the this older facies aeolian was 8.87 facies MPa was with 228.4 a m, which was standard deviationabout σ 2.7%= 3.12 of MPa. the examinedThe average deposits. friction Cone ratio resistancewas Rf = 2.82%qc varied with in a standard a very wide range from deviation of σ 1.6= 0.86%. to 21.8 The MPa. data About for the 69% older of aeolian the results facies were were in compiled the range in from a diagram 6.0 to 11.5 MPa with showing the distributiona median ofof 8.7qc values MPa. The(Figure average 9a) and cone on resistanceRobertson’sqc forchart this (Figure facies 9b). was 8.87 MPa with a Appl. Sci. 2021, 11, x FOR PEER REVIEW standard deviation σ = 3.12 MPa. The average friction ratio was Rf = 2.82%10 of 15 with a standard deviation of σ = 0.86%. The data for the older aeolian facies were compiled in a diagram showing the distribution of qc values (Figure9a) and on Robertson’s chart (Figure9b).

(a) (b)

Figure 9. SummaryFigure 9. of Summary results for of the results older for aeolian the older facies: aeolian (a) distribution facies: (a) distribution of qc values of and qc values (b) sounding and (b) parameters sound- plotted against Robertson’sing parameters chart (1—sensitiveplotted against fine Ro grained;bertson’s 2—organic chart (1—sensitive material; fine 3—clay; grained; 4—silty 2—organic clay to material; clay; 5—clayey 3— silt to clay; 4—silty clay to clay; 5—clayey silt to silty clay; 6—sandy silt to clayey silt; 7—silty sand to silty clay; 6—sandy silt to clayey silt; 7—silty sand to sandy silt; 8—sand to silty sand; 9—sand; 10—gravely sand to sand; sandy silt; 8—sand to silty sand; 9—sand; 10—gravely sand to sand; 11—very silty fine grained; 11—very silty fine grained; 12—sand to clayey sand; Dr—density ratio; OCR—overconsolidation ratio; Sf—sensitivity factor; 12—sand to clayey sand; Dr—density ratio; OCR—overconsolidation ratio; Sf—sensitivity factor; e—void ratio).e—void ratio). 4. Discussion 4. Discussion The obtained results allowed the authors to characterize loess soils from the Lublin The obtainedarea. results Cumulative allowed data the fromauthors soundings to characterize are presented loess soils in thefrom diagram the Lublin (Figure 10), while area. CumulativeTable data2 includes from soundings characteristic are valuespresented of each in the loess diagram facies. The(Figure analyzed 10), while data show that the Table 2 includesvast characteristic majority of values loess soils of each belong loess to facies. the aeolian The analyzed facies and data its show parameters that the were crucial for vast majority ofthe loess foundation soils belong of building to the aeolian structures. facies The and highest its parametersqc values were were crucial obtained for for this facies. the foundation of building structures. The highest qc values were obtained for this facies. The diluvial and alluvial facies occurred to a much smaller extent and the obtained results constituted a similar percentage. It should be borne in mind that diluvia were found in the upper parts of the subsoil and this zone was included in each sounding. Alluvia were most often found in the deeper parts of the subsoil and not all of the soundings covered this zone. The same applies to the older aeolian facies, the parameters of which were only examined in some of the tests. According to the authors, the particular facies of the loess subsoil in the Lublin area were distributed as follows: aeolian facies in a range from 75 to 80%, alluvial facies in a range from 8 to 15% and diluvial facies in a range from 8 to 10%.

Appl. Sci. 2021, 11, x FOR PEER REVIEW 10 of 14

(a) (b) Figure 9. Summary of results for the older aeolian facies: (a) distribution of qc values and (b) sound- ing parameters plotted against Robertson’s chart.

4. Discussion The obtained results allowed the authors to characterize loess soils from the Lublin area. Cumulative data from soundings are presented in the diagram (Figure 10), while Appl. Sci. 2021, 11, 6020 Table 2 includes characteristic values of each loess facies. The analyzed data show that10 ofthe 14 vast majority of loess soils belong to the aeolian facies and its parameters were crucial for the foundation of building structures. The highest qc values were obtained for this facies. The diluvial and alluvial facies occurred to a much smaller extent and the obtained results constitutedThe diluvial a and similar alluvial percentage. facies occurred It should to abe much borne smaller in mind extent that and diluvia the obtained were found results in theconstituted upper parts a similar of the percentage.subsoil and this It should zone was be borne included in mind in each that sounding. diluvia were Alluvia found were in mostthe upper often partsfound of in the the subsoil deeper and parts this of zone the wassubsoil included and not in all each of sounding.the soundings Alluvia covered were thismost zone. often The found same in applies the deeper to the parts older of aeolia the subsoiln facies, and the not parameters all of the of soundings which were covered only examinedthis zone. in The some same of applies the tests. to theAccording older aeolian to the facies,authors, the the parameters particular of facies which of were the loess only subsoilexamined in the in someLublin of area the tests.were Accordingdistributed toas the follows: authors, aeolian the particular facies in a facies range of from the loess75 to 80%,subsoil alluvial in the facies Lublin in areaa range were from distributed 8 to 15% as and follows: diluvial aeolian facies facies in a range in a range from from8 to 10%. 75 to 80%, alluvial facies in a range from 8 to 15% and diluvial facies in a range from 8 to 10%.

Figure 10. DistributionDistribution of qcc valuesvalues from from CPT CPT static static soundings soundings in in the the Lublin Lublin area with division into facies.

Table 2. Characteristic values of CPTU parameters for loess facies. Most of the results obtained for the aeolian facies at the level of qc in range from 4.5

to 8.0 MPa indicateCharacteristic that these Values soils were a qgoodc,mean load-bearing/σ R f,meansubstrate/σ for building struc- u2 tures.Facies Cone resistances mostly at the level of(MPa) 1.5–4.0 MPa for the(%) diluvial and alluvial facies confirm thatDiluvial these (younger)facies constituted less 2.88/1.29favorable foundation 3.77/1.65 conditions. closeThe toreduced zero resistance results mainly from the increased in ground pores. This results Diluvial (older) 3.11/1.13 4.09/1.20 >0 kPa in lower soil strength, but above all in increased deformability. Cone resistances qc were the basis for theAlluvial interpretation of the constrained 2.98/1.27 modulus 4.68/1.62M. It is especially the >0kPa soils of the diluvialAeolian facies (mechanical that provide cone) unfavorable 7.23/1.81 foundation conditions, 4.48/1.12 as they occur near - the surface. TheAeolian deeper (electric alluvia cone) were partially 6.48/2.20consolidated by the 2.44/0.65 soils lying onclose them. to zero or slightly negative Aeolian (older) 8.87/3.12 2.82/0.86 Table 2. Characteristic values of CPTU parameters for loess facies.

Characteristic Most of the results obtained forqc,mean the/ aeolianσ facies atR thef,mean level/σ of qc in range from 4.5 to 8.0 MPa indicate thatValues these soils were a good load-bearing substrate for buildingu structures.2 (MPa) (%) FaciesCone resistances mostly at the level of 1.5–4.0 MPa for the diluvial and alluvial facies confirm that these facies constituted less favorable foundation conditions. The reduced resistance results mainly from the increased water content in ground pores. This results in lower soil strength, but above all in increased deformability. Cone resistances qc were the basis for the interpretation of the constrained modulus M. It is especially the soils of the diluvial facies that provide unfavorable foundation conditions, as they occur near the surface. The deeper alluvia were partially consolidated by the soils lying on them. A common problem for loess is collapsibility [40–44]. Although this behavior is strongly associated with this soil, in practice it only affects a small part of it. According to the research by Frankowski [25], collapsible loess soils are solid loess from the aeolian facies whose cone resistance is qc < 3.0 MPa. This is an approximate criterion as the actual collapsibility test is performed with an oedometer. However, the is Appl. Sci. 2021, 11, x FOR PEER REVIEW 11 of 14

Diluvial (younger) 2.88/1.29 3.77/1.65 close to zero Diluvial (older) 3.11/1.13 4.09/1.20 >0 kPa Alluvial 2.98/1.27 4.68/1.62 >0 kPa Aeolian (mechanical cone) 7.23/1.81 4.48/1.12 - Aeolian (electric cone) 6.48/2.20 2.44/0.65 close to zero or Aeolian (older) 8.87/3.12 2.82/0.86 slightly negative

A common problem for loess is collapsibility [40–44]. Although this behavior is strongly associated with this soil, in practice it only affects a small part of it. According to Appl. Sci. 2021, 11, 6020 the research by Frankowski [25], collapsible loess soils are solid loess from the aeolian11 of 14 facies whose cone resistance is qc < 3.0 MPa. This is an approximate criterion as the actual collapsibility test is performed with an oedometer. However, the oedometer test is per- formed on selected samples, and CPT sounding gives as many as 100 measurements per performed1 m of the test. on selected In the light samples, of the andpresented CPT sounding research, gives only as3.0–4.0% many asof 100loess measurements within Lublin per 1 m of the test. In the light of the presented research, only 3.0–4.0% of loess within may be collapsible. Despite the small range of collapsible loess, it is very important to Lublin may be collapsible. Despite the small range of collapsible loess, it is very important perform CPT soundings in these soils. The diagrams of sounding parameters give a very to perform CPT soundings in these soils. The diagrams of sounding parameters give a good picture of the soil stiffness and make it possible to identify zones that are prone to very good picture of the soil stiffness and make it possible to identify zones that are prone collapsibility. As it can be seen, the of the cone resistance qc values is very high. to collapsibility. As it can be seen, the dispersion of the cone resistance q values is very The diagrams from CPT soundings are a very good basis for the developmentc of geotech- high. The diagrams from CPT soundings are a very good basis for the development of nical cross-sections for design purposes. It is not possible to develop a correct model of geotechnical cross-sections for design purposes. It is not possible to develop a correct the loess subsoil based on the boreholes alone. An example of the division of the loess model of the loess subsoil based on the boreholes alone. An example of the division of the subsoil based on the results of static soundings is shown in Figure 11. loess subsoil based on the results of static soundings is shown in Figure 11.

FigureFigure 11.11. GeotechnicalGeotechnical cross-sectioncross-section developeddeveloped onon thethe basisbasis ofof CPTUCPTU soundings.soundings.

SBT charts (e.g., Robertson’s chart) classify soils in terms of their behavior and are widely used to interpret the soil profile [20,38,45–47]. For aeolian loess soils, Rf values most often range from 1.7 to 3.2%, which, with relatively high cone resistances qc, locates them in the area on the border between silty and sandy loess, and very often they are classified as sandy. Silt are soils classified on the border between cohesive and non-cohesive, and such soils are often referred to as “transitional”. SBT charts confirm that loess silt are transitional soils. Aeolian loess soils resemble non-cohesive deposits in their behavior, and the that occurs in them is largely the result of cementation with carbonate. Diluvial and alluvial loess soils are characterized by an increased content of clay fraction and are referred to as “clayey loess”. Rf values in the range from 2.8 to 6.2% and lower qc values locate the soils of this facies within clayey silt and silty clay. Moreover, increased pore water pressure u2 is observed within the alluvial facies. Appl. Sci. 2021, 11, 6020 12 of 14

5. Conclusions The aim of the paper was to estimate the statistical distribution of the Lublin loess CPT results. The presented analysis is a continuation of previously published studies [12,37]; it provides an extended range of data and offers a division of results into particular facies. These data confirmed the previous findings and decreased the statistical error. Due to the large number of CPT records, each considerable Lublin loess facies was characterized and the values of parameters from static soundings were determined. The description of the characteristic features of facies allows for using future CPT results not only to find values of geotechnical parameters but also to determine loess soil genesis. The distribution of particular facies in the Lublin subsoil and the probability of the occurrence of collapsible loess soils constitute important findings of the study. After the analysis, it can be assumed that only 3.0–4.0% loess soils in Lublin can be collapsible. CPT and CPTU soundings provide a very large amount of data and should constitute the basic tool in loess subsoil identification. Moreover, apart from the numerical data, these tests provide a very good material for genetic classification, but the results should be correlated with the observations from boreholes and regional dependencies. Parameters from soundings may constitute both direct data for determining the of the subsoil and designing foundations, and the basis for deriving other parameters using conversion formulas. The main example of a parameter obtained using CPT records is constrained modulus that is essential for predicting building settlement. The obtained database enables not only predicting the settlement of a future building located on the loess subsoil but also the usefulness of the loess subsoil for civil engineering investments in general.

Author Contributions: Conceptualization, K.N.; Data curation, K.N.; Formal analysis, K.N. and A.L.; Investigation, K.N. and A.L.; Methodology, K.N.; Supervision, K.N.; Validation, K.N.; Visualization, A.L.; Writing—original draft, A.L.; Writing—review and editing, K.N. and A.L. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.

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