中文摘要：

受枢纽布置和地形地质条件的限制,三峡工程地下厂房布置于右岸白岩尖山体中,主厂房洞室上覆岩体最薄处仅1倍厂房跨度,显然不满足现行规范关于上覆岩体厚度不小于2倍开挖宽度的要求。对于这类浅埋式的大跨度高边墙地下厂房,在上覆岩体厚度有限及一定初始应力条件下,洞室顶拱的稳定性是必须解决的首要技术问题。从岩体结构、岩体强度和地应力水平对围岩稳定性控制的角度出发,通过对地下厂房洞室围岩顶拱承载力学机制的研究,提出地下洞室岩体稳定拱的定义及其存在的力学条件,给出地下洞室岩体稳定拱的确定方法,分析采用地下洞室岩体稳定拱确定上覆岩体厚度的可行性,形成一套确定浅埋式地下厂房洞室埋置深度的稳定拱设计方法。研究结果表明,三峡工程地下厂房顶拱围岩具备形成稳定拱的埋深条件和水平应力等条件,形成稳定拱的最小埋深约为2/3倍洞跨,在上覆岩体中形成稳定拱的最小水平侧压系数应大于1.5,而最大水平侧压系数不宜高于3.0。据此进行主厂房顶拱设计,多年的应用成效显示,地下厂房顶拱围岩是稳定安全的,表明三峡工程地下厂房顶拱在既定的围岩强度、岩体结构以及初始地应力水平等条件下,采用稳定拱设计方法确定洞室上覆岩体厚度是合适、可靠的,能够保障洞室围岩稳定,满足工程安全的要求,可为解决大型浅埋洞室的设计提供理论基础和科学依据。

英文摘要：

As restricted by project layout,geological and topographical conditions,the underground powerhouse of Three Gorges Project is arranged inside the mountain on right bank.The minimum thickness of rockmass over powerhouse is almost the same magnitude of powerhouse span.Obviously,it cannot meet the code？s requirement that overburden thickness of caverns should be not less than 2 times of the excavation span.For such shallowly buried underground cavern with large span and high sidewall,overburden thickness of rock mass is limited but initial geostress magnitude should be also taken into account.Therefore,the top arch stability is viewed as the primary issue that should be addressed.Based on rockmass structure and rock mass strength characteristics,and the concept that horizontal geostress controls surrounding rock stability,the bearing mechanism of surrounding rock at top arch area of underground cavern is studied.Definition of stable arch and its existence mechanical condition are presented.The method for determining stable arch of underground cavern is proposed as well.The feasibility of applying stable arch concept to determine overburden depth of underground cavern is analyzed.A methodology for stable arch design of overburden depth of shallowly buried underground cavern is then formed.It is revealed that surrounding rock at top arch area of underground powerhouse of Three Gorges Project possesses such stable arch formation conditions in terms of overburden depth and horizontal stress.Its minimum overburden thickness for stable arch formation is two-thirds of powerhouse span.The minimum and maximum values of horizontal lateral pressure coefficients for stable arch formation are 1.5 and 3.0,respectively.The proposed methodology was adopted in the arch design of underground powerhouse of Three Gorges Project.The observations of several years show that the surrounding rock at top arch area of underground powerhouse is stable,thus indicating that under given rock mass strength,rock mass structure and initial geostre