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外文文獻(xiàn)： 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 PETERSBURG V. M. Ulitskii and S. I. Alekseev Saint 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 γ = 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 γ = 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 γ = 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 man’s 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, m H, m Fig .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 foundation’s 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. REFERENCES 1.V.M.Ulitskii, Geotechnical Substantiation of Building Reconstruction on Weak Soils[in 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). 中文譯文： 土力學(xué)與基礎(chǔ)工程, 2002年第39卷第四期 圣彼得堡在基坑安裝和公共設(shè)施鋪設(shè)過程中 對建筑的保護 V. M. Ulitskii 和 S. I. Aleksee UDC 699.84:625.78+624.152 圣彼得堡國立大學(xué)的新聞公報 在城市中央核心位置鋪設(shè)公共設(shè)施所涉及到的巖土工程問題有一種新的解決方法，它就是集熱器的非開挖施工所采用的微型隧道技術(shù)。這項技術(shù)已被廣泛應(yīng)用于歐盟，美國和日本。在柏林，早在1994年，已經(jīng)有55％的管道應(yīng)用了微型隧道這種方法。第一公里這樣的秉承德國技術(shù)的隧道建于圣彼得堡，由海瑞克公司制造的一套設(shè)備加工而成。 與鋪設(shè)公用設(shè)施和開放溝槽的傳統(tǒng)方法相比，這種方法具有明顯的優(yōu)勢，微型隧道的安裝使得需要解決一些巖土工程問題。 在城市中央核心位置鋪設(shè)公共設(shè)施所涉及到的巖土工程問題有一種新的解決方法，它就是集熱器的非開挖施工所采用的微型隧道技術(shù)。 集流管的軸（腔）通常具有4×4米（5×5米）的截面和8-12米的深度。在圣彼得堡，分庭軸也是用板樁的外殼和多層的弱飽和土相交而造成的。應(yīng)當(dāng)認(rèn)為，在圣彼得斯堡的中央核心處，較為密集 (磧) 的屋頂留14-20 米左右甚至更大的深坑。在這種情況下，制造商往往使用14-16米長的鋼板樁，以確保工作生產(chǎn)化，而無需在排水設(shè)計的腔/槽。在一個人口密集的城市環(huán)境，必須讓軸靠近現(xiàn)有唐樓安裝，然而，長板樁的振動嵌入， 特別是其后續(xù)的提取創(chuàng)造，為建設(shè)經(jīng)驗表明，在一個負(fù)面上影響河畔建筑物的舍入。在這些條件下，復(fù)雜的監(jiān)控現(xiàn)有建筑物的狀況是nec-essary的建設(shè)工作所得到的結(jié)果，這個結(jié)果應(yīng)該，至少要包括以下內(nèi)容： -動態(tài)監(jiān)測土層還有那些可在嵌入和提取片材堆的外殼之時進行的封裝結(jié)構(gòu)的軸承和建筑物的振蕩; -大地測量監(jiān)測現(xiàn)有建筑物的承載結(jié)構(gòu)的相鄰的施工現(xiàn)場的變形;和， -監(jiān)測，以確保在建造期間地下水位的位置保持在一定程度。 為了減少對周圍發(fā)展的負(fù)面影響，今后的趨勢是構(gòu)造無解壓打樁軸的室/短板樁機箱（長8-9米）。需要采取額外措施，以穩(wěn)定的底部（變異的基床過濾性能）來避免地下水滲流到軸里去。這些問題是完全解析與使用 現(xiàn)代高端技術(shù)，然而，然而，需要小心巖土實體化，并在監(jiān)測工作中既注重質(zhì)量，同時也保護周圍介質(zhì)。 測定土體的應(yīng)力-應(yīng)變狀態(tài)下的運行圖和結(jié)果的彈塑性是Mohr-Coulomb準(zhǔn)則中描述的有限元法語句所執(zhí)行的，如圖1所示的例子。 1 ?！癎eomekhanik”軟件包被用于分析。計算，以確定在一個室/軸8米深的樁外殼的基礎(chǔ)上土的10米長極限狀態(tài)進行了以下的土壤分層（ GEE第1號）地質(zhì)工程元素 - 一個沉重粉質(zhì)高塑性粘土高達(dá)6.3米厚， γ = 19 kN/m3 ， φ = 12° ， C = 8.0千帕， E = 0.93 ，E = 7.0兆帕; GEE 2號 - 一個灰色粉質(zhì)高塑性的砂土高達(dá)2米厚， γ = 20.5 kN/m3 ， φ = 16 ° ， C = 11.0千帕， E = 0.61 ，E = 10.0兆帕;和， GEE 3號 - 中密度與γ的粗肉桂砂= 20.7 kN/m3 ， φ = 40 ° ， C = 1.0千帕， E = 0.55 ，E = 40兆帕。地面水位位于從表面向下1.5μm的深度。 Fig. 1. 于限制在基床土壤狀態(tài)的區(qū)域（軸的底部庫侖 極限狀態(tài)為灰色，并且斷裂區(qū)域被劃上陰影）。 1-3）與GEE沒有土壤穩(wěn)定數(shù)軸的底部。 從我們所提出的解決方案的結(jié)果可以看出（參見圖1），土壤作為設(shè)計軸的最底層，在破裂變形后其深度超過鋼板樁的埋深，通過水的靜水壓，將超出極限狀態(tài)。因此，將會發(fā)生這樣的情況：正在挖掘的底部土壤將要溢出，地下水將開始進入基坑。這個解決方案不能無條件接受。不同厚度的穩(wěn)定土體的幾個備用的計算方案進行審查，來創(chuàng)建一個使用射流技術(shù)的反過濾帷幕。 對解決辦法的結(jié)果的分析表明，在軸的底部，限制性態(tài)發(fā)展減少、穩(wěn)定土厚度增加，并且區(qū)域完全消失時的穩(wěn)定層的厚度為3μm。因此，從創(chuàng)造中的基床反過濾性能的角度來看，在軸的基床2.53米厚的土層穩(wěn)定應(yīng)被視為一種可靠的解決方案。 當(dāng)一個隧道污水收集器是在Karpovka河的路基下鋪設(shè)，有效室/基坑采用短（9米）板樁機箱安裝，其仍留在土體中的結(jié)構(gòu)的工作已經(jīng)完成。類似的腔室分別安裝在弱飽和粘土中，其中分層的典型特征可以通過下面的（從表面向下）來表示： - 補土3μm厚，其中土的來源與人的活動有關(guān); - 高塑性狀態(tài)的粉質(zhì)砂壤土可達(dá)2-3米厚; - 從6到7.5米厚的流體和流體塑性稠度一個帶粉質(zhì)粘土壤土; 和， - 一個粉砂質(zhì)壤土砂袋，礫石，卵石以及在高塑性狀態(tài)（從15-16米的深度稍微塑料）可達(dá)4-5米厚。 電流源 1 2 3 4 5 Fig. 2. 工作原理圖制作完成，以穩(wěn)定構(gòu)成基坑粘質(zhì)壤土底的板樁外殼和地下水位高。 1）含有穩(wěn)定灌漿（硬化劑）罐; 2）金屬板樁;3）前期挖掘出的泥土;4）管狀電極 （陰極）;5）管狀電極（陽極）;6）地下水表;7）不穩(wěn)定的土壤;電極8）絕緣部分;9）穩(wěn)定土;電極10）穿孔區(qū)。 生產(chǎn)上的片材堆的外殼的沉沒工作的目的是要在板樁的底部放置到土壤的第三層，其與水的表在從表面2米的深度，從抗過濾性的觀點出發(fā)是不可靠的。電動硅化法過程，使得可以在一個干燥基坑給定深度進行基本的建筑和裝配工作變得可能，它用于沿基坑開挖距表面6米深度的底部建立一個可靠的防濾簾（AFC）。用于改善這種土壤的性質(zhì)的工作按下列順序執(zhí)行（圖2）： ?基坑被挖掘到在板莊機柜3米的深度; ?穿孔的管狀電極從基坑底部下沉; ?該電極連接到直流源的70-80?V時平均電壓; ?土壤是與交流電（200-300）與改變極性處理; ?從陰極進入的水被抽空; ?硅酸鈉和氯化鈣溶液中依次注入到陽極;并 ?穿孔的管狀電極，提取和孔堵塞。 降低質(zhì)量穩(wěn)定化的土壤水分含量的方法是自由水在孔中的電平的測量的基礎(chǔ)上監(jiān)測。因此，圖解3所示的數(shù)據(jù)80孔水位的波動的質(zhì)量所治療的噴射器。在其中帶粉質(zhì)黏土質(zhì)壤土被觀察的兩個星期內(nèi)，觀察到對于孔/陰極從自由水已經(jīng)完全撤離的影響最大。 H,m a H,m b Fig. 3. 執(zhí)行工作的過程中變化的水位在孔/噴油器動態(tài): 一） 于1999年2月14日孔水位測量數(shù)據(jù); 二）于1999年2月28日孔水位測量數(shù)據(jù) 穩(wěn)定的土壤的物理 - 力學(xué)性能的改變成為了electrosilification的結(jié)果。因此，土壤的壓縮彈性模量增加了60％，而內(nèi)摩擦和凝聚力幾乎能達(dá)到70％的角度。延長脫水導(dǎo)致了土壤的侵蝕沙分?jǐn)?shù)的自然流失，這已經(jīng)從粉質(zhì)粘土壤土類轉(zhuǎn)換為粘土類的粒度分布的變化。其結(jié)果是，穩(wěn)定的土壤，并于始終處于略微塑料半硬的狀態(tài)。這種土壤的通透性也從0.08降低到0.003-0.006米/天，也就是說，一個防滲帷幕正在基坑底部下安裝。 對于已安裝的基坑土穩(wěn)定的工作，不僅做出了有可能在一個“干”基坑執(zhí)行所需的建筑和裝配業(yè)務(wù)，而且通過顯著改善基床的物理機械性能，創(chuàng)造條件為整體上的整個結(jié)構(gòu)提供更可靠的服務(wù)。 在圣彼得堡，涉及的深基坑開挖工作，如果沒有穩(wěn)定土體的坑，即，與使用開放引流，會導(dǎo)致地下水位急劇下降，并導(dǎo)致周圍建筑物的不均勻沉降。 在圣彼得堡下方的地下人行天橋建設(shè)的TRUD廣場（Blagoveshchenskaya廣場）是一個典型例子。 在高達(dá)5.8米深的基坑工程中采用開放引流技術(shù)，因為質(zhì)量差的被擠出，從金屬板樁（拉森Ⅳ）形成到深地允許水通過14米板樁圍墻。因此，凹