Accumulation of a Last Deglacial Gravel Layer at Diexi, Eastern Tibetan Plateau and its Possible Seismic Significance

Tectonic and climatic process controlling gravel accumulation in tectonically active regions is the subject of active debate. In this study, the formation mechanism of a gravel layer in the Diexi lacustrine section, eastern Tibetan Plateau, was investigated using mutually validated dating methods and detailed analysis of sedimentary processes. Optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) 14C dating show that the gravel layer in the Diexi section accumulated at approximately 16.79 ka BP. The sedimentary characteristics of the gravel layer and the contact between upper and lower strata indicate that the formation of the Diexi gravel layer was triggered by an earthquake rather than by a debris flow caused by torrential rain. And the result based on the intensity attenuation model are consistent with the characteristics of frequent large earthquakes in Diexi area. Detailed analysis of satellite images and sedimentary characteristics of the gravel layer provide evidence for an ancient landslide, which may be related to the gravel layer at Muer village (to the north of the Diexi section). Overall, this study reconstructs a gravel event at approximately 16.79 ka BP and has important theoretical and practical significance for understanding the formation mechanism of gravel deposits and analysing seismic events through gravel accumulation.

Force Chain Effect of Deep Foundation Pit Supported by Soldier Piles in the Sand-Gravel Layer

Soldier pile support is an important tool for supporting deep foundation pits in the sand-gravel layer. However, since the sand-gravel layer itself is an aggregate of particles, its noncontinuity will cause extremely complex changes in the properties of the surrounding soils during pile supporting, and the changes in the mechanical properties of the soil behind the piles can also affect the safety and stability of the pit. To study the changing pattern of the surrounding soil in the course of pile supporting, we used the numerical method to simulate an excavation in the sand-gravel layer, followed by an analysis of the movement and stress distribution of the surrounding rocks. A photoelastic experiment was carried out to simulate the excavation process and study the force chain network of the surrounding soil as well as its changing characteristics. As shown by the results, (1) during the excavation of a deep foundation pit supported by soldier piles, on the same horizontal plane, the force chain changed most dramatically at the position that was 13.8 m (depth of the foundation pit) away from the edge of the foundation pit; (2) during the excavation, the force chain structure of the surrounding soil changed from vertical development to both vertical and horizontal developments; when there was a hard rock layer at the bottom of the soldier piles, the supporting effect of the piles was mainly provided by the hard rock layer; (3) the free face should be reinforced, and the excavation face should be adjusted based on the underground conditions of surrounding buildings (structures).

Performance Comparison of Geodrain Drainage and Gravel Drainage Layers Embedded in a Horizontal Plane

Drainage materials are widely used, among other uses, in the construction of landfills. Regulations require a drainage layer in the base and a covering for the landfill. The implementation of a gravel drain requires a lot of material and financial outlays. New geocomposite materials are an alternative, and facilitate construction. The aim of the research was to compare the drainage properties of the Pozidrain 7S250D/NW8 geocomposite and gravel drainage. The model test was performed on a specially prepared test stand. The research was carried out for model #1, in which the gravel drainage was built. Model #2 had a drainage geocomposite built into it. The test results show the values of the volumetric flow rate for geodrains, with a maximum value of 40 dm3·min−1. For the gravel layer, values of up to 140 dm3·min−1 were recorded. Another parameter recorded during the damming of water by the embankment was the speed of water suction by the geosynthetic and gravel drainage; the values were 0.067 and 0.024 m3·s−1, respectively. The efficiency of water drainage through the geocomposite was sufficient. It is possible to use the slopes of the landfill for drainage, which will reduce material and financial outlays.

The impact of large-scale afforestation on ecological environment in the Gobi region

In recent year, there has been large-scale afforestation in the gobi region of western Inner Mongolia, China. However, this area has low annual precipitation of 35–55 mm, and a high annual evaporation capacity of 3842 mm. Further, water resources in this region are scarce and cannot support the sustainable growth of shrubs. Thus, without effective irrigation, the shrubs cannot survive and ultimately, large-scale afforestation in the gobi region will destroy “black vegetation”. The surface of this area is covered by dense gravel (65.43–82.08%; average of 77.14%) as a result of long-term erosion caused by strong winds. The sediments underlying the gravel layer are rich in sand (60.34–87.51%) and silt (11.26–35.18%). Once the surface gravel layer is destroyed, the underlying sand and silt expose and increase dust supply, and result in increased intensity and frequency of dust storms. Thus, large-scale afforestation in the gobi region is an ecological disaster for these very dry lands.

Migration characteristics of atrazine in porous media during managed aquifer recharge

To study the influences of sand and gravel layer and groundwater velocity of Yufuhe River on atrazine migration, adsorption-desorption and sand column experiments were carried out. Results show that the adsorption capacity of montmorillonite, raw sand and washed sand to atrazine sequentially weakens. In different media, the time for atrazine concentrations to peak in washed sand with motomorillonite (WSM), raw sand and washed sand is 60, 135 and 105 minutes respectively, and the peak concentration accounts for 84, 90 and 95% of the initial concentrations. Under different flow rates, the peak time in washed sand at flow rates of 100, 150 and 200 mL/min is 135, 105 and 75 minutes, and the peak time in WSM is 90, 60 and 45 minutes, respectively. Results from this study indicate that increasing flow velocity and suspended colloids concentrations can promote the migration of atrazine in aquifers, while the presence of clay minerals in sand and gravel layer can reduce atrazine migration. Thus, during Yellow River water recharging, the sand and gravel layer of Yufuhe River is helpful to protect the aquifer, but the colloids-associated migration of atrazine can contaminate groundwater in underlying karst aquifer.

Interpretation of 1D-Resistivity Data to Describe the Aquifer Model in the Serayu Watershed Area of Somagede Village, Somagede District, Banyumas Regency

Acquisition of resistivity data using the Schlumberger configuration has been carried out in the Serayu watershed area of Somagede Village, Somagede District, Banyumas Regency. The purpose of this research was to describe a groundwater aquifer model based on the interpretation of 1D-resistivity data. The research results are resistivity logs of subsurface rock distributed over seven sounding points with resistivity values ranging from 2.24-192.78 m. The sounding points are located at positions of 7°31′28.55″ and 109°19′8.65″ (Sch-1) to 7°31′18.79″ and 109°19′21.45″ (Sch-7). The interpretation of the resistivity logs has resulted in a lithology log at each sounding point. Based on the interpretation, the lithology of the research area is composed of topsoil (42.85-85.13 m), sandy clay which partly slightly wet (7.08-17.18m), sandy clay inserted with gravel (22.44-31.70 m), sand, gravel, and pebble, with various consolidated (22.16-192.78m), sand inserted by gravel (6.77m), alternating sandstone and claystone, some of which are alternated with marl and tuff (8.71-21.99m), and sandstones with various porosity (3.25-8.76m). Shallow aquifers are interpreted to exist in sand inserted by gravel layer (13.23-27.67 m) at the sounding point of Sch-2 where the potential is quite good. While deep aquifers are estimated to be present in the sandstone layer with various porosity (> 46.67 m) at all sounding points with very good potential.Keywords: 1D-resistivity, Serayu watershed, resistivity log, aquifer, Somagede Village.

Usaha Peningkatan Daya Dukung Tanah Lempung Menggunakan Layer Krikil, Anyaman Bambu dan Kombinasi Kolom-Layer Pasir

ABSTRACT Clay soil is soil that has a low value of pressure strength and bearing capacity. The purpose of this study is using a layer of gravel, woven bamboo, and a combination of column-layer sand as an alternative to improve the carrying capacity of clay soil, then the results from the tests are compared with each other. The method in this study is experimental. The samples of soil were taken from Kalangan, Kasihan, Bantul, D.I. Yogyakarta. The foundation soil model using steel tub size 100x100x40 cm, with soil volume 100x100x30 cm. Soil loading uses steel plates that are loaded with hydraulic jacks, equipped with a proving ring as a load reader. The column-layer combination consists of 3 sand layers, 1 cm thick horizontal position and 5 cm spacing between layers. The sand column is 1 cm in diameter with a hole depth of 20 cm. The gravel layer pattern consists of 3 layers of gravel with a layer thickness of 2 cm, the distance between the layers is 5 cm. Woven bamboo pattern: 1 layer with a length of 20x20 cm. Placement of woven bamboo at a depth of 2 cm from the ground. The results of the research are; (1) The Soil is a high plasticity (CH) inorganic clay based on the USCS system, including the medium to poor clay soil group (A-7-6 (40)) based on the AASHTO system. (2) The Strengthening of gravel layer increases the ultimate bearing capacity by 2.5 times or 159.02%, while bamboo matting provides an increase in bearing capacity by 2.7 times or 170.49%, and the combination of column-layer sand by 2.2 times. or 127, 87%. (3) The reinforcement of bamboo mats provides the highest increase in bearing capacity in clay soil between the gravel layer and the combined reinforcement of the sand column and the sand layer. This shows that the use of woven bamboo is more effective as a material for strengthening clay. ABSTRAKTanah lempung adalah tanah yang mempunyai nilai kekuatan tekanan serta nilai daya dukung rendah. Tujuan penelitian ini adalah penggunaan layer kerikil, anyaman bambu, dan kombinasi kolom-layer pasir sebagai alternatif perbaikan peningkatan daya dukung tanah lempung, kemudian hasil dari pengujian dibandingkan satu sama lain. Metode yang digunakan adalah experimen. Sampel tanah diambil dari Kalangan, Kasihan, Bantul, D.I. Yogyakarta. Pemodelan tanah pondasi menggunakan bak baja ukuran 100x100x40cm, volume tanah 100x100x30cm. Pembebanan tanah menggunakan pelat baja yang dibebani dengan dongkrak hidrolik, dilengkapi proving ring sebagai pembaca beban. Kombinasi kolom-layer pasir terdiri dari 3 lapis pasir, posisi horizontal tebal 1 cm dan jarak antar lapisan 5 cm. Kolom pasir diamter 1 cm dengan kedalaman lubang 20 cm. Pola layer kerikil terdiri 3 lapis kerikil dengan ketebalan lapisan 2 cm, jarak antar lapisan 5 cm. Pola anyaman bambu:1 lapis dengan panjang-lebar anyaman 20x20 cm. Penempatan anyaman bambu pada kedalaman 2 cm dari permukaan tanah. Hasil penelitian yaitu ; (1) Tanah merupakan tanah lempung anorganik plastisitas tinggi (CH) berdasarkan sistem USCS, termasuk kelompok tanah berlempung kualitas sedang sampai buruk (A-7-6(40)) berdasarkan sistem AASHTO. (2) Perkuatan layer kerikil meningkatkan daya dukung ultimit sebesar 2,5 kali atau 159,02 %, sedangkan anyaman bambu memberikan peningkatan daya dukung sebesar 2,7 kali atau 170,49 %, dan kombinasi kolom-layer pasir sebesar 2,2 kali atau 127, 87%. (3) Perkuatan anyaman bambu memberikan peningkatan daya dukung paling tinggi pada tanah lempung diantara bahan perkuatan layer kerikil dan perkuatan gabungan kolom pasir dan layer pasir. Hal ini menunjukkan bahwa penggunaan anyaman bambu lebih efektif sebagai bahan perkuatan tanah lempung.

On a noteworthy habitat type in the savannahs of Central Cuba and a remarkable new species of Elytraria (Acanthaceae)

A peculiar habitat type found in the savannahs of Central Cuba, Villa Clara Province and characterised by the presence of a surface gravel layer of “perdigones”, an assemblage of small ferralitic concretions, upon the “mocarrero” soil prevailing in the area, is described. On sterile gravel patches, only one species grows: Elytraria serpens, a new species described and named here. It is noteworthy for possessing long and wide creeping, stoloniform subterranean peduncles with apical gemmae developing into rooting leaf rosettes enabling vegetative propagation. The new species is close to E. shaferi and considered to derive from the latter by adaptive evolution, enabling it to survive in its hostile habitat, sheltered from the competition of other plant species. Small soil insects, for example, ants, are believed to act as pollinators.

Laboratory Model Tests on Flow Erosion Failure Mechanism of a Slope Consisting of Anqing Group Clay Gravel Layer

The Anqing group clay gravel layer is a special geological body composed of gravel and clay. In excavation projects, involving this soil, such a gravel layer, is prone to slope collapse and instability under the influence of rainfall. To clearly understand the failure mechanism and influencing factors of clay gravel slopes, an indoor artificial rainfall erosion model testing was carried out to analyse the effect of various slope ratios, gravel contents, and rainfall intensities. The slope erosion damage form, runoff rate, infiltration rate, scoured material, and slope stability of the clay gravel slope were studied. The test results show that sloping surfaces of the gentle slope were mainly damaged by erosion, and the degree of damage gradually increased from the top to the bottom of the sloping surface; however, the stability of the surface was good. In the case of the sloping surface layer of the steep slope, large-scale landslides occurred, and the stability of the surface was poor. When the gravel content was small, the surface failure was manifested as a gully failure. When the gravel content was large, it was manifested as a “layer-by-layer sliding” failure. The degree of influence of different conditions on the stable runoff rate was as follows: rainfall intensity>slope ratio>gravel content. The degree of influence of the parameters on the stable infiltration rate was as follows: slope ratio>rainfall intensity>gravel content. On gentle slopes, the total mass of the scoured material was inversely proportional to the gravel content and directly proportional to the rainfall intensity; on a steep slope, the total mass of the scoured material increased with an increase in the rainfall intensity and gravel content. Moreover, the slope ratio was the key influencing factor to decide whether there was gravel in the scoured material.