外文翻译-圣彼得堡在基坑安装和公共设施铺设过程中对建筑的保护

外文文献：Soil Mechanics and Foundation Engineering, Vol. 39, No. 4, 2002 PRESERVATION OF BUILDINGS DURING THE INSTALLATION OF FOUNDATION PITS AND THE LAYING OF UTILITIES IN SAINT PETERSBURGV. M. Ulitskii and S. I. AlekseevSaint Petersburg State University for Means of Communication.One means of solving geotechnical problems involving the laying of utilities in the central core of cities is the trenchless construction of collectors using microtunneling technology. This technology has come into widespread use in countries of the European Union, the United States, and Japan. In Berlin, therefore, 55% of all pipelines had been laid by the microtunneling method as early as 1994. The first kilometers of such a tunnel were constructed in Saint Petersburg in accordance with the German technology using an equipment set manufactured by the Herrenknecht Company.In addition to the obvious advantage of this method of laying utilities as compared with the traditional procedure of construction in open trenches, the installation of a microtunnel makes it necessary to solve a number of geotechnical problems.One of the problems is the installation of starting and receiving shafts for the collector.The shafts (chambers) of the collector usually have planform dimensions of 4 4 m (5 5 m) and a depth of 8-12 m. In Saint Petersburg, chambers-shafts are also constructed using a sheet-piling enclosure intersecting numerous layers of weak saturated soils. It should be considered that in the central core of Saint Petersburg, the roof of relatively dense (morainic) deposits resides at depths of the order of 14-20 m and greater. Under these conditions, builders tend to use sheet piling 14-16 m long so as to ensure work produc-tion without having to drain water in the as-designed chambers/shafts. In a dense urban setting where shafts must be installed near existing tenement buildings, however, vibratory embedment of long sheet piling, and, especially its subsequent extraction create, as construction experience indicates, a negative effect on the surrounding buildings. Under these conditions,complex monitoring of the condition of existing buildings is necessary as construction work proceeds; this monitoring should, at a minimum, include the following:- dynamic monitoring of the oscillations of bed soils, and also the bearing and enclosing structures of the building, which can be conducted at the time of embedment and extraction of the sheet-piling enclosure;- geodetic monitoring of deformations of the bearing structures of existing buildings adjacent to the construction site; and,- monitoring to ensure that the position of the ground water table is maintained during construction.To reduce the negative effect on surrounding development, the tendency is to construct chambers/shafts in short sheet-piling enclosures (8-9 m in length) and without extracting the piling. Additional measures to stabilize the bottom (variation in filtration properties of the foundation bed) are required here to avoid percolation of ground water into the shaft. These problems are fully resolvable with the use of modern high-head technologies, which, however, require careful geotechnical substantiation and accompanying monitoring for both quality of work, and also preservation of the surrounding medium.A working diagram and results of determination of the stress-strain state of the soil mass, which was performed by the finite-element method in the elastoplastic statement described by the Mohr-Coulomb criterion, are shown as an example in Fig. 1. The “Geomekhanik” software package was used for the analysis. Calculations to determine the limiting state of the soil in the foundation of a chamber/shaft 8 m deep in a sheet-piling enclosure 10 m long were performed in the following soil stratifications; geologic-engineering element (GEE No. 1) - a heavy silty highly plastic clayey loam up to 6.3 m thick with = 19 kN/m3, = 7, c = 8.0 kPa, e = 0.93, and E = 7.0 MPa; GEE No. 2 - a silty gray highly plastic sandy loam up to 2 m thick with = 20.5 kN/m3, = 16, c = 11.0 kPa, e = 0.61, and E = 10.0 MPa; and, GEE No. 3 - a coarse cinnamon sand of medium density with = 20.7 kN/m3, = 40, c = 1.0 kPa, e = 0.55, and E = 40 MPa. The ground-water table is situated at a depth of 1.5 m from the surface. Fig. 1. Regions of limiting state of soil in foundation bed at bottom of shaft with no soil stabilization (regions of Coulomb limiting state are shaded, and ruptured regions are crosshatched). 1-3) numbers of GEE.As is apparent from results of the solution that we have presented (see Fig. 1), the soils at the bottom of the as-designed shaft will, by taking up the hydrostatic pressure of the water, go over into the limiting state, experiencing rupture deformations over a depth corresponding to the embedment depth of the sheet piling. As a result, overflow of soils will occur at the bottom of the excavation being worked, and ground water will begin to enter the foundation pit. This solution cannot be accepted without conditions. Several alternate computational schemes with different thicknesses of stabilized soil mass were examined to create an anti-filtration curtain using jet technology.Analysis of results of the solutions indicated that regions of limiting-state development decrease with increasing thickness of stabilized soil at the bottom of the shaft, and vanish completely when the thickness of the stabilized layer is 3 m. Consequently, the latter solution with stabilization of a 2.5-3-m thick soil stratum in the foundation bed of the shaft should be considered reliable from the standpoint of the creation of anti-filtration properties in the foundation bed.Fig. 2. Schematic production diagram of work performed to stabilize 吧clayey loam-soil bottom of constructed foundation pit in sheet-pile enclosure and high water table. 1)tank containing stabilizing grout (hardener); 2)metallic sheet pile; 3)preexcavated soil;4)tubular electrodes(cathodes); 5)tubular electrodes(anodes);6)ground-water table; 7) unstabilized soil; 8) insulated section of electrode; 9) stabilized soil; 10) perforated section of electrode.When a tunnel sewage collector was laid under the embankment of the Karpovka River, effective chambers/foundation pits were installed using a short (9m) sheet-pile enclosure, the structure of which remained in the soil mass after the work had been completed. Similar chambers were installed in weak saturated clays, the typical character of the stratification of which can be represented by the following (from the surface downward):- fill soils 3 m thick, the origin of which is associated with mans activity; - a silty sandy loam up to 2-3 m thick in the highly plastic state;- a strip silty clayey loam of fluid and fluid-plastic consistencies from 6 to 7.5 m thick; and,- a silty sandy loam with pockets of sand, gravel, and pebbles in a highly plastic state (slightly plastic from a depth of 15-16 m) up to 4-5 m thick.Production of work on the sinking of the sheet-pile enclosure was intended to place the bottom of the sheet piles into the third layer of soil, which with the water table at a depth of 2 m from the surface, was not a reliable element from the standpoint of anti-filtration properties. An electrosilification procedure, which makes it possible to conduct basic construction-assembly work at a given depth in a dry foundation pit, was used to create a reliable anti-filtration curtain (AFC) along the bottom of the foundation pit being excavated to a depth of 6 m from the surface. The work procedure used to improve the properties of this soil was carried out in the following sequence (Fig. 2): the foundation pit was excavated to a depth of 3 m in the sheet-pile enclosure; perforated tubular electrodes were sunk from the bottom of the foundation pit; the electrodes were connected to a direct-current source with an average voltage of 70-80 V; the soil was treated with an alternating current (200-300 A) with changing polarity; incoming water from the cathodes was evacuated; sodium silicate and calcium chloride solutions were successively injected into the anodes; and, the perforated tubular electrodes were extracted and the holes plugged.The process of lowering the moisture content of the soil mass being stabilized was monitored on the basis of measurement of the level of free water in the holes. Thus, Figure 3 shows data on the fluctuation of the water level from 80 holes - the injectors of the mass being treated. During the two-week period in which the strip silty clayey loam was treated, the greatest effect was observed with respect to the holes/cath-odes from which free water had been completely evacuated.H, mH, mFig .3 . Dynamics of variation in water level in holes/injectors during execution of work: a) measurement data on water level in holes on 14 February 1999; b) on 28 February 1999.The physico-mechanical properties of the soil being stabilized were altered as a result of the electrosilification. Thus, the compression modulus of the soil was increased by 60%, and the angle of internal friction and cohesion by almost 70%. Prolonged dewatering with a natural loss of the sand fraction on erosion led to a change in the grain-size distribution of the soil, which had converted from the silty clayey loam category to the clay category. As a result, the soils of the stabilized bed took on a state from slightly plastic to semi-hard. The permeability of this soil was reduced from 0.08 to 0.003-0.006 m/day, i.e., a virtually impermeable curtain was created beneath the bottom of the foundation pit being installed.The work conducted on soil stabilization of the installed foundation pit made it possible not only to perform the required construction-assembly operations in a “dry” foundation pit, but also, by significantly improving the physico-mechanical characteristics of the foundation bed, creat conditions for more reliable service of the entire structure on the whole.In Saint Petersburg, work involving the excavation of deep foundation pits with no stabilization of the soil mass, i.e., with the use of open drainage, will lead to a sharp drop in the water table, and result in the manifestation of nonuniform settlements of surrounding buildings.Construction of an underground pedestrian walkway beneath Trud Square (Blagoveshchenskaya Square) in Saint Petersburg is a characteristic example.Work in the foundation pit up to 5.8 m deep was performed using open drainage, since the poorquality driven sheet-pile enclosing wall formed from metallic sheet piling (Larsen IV) up to 14 m deep allowed ground water to pass. As a result, a depression funnel with the water table at an absolute elevation of -0.890 developed around the foundation pit during its nearly four-year existence, and also the existence of heavy drainage. Thus, ground water near the sheet-piling wall of the foundation pit was lowered below the surface of the water in the Neva River, and also the Admiralteiskyi and Kryukov Canals. Buildings surrounding the construction site fell within the radius of the depression funnel.Geotechnical investigations indicated that tenement building No. 6 along Konnogrdeiskyi Boulevard, which was situated at a minimum distance (approximately 16 m) from the existing foundation pit of the under ground walkway, had experienced nonuniform settlements and cracking in its bearing structures. The cause of these deformations was the manifestation of suffosion phenomena in the silty and fine sands of the foundation bed under heavy permanent drainage. Tests that were performed confirmed that the void ratio of the fine sands in the foundation bed had increased by one-fourth, and, consequently, the compression modulus of the soils in question was reduced by nearly half; this also led to the development of additional building settlements.Fig. 4. Diagram showing use of geologic-engineering measures to preserve foundations of existing building during construction of underground pedestrian walkway. 1) position of ground-water table on 8 August 1997 (prior to installation of anti-filtration curtain and grouting of foundation bed); 2) position of ground-water table on 22 October 1997 (after installation of anti-filtration curtain); 3) underground walkway; 4) axis of sheet piling; 5) injection holes.Numerical modeling of the change in geotechnical conditions of the foundation bed for the structure in question was performed by calculation on the basis of the procedure developed by one of the authors of 2. In analyzing the rubble strip foundation beneath the wall of the building, it was established that the fine sands with a compression modulus of 30 MPa are rather reliable foundation beds for the structure and type of loading in question, since the settlements of these foundations amount to all of 1.53cm.Variation in the geotechnical situation associated with softening of the soils, however, led to a sharp reduction in the compression modulus to 15 MPa, and, as a result, to an increase in the foundations settlement to 3.07 cm. This softening of the fine bed sands is most characteristic of the end section of the building, which is situated near the underground walkway under construction. As a result, the relative difference in settlements at a distance to 7 m along the length of the wall exceeded the limiting value; this also was one of the causes of the manifestation of cracks in bearing structures of the building.To eliminate the dangerous situation and terminate developing nonuniform settlement of the building, the contact layer of the foundation bed beneath the lower surface of the foundation was grouted over a thickness of no less than 0.5m (filling of the suffosion cavities that had developed). This artificial change in the geotechnical situation halted the increase in settlement and terminated deformations of the structure.It should be pointed out that the geotechnical circumstances for the building in question were aggravated in connection with long-term lowering (by 20-25 cm) of the ground water below the lower surface of the foundations and the threat of decay of the wooden beams in the foundation bed that had developed as a result. As a rule, similar phenomena lead to a sharp increase in settlement and the creation of emergency situations for the structures. To eliminate conditions favorable to the development of this dangerous phenomenon, an anti-filtration curtain was built along the sheet-pile enclosure of the foundation pit being installed for the underground walkway. The effectiveness of the measures that were taken was confirmed by measurement of the water table before and after installation of the anti-filtration curtain (Fig. 4).The path of motion of water as it entered the foundation pit for the underground walkway was increased by several times as a result of an imperfect anti-filtration curtain; this created the premise that the ground-water table had risen from position 1 (see Fig. 4) to position 2 - after completion of work on installation of the anti-filtration curtain. As a result, ground water around the foundation of the existing tenement building was lowered above the elevation of the lower surface of the foundations, and the wooden beams were again under water. The condition was created whereby further service of the building will not cause anxiety, and will ensure the reliability of its existence.REFERENCES1.V.M.Ulitskii, Geotechnical Substantiation of Building Reconstruction on Weak Soilsin Russian, SpbGASU (1995)2.S.I.Alekseev, Automated Method of Analyzing Foundations with Respect toTwo Limiting States in Russian, SpbGTU (1996)3.V.M.Ulitskii, S.I.Alekseev, and S.V.Lombas, “Use of modern technologies in reconstructing urban utility systems,” Rekonstr. Rorodov Geotekh. Stroit., No. 1 (2001). 中文译文：土力学与基础工程, 2002年第39卷第四期圣彼得堡在基坑安装和公共设施铺设过程中对建筑的保护V. M. Ulitskii 和 S. I. Aleksee UDC 699.84:625.78+624.152圣彼得堡国立大学的新闻公报 在城市中央核心位置铺设公共设施所涉及到的岩土工程问题有一种新的解决方法，它就是集热器的非开挖施工所采用的微型隧道技术。这项技术已被广泛应用于欧盟，美国和日本。在柏林，早在1994年，已经有55的管道应用了微型隧道这种方法。第一公里这样的秉承德国技术的隧道建于圣彼得堡，由海瑞克公司制造的一套设备加工而成。与铺设公用设施和开放沟槽的传统方法相比，这种方法具有明显的优势，微型隧道的安装使得需要解决一些岩土工程问题。在城市中央核心位置铺设公共设施所涉及到的岩土工程问题有一种新的解决方法，它就是集热器的非开挖施工所采用的微型隧道技术。集流管的轴（腔）通常具有44米（55米）的截面和8-12米的深度。在圣彼得堡，分庭轴也是用板桩的外壳和多层的弱饱和土相交而造成的。应当认为，在圣彼得斯堡的中央核心处，较为密集 (碛) 的屋顶留14-20 米左右甚至更大的深坑。在这种情况下，制造商往往使用14-16米长的钢板桩，以确保工作生产化，而无需在排水设计的腔/槽。在一个人口密集的城市环境，必须让轴靠近现有唐楼安装，然而，长板桩的振动嵌入， 特别是其后续的提取创造，为建设经验表明，在一个负面上影响河畔建筑物的舍入。在这些条件下，复杂的监控现有建筑物的状况是nec-essary的建设工作所得到的结果，这个结果应该，至少要包括以下内容：-动态监测土层还有那些可在嵌入和提取片材堆的外壳之时进行的封装结构的轴承和建筑物的振荡;-大地测量监测现有建筑物的承载结构的相邻的施工现场的变形;和，-监测，以确保在建造期间地下水位的位置保持在一定程度。为了减少对周围发展的负面影响，今后的趋势是构造无解压打桩轴的室/短板桩机箱（长8-9米）。需要采取额外措施，以稳定的底部（变异的基床过滤性能）来避免地下水渗流到轴里去。这些问题是完全解析与使用 现代高端技术，然而，然而，需要小心岩土实体化，并在监测工作中既注重质量，同时也保护周围介质。测定土体的应力-应变状态下的运行图和结果的弹塑性是Mohr-Coulomb准则中描述的有限元法语句所执行的，如图1所示的例子。 1 。“Geomekhanik”软件包被用于分析。计算，以确定在一个室/轴8米深的桩外壳的基础上土的10米长极限状态进行了以下的土壤分层（ GEE第1号）地质工程元素 - 一个沉重粉质高塑性粘土高达6.3米厚， = 19 kN/m3 ， = 12 ， C = 8.0千帕， E = 0.93 ，E