Application of Feedforward Neural Network and SPT Results in the Estimation of Seismic Soil Liquefaction Triggering

Soil liquefaction is a dangerous phenomenon for structures that lose their shear strength and soil resistance, occurring during seismic shocks such as earthquakes or sudden stress conditions. Determining the liquefaction and nonliquefaction capacity of soil is a difficult but necessary job when constructing structures in earthquake zones. Usually, the possibility of soil liquefaction is determined by laboratory tests on soil samples subjected to dynamic loads, and this is time-consuming and costly. Therefore, this study focuses on the development of a machine learning model called a Forward Neural Network (FNN) to estimate the activation of soil liquefaction under seismic condition. The database is collected from the published literature, including 270 liquefaction cases and 216 nonliquefaction case histories under different geological conditions and earthquakes used for construction and confirming the model. The model is built and optimized for hyperparameters based on a technique known as random search (RS). Then, the L2 regularization technique is used to solve the overfitting problem of the model. The analysis results are compared with a series of empirical formulas as well as some popular machine learning (ML) models. The results show that the RS-L2-FNN model successfully predicts soil liquefaction with an accuracy of 90.33% on the entire dataset and an average accuracy of 88.4% after 300 simulations which takes into account the random split of the datasets. Compared with the empirical formulas as well as other machine learning models, the RS-L2-FNN model shows superior performance and solves the overfitting problem of the model. In addition, the global sensitivity analysis technique is used to detect the most important input characteristics affecting the activation prediction of liquefied soils. The results show that the corrected SPT resistance (N1)60 is the most important input variable, affecting the determination of the liquefaction capacity of the soil. This study provides a powerful tool that allows rapid and accurate prediction of liquefaction based on several basic soil properties.

PERANCANGAN FONDASI TIANG PANCANG PADA TANAH BERPOTENSI LIKUIFAKSI DI SULAWESI

ABSTRACTIndonesia is a country located in the most active earthquake paths in the world. This makes Indonesia prone to earthquakes and has the potential to experience liquefaction. Liquefaction can cause pile failure, so several things need to be considered in designing piles on potentially liquefied soils. One project in Sulawesi has a profile of uniform grained saturated soil that is susceptible to liquefaction. Two things that need to be considered in the design of piles on potentially liquefied soils is to ignore the capacity of pile friction and calculate the moment due to lateral spreading effects. Calculation of liquefaction potential is done by comparing the ratio of the cyclic stress and the cyclic resistance ratio and is compared by four other methods namely: the Seed et al. (2003), Tsuchida (1970), Seed et al. (2003), and Bray & Sancio (2004). The lateral spreading effect is calculated by referring to the JRA Code where the liquefied soil layer gives pressure to the pile at 30% of the overburden stress and the soil layer above the liquefied soil gives passive soil pressure to the pole. The moment effect caused by lateral spreading results in the addition of dimensions or number of poles.Keywords: liquefaction; lateral spreading; bearing capacity; JRA Code; pile foundationABSTRAKIndonesia adalah negara yang terletak di jalur gempa teraktif di dunia. Hal ini menyebabkan Indonesia rawan gempa dan memiliki potensi untuk mengalami likuifaksi. Likuifaksi dapat menyebabkan kerusakan/kegagalan struktur yang sangat merugikan, sehingga perlu diperhatikan beberapa hal dalam merancang tiang pada tanah berpotensi likuifaksi. Salah satu proyek di Sulawesi memiliki profil tanah pasir berbutir seragam dan jenuh air yang memiliki potensi likuifaksi. Dua hal yang perlu diperhitungkan dalam perancangan tiang pada tanah berpotensi likuifaksi adalah mengabaikan daya dukung friksi tiang dan memperhitungkan momen akibat efek lateral spreading. Perhitungan potensi likuifaksi dilakukan dengan membandingkan rasio tegangan siklik (CSR) dan rasio hambatan siklik (CRR) serta dibandingkan dengan empat metode lainnya yaitu: metode Seed et al. (2003), Tsuchida (1970), Seed et al. (2003), dan Bray & Sancio (2004). Daya dukung aksial pada tiang pancang mengalami pengurangan 32% akibat lapisan tanah yang terlikuifaksi. Efek lateral spreading dihitung dengan acuan JRA Code dimana lapisan tanah terlikuifaksi memberikan tekanan ke tiang sebesar 30% dari tegangan overburden dan lapisan tanah di atas tanah terlikuifaksi memberikan tekanan tanah pasif ke tiang. Efek momen yang diakibatkan oleh lateral spreading mengakibatkan penambahan dimensi ataupun jumlah tiang.Kata kunci: likuifaksi; lateral spreading; daya dukung; JRA Code; fondasi tiang

A preliminary analysis of the ability of seismic liquefaction of soils (for example, water-saturated sandy-clay deposits in Kudepsta village, Adler district of Sochi)

Территория города Сочи относится к зоне 9-балльной сейсмичности по шкале МСК-64. В условиях обводненных песков и мягкопластичных суглинков землетрясение может достигать 10-балльной сейсмичности, что может создать очень серьезную ситуацию городской инфраструктуре. На примере анализа грунтов поселка Кудепста (район Большого Сочи) описан предварительный этап оценок опасности разжижения слабых водонасыщенных отложений под воздействием возможных здесь сильных землетрясений. Прогнозирование устойчивости различных грунтовых комплексов к сейсмогенному разжижению произведено на качественном уровне, т.е. показано в принципе разжижение возможно или нет. Количественная оценка этой возможности (вероятности) при этом не делается. Приведено описание последовательности, содержания и результатов, выполненных в процессе анализа процедур. В частности показано, что к потенциально разжижаемым грунтам в условиях изучаемого участка могут быть отнесены залегающие в верхней части разреза почвы и суглинки мощностью 2–3 м. К практически не разжижаемым относятся залегающие на глубине 5–10 м суглинки. Грунты на промежуточных глубинах требуют дополнительного изучения. Полученные данные будут использованы при дальнейшей (количественной) оценке вероятности сейсмогенного разжижения исследуемых грунтов и мощности потенциально разжижаемой толщи. Сейсмическое разжижения слабых обводненных грунтов во время землетрясений, как правило, проявляется в виде мгновенных осадок и, как следствие, массовыми разрушениями зданий. Такие землетрясения характеризуются трещинами в земной коре до метра шириной, оползнями и обвалами со склонов, разрушением каменных построек, искривлением железнодорожных рельсов. Тектоническая раздробленность региона, изрезанный рельеф, избыточная обводненность способствуют проявлению масштабных оползней. В зоне морской абразии велика вероятность обвалов, сопряженных с разрушениями портовых сооружений. За последние 100 лет в этом регионе произошли землетрясения силой более 7 баллов. The territory of Sochi belongs to the 9-point seismicity zone according to the MSK-64 scale. Under the conditions of flooded sands and soft plastic loams, an earthquake can reach 10-point seismicity, which can create a very serious situation for the urban infrastructure. Using the example of soil analysis of the settlement of Kudepsta (the area of Big Sochi), a preliminary stage of risk assessment of liquefaction of weak water-saturated sediments under the influence of possible strong earthquakes is described. Prediction of the stability of various soil complexes to seismogenic liquefaction is made at a qualitative level, i.e.it is shown in principle is liquefaction possible or not. A quantitative assessment of this possibility (probability) is not made. A description of the sequence, content and the results performed during the analysis of procedures is given. In particular, it is shown that under the conditions of the studied area the soil and the loam with a thickness of 2–3 m can be classified as potentially liquefied soils. The loam lying at a depth of 5–10 m is considered to be practically non-liquefiable. Soils at intermediate depths require an additional study. The obtained data will be used in the further (quantitative) assessment of the probability of seismogenic liquefaction of the studied soils and the thickness of a potentially liquefied stratum. Seismic liquefaction of weak flooded soils during earthquakes, as a rule, manifests itself in the form of instantaneous precipitation and, as a result, massive destruction of buildings. Such earthquakes are characterized by cracks in the earth's crust up to a meter wide, landslides and avalanches from the slopes, the destruction of stone buildings, the deformation of railway rails. Tectonic fragmentation of the region, rugged relief, excessive water cut contribute to the manifestation of large-scale landslides. In the zone of marine abrasion, there is a high probability of landslides associated with the destruction of port facilities. Over the past 100 years in this region earthquakes of more than 7 points occurred

Geoecological aspects of civil engineering on the sands

Civil structures are often built on sands, which are widespread in the upper part of the geological section. These soils usually serve as a reliable basis for engineering structures, but under certain conditions can cause large complications and even endanger the life safety. Analysis and generalization of the construction experience allows us educe three groups of problems that need to be identified and addressed timely. Most of the problems are related to water-bearing sands. Water flows, breakthrough of pressure water and quicksand are very common phenomena that complicate the excavation of construction pits and the device of underground structures. To protect against groundwater is often used dewatering, which can disrupt the stability of the surrounding buildings in high-density urban development. The second group of problems is related to the process of suffusion. The most dangerous of its manifestations are suffusion failures, leading to emergency situations and sometimes to the destruction of structures. The third group of problems is caused by specific reaction of sands to dynamic impacts, in particular, by liquefaction of water-saturated sandy soils. The consequences of such a reaction can be very serious: the immersion of the structure in the ground, the uplift of piles or bridge supports, the float up of underground tanks, the uplift of liquefied soils from under the foundation until the formation of a building tilt or overturning of the structure.

Characteristics and Triggering Conditions for Naturally Deposited Gravelly Soils that Liquefied following the 2008 Wenchuan Mw 7.9 Earthquake, China

The 2008 Mw 7.9 Wenchuan, earthquake caused naturally deposited ravelly soils to liquefy over a wide area. Although liquefaction of gravely soils is recognized by the geotechnical profession, observations of liquefaction and nonlique-faction case histories within the literature are few. Through several years of systematic study following the 2008 Wenchuan earthquake (Mw 7.9), 92 locations of gravel liquefaction were identified, described, and mapped. These locations lie within an approximately 3,000 km2 area of the Chengdu Plain. Peak ground accelerations estimated at the sites range from 0.15 g to 0.49 g. Taken collectively, these studies reveal the necessary conditions for liquefaction triggering in gravelly materials. Grain size analyses indicates that the ejecta was much finer than the gravels that liquefied. Gravel contents of liquefied soils ranged from 5% to more than 85%. The liquefied gravelly soils were loose, but their measured shear wave velocities range from 133 m/s to 267 m/s, with corrected values ranging from 154 m/s to 31 4m/s. The unique depositional conditions under Chengdu Plain provide favorable conditions for extensive liquefaction of gravelly soils. The shallow soil profiles consist of a 0.5 m to 5.5 m impermeable soil (i.e., the capping layer) overlying gravels ranging in thickness from a few meters to hundreds of meters.