Weathered Rock Layer Research Articles

Field Study on Bearing Capacity of Large-Diameter Rock-Socketed Bored Piles with Combined Grouting in Highly Weathered Rock Layers

Field Study on Bearing Capacity of Large-Diameter Rock-Socketed Bored Piles with Combined Grouting in Highly Weathered Rock Layers

A Study on the Production Characteristics of Ceramic-quality Pottery from Aragaya (Haman-style Pottery): Focused on Excavated Artifacts from Ugeo-ri Kiln Site V in Haman

In this study, for the purpose of securing basic data and examining the production characteristics of pottery produced in Aragaya, 57 pieces of pottery excavated from the kiln of Haman Ugeo-ri Ⅴ and 22 pieces of kiln construction facilities were selected and compared by type and the homogeneity of the production raw materials was reviewed. As a result, most of the earthenware was made with thin walls and carefully selected clay, and smooth and dense cross-sectional structure and color change of the core were confirmed due to firing in a high-temperature environment of 1,300℃ or more. Additionally, considering the differences in chemical composition for each type, it is presumed that different raw material preparation processes were used depending on the firing degree intended by the potter. In the case of some samples that do not match the actual firing degree, it is judged to be a failure product or the result of multiple re-firing. As a result of analysis of the kiln construction section facility, mica and chlorite were detected in the weathered rock layer corresponding to the lowest layer of the combustion zone, so it appears that high temperatures were not reached in this section. On the other hand, high-temperature generated minerals such as Cristobalite and Mullite were detected in the soil of the fired section, indicating that it was fired at high temperature. Compared to the kiln-built facility, a higher viscosity composition of earthenware clay is confirmed. Therefore, it is presumed that earthenware was made using soil with higher plasticity than kiln-building facilities. In addition, since the clay content of the kiln construction facilities showed a more diverse composition range than that of earthenware, it is assumed that clay of various compositions was used when repairing the kiln.

Geophysical research on the interplays between soil–rock variability and hydrogeological structures: a case study

Understanding the spatial variations in soil–rock profiles is crucial for identifying weathered rock layers and mapping geological structures, particularly in the complex feldspar-rich granitic terrain of Penang Island, Malaysia. This study employs a combination of electrical resistivity and seismic refraction tomographic techniques, along with borehole lithological data, in three distinct areas on the island. Its goal is to provide insights into surficial and subsurface soil–rock characteristics and water-bearing structures within the North Penang Pluton (including a part of the Sungai Ara axis) for sustainable groundwater development, addressing the needs of the region's growing population. The research identifies three distinct geological units at the near-surface: residual soils, highly to moderately weathered/fractured granitic layers and fresh bedrock, each with its hydrogeological properties. Promisingly, the weathered layers offer significant groundwater development potential, with deep weathered and potentially fractured zones exceeding depths of 30 m in the study area. These findings have substantial implications for sustainable groundwater development, especially in tropical hard-rock terrains. In addition, the study underscores the limitations of small geophysical spacings when probing deeper groundwater resources. This knowledge is essential for informed decision-making in water resource management and infrastructure development, addressing the ongoing global challenge of ensuring access to clean water resources amid population growth.

Apple trees utilize 3–5% of root biomass in the weathered rock layer to absorb 33–34% of their transpiration water consumption

Rocky regolith layer can restrain plant root growth, which may affect soil water unitization of deep-rooted fruit trees in rocky mountain areas. However, how and to what magnitude the rocky regolith layer shapes root features and thus changes trees’ water consumption, remains unclear. Here, we investigated the root features and water uptake strategies of apple trees in three apple orchards with the underlying weakly (WWP), strongly (SWP), and completely (CK) weathered regolith layer within soil profiles, in the hilly areas of Jiaodong Peninsula, China. The results showed that the fine root biomass density (FRBD) of apple trees decreased while the specific root length (SRL) increased with increasing soil depths in the three orchards. The FRBD within the rocky regolith layer only accounted for 3–5% of the total FRBD in the WWP and SWP orchards, which were significantly lower than that in the CK orchard (3.31–5.11% vs. 29.96%) (P < 0.05). The maximum SRL was 76.61 m·g-1 and 72.38 m·g-1 in the WWP and SWP orchards, respectively, being significantly higher than that in the CK orchard (55.26 m·g-1). Both the FRBD and SRL within the rocky regolith layer showed no significant difference between the WWP and SWP, which indicated that it was the presence but not the weathering intensity of the rocky regolith layer shaped apple trees’ root features. The MixSIAR model estimated that the water uptake of roots in the rocky regolith layer accounted for an average of 33.14% of the total water uptake in the WWP and SWP orchards. During the fruit expansion period (July-August) with high water consumption, apple trees’ water uptake in the rocky regolith layer contributed 41.40% of water consumption in the WWP orchardand 34.77% in the SWP, which can be comparable to that in the corresponding soil depth in the CK orchard (46.70%). This suggested that apple trees may prime root activity to absorb more soil water with decreased root biomass in the rocky regolith layer. Overall, apple trees could utilize 3–5% of root biomass to absorb 33–34% of water consumption in the rocky regolith layer. Our study highlights the specific water use strategies in rocky mountain areas and will benefit the sustainable water management in the orchards in these areas.

Fractal Characteristics of Overburden Rock Fractures and Their Impact on Ground Fissures in Longwall Coal Mining

Ground fissures are generated during the coal mining process due to overlying strata migration, which provides gas and water seepage channels and usually contributes to coal mining accidents in shallow buried coal seams with larger mining height working faces. Thus, the evolution features of ground fissures in large mining height working faces and shallow buried coal seams were explored by considering field observation data, similar simulation, and numerical simulations. The results show that the weathered rock layer above the thin bedrock inhibits fracture growth caused by coal mining. Overlying strata fracture expansion can be quantitatively divided into three stages based on fractal dimension: the overburden fracture formation stage, the overburden deformation fracture expansion stage, and the overburden fracture stable development stage. The movement deformation region of the ground fissure can be described by three characteristic zones: the boundary tension zone, the central compression zone, and the central dynamic tension and compression zone. Central dynamic fissures usually have 3–5 fissure counts with 2–5 m intervals between each group of fissures; central fissures develop twice from open to closed widths; the time period for two central fissures to reach their with maximum widths is 11–20 days; and border fissures expand rapidly with maximum values in a time period of 5–6 days.

Compilation of Parameter Control for Mapping the Potential Landslide Areas

Batu Tourism City is located in a mountainous area, so based on information from the BNPB, it has quite a large potential for landslides. Landslide hazards can frequently disrupt public traffic due to road cuts. Landslide mapping digitally will contribute to handling and mitigation activities since the database can be updated in real time to anticipate landslide hazards. This study aims to map landslide-prone areas located in the Payung zone, Songgokerto Village, and Batu City. Landslide areas can be determined by mapping analysis using GIS software. GIS can determine the classification level for a landslide susceptible area. Some input data that will influence landslides, such as rainfall, wind, earthquakes, etc., was collected as the control parameters. All parts of the study area could be classified as areas with minor, medium, and major potential for landslides. Primary data are collected from geo-surveying (aerial images) using drone devices for interpretation of landslide susceptibility areas, geophysical to identify the type of soil or rock layers that completed their behavior, and slip planes as well using geo-electric, geotechnical engineering to predict slope stability with the correlation from cone penetration test (CPT) data, and geo-hydraulic to observe the rainfall and the catchment area model using the available secondary data. Geometrically, measurement data found that the average slope angle at the upper and lower of the East Java Province highway is around 40–50o. Studies from geophysical data identified that the hilly terrain in the object study area has been dominated by the weathered rock layer. Geotechnical data obtained shows the soil layers at the slope location will be stable with the water content under 35% during the dry season and may become unstable with the water content reaching over 50% due to the increase in saturation during the rainy season. The landslide that occurred was more caused by seepage behavior from surface water flow towards the sloping plane, and then the safety factor during the rainy season reached the critical values at SF = 0.58. During the dry season, the unsaturated process due to the temperature change generates a safety factor (SF) of more than 1.2. The compilation data produced maps of susceptible landslides and surface flow distribution. Doi: 10.28991/CEJ-2023-09-04-016 Full Text: PDF

Field tests of rock-socketed monopile in coastal area subjected to lateral cyclic loading

Field tests were carried out to study the lateral cyclic loading characteristics of rock-socketed monopile in coastal area, and the variation law of pile body accumulative displacement, unloading stiffness, and pile body bending moment with the cyclic number and cyclic loading amplitude were obtained by actual measurement. Test results show that the cyclic loading history with sa small amplitude has a certain effect on the cyclic accumulative displacement and the degradation of unloading stiffness, and both the peak bending moment and locking moment of the pile body increase with the increase of cyclic numbers. By using the normalization method and formula fitting method, it is found that, the accumulative rate of cyclic displacement, the degradation rate of unloading stiffness, and the variation rate of peak bending moment of single piles in weathered rock layers are significantly smaller than those of sand foundation or clay foundation. The cyclic p-y curves at different depths are derived, and the different hysteretic characteristics between shallow cyclic p-y curve and deep cyclic p-y curve are explored. Finally, the static load test after cyclic tests was carried out, and it was found that the lateral bearing performance of the rock-socketed monopile was greatly degraded after a total of 3000 times of lateral cyclic loading.

Numerical simulation of load distributive compression anchor installed in weathered rock layer

Numerical simulation of load distributive compression anchor installed in weathered rock layer

Load transfer mechanism of a load distributive compression anchor installed in weathered rock layer

The demand for a load distributive compression anchor (LDCA) in construction sites has been increasing, owing to its high bearing capacity and removable steel strands. As an LDCA comprises multiple anchor bodies and unbonded steel strands, the load applied to the strands generates a distributive compressive stress in the grout, preventing high concentration of grout–ground shear stress. Unlike in the conventional anchors, in an LDCA, independent load transfer of each anchor body induces interference effect between adjacent anchor bodies. Therefore, for an efficient design of an LDCA, it is necessary to investigate the load transfer mechanism considering the effect of multiple anchor bodies. In this study, a series of anchor pull-out field tests was conducted for LDCAs consisting of a single anchor body, and double and triple anchor bodies spaced by 1, 2, and 3 m. According to the test results, the LDCA showed a stiffer load–displacement behavior with an increase in the number and spacing of the anchor bodies. The multiple anchor bodies of the LDCA generated an overlapping of the grout axial load and induced its rapid dissipation, increasing the grout–ground shear stress. This interference effect was more clearly observed with a decrease in the anchor body spacing.

Evaluation of groundwater potential of bedrock aquifers in Geological Sheet 223 Ilorin, Nigeria, using geo-electric sounding

Electrical resistivity data acquired in one hundred and ten (110) locations using vertical electrical sounding method of Schlumberger array have been used to study the hydrogeological properties and groundwater storage potential of bedrock aquifers in an area covered by Geological Sheet 223 Ilorin, Nigeria. The aim of the study was to identify productive aquifer zones for citing boreholes for community water supply. The data acquired were processed and interpreted using auxiliary curve matching and computer automation method to delineate the different geo-electric layers, their resistivities, thicknesses, and depths. Geo-electrical layers were interpreted to their equivalent geological layers using borehole lithological logs from the study area. Then, the hydraulic conductivity, transmissivity, fracture contrast, reflection coefficient were estimated and plotted in the form of 2D maps to describe the spatial variations of these parameters in the area. The results of the study revealed the presence of three to five geo-electric layers. The geo-electric layers, from top to the bottom, corresponds to the topsoil layer, lateritic layer, weathered rock layer, fractured rock layer, and the fresh basement rock. Lateritic and/or fractured rock layers were not delineated in some places. The weathered and fractured rock layers, where present, correspond to the aquifer units. The thickness of the fracture aquifer ranges from 0.6 to 33.6 m while the thickness of the weathered aquifer ranges from 1.4 to 49.3 m. The transmissivity, T , and hydraulic conductivity, K , range from 3 to 1200 m2/day and 1 to 48 m/day, respectively. The reflection coefficient and fracture contrast map showed the presence of water-bearing fractures and shared some similarities with T and K maps. A mathematical model for predicting groundwater potential, {text{GW}}_{text{P}} , of weathered aquifer in the basement complex terrain was proposed in this study. The consistencies between the overall groundwater potential map and aquifers parameters distributions maps suggest the appropriateness of the proposed mathematical model for predicting groundwater potential of weathered rock in the basement complex area of Nigeria. The western, northwestern, and central parts of the study area, having {text{GW}}_{text{P}} greater than 0.6 (60%), were recommended for groundwater development through boreholes drilled to a depth ranging between 75 and 100 m.

Soil, regolith, and weathered rock: Theoretical concepts and evolution in old-growth temperate forests, Central Europe

Evolution of weathering profiles (WP) is critical for landscape evolution, soil formation, biogeochemical cycles, and critical zone hydrology and ecology. Weathering profiles often include soil or solum (O, A, E, and B horizons), non-soil regolith (including soil C horizons, saprolite), and weathered rock. Development of these is a function of weathering at the bedrock weathering front to produce weathered rock; weathering at the boundary between regolith and weathered rock to produce saprolite, and pedogenesis to convert non-soil regolith to soil. Relative thicknesses of soil (Ts), non-soil regolith (Tr) and weathered rock (Tw) can provide insight into the relative rates of these processes at some sites with negligible surface removals or deposition. Scenarios of weathering profile development based on these are developed in current study. We investigated these with ground penetrating radar, electrical resistance tomography, and seismic profiling at three old growth forest sites in the Czech Republic, on gneiss, granite, and flysch bedrock.We found that the geophysical methods – which generated thousands of separate measurements of Ts, Tr, Tw – to produce good estimates. The weathered rock layer (sensu lato) was generally the thickest of the weathering profile layers. Mean soil thicknesses were about 0.64–0.75 m at the three sites, with typical maxima around 1.5 m. Non-soil regolith thicknesses averaged about 2.5 m on the gneiss site and 1.2–1.4 at the other sites. Weathered rock had a mean thickness of 7 m at the gneiss site (up to 10.3), 4.6 at the granite site, and 3.4 on flysch. Results indicate that weathering at the bedrock weathering front is more rapid than conversion of weathered rock to regolith, which is in turn more rapid than saprolite-to-soil conversion by pedogenesis on all three bedrock types. No evidence was found of steady-state soil, non-soil regolith, or weathered rock thicknesses or evolution toward steady-state. Steady-state would require that weathering rates at the bedrock and/or regolith weathering fronts decline to negligible rates as profiles thicken, but the relative thicknesses at our study sites do not indicate this is the case.

Numerical simulation study of eye-shaped foundation pit

In order to study the stability of the “eye-shaped” foundation pit support, the rectang ular and the “eye-shaped” deep foundation pit are studied by using the numerical simulation sof tware Midas GTS NX. The results show that the rectangular deep foundation pit is subjected to lateral extrusion and the maximum lateral displacement exceeds 6m. In practical engineering, t he foundation pit has been destroyed and collapsed. Therefore, the safety of rectangular deep fo undation pit without internal support is very poor. For the “eye-shaped” foundation pit, the lat eral displacement at different vertical depths shows obvious characteristics of soil layer, in whi ch the silty clay layer increases sharply, which is a weak layer liable to damage. The tight effec t of middle weathered rock is remarkable due to different strength of silty clay layer and weath ered rock layer, and the negative displacement at the top appears. The lateral displacement of t he wall in the transverse inner wall region is significantly smaller than that in the circular arch r egion. The maximum lateral displacement of the wall is 2.96 cm at the intersection of the two “arches” in the transverse region and the vertical one at the silty clay layer. Along the depth of e xcavation, the uplift value is excavated by 1> excavation and 3> excavation 2. The research res ults fully prove that the eye-shaped foundation pit has good stability and the deformation is con trolled within a reasonable range.

Characteristics and numerical runout modeling of the heavy rainfall-induced catastrophic landslide–debris flow at Sanxicun, Dujiangyan, China, following the Wenchuan Ms 8.0 earthquake

The 2008 Ms 8.0 Wenchuan earthquake triggered a large number of extensive landslides. It also affected geologic properties of the mountains such that large-scale landslides followed the earthquake, resulting in the formation of a disaster chain. On 10 July 2013, a catastrophic landslide–debris flow suddenly occurred in the Dujiangyan area of Sichuan Province in southeast China. This caused the deaths of 166 people and the burying or damage of 11 buildings along the runout path. The landslide involved the failure of ≈1.47 million m3, and the displaced material from the source area was ≈0.3 million m3. This landslide displayed shear failure at a high level under the effects of a rainstorm, which impacted and scraped an accumulated layer underneath and a heavily weathered rock layer during the release of potential and kinetic energies. The landslide body entrained a large volume of surface residual diluvial soil, and then moved downstream along a gully to produce a debris flow disaster. This was determined to be a typical landslide–debris flow disaster type. The runout of displaced material had a horizontal extent of 1200 m and a vertical extent of 400 m. This was equivalent to the angle of reach (fahrboschung angle) of 19° and covered an area of 0.2 km2. The background and motion of the landslide are described in this study. On the basis of the above analysis, dynamic simulation software (DAN3D) and rheological models were used to simulate the runout behavior of the displaced landslide materials in order to provide information for the hazard zonation of similar types of potential landslide–debris flows in southeast China following the Wenchuan earthquake. The simulation results of the Sanxicun landslide revealed that the frictional model had the best performance for the source area, while the Voellmy model was most suitable for the scraping and accumulation areas. The simulations estimated that the motion could last for ≈70 s, with a maximum speed of 47.7 m/s.

Image-based near-surface modeling for statics corrections

The near-surface is usually defined as the depth interval below the topography, composed of a low-velocity soil column and weathered rock layer. In contrast with the near-surface, the subsurface is composed of relatively higher velocity rock layers. This means that the interface between the near-surface and the subsurface often gives rise to a strong shallow reflection. The image-based method described in this paper makes use of the strong reflection at the base of the near-surface to estimate a model for the near-surface for statics corrections. The method is based on construction of constant-velocity migration volume by prestack time migration of shot records. The near-surface rms velocities associated with the strong reflector at the base of the near-surface are picked from the semblance spectra to create the near-surface rms velocity field. This laterally varying, but vertically invariant, velocity field actually is equivalent to the near-surface interval velocity field, which can be used to perform prestack depth migration of shot records to obtain a shallow seismic image of the near-surface. Finally, the depth horizon associated with the base of the near-surface is delineated from this shallow seismic image. The image-based near-surface model is formed by combining this depth horizon with the interval velocity field. This image-based model for the near-surface yields essentially the same statics that one calculates from a more complicated model for the near-surface that may be estimated from inversion methods.

Investigating the role of geology in the hydrological response of Mediterranean catchments prone to flash-floods: Regional modelling study and process understanding

Summary In this study, a regional distributed hydrological model is used to perform long-term and flash-flood event simulations, over the Cevennes–Vivarais region (south of France). The objective is to improve our understanding on the role played by geology on the hydrological processes of catchments during two past flash-flood events. This modelling work is based on Vannier et al. (“Regional estimation of catchment-scale soil properties by means of streamflow recession analysis for use in distributed hydrological models”, Hydrological Processes , 2014), where streamflow recessions are analysed to estimate the thickness and hydraulic conductivity of weathered rock layers, depending on the geological nature of catchments. Weathered rock layers are thus implemented into the hydrological model CVN-p, and the contribution of these layers is assessed during flash-flood events simulations as well as during inter-event periods. The model is used without any calibration, to test hypotheses on the active hydrological processes. The results point out two different hydrological behaviours, depending on the geology: on crystalline rocks (granite and gneiss), the addition of a weathered rock layer considerably improves the simulated discharges, during flash-flood events as well as during recession periods, and makes the model able to remarkably reproduce the observed streamflow dynamics. For other geologies (schists especially), the benefits are real, but not sufficient to properly simulate the observed streamflow dynamics. These results probably underline the existence of poorly known processes (flow paths, non-linear spilling process) associated with the planar structure of schisty rocks. On a methodological point of view, this study proposes a simple way to account for the additional storage associated with each geological entity, through the addition of a weathered porous rock layer situated below the traditionally-considered upper soil horizons, and shows its applicability and benefits for the simulation of flash flood events at the regional scale.

국내 암반지층의 전단파속도에 근거한 지진공학적 기반암 결정

대부분의 내진설계 기준에서 설계지진지반운동은 기반암에서의 기준 스펙트럼과 지반동적 조건 정량화를 위한 부지증폭계수에 의해 정의된다. 특히, 지진공학적 기반암은 지진파가 증폭 없이 감쇠전파되는 기초적 지반구성층이다. 지진공학 관점에서 기반암을 파악하기 위하여, 원위치 탄성파시험으로 획득한 전단파속도(<TEX>$V_S$</TEX>) 자료를 시추조사 시 구분되는 암반층에 대해 살펴보았다. 국내 연암에서 대부분의 <TEX>$V_S$</TEX> 자료는 강지진 관측소 설치 시 고려되는 공학적 기반암의 최저 <TEX>$V_S$</TEX> 값인 750 m/s에 비해 크게 나타났으나, 풍화암에서는 전체의 60 % 정도가 작게 나타났다. 따라서 국내 풍화암 하부의 연암 및 그 이상 경도의 암반층을 지진공학적 기반암으로 고려해야 한다. In most current seismic design codes, design earthquake ground motions are defined by a reference spectrum, based on bedrock and site amplification factors that quantify the geotechnical dynamic conditions. Earthquake engineering bedrock is the fundamental geotechnical formation where the seismic waves are attenuated without amplification. To better define bedrock in an earthquake engineering context, shear wave velocity (<TEX>$V_S$</TEX> ) data obtained from in-situ seismic tests were examined for several rock strata in Korea; these data were categorized by borehole drilling investigations. The <TEX>$V_S$</TEX> values for most soft rock data in Korea are > 750 m/s, which is the threshold <TEX>$V_S$</TEX> value for identifying engineering bedrock from a strong motion station. Conversely, VS values are < 750 m/s for 60% of <TEX>$V_S$</TEX> data in weathered rock in Korea. Thus, the soft (or harder) rock strata below the weathered rock layer in Korea can be regarded as earthquake engineering bedrock.

Availability of coastal groundwater discharge as an alternative water resource in a large-scale reclaimed land, Korea

This study was conducted to identify the availability of coastal groundwater discharge (CGD), subsurface fluids flowing from inland through the coastal area to sea, as an alternative water resource for a large-scale reclaimed land. The behaviors of stable isotopes indicated that groundwater originated from inland precipitation and traveled as CGD along the coast line. Most of the groundwater samples collected from domestic wells installed along the old coast line were considered to be relatively fresh from the correlation analysis among chemical constituents. The average electrical conductivity (EC) values of the samples were identified as averaging 1,125–1,297 μS cm−1, corresponding to appropriate crop growth. A weathered-rock layer in a small catchment within the reclaimed land was proved to be a main CGD pathway, with electrical resistivity anomalies ranging from 7 to 14 Ω m. Five monitoring wells were placed in this catchment to delineate the occurrence of CGD. Long-term vertical EC profiling results for the monitoring wells indicated that CGD occurs within a depth of 30 m below the ground surface. Annual monitoring data for groundwater level and EC demonstrated that the water quality of CGD was improved by introducing fresh terrestrial groundwater. A remarkable improvement in water quality (EC decrease of 900–1,600 μS cm−1) of CGD was observed during the saline water pumping test that explains how CGD could be an alternative water resource for the reclaimed land.

Comparison of potentially toxic metals leaching from weathered rocks at a closed mine site between laboratory columns and field observation

Abstract Potentially toxic metals, such as Cu, Pb and Zn, are leached from weathered rocks at many closed mine sites due to the acidic environments and mineralogical modifications. The mobilized toxic metals may cause contamination of surrounding water bodies. In this study, both laboratory column experiments and field observations at a former mine located in the north of Japan were carried out to compare the leaching behavior of Cu, Pb and Zn. The thickness of the surface weathered rock was varied (10, 20 and 30 cm) for the columns experiments while porous cups for porewater sampling were set up at different depths (GL-15, -45, -70, and -95 cm) for the field observations. Deionized water was added once a week over 75 weeks to the columns to simulate rainfall while porewater was extracted by a vacuum pump in several sampling campaigns (over 18 months). Similar low pH and leaching behavior of potentially toxic metals were observed for column experiments and field observations. A moderate increase in concentration with depth was observed for Cu and Zn. However, no increase in concentration was observed for Pb. This suggests that the leaching of Cu and Zn is enhanced by the length of the flow pathway through the weathered rock layer while Pb concentration is restricted by the precipitation of insoluble Pb sulfate. Thus, the thickness of the weathered rock layer is an important parameter that should be taken into consideration to estimate the loads of some potentially toxic metals, which is important when designing remediation schemes.

춘천지역의 천부 횡파속도를 구하기 위한 레일리파 분산곡선 역산

천부 횡파속도(<TEX>${\nu}_s$</TEX>)를 구하기 위한 효율적 방법을 모색하기 위하여, 수동적 및 능동적 방법으로 발생된 레일리파의 분산곡선 특성을 분석하였다. 춘천지역에서 반경 5 ~ 40 m인 4개 삼각형 배열을 이용하여 5분간 감지한 상시미동을 확장된 공간자기상관법으로 분석하였다. 동일한 지역에서 해머로 발생시키고 4.5 Hz 지오폰 24개로 2초간 기록한 인공적 레일리파는 다중채널 표면파 분석법으로 처리하였다. 7 ~ 19 Hz와 11 ~ 50 Hz 구간에서 상대적으로 높은 신호/잡음비를 보이는 상시미동과 인공적 레일리파의 분산곡선을 병합하고 역산한 결과를 시추공 주상도와 비교하였다. 토사층 및 연암층의 <TEX>${\nu}_s$</TEX>는 각각 221 m/s와 846 m/s 정도로 비교적 일정하나, 사력-혼전층 및 풍화암층 구간에서는 깊이에 따라 선형으로 증가하는 양상을 보인다. 횡파속도에 의한 지반분류를 적용할 경우, 풍화암/연암의 경계는 시추주상도에 표시된 깊이보다 5 m 깊은 것으로 분석된다. To evaluate methods of determining near-surface shear-wave velocities (<TEX>${\nu}_s$</TEX>), we derived dispersion curves of Rayleigh waves generated by both passive and active sources in Chuncheon, Korea. Microtremors were recorded for 5 minutes in each of four triangular arrays with radii of 5 ~ 40 m. Those data were analyzed using the Spatial Autocorrelation method. Rayleigh waves were also generated by a hammer source and recorded in the same area for 2 s using 24 4.5-Hz geophones. Multichannel Analysis of Surface Waves was applied to those data. Velocity spectra were derived with relatively high signal-to-noise ratios in the frequency ranges of 7 ~ 19 and 11 ~ 50 Hz for the microtremors and synthetically generated Rayleigh waves, respectively. The resultant dispersion curves were combined as one and then input to inversion to derive shear wave velocities that were compared with a lithology log from a nearby well. Shearwave velocities in the top soil and soft-rock layers are almost constant with values of 221 and 846 m/s, respectively; while the inverse-modeled <TEX>${\nu}_s$</TEX> increases linearly in the gravelly sand, cobbles, and weathered-rock layers. If rock type is classified based on shear-wave velocity, the inversion-derived boundary between weathered-rock and soft rock may be about 5 m deeper than in the well log.

Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing

In the mountainous Rio Icacos watershed in northeastern Puerto Rico, quartz diorite bedrock weathers spheroidally, producing a 0.2–2 m thick zone of partially weathered rock layers (∼2.5 cm thickness each) called rindlets, which form concentric layers around corestones. Spheroidal fracturing has been modeled to occur when a weathering reaction with a positive Δ V of reaction builds up elastic strain energy. The rates of spheroidal fracturing and saprolite formation are therefore controlled by the rate of the weathering reaction. Chemical, petrographic, and spectroscopic evidence demonstrates that biotite oxidation is the most likely fracture-inducing reaction. This reaction occurs with an expansion in d (0 0 1) from 10.0 to 10.5 Å, forming “altered biotite”. Progressive biotite oxidation across the rindlet zone was inferred from thin sections and gradients in K and Fe(II). Using the gradient in Fe(II) and constraints based on cosmogenic age dates, we calculated a biotite oxidation reaction rate of 8.2 × 10 −14 mol biotite m −2 s −1. Biotite oxidation was documented within the bedrock corestone by synchrotron X-ray microprobe fluorescence imaging and XANES. X-ray microprobe images of Fe(II) and Fe(III) at 2 μm resolution revealed that oxidized zones within individual biotite crystals are the first evidence of alteration of the otherwise unaltered corestone. Fluids entering along fractures lead to the dissolution of plagioclase within the rindlet zone. Within 7 cm surrounding the rindlet–saprolite interface, hornblende dissolves to completion at a rate of 6.3 × 10 −13 mol hornblende m −2 s −1: the fastest reported rate of hornblende weathering in the field. This rate is consistent with laboratory-derived hornblende dissolution rates. By revealing the coupling of these mineral weathering reactions to fracturing and porosity formation we are able to describe the process by which the quartz diorite bedrock disaggregates and forms saprolite. In the corestone, biotite oxidation induces spheroidal fracturing, facilitating the influx of fluids that react with other minerals, dissolving plagioclase and chlorite, creating additional porosity, and eventually dissolving hornblende and precipitating secondary minerals. The thickness of the resultant saprolite is maintained at steady state by a positive feedback between the denudation rate and the weathering advance rate driven by the concentration of pore water O 2 at the bedrock–saprolite interface.