CN107587515A - A kind of across railway line bridge bearing platform foundation construction method - Google Patents

Abstract

A construction method for the cap foundation of a bridge spanning a railway line. Before excavating the foundation pit of the cap platform, a railway embankment protection structure is first constructed. The steel sheet piles in the ground on the other side of the subgrade; the exposed ends of the steel sheet piles are integrated by channel steel; one end of the tension steel bar is welded to the ground anchor, and the other end passes through the bottom of the railway rail along the gravel bed of the railway, and the tensile force calculated according to the formula Tension and anchoring on the channel steel; adjust the excavation method of the foundation pit according to the ground anchor welding point, channel steel anchor point, horizontal displacement of the top of the steel sheet pile and the monitoring results of the railway rail elevation during the excavation of the foundation pit of the cap; Roadbed protection structure. This construction method can make the stability of the subgrade unaffected by the construction of the bridge foundation; stretching the tensioned steel bars according to the limited tension can achieve the best protection effect; the construction process of the protective structure is simple, and the steel sheet piles, the tensioned steel bars and the steel backing plate can be repeated Utilization, the engineering cost is low.

Description

A construction method for the foundation of a bridge spanning a railway line

technical field

The invention relates to railway subgrade protection and bridge foundation construction, in particular to a bridge cap foundation construction method in which a railway subgrade protection structure is constructed first and then foundation pits are excavated during bridge cap foundation construction across railway lines.

Background technique

During the construction of the bridge cap foundation across the railway line, the excavation of the foundation pit of the bridge cap adjacent to the railway line will affect the stability of the railway subgrade. Based on the strict requirements on the deformation of the subgrade by the railway line, in order to ensure that the deformation of the railway subgrade is within the allowable range during the excavation of the foundation pit of the cap platform, necessary active protection must be carried out on the railway subgrade. At present, measures such as retaining walls or anti-slide piles are often used for roadbed protection. However, a single retaining wall or anti-slide pile cannot exert active protective force, and it is difficult to restrain the impact of foundation pit excavation on the railway subgrade, which can easily lead to subgrade deformation exceeding the limit. Although the prestressed anchor (cable) retaining wall or anti-slide pile can reduce the impact of foundation pit excavation on the subgrade, the construction of too long anchor (cable) itself will cause certain damage to the railway line. degree of damage, and the loss of protective prestress after excavation is too large, and the protective effect is not good. In addition, this method also has the problems of complicated construction technology, large construction work volume and high cost.

Contents of the invention

Aiming at the problems existing in the above-mentioned prior art, the object of the present invention is to provide a method that can effectively protect the stability of the railway embankment from being affected by the construction of the cap foundation pit, and the construction process is relatively simple, the construction quantity is small, and the construction cost is low and The invention relates to a construction method for the cap foundation of a bridge spanning a railway line with recyclable materials.

The method for constructing foundation pits of bridge caps across railway lines provided by the invention comprises the following steps:

Step 1. Build roadbed protection structure

Before the excavation of the foundation pit of the cap platform, the subgrade protection structure is constructed for the railway subgrade spanned by the bridge. Steel sheet piles in the ground (the number of ground anchors and steel sheet piles is determined according to the length of the cap foundation pit along the direction of the railway line); the horizontal direction of the ground anchors corresponds to between adjacent railway sleepers; The channel steel welded at the end is integrated; the ground anchor and the channel steel are connected to each other through the tension reinforcement in the following way:

The opposite-tensioned steel bars pass through the bottom of the railway rail between the railway sleepers along the upper surface of the railway crushed stone bed, and there is a steel backing plate with the same width as the distance between the adjacent railway sleepers between the opposite-drawn steel bars and the surface of the railway crushed stone bed. One end of the tensioned steel bar is welded to the exposed end of the ground anchor, and the other end of the tensioned steel bar is anchored on the channel steel after stretching with the tension F calculated by the following formula:

In the formula:

E _{ak —Standard} value of resultant force of active earth pressure outside the foundation pit of bridge cap (kN/m),

E _{pk —Standard} value of resultant force of passive earth pressure inside the foundation pit of bridge cap (kN/m),

Z _a — the distance from the resultant force of active earth pressure outside the foundation pit of the bridge cap to the lower end of the steel sheet pile (m),

Z _p — the distance from the resultant force of passive earth pressure inside the foundation pit of the bridge cap to the lower end of the steel sheet pile (m),

e—the distance from the anchor point of the tensioned reinforcement to the lower end of the steel sheet pile (m),

m—the number of braces in the foundation pit of the bridge cap,

n—the number of tensioned steel bars per linear meter along the railway line (same as the number of ground anchors);

When constructing the protective structure of the roadbed, the surface soil on the ground on both sides of the railway roadbed should be cleaned first, and the position of the steel sheet piles should be determined by laying out positioning according to the design of the construction drawing; Insert and drive steel sheet piles, weld the channel steel horizontally at the exposed end of the steel sheet piles, connect the steel sheet piles into one, and lay out reserved holes corresponding to the ground anchor positions of the channel steel; then drill holes and grout the ground anchors on the other side of the railway subgrade ; Pass the opposite tension reinforcement along the surface of the railway gravel track bed from the bottom of the railway rail between the railway sleepers, and lay the steel backing plate between the opposite tension reinforcement and the surface of the railway gravel track bed; One end is welded with the ground anchor; the other end of the tensioned steel bar is stretched according to the tension calculated by the calculation formula, and anchored to the channel steel through the reserved hole;

When the railway line spanned by the bridge is an electrified railway, rubber tubes need to be placed on the outside of the tension reinforcement in the subgrade protection structure to insulate the reinforcement from the railway rail;

Step 2. Excavate the foundation pit of the bridge cap

Excavation of the foundation pit of the bridge cap is carried out after the construction of the above roadbed protection structure is completed: the excavation of the foundation pit of the bridge cap starts from the side away from the railway line, and gradually advances towards the railway embankment. After the excavation is completed, set up the corresponding internal support; during the excavation process, observe in real time whether the ground anchor welding point, the channel steel anchor point and the backing plate are distorted, deformed or broken, and measure the horizontal displacement of the top of the steel sheet pile and the position of the railway rail at a monitoring frequency of once a day. Elevation; when the local anchor welding points and channel steel anchor points break, the construction must be suspended, and the welding and anchor points should be repaired and reinforced. When the horizontal displacement of the top of the steel sheet pile reaches 0.002 times the warning value of the depth of the foundation pit or the vertical displacement of the rail When the accumulative warning value of 4mm is reached, the excavation must be stopped immediately and the excavated foundation pit shall be backfilled and compacted, and then the gravel bed of the railway shall be corrected, the geometric shape of the railway track shall be corrected, and the railway rail shall return to its original state; then the protective structure of the railway subgrade shall be used The method of enlarging the tensioned steel bars (correspondingly increasing the number of ground anchors) improves its protective performance; adopting the method of reducing the excavation thickness of each layer in blocks and adding internal supports in time to excavate and monitor the foundation pit of the bridge cap until Complete the excavation of the foundation pit of the entire bridge cap, and finally set the inner support of the foundation pit in the foundation pit of the cap;

Step 3. Build the bridge foundation

After the excavation of the foundation pit of the bridge cap is completed, the bridge cap, pier body and backfilling shall be carried out according to the conventional method to complete the construction of the bridge foundation;

Step 4: Remove roadbed protective structure

After completing the construction of the bridge foundation, cut off the opposite tension reinforcement anchored with the channel steel, weld and cut to remove the steel beam; use a vibrating hammer to vibrate the steel sheet pile, and use the lifting force of a crane to pull out the steel sheet pile, trim the steel sheet pile for reuse, and then backfill The pile hole of the steel sheet pile is compacted with a vibrating hammer; then the exposed end of the ground anchor is sawed off along the ground with a hacksaw (the ground anchor inserted into the ground does not need to be pulled out), so as to avoid it affecting normal production and life; pull out the opposite tension steel bar from the bottom of the rail , remove the steel backing plate to complete the dismantling of the subgrade protective structure.

Compared with prior art, the advantage of the present invention is:

1. The subgrade protection structure in the present invention is to actively protect the railway subgrade in advance by prestressing the tensioned steel bars before excavating the foundation pit of the bridge cap. The design principle of the protection structure is based on the excavation and unloading during the excavation of the foundation pit Stress redistribution is regular, and the maintenance of subgrade is highly targeted and effective. The bridge foundation construction is carried out according to the method of the invention, so that the stability of the railway embankment is basically not affected by the bridge foundation construction.

2. The anti-stretching steel bars in the roadbed protection structure of the present invention are stretched according to the limited tension calculation formula, so that the roadbed protection structure can achieve the best protection effect on the roadbed: neither can the effective protection of the roadbed be achieved because the tension force is too small The role; and will not cause damage to the original structure of the subgrade due to excessive tension.

3. The roadbed protection structure and its construction technology in the present invention are simple, and the engineering cost is significantly reduced.

4. The steel sheet piles, anti-tension steel bars and steel backing plates in the present invention can be recycled and reused after the backfilling of the bridge foundation construction is completed, saving materials.

Description of drawings

Fig. 1 is the schematic diagram (cross-sectional view) of subgrade protection structure and bridge cap foundation pit among the present invention;

Fig. 2 is the top view of Fig. 1;

Fig. 3 is the A-A sectional view of Fig. 2;

Fig. 4 is the B-B sectional view of Fig. 2;

Fig. 5 is a C-C sectional view of Fig. 2 .

In the figure: 1-steel sheet pile, 2-tie steel bar, 3-rubber tube, 4-railway rail, 5-railway sleeper, 6-railway gravel bed, 7-railway subgrade, 8-ground anchor, 9-ground. 10-channel steel, 11-steel backing plate, 12-cap foundation pit, 13-support inside the foundation pit, 14-waist beam, 15-top pile.

detailed description

The present invention will be further described below in conjunction with drawings and embodiments.

This embodiment is the foundation construction of a certain bridge across the electrified railway line.

The cap foundation pit 12 of the bridge is 15m long along the railway line direction, 11m wide laterally, and has an excavation depth of 6m, and is 5m away from the slope foot of the railway embankment. The excavation depth of the foundation pit is 5m, mainly composed of silty clay and fine sand, and below 5m mainly composed of sandy gravel.

The standard value of the resultant force of active earth pressure on the outside of the foundation pit is E _ak ＝ _454.25kN /m, and the standard value of the resultant force of passive earth pressure on the inside of the foundation pit is Epk＝883kN/m (the two standard values are based on the weight, cohesion and internal friction angle of the soil and other parameters, obtained after calculating the active earth pressure intensity and distribution using the active earth pressure calculation formula). The distance from the resultant active earth pressure outside the foundation pit to the lower end of the steel sheet pile is Z _a =3.83m, the distance from the resultant passive earth pressure inside the foundation pit to the lower end of the steel sheet pile is Z _p =2.15m, and the number of braces in the foundation pit of the bridge cap is m=1.

In order to ensure that the stability of the railway embankment is not affected by the bridge foundation construction across the railway line, the bridge foundation construction is carried out according to the following steps:

Step 1. Construction of the railway subgrade protection structure before excavation of the foundation pit of the bridge cap

In conjunction with Fig. 1 to Fig. 5, utilize pile driver on the ground 9 on one side of railway subgrade 7 and vertically drive and insert the ground anchor 8 that is made of a steel bar with a diameter of φ30-40mm and a length of 10m along the direction of the railway line at intervals of 1000mm (such as Shown in Figure 3), there are 16 in total, and the ground anchor horizontally corresponds to the adjacent railway sleeper 5 respectively, and its upper end exposes 0.5m. Insert 38 steel sheet piles 1 with a length of 12m, a width of 500mm, and a thickness of 200mm along the direction of the railway line at a density of 2.5 per linear meter on the ground on the other side of the railway subgrade 7, with 0.5m exposed at the upper end of the steel sheet piles. Weld channel steel 10 horizontally from the top of the steel sheet pile 0.4m to connect the steel sheet piles together. The size of the channel steel (waist height×leg width×waist thickness) is 120mm×53mm×5mm, and the channel steel is equipped with reserved holes corresponding to the ground anchor position (not shown). The ground anchor is connected to the channel steel through the φ10mm anti-tension steel bar 2. The number of anti-tension steel bars along the railway line is n=1, and the distance between the anchor point of the anti-tension steel bar and the lower end of the steel sheet pile is e=11.6m. The middle section of the crushed stone track bed 6 is covered with a rubber tube 3 with an inner diameter of φ12mm and an outer diameter of φ16mm (as shown in Figure 5), and the distance between the two ends of the rubber tube and the railway rail is more than 1m (as shown in Figures 1 and 2). shown) to ensure that the tension reinforcement is insulated from the railway rails. Make the opposite-tensioned steel bars pass through the bottom of the railway rail 4 between the railway sleepers 5 along the surface of the railway crushed stone bed 6, and lay the same distance between the opposite-drawn steel bars and the surface of the railway crushed stone bed with the same spacing as the adjacent railway sleepers 1. A steel backing plate 11 with a thickness of 10mm.

Then weld one end of the tension steel bar to the exposed end of the ground anchor, and the other end is tensioned

After being stretched, it is anchored on the channel steel 10 and locked to complete the construction of the subgrade protection structure.

Step 2. Excavate the foundation pit of the bridge cap after completing the construction of the roadbed protection structure

The excavation of the foundation pit starts from the side away from the railway embankment, and gradually advances towards the railway embankment. It is divided into 3 sections, and each section is divided into 2 layers. During the excavation process, observe whether the ground anchor welding points and channel steel anchor points are twisted or deformed. and cracks, and measure the horizontal displacement of the top of the steel sheet pile and the elevation of the railway rail with a monitoring frequency of once a day. According to the actual monitoring during the construction process, the ground anchor welding point and the channel steel anchor point have no cracks, and the cumulative vertical displacement of the rail is 2.5mm, which meets the conditions for continued excavation until the excavation elevation is reached. The side of the foundation pit away from the subgrade corresponds to the steel plate Pile 1 is equipped with the same supporting pile 15 as the steel sheet pile, and the number m = 1 is installed horizontally at the horizontal position 4m from the top of the steel sheet pile. The inner support 13 of the bridge cap foundation pit composed of steel pipes with a diameter of 650mm, the two ends of the inner support of the foundation pit are respectively A waist beam 14 made of 350*350mm H-shaped steel leans against the steel sheet pile and the pile against the pile.

Step 3. After the excavation of the foundation pit of the bridge cap is completed, the bridge cap, pier body and backfilling are carried out according to the conventional method, and the bridge foundation construction is completed.

Step 4. After the completion of the bridge foundation construction, cut off the opposite tension bars anchored with channel steel, weld and cut and remove the steel beams; use a vibrating hammer to vibrate the steel sheet piles, and at the same time use the lifting force of a crane to pull out the steel sheet piles, and repair the steel sheet piles for reuse , then backfill the steel sheet pile pile hole and tamp it with a vibrating hammer; then use a hacksaw to cut off the exposed end of the ground anchor along the ground (the ground anchor inserted into the ground will not be pulled out), so as to avoid it affecting normal production and life; Pull out the bottom, remove the steel backing plate, and complete the demolition of the roadbed protection structure.

After the protective structure of the subgrade was removed, the stability of the subgrade of this section of the railway was not greatly affected by the construction of the bridge foundation.

Claims (1)

1. A kind of 1. across railway line bridge bearing platform foundation construction method, it is characterized in that comprising the following steps：

   Step 1, construct subgrade protection structure

   The railway bed first crossed over before cushion cap excavation of foundation pit to bridge constructs subgrade protection structure, and the subgrade protection structure includes Earth anchor (8) in insertion railway bed (7) the side ground of one group of downline direction and one group of insertion railway bed opposite side Steel sheet pile (1) in face；The earth anchor laterally corresponds between adjacent railway sleeper (5) respectively；The steel sheet pile by with steel sheet pile The channel-section steel (10) of exposed junction welding is connected；Earth anchor passes through to drawing reinforcing bar (2) to be connected with each other in the following manner with channel-section steel：

   To drawing upper surface of the reinforcing bar along railway ballast bed (6) to be passed through from railway track (4) bottom between railroad sleeper (5), There is the spacing identical billet (11) of width and adjacent railway sleeper between reinforcing bar and the ballast bed upper surface of railway to drawing, it is right One end of reinforcing bar and the exposed junction of earth anchor is drawn to weld, anchor after the stretching force F tensioning that the other end for drawing reinforcing bar is calculated as follows out Gu on channel-section steel：

   <mrow> <mi>F</mi> <mo>=</mo> <mn>0.6</mn> <mo>&amp;times;</mo> <mfrac> <mrow> <mn>1.25</mn> <msub> <mi>E</mi> <mrow> <mi>a</mi> <mi>k</mi> </mrow> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>Z</mi> <mi>a</mi> </msub> <mo>-</mo> <msub> <mi>E</mi> <mrow> <mi>p</mi> <mi>k</mi> </mrow> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>Z</mi> <mi>p</mi> </msub> </mrow> <mrow> <mi>n</mi> <mo>&amp;CenterDot;</mo> <mi>e</mi> <mrow> <mo>(</mo> <mi>m</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow>

   In formula：

   E_akActive earth pressure is made a concerted effort standard value on the outside of-bridge bearing platform foundation ditch,

   E_pkPassive earth pressure is made a concerted effort standard value on the inside of-bridge bearing platform foundation ditch,

   Z_aActive earth pressure is made a concerted effort to the distance of steel sheet pile lower end on the outside of-bridge bearing platform foundation ditch,

   Z_pPassive earth pressure is made a concerted effort to the distance of steel sheet pile lower end on the inside of-bridge bearing platform foundation ditch,

   E-to draw Bar Anchorage point to steel sheet pile lower end distance,

   M-bridge bearing platform foundation ditch inner support quantity,

   N-downline is per linear meter(lin.m.) to the radical of drawing reinforcing bar；

   When constructing the subgrade protection structure, the topsoil on railway bed both sides ground is first cleared up, passes through unwrapping wire by construction drawing design Positioning determines the position of steel sheet pile；Using piling machine in railway bed side downline trend by setting interval and absolute altitude inserting piling Steel sheet pile, in the exposed junction transverse weld channel-section steel of steel sheet pile, each steel sheet pile is connected, channel-section steel accordingly lay in advance by anchor location Box out；Then earth anchor is laid in the drilling of railway bed opposite side, slip casting；By to drawing reinforcing bar along the ballast bed surface of railway from iron Railway track bottom between rail pillow passes through, and is laying the steel pad between reinforcing bar and the ballast bed upper surface of railway to drawing Plate；By to drawing one end of reinforcing bar and earth anchor to weld；By the tensioning to drawing the other end of reinforcing bar to be calculated by the calculation formula Power tensioning, and be anchored at by the preformed hole on channel-section steel；

   When bridge cross over railway line be electric railway when, need to be in the subgrade protection structure to drawing reinforcing bar outer cover rubber Sebific duct, reinforcing bar is set to be insulated with railway track；

   Step 2, excavate bridge bearing platform foundation ditch

   Bridge bearing platform foundation ditch excavation is carried out after completing above-mentioned subgrade protection structure construction：Bridge bearing platform excavation of foundation pit is by remote Railway line side starts, and is gradually promoted to railway bed, takes staged and layered to excavate, and is correspondingly arranged after being excavated at each layer Inner support；Real Time Observation earth anchor pad, channel-section steel anchor point and backing plate whether there is torsional deformation or rupture in mining process, and with daily The upper horizontal displacement of monitoring frequency measurement steel sheet pile once and the absolute altitude of railway track；When earth anchor pad, channel-section steel anchor Necessary suspension of works when point ruptures, butt welding point and anchor point carry out repair welding and reinforcing, when the upper horizontal displacement of steel sheet pile Reach 0.002 times of foundation depth warning value or when rail vertical displacement has reached 4mm warning values, it is necessary to stop excavating simultaneously immediately The foundation ditch excavated is backfilling and compacted, then amendment railway is ballast bed, correction railroad track geometric type position, returns railway track Restore shape；Then its barrier propterty is improved to the method for drawing reinforcing bar with encryption to railway bed safeguard structure；Blockette is taken to subtract Small every layer is excavated thickness and sets up the method for inner support in time bridge bearing platform foundation ditch is excavated and monitored again, until completion is whole The excavation of individual bridge bearing platform foundation ditch, foundation ditch inner support (13) is finally set in cushion cap foundation ditch；

   Step 3, construct bridge foundation

   After completing the excavation of bridge bearing platform foundation ditch, bridge bearing platform, pier shaft and backfill construction are conventionally carried out, completes bridge Basic construct；

   Step 4：Remove subgrade protection structure

   After completion bridge foundation is constructed, cut-out is with channel-section steel anchoring to drawing reinforcing bar, welding dismounting girder steel；Steel is vibrated using vibration hammer Sheet pile, while hang power using crane and extract steel sheet pile, then finishing steel sheet pile backfills steel sheet pile stake holes simultaneously in case recycling Tamped with vibration hammer；Again it is avoided with hacksaw along the sawed-off earth anchor exposed junction in ground (earth anchor in insertion ground need not can be extracted) Influence normal production and life；Billet will be removed, complete to remove subgrade protection knot to drawing reinforcing bar to be extracted out from rail foot Structure.