Modified Factor for Segmented Pipes in Chinese Pipe Seismic Design Code Based on Probability Density Evolution Method

Wei Liu,Zhaoyang Song,Huiquan Miao 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.3

Buried pipes are important components of water and gas supply systems. A series of investigations indicate that buried pipes in China suffered serious damages in previous strong earthquakes. Therefore, seismic response analysis and design of buried pipes is an important research topic. In this study, a program is proposed to give the modified factors for segmented pipes in Chinese pipe seismic design code based on the probability Density Evolution Method (PDEM). A stochastic analysis method based on a finite element model of buried pipes and the Probability Density Evolution Method (PDEM) is proposed to determine probability density functions of seismic responses of buried segmented pipes. Then, seismic responses with different guaranteed rates can be derived and adopted for the design of buried pipes in preparation for earthquakes. Stochastic seismic responses of three segmented pipes buried in four sites are calculated using the proposed method. Joint deformations with guaranteed rates of 50%, 80%, 90%, 95%, and 99% are then summarized, and the modified factors for segmented pipes are derived to modify the Chinese code.

Interaction between Flexible Buried Pipe and Surface Load

Yoo, Chung-Sik,Chung, Suk-Won,Lee, Kwang-Myung,Kim, Joo-Suk Korean Geotechnical Society 1999 지반 : 한국지반공학회지 Vol.15 No.3

본 논문에서는 연성 매설관과 지표 상재하중의 상호작용에 관한 내용을 다루었다. 본 연구에서는 유한요소해석을 이용한 매개변수 연구를 수행하였으며, 이와 아울러서 적용된 유한요소해석 모형의 검증 및 지표 상재하중을 부담하는 연성 매설관의 거동 파악을 목적으로 실내모형실험을 수행하였다. 해석결과를 토대로 지반/매설관 접촉면에서의 연직응력 및 파이프의 축력 분포 경향 등 지표 상재 하중하에서 매설관의 하중응답 특성을 구체적으로 고찰하였으며, 그 결과를 종합적으로 분석하여 추후 수행될 보다 효율적인 매설관 설계/해석법의 개발에 사용될 데이터 베이스를 구축하였다. 해석결과를 분석한 결과 매설관과 지표 상재하중의 상호작용 정도는 매설관과 상재하중의 상대적 위치에 따라 좌우되며, 지반-구조물 상호작용을 고려하지 않고 있는 현 설계방법은 연성 매설관의 지표 상재 하중에 대한 응답특성을 효율적으로 반영하지 못하는 것으로 나타났다. 또한 본 연구의 결과를 토대로 지표 상재하중에 의한 연성 매설관의 최대 축력을 예측할 수 있는 반경험적 평가식을 제시하였다. This paper presents the results of a parametric study on the interaction between buried pipes and surface load using the finite element method of analysis. A series of laboratory model tests were also performed in order to validate the adopted finite element model and to capture essential features of the physical behavior of buried pipes subjected to surface load. In the parametric study, a wide range of boundary conditions were analyzed with emphasis on the response of the buried pipes to surface load. The results of analysis such as contact stress distribution at the soil/pipe interface and axial thrust of the pipe were thoroughly analyzed, and a database on the response of buried pipe under surface load was established for future development of a semi-empirical design/analysis method. The results indicated that the degree of interaction between buried pipes and surface load significantly varies with the vertical and lateral location of pipe with respect to surface load, and that the current design method, which does not consider soil-structure interaction, cannot correctly capture the pipe response to surface loading. Furthermore, based on the results of analysis, a semi-empirical equation was suggested, which estimates the maximum pipe thrust due to surface load for flexible buried pipes.

지중매설관 손상 방지를 위한 콘크리트매트와 팽창매트의 지반보강효과에 관한 실험적 연구

박정준,신희수,유중조,홍기권 한국지반신소재학회 2019 한국지반신소재학회 논문집 Vol.18 No.1

최근 도심지내에서는 지반공동 복구공사, 관로교체 공사 등 생활의 편의성 확보를 위한 소규모 굴착공사가 이루어지고 있다. 본 연구에서는 지중매설관 하부의 미흡한 다짐관리로 인하여 부등침하가 발생할 경우, 관의 파손에 의한 피해를 저감하기위해 관 하부를 보강할 수 있는 방안에 대하여 실험적 연구를 수행하였다. 즉, 콘크리트매트와 팽창매트를 이용한 매설관주변지반의 보강효과에 관한 평판재하시험을 실시하였다. 실험결과, 콘크리트매트와 팽창매트 보강에 따른 지중응력 감소율은재하하중 크기에 따라 각각 약 46%∼48% 및 39%∼42%로 분석되었다. 즉, 콘크리트매트와 팽창매트의 지반보강효과에 기인하여, 연구에 적용된 각각의 재료는 매설관의 침하 및 매설관 하부지반의 변형을 감소시키는 효과가 있는 것으로 판단되었다. 이를 바탕으로 지중매설관 하부지반 또는 매설관 사이의 지반에 콘크리트매트 및 팽창매트를 보강한다면, 지중에서 예측하기어려운 공동발생 및 지반침하에 따른 매설관 손상을 다소 방지할 수 있는 것으로 평가되었다. Recently, small-scale excavation like ground cavity restoration and buried pipe replacement works are being carried out in urban area, in order to improve living convenience. This paper describes experiment results on the ground reinforcement method that can reduce the buried pipe damage, when the differential settlement occurred due to poor compaction of ground below the buried pipe. Plate load tests were conducted to evaluate a reinforcement effect of ground using concrete mat and expansion mat in the ground below the buried pipe. The results showed that the stress reduction ratio by concrete mat and expansion mat according to the surcharge load was about 46%∼48% and 39%∼42%, respectively. Therefore, the differential settlement of the buried pipe and the ground deformation below the buried pipes were reduced by the reinforcement effect of the concrete mat and expansion mat. This means that it is possible to prevent a buried pipe damage due to underground cavity and ground subsidence, if concrete mat and expansion mat are reinforced in the ground below the buried pipe or on the ground between the buried pipes.

REAL-TIME CORROSION CONTROL SYSTEM FOR CATHODIC PROTECTION OF BURIED PIPES FOR NUCLEAR POWER PLANT

( Ki Tae Kim ),( Hae Woong Kim ),( Young Sik Kim ),( Hyun Young Chang ),( Bu Taek Lim ),( Heung Bae Park ) 한국부식방식학회 2015 Corrosion Science and Technology Vol.14 No.1

Since the operation period of nuclear power plants has increased, the degradation of buried pipes gradually increases and recently it seems to be one of the emerging issues. Maintenance on buried pipes needs high quality of management system because outer surface of buried pipe contacts the various soils but inner surface reacts with various electrolytes of fluid. In the USA, USNRC and EPRI have tried to manage the degradation of buried pipes. However, there is little knowledge about the inspection procedure, test and manage program in the domestic nuclear power plants. This paper focuses on the development and build-up of real-time monitoring and control system of buried pipes. Pipes to be tested are tape-coated carbon steel pipe for primary component cooling water system, asphalt-coated cast iron pipe for fire protection system, and pre-stressed concrete cylinder pipe for sea water cooling system. A control system for cathodic protection was installed on each test pipe which has been monitored and controlled. For the calculation of protection range and optimization, computer simulation was performed using COMSOL Multiphysics (Altsoft co.).

상재하중의 재하위치 및 매설심도를 고려한 지중 매설관의 구조거동 평가

류연선(Ryu Yeon Sun),조현만(Cho Hyun Man),김영빈(Kim Young bin) 한국방재학회 2017 한국방재학회논문집 Vol.17 No.2

지중매설관은 산업의 각종분야 및 지하 기반시설에 널리 사용되고 있다. 지중 매설관에 작용하는 하중으로는 토압, 차량하중, 온도, 지진 하중, 부양하중 등이 있다. 특히 다수의 매설관은 도로 포장아래에 매설되어 있고, 과도한 차량하중이나 예상치 못한 하중을 받는 경우가 있다. 본 논문에서는 매설관의 상부 및 인근에 상재하중이 작용할 때 나타나는 매설관의 구조적 거동을 상재하중의 재하위치, 매설관의 매설깊이, 매설관의 크기를 고려하여 평가하였다. 이를 위해 수치모델을 구성하고 유한요소해석을 수행하였다. 매설깊이와 재하위치에 따라 매설관의 변위와 응력의 변화를 산정하고, 그 결과로부터 거동특성을 파악하였다. Buried pipes have been applied in a wide range of industry and the subsurface infrastructures. The loads acting on buried pipes include soil pressure, traffic load, seismic load, flotation. Many underground pipes are buried under the road pavement and subjected to excessive vehicle load or unexpected load. In this paper, the structural behavior of the buried pipe under the surcharge load is evaluated considering load location, buried depth and dimension of pipe. Finite element analysis was perform for the assessment of the displacement and stress of buried pipe. The results showed the effect of the load location and buried depth on performance of the underground pipe.

Stress Distribution of Buried Concrete Pipe Under Various Environmental Conditions

Lee, Janggeun,Kang, Jae Mo,Ban, Hoki,Moon, Changyeul Korean Geo-Environmental Society 2016 한국지반환경공학회논문집 Vol.17 No.12

There are numerous factors that affect stress distribution in a buried pipe, such as the shape, size, and stiffness of the pipe, its burial depth, and the stiffness of the surrounding soil. In addition, the pipe can benefit from the soil arching effect to some extent, through which the overburden and surcharge pressure at the crown can be carried by the adjacent soil. As a result, the buried pipe needs to support only a portion of the load that is not transferred to the adjacent soil. This paper presents numerical efforts to investigate the stress distribution in the buried concrete pipe under various environmental conditions. To that end, a nonlinear elasto-plastic model for backfill materials was implemented into finite element software by a user-defined subroutine (user material, or UMAT) to more precisely analyze the soil behavior surrounding a buried concrete pipe subjected to surface loading. In addition, three different backfill materials with a native soil were selected to examine the material-specific stress distribution in pipe. The environmental conditions considering in this study the loading effect and void effects were investigated using finite element method. The simulation results provide information on how the pressures are redistributed, and how the buried concrete pipe behaves under various environmental conditions.

매설관 주변부 누수 탐지를 위한 매설형 TDR 모듈 개발

홍원택(Wontaek Hong) 한국지반환경공학회 2021 한국지반환경공학회논문집 Vol.22 No.11

매설관으로부터의 누수에 의한 지반 내 공동 및 이완구간 형성에 따른 사고를 사전에 방지하기 위하여 매설관의 파손 및 누수와 동반한 지반 내 함수상태 변화의 평가가 요구된다. 흙의 함수상태 평가를 위한 기법으로써 시계열반사계(TDR)의 적용이 고려될 수 있으나 표준 TDR 프로브의 경우 세장비가 매우 큰 전극을 이용하므로 지반 내 설치 시 전극의 변형 및 파손이 발생할 수 있다. 본 연구에서는 지반 내에서 안정적으로 형태를 유지하며 함수상태를 평가할 수 있는 매립형 TDR 모듈을 개발하였다. 매립형 TDR 모듈은 동축케이블의 내부도체 및 외부도체에 연결되는 세 개의 전극과 지반 내에서 전극의 변형방지 및 평행배열 유지를 위한 MC Nylon 재질의 케이싱으로 구성된다. 매립형 TDR 모듈로부터 획득된 유도전자기파의 신뢰도 검증을 위하여 표준 TDR 프로브로부터 획득한 유도전자기파와 상호비교 하였으며 보정실험을 통하여 체적함수비와 유도전자기파의 전파시간 상관관계가 수립되었다. 매립형 TDR 모듈의 현장적용 적정성을 평가하기 위하여 실내 모형실험이 수행되었으며, 모형 매설관으로부터의 누수에 따른 흙 시료의 체적함수비 변화가 명확히 관찰되었다. 그러므로 본 연구에서 개발된 매립형 TDR 모듈은 도심지 포장 하부에 설치된 매설관의 건전도 평가 및 매설관 주변부 지반의 함수상태 평가에 효과적으로 이용될 수 있을 것이라 판단된다. To prevent accidents due to the cavities and loosened layers formed due to water leakage from the deteriorated buried pipes, evaluation of the changes in water contents around the buried pipes is required. As a method to evaluate the water contents of the soils, time domain reflectometry (TDR) system can be adopted. However, slender electrodes used in standard TDR probe may be damaged when buried in the ground. Thus, in this study, buried type TDR module was developed for the evaluation of the water contents with maintaining required shape of the electrodes in the ground. The TDR module is composed of three electrodes connected to the core conductor and outer conductor and a casing to prevent deformation and maintain alignment of the electrodes in the ground. For the verification of TDR waveforms measured using the TDR module, comparative analysis was conducted with the TDR waveforms measured using the standard TDR probe, and the relationship between the volumetric water content of the soils and the travel time of the guided electromagnetic wave was constructed. In addition, a model test was conducted to test the applicability of the buried type TDR module, and the experimental result shows that the TDR module clearly evaluates the changes in volumetric water contents due to the leakage from the modeled buried pipe. Therefore, the buried type TDR module may be effectively used for the health monitoring of the buried pipe and the evaluation of the water contents around the pipes buried in the urban pavements.

Pipe-Soil Interaction and Sensitivity Study of Large-Diameter Buried Steel Pipes

He-Gao Wu,Jin-Hong Yu,Chang-Zheng Shi,Zhu Ma 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.3

Large-diameter buried steel pipes (BSPs) have been widely utilized in water diversion and hydropower fields. This paper presents a comprehensive numerical investigation on the interaction between the large-diameter pipe and soil under three typical working conditions, to capture the structural mechanical behaviors of pipe deformation, soil displacement, and soil pressure. Furthermore, a parametric analysis of pipe diameter is conducted, along with the sensitivity study of soil parameters based on the orthogonal test method. The results show that the water weight increases the pipe deformation significantly by 14%, while the high internal water pressure decreases the deformation greatly with the maximum effect of 39%. The pattern of soil pressure at the top of the pipe changes from parabola to double-hump as the pipe diameter varies from 0.5 m to 5.0 m. The pipe deformation and soil pressure keep increasing with the pipe diameter, but the safety margin for prism load decreases gradually. Pipe deformation and soil pressure are very sensitive to the elastic modulus and Poisson's ratio of backfill. Friction coefficients of soil-soil (trench sidewall) and pipe-soil have great influences on the soil pressure, while the bedding material and backfill cohesion have small effects on it.

매설조건에 따른 연성관의 변형특성

이봉직(Bongjik Lee) 한국지반환경공학회 2014 한국지반환경공학회논문집 Vol.15 No.10

국내의 경우 하수관으로 많이 사용되어 온 관종은 콘크리트 흄관으로 대표되는 강성관이 주를 이루고 있으나, 시간 경과에 따른 관 부식 및 수밀성 부족 등의 이유로 사용이 급격히 감소하고 있다. 반면에 연성관은 부식에 강할 뿐만 아니라 자재의 무게가 경량이어서 시공성이 우수한 장점이 있어 사용이 증가하고 있는 실정이다. 그러나 연성관에 대한 시장의 신뢰성 부족과 미흡한 다짐관리로 인한 국부적인 파손사례가 발생하고 있어 이에 대한 원인분석 및 관리방안이 필요한 실정이다. 이에 본 연구에서는 시공순서, 관의 강성, 관 하부 콘크리트 기초의 강도, 관 하부 모래기초의 다짐도, 관 주변 모래의 다짐도 및 관 상단 되메움재의 다짐도 등을 변화시켜 가며 각각의 조건에 따른 관의 변형특성을 수치해석을 통하여 평가하였다. 평가결과 각 인자에 대한 영향을 확인할 수 있었으며 특히 연성관의 경우 관 주변 모래의 품질관리가 중요한 것으로 나타났다. In Korea, the pipe type that has been well used as sewage pipe from the past is primarily a rigid pipe which is represented by concrete hume pipe, but the use of it is being decreased sharply because of the problems such as tube erosion and incomplete watertightness securing through the time. On the other hand, the use of flexible pipe has been increased because its construction ability is excellent on account of its light weight as well as it is resistant to corrosion. However, because there are lacks of market’s confidence in flexible pipe and occurrence cases of partial damage incomplete caused by compaction control, cause analysis and management for them are needed. Therefore, this study tried to estimate the deformation characteristics of pipe caused by each condition through numerical analysis changing construction sequence, rigidity of pipe, strength of ground concrete under the pipe, relative compaction ratio of sand foundation under the pipe and relative compaction ratio of backfill material above the pipe. Evaluation result is that influence on each factor is confirmed and the quality control of sand around the pipe are turned up to be important.

Numerical Investigation of the Method of Structural Performance and Rehabilitation of Large-Diameter Buried Steel Pipes Subjected to Excessive Deformation: A Case Study of China

Jin-Hong Yu,Chang-Zheng Shi,He-Gao Wu,Zhu Ma 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.12

Large-diameter buried steel pipes (BSPs) play critical roles in water transport for major water diversion and hydropower projects. Due to poor pipe-soil composite system properties and installation conditions, they are prone to excessive deformation, resulting in safety hazards. This paper takes a BSP project subjected to excessive deformation as an example. A simplified numerical model is first established to analyze the structural performance, including the stress and plasticity, and the relationship between the stress and deformation of the pipe. Furthermore, a jacking method to rehabilitate the pipe-soil composite system is conducted to explore its influences on pipe deformation, stress, and plasticity. The results show that considerable bending stresses occur in the pipe and that sections of the midspan and stiffening ring are in the pure bending state and eccentric bending state, respectively. Areas of high stress and plasticity center at the crown, springline, and invert of the pipe, and steel pipes with ring deformation of 8.9% can be continued to be used, as the full yielding of the pipe walls occurs at the ring deformation of 15.8%. The jacking method is an effective solution for the rehabilitation of BSPs subjected to large deformation and can reduce pipe deformation significantly while increasing the stress at the pipe crown and the pipe plasticity only slightly.