Probabilistic Method to Assess Model Uncertainty of Rigid Inclusion on a Granular Fill Supporting a Slab Foundation

Probabilistic approaches to deal with uncertainty on soil mechanic predictions are on the rise. We developed a procedure to deal with uncertainty coming from soil conditions. It was applied to an analytical model to simulate the behavior of a soil improvement work based on rigid inclusion below a slab foundation. The model can predict the settlements of the slab. Even more, it was also able to provide a confidence level based on a probabilistic approach to the input’s variables. Outputs were compared to large-scale tests. The agreement is outstanding. We try to encourage the use of probabilistic models to solve complex geotechnical problems.

SPATIAL VARIABILITY OF RESISTANCE TO PENETRATION IN SOIL UNDER SUGARCANE CROPS WITH DIFFERENT HARVEST METHODS

ABSTRACT The objective of this work was to evaluate the spatial variability of resistance to penetration in soil under sugarcane crops subjected to different harvest methods in the North Coast microregion of the state of Paraiba, Brazil. The study was conducted in a Typic Hapludult under sugarcane crops, at the farms Santa Emília-II and Maria da Luz-I of the company Miriri Food and Bioenergy S/A, in the municipalities of Rio Tinto and Capim, respectively, state of Paraíba, Brazil. Three sugarcane areas with different harvest methods (manual, mechanized, and manual/mechanized) were selected. The sampling was done in plots of 100 × 100 m, using a grid of 20 × 20 m, covering planting rows and interrows; each intersection point of the grid was georeferenced, and the soil mechanic resistance to penetration was evaluated with the aid of an impact penetrometer (IAA/Planalsucar-Stolf) up to the depth of 0-0.6 m. Soil disturbed and undisturbed samples from the 0.0-0.1 and 0.1-0.2 m layers were collected for analyses of soil moisture, texture, clay dispersed in water, flocculation degree. A pure nugget effect was found in the 0.0-0.1 and 0.4-0.5 m soil layers in the rows of the areas with manual/mechanized harvest. The spherical model was found for most conditions evaluated. The results for the areas were similar, with amplitude of 25-49 m, indicating that the harvest management had no effect on the soil resistance to penetration. No compacted areas were found, and the spatial dependency of the resistance to penetration was characterized as moderate to strong.

STUDI PENURUNAN SEDIMEN KUARTER DI PERAIRAN CIREBON, PROPINSI JAWA BARAT

Penelitian ini lebih difokuskan dalam mengaplikasikan data geologi teknik untuk menganalisis kemungkinan potensi penurunan sedimen Kuarter apabila didirikan suatu bangunan laut. Secara umum litologi daerah penelitian diperkirakan terdiri dari sedimen berumur Plistosen sampai Kuarter Data yang dipergunakan adalah data hasil pemboran teknik di laut dengan uji SPT dan hasil analisa laboratorium mekanika tanah. Berdasarkan pada perhitungan nilai SPT untuk setiap tiang pancang menunjukkan bahwa nilai daya dukung dijinkan (Qa) adalah 83,726 ton. Perkiraan nilai penurunan (St) adalah 0,992 cm atau 0,390 inci. Hasil perhitungan untuk dimensi dermaga yang direncanakan memperlihatkan bahwa beban total yang terjadi pada dermaga (q) adalah 2,18 ton/m2. Potensi penurunan lapisan tanah berdasarkan hasil uji laboratorium adalah 2,35 cm. Lamanya penurunan untuk terjadinya konsolidasi 10% adalah 94,81 hari (3,16 bulan), konsolidasi 20% adalah 367,41 hari (1,06 tahun), konsolidasi 50% adalah 2334,81 hari (6,39 tahun) dan konsolidasi 90% adalah 100503,7 hari (27,54 tahun). Berdasarkan kondisi tersebut di atas, menunjukan bahwa daerah penelitian memiliki potensi penurunan kecil dan dalam dalam waktu yang relatif lama. Kata kunci : geologi teknik, penurunan, bangunan laut, perairan Cirebon The aim of the study is mainly to apply the engineering geological data for analyzing the settlement potency of Quaternary sediments if the sea construction is built. In general, the litology in the study area consist of Plistocene to Recent sediments. The data used in this study are the offshore cores, namely, the SPT test and soil mechanic analyses. The SPT values of each pile shows that the allowable bearing capacity value is 83,726 ton. The estimation of settlement value ((St) is 0,992 cm or 0,390 inches. The total sediment loaded at the port (q) is 2,18 ton/m2, whereas based on the laboratory test analysis, it shows that the potential of soil settlement layer is 2,35 cm. The settlement period for 10% of consolidation is 94,81 days (3,16 months), 20% of consolidation is 367,41 days (1,06 years), 50% of consolidation is 2334,81 days (6.39 years), and 90% of consolidation is 100503,7 days (27.54 years). The above conditions indicate that the settlement in the study area is under going subsidence in small potential and in relatively long period. Key word : engineering geology, settlement, offshore structur, Cirebon waters

KARAKTERISTIK ENDAPAN SEDIMEN PANTAI TERHADAP PENGARUH LIQUIFAKSI DI KAWASAN PESISIR PANGANDARAN DAN SEKITARNYA, KABUPATEN CIAMIS, JAWA BARAT

Liquifaksi adalah salah satu bencana geologi yang berhubungan dengan kegempaan, dimana tekanan pori dalam tanah atau sedimen mengalami peningkatan akibat getaran, sehingga mengakibatkan aliran air ke arah permukaan tanah. Liquifaksi umumnya terjadi pada dataran rendah termasuk kawasan pesisir. Daerah penelitian yang terletak di sekitar pantai Pangandaran dan Parigi terdiri dari endapan lempung, lanau, pasir dan kerikil yang bersifat lepas dan jenuh air, secara regional sering dipengaruhi oleh kekuatan gempa antara 5,5 – 6 skala Richter dengan percepatan tanah antara 150 – 200 mgal. Kondisi seperti ini apabila terjadi gempa sangat memungkinkan untuk terjadi liquifaksi. Berdasarkan hasil perhitungan secara kuantitatif nisbah pori kritis, tidak semua lokasi penelitian akan mengalami liquifaksi pada percepatan permukaan 150 – 200 mgal. Berdasarkan nilai tumbukan SPT yang dipakai untuk analisis “simplified procedure”, daerah penelitian secara umum relatif kecil terhadap bahaya liquifaksi. Namun demikian berdasarkan korelasi antara sifat mekanik tanah dengan nilai SPT, pada kedalaman 0 – 8 m terdapat lapisan sedimen yang cukup rentan terhadap liquifaksi. Kata kunci: Liquifaksi,sedimen pantai,Pangandaran Liquefaction is one of many geological hazards related to an earthquake, where the void ratio pressure in soil or sediment will increase due to the vibration, that causing water flow up to the ground surface. Generally liquefaction is occurred in the low lying areas including coastal zone. The survey area located in the Pangandaran and Parigi coasts, is consisted of clay, silt, sand and gravel, of loose and saturated properties, generally is frequently influenced by 5,5 – 6 Richter scale of earthquake strength with the ground acceleration between 150 – 200 mgal. The liquefaction will be occurred in this condition if there is an earthquake. Based on the quantitatively calculation of critical void ratio, the liquefaction at ground acceleration of 150 – 200 mgal will not be occurred at all of the survey area. Based on the number of blows of SPT which is used for simplified procedure analysis, it shows that the study area is less influenced by the liquefaction. Nevertheless , based on the correlation between soil mechanic properties and SPT value, there is potential liquefiable sediments layer between the depth of 0 – 8 meters. Key words: liquefaction, coastal sediment, Pangandaran

INFLUENCE OF GEOLOGICAL CONDITION TOWARDS SLOPE STABILITY ON LANDSLIDE: CASE STUDY IN TENGKLIK VILLAGE, TAWANGMANGU DISTRICT, KARANGANYAR REGENCY, CENTRAL JAVA PROVINCE, INDONESIA

A rain-induced landslide has occured in Guyon Village, Tengklik Tawangmangu District Karanganyar Regency, Central Java Province, Indonesia on February 2009. The movement was initiated by crack occurrence, 30 cm in depth and 2 meter in length. Such crack continuously developed in depth, extention and numbers, until then it resulted in land subsidence up to 260 cm in depth. Accordingly, ten houses were damaged and ten of families must be evacuated. This subsidence is very potential to further grow and create more consequences for human life and houses / land damage. Therefore, this research is carried out to understand the influence of geological factors and rainfall to the landslide phenomena. This research conducted engineering geology investigation such as mapping, drilling, insitu test, XRD test, soil mechanic test and slope stability analysis by limit equilibrium method i.e. Seep/W and Slope/W. By those research activities, the cause and mechanism of landslide can be understood. Rainfall characteristics which triggered such landslide can also be identified. Based on those investigations, it is found that the landslide occurred in slow rate sliding (creep) due to the control of slope stratigraphy conditions and gentle slope inclination, which is induced by rainfall. Stratigraphy condition that plays important role in landslide mechanism are the permeable layers consisted of sandy silt (shear strength 12 kPa) and silty sandstone (shear strength 18 kPa) overlaid above impermeable andesite breccia (shear strength 104 kPa). Undulating slope may induce landslide in creep rotational type. Based on slope stability simulation, it is known that rainfall triggered landslide is rainfall 20 mm/ day average precipitation in 55 days and rainfall 20 mm/ day average precipitation in 49 days followed by one day with 178 mm/ day average precipitation. Keywords: Landslides, slope stability

SUMMARY OF RESEARCH WORK ON THE EVALUATION ON LONG TERM STABILITY OF ARTIFICIAL SLOPE PROTECTION

Application of GPR, RedExplorer1.4 and GeoStudio2004 have been used to evaluate the overall stability condition of a steep slope along Kalibawang irrigation channel km 8.5, Kulon Progo Regency, Yogyakarta Special Province, Indonesia, that this slope slid down in 1990 and was restabilized by cut to be gentler and covered by shotcrete. Topographic map and engineering geological map in scale 1:2000 have been established prior to the detail investigation. Three drilling logs with in-situ test, SPT and CPT, and samplings have been made and sent to soil mechanic laboratory for index properties tests, and a slope profile along the main axe will be also created for stability analysis through GeoStudio2004. Moreover, GPR has been used to run on a full slope surface to detect the distribution of fractures and/or cavities behind the shotcrete and the results have been interpreted by the aid of RedExplorer1.4.Three profiles showing the rate and depth of fractures and/or cavities are established whereas the slope stability analysis through GeoStudio2004 is the next target of the research. The author is expecting the result from the integration of GPR interpretation and GeoStudio2004 to figure out the overall stability with respect to its existing conditions and its own geometry. Keywords: GPR, GeoStudio2004, overall stability, fracture and/or cavities.

Heat Effect Analysis of Buried Oil Pipeline in the Qinghai-Tibet Plateau

The Geermu-Lasa oil pipeline was located in the Qinghai-Tibet Plateau permafrost regions. The building and operating of pipeline will change the temperature field of soil around it, which can lead to changes of frozen soil mechanic properties, and this will induces deformation or even fracture of pipeline. These phenomena will affect the normal transportation of oil. In this paper, temperature field around the pipelines were analyzed due to different pipe diameters and different insulation layer thicknesses in the way of finite element method. The rule of thawing and freezing of soil around the pipeline in an annual cycle was obtained. Artificial permafrost table variations under the pipeline were also obtained due to different operating conditions. For 30cm diameter pipeline with 7cm insulation layer, its artificial permafrost table depth change value is just 0.48m after 30-year running. These analysis results can provide references to the construction of the new Geermu-Lasa oil pipeline.

Excellent Performance of Earth Dams under Resonance Motion Using Isolator Damping Layer

The effect of blanket layer using isolator damping layer (IDL) between river sand foundation and short embankment to remove damage under severe earthquake was investigated in the present study. In case of numerical analysis by ANSYS program, dominant frequency (DF) was computed by free vibration analysis. Soil mechanic tests for thirteen samples to design IDL formula were carried out. In terms of critical condition for earthquake effect such as resonance, five physical small models were tested using vibrator table under the dominant frequency with scale parameter 1/100. As a result, dam was significantly damaged without blanket layer IDL. In order to reduce damage, the best performance was observed using blanket layer (IDL) when this layer was expanded below the reservoir region. The reinforced thickness layer size is one-fourth of dam height. This method is a novel suggestion for earth dam design in seismic zone.